Typeset using LATEX twocolumn style in AASTeX62 Draft version October 9, 2018

The AGN Ionization Cones of NGC 5728 : I - Excitation and Nuclear Structure Mark Durre´1 and Jeremy Mould1

1Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122, Australia

ABSTRACT We explore the gas morphology and excitation mechanisms of the ionization cones of the Type II Seyfert galaxy NGC 5728. Near-IR and optical data from the SINFONI and MUSE IFUs on the VLT are combined with HST optical images, Chandra X-ray data and VLA radio observations. The complex nuclear structure has a star-forming (SF) ring with a diameter of 2 kpc. A radio jet impacts on the ISM at about 200 pc from the nucleus, with the SN remnants in the SF ring also present. Emission-line ratios of [Fe II] and H II show heavy extinction towards the nucleus, moderate extinction in the SF ring and reduced extinction in the ionization cones. The AGN is hidden by a dust bar with up to 19 magnitudes of visual extinction; the dust temperature at the nuclear position is ∼ 870 K. An X-ray jet is aligned with the ionization cones, and associated with high-excitation emission lines of [Si VI] in a coronal-line region extending 300 pc from the nucleus. Molecular hydrogen is spatially independent of the cones, concentrated in a disk equatorial to the star-forming ring, but also showing entrainment along the sides of the bicone. Gas masses for warm and cold H2,H I and H II are estimated, and the excitation mechanisms for ionized and molecular gas are elucidated, from both optical (which shows a clean SF-AGN mixing sequence) and infrared diagnostics (which show more complicated, multi-component excitation regimes).

Keywords: galaxies: active - galaxies: individual (NGC 5728) - galaxies: nuclei - galaxies: Seyfert – galaxies: structure – galaxies: star formation – ISM: jets and outflows

1. INTRODUCTION it a prime target for investigation, particularly using ob- The Unified Model of active galactic nuclei (AGN) servations in the near infrared, allowing penetration of predicts that radiation from the accretion disk around obscuring dust. In the present paper (‘Paper I’), we will the super-massive black hole (SMBH) is collimated by a explore in detail the nuclear structure of this galaxy at torus of obscuring dust and gas, which is broadly sym- multiple wavelengths and characterize the narrow-line metric around the accretion flow axis. This radiation region (NLR) gas morphology and excitation. In the impinges on the interstellar medium (ISM), exciting the companion paper (Durr´e et al. , in submission, hereafter gas by photo-ionization and transferring mechanical en- ‘Paper II’), we will use these data to explore the kine- ergy to the gas by radiation pressure and disk winds; this matics of the cones, showing that they are AGN-driven appears in the form of cones extending from the nucleus. outflows, determining mass outflow rates and power and These cones are observed in local Seyfert galaxies, and relating these to the AGN bolometric luminosity and are more frequently seen in type II (obscured) Seyferts the amount of gas that can be expelled during the AGN than type I (un-obscured) Seyferts (Schmitt & Kinney activity cycle; the super-massive black hole (SMBH) at- tributes are also derived. We will also determine the

arXiv:1810.03258v1 [astro-ph.GA] 8 Oct 2018 1996), consistent with unification. The kinematics and excitation of the gas in these cones is of interest to eluci- stellar kinematics and relate them to the gas kinemat- date excitation mechanisms, to examine the interaction ics. of the AGN with its host galaxy and to correlate optical The basic parameters for NGC 5728 are given in Ta- and infrared observations with radio and X-ray. ble1. Apart from the AGN activity, the nucleus has a Urry & Padovani(1995), in the seminal review paper highly complex structure. The Spitzer Survey of Stel- on AGN unification, cited NGC 5728 as the paradigm of lar Structure in Galaxies (S4G) (Buta et al. 2015) lists 0 a Type II AGN with these ionization cones. This makes the morphology as (R1)SB(r l,bl,nr,nb)0/a, which indi- cates a barred spiral with a closed outer ring, an inner pseudo-ring/lens and a nuclear ring and bar/bar-lens. [email protected] 2 Durre´ & Mould

This morphology is important in the context of SF in the nuclear region.

Table 1. NGC 5728 Basic Parameters Far Parameter Value Reference

RA 14h42m23.9s Dec -17d15m11s Distance 41.1±2.9 Mpc Mould et al.(2000) * Scale 200 pc arcsec−1 z 0.009353 Catinella et al.(2005) Morphology SAB(r)a? de Vaucouleurs et al.(1991) Activity Sy 2 (Sy 1.9?) V´eron-Cetty & V´eron(2006) Near

MH (2MASS) -23.85 Skrutskie et al.(2006)

∗Virgo+GA+Shapley flow-corrected distance, H = 73 0 N km s−1Mpc−1

From the 2MASS H -band absolute magnitude with 30"(600 pc) a mass-to-light ratio of 1 at H and a Solar absolute magnitude of MH = 3.3 (Binney & Merrifield 1998), the Figure 1. NGC 5728 star-cleaned color-composite image 10 estimated galaxy mass is 7.2 × 10 M . from CGS, created from the B, V and I images and cleaned The Carnegie-Irvine Galaxy Survey (Ho et al. 2011) of stars, as described in Ho et al.(2011). The image is ori- 0 image (Fig.1) clearly shows the outer ring with faint ented north up, east left. The sides of the image are 4 .6, trailing spiral arms. The bar is weak, with the region equivalent to 55 kpc at the distance of NGC 5728. The fea- tures visible are the outer ring, faint arms trailing from SF between the nucleus and the outer ring being reason- peaks at the end of the major bar, a smooth disk with dust ably smooth with some faint dust rings. Rubin(1980), lanes, and the complex inner nuclear structure, composed of using H α emission line measurements, found that the a ring with a bar. The dotted line indicates the morphologi- rotation curve along the NE-SW axis was flat and that cal axis and kinematic line of nodes, and the arrows indicate the NE axis was approaching; that study concluded that the rotation direction. The near and far sides of the galaxy the near side was to the NW, based on the trailing faint are labeled. spiral arms. She also deduced that the non-circular ve- locities could be modeled equally well by an additional HST UV imaging polarimetry of the nucleus (Capetti axisymmetric expansion, or by a displaced inner disk et al. 1996), using the Faint Object Camera, revealed or spheroidal/triaxial inner bulge. NGC 5728 has ion- a centro-symmetric pattern of scattered light originat- ization cones that are oriented across our line of sight. ing in the hidden nucleus; the polarization upper limit Gorkom(1982) first observed asymmetrical optical and was 1.9%, in line with ground-based observations. This radio emissions from this galaxy; their VLA 6 and 20 showed that the cones were much wider than that in- ◦ cm observations showed a diffuse 1000 region which was ferred from the emission lines (55–65 ), implying that coextensive with the optical emission, with a compact some of the torus is transparent to UV light while still nucleus and jet. These observations were followed up by blocking the ionizing radiation. The cone symmetry was Schommer et al.(1988); they concluded that the gas was used to locate the nucleus behind a dust lane. The ac- streaming inwards, however their data did not exclude tivity type is classified as Seyfert 1.9 (V´eron-Cetty & outward motions, as suggested by the double-peaked H α V´eron 2006), based on broad H α Balmer line visibility. emission line region near the nucleus. Arribas & Me- The kinematics and excitation mechanisms of H2 and diavilla(1993) noted that the kinematic center of the [Fe II] lines in a sample of active galaxies were studied H α, [N II], and [S II] emission lines and the radio flux in Rodr´ıguez-Ardilaet al.(2004a, 2005), which included did not coincide with the emission line flux maximum, this galaxy, using long-slit observations from the 0.8– suggesting that the nucleus was highly obscured. The 2.4 µm IRTF Spex spectrograph. They showed that, in H α+[N II] and [O III] emission line images from the general, the H2 was kinematically decoupled from the HST observations of Wilson et al.(1993) revealed a NLR, with this particular galaxy having the highest ra- spectacular bi-conical structure with an overall extent tio of H2 to Br γ flux in their sample of 22 AGN. They of 1.8 kpc. estimated a warm H2 mass of ∼900 M in the nucleus. NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 3

Rodr´ıguez-Ardilaet al.(2011) also detected the coro- maps and wavelength calibrations. Sky frames are sub- nal line of [Si VI], however they did not observe any tracted from object frames, corrected for flat field and coronal lines in this object with an ionization poten- dead/hot pixels, interpolated to linear wavelength and tial (IP) > 167 eV, indicating a limit to the hard X- spatial scales and re-sampled to a wavelength calibrated ray flux. From WiFeS optical IFU observations, Dopita cube, at the required spatial scale. The sequence of re- et al.(2015) reported that the NLR was much more ex- duced object cubes are mosaicked and combined to pro- tended than from Wilson et al.(1993); 4.4 kpc rather duce a single data cube. Subsequent cube manipulation than 1.8 kpc in extent. Using the spectra for this ob- and computation is done using the the cube data viewer ject from Rodr´ıguez-Ardilaet al.(2004a), which were and analysis application QFitsView (Ott 2012), which taken with a 000.8 × 1500 slit, Riffel et al.(2009) deduced incorporates the DPUSER language. a mixture of 70% intermediate age (100 Myr to 2 Gyr) Standard stars are used for both telluric correction and 30% old (> 2 Gyr) stellar population contributions and flux calibration; these had the spectral types of B2 to the continuum, with corresponding mass fractions of to B9, which only have hydrogen and helium lines in 25% and 75%, with no black-body dust component. their spectra. Flux calibration is done by extracting the In this paper, we use the standard cosmology of H0 = stellar spectrum from the data cube within a aperture, −1 −1 73 km s Mpc ,ΩMatter = 0.27 and ΩV acuum = 0.73. chosen using logarithmic scaling on the collapsed ‘white- All images are oriented so that North is up, East is left. light’ image. A segment of the spectrum is chosen that avoids telluric features and stellar absorption lines, on 2. OBSERVATIONS, DATA REDUCTION AND or near the effective wavelength for the filter. The total CALIBRATION counts in a 10 nm window centered on the chosen wave- We obtained near infrared (NIR) IFU data from SIN- length is divided by the exposure time and the window FONI on VLT-U4 (Yepun), both from our own observa- wavelength width to get a value of counts s−1 nm−1. tions (J -band filter) and from the MPE group (H+K - This is equated to the stellar magnitude is found from band filter) who kindly let us use the data from their the 2MASS catalog (Skrutskie et al. 2006, through the LLAMA (Luminous Local AGN with Matched Ana- SIMBAD astronomical database2), converted to a flux logues) survey (Davies et al. 2015). Each dataset con- density using the website ‘Conversion from magnitudes sists of two object frames, combined with a sky frame to flux, or vice-versa’3. The telluric correction spec- with the same exposure, in the observing mode ‘Object- trum was created from the standard star spectrum by Sky-Object’. For the J -band SINFONI observations, manually fitting and removing the hydrogen and helium 00 00 the offset was 30 in Dec, plus a 0 .05 jittering proce- absorption features, then dividing by a black-body spec- 00 dure; the offset for the H+K observations was was 60 trum of the correct temperature for the spectral type. 00 in RA, plus a 0 .1 jitter. Standard stars are observed This spectrum is normalized and is divided into each close to the observation at a similar airmass. spectral element. This temperature is somewhat higher We also obtained archival data at optical wavelengths than given in standard references (e.g. 17000 K vs. from the MUSE optical IFU instrument (Bacon et al. 14300 K for B6 stars), as the hydrogen opacity is lower at 2010) on the ESO VLT for the TIMER (‘Time Inference infrared wavelengths; we observe a lower (and therefore with MUSE in Extragalactic Rings’) survey (P.I. Dimitri hotter) layer in the stellar atmosphere (see Durr´eet al. A. Gadotti , European Southern Observatory); this data 2017). After telluric correction and flux calibration, the was reduced before archival release and is used with the data cubes from the SINFONI H+K observations for kind permission of Dr. Gadotti. separate dates were combined into single cubes. These Our observations are summarized in Table2, which were centered on the brightest pixel (in the image cre- also includes the details of the MUSE TIMER program ated by collapsing the cube along the wavelength axis). optical observations. The whole observed field for the H+K filter is 300 × 300, The SINFONI data reduction was performed using the which equates to 600 × 600 pc. recommendations from the ESO SINFONI data reduc- Initially, the J SINFONI cube showed a strong tel- 1 tion cookbook and the gasgano (ESO 2012) software luric absorption feature at 1268.9 nm; normally this is pipeline (version 2.4.8). Bad read lines are cleaned from not an issue, but for this object, the redshift moved the the raw frames using the routine provided in the cook- [Fe II] 1257 nm line to this wavelength and producing a book. Calibration frames are reduced to produce non- linearity bad pixel maps, dark and flat fields, distortion 2 http://simbad.u-strasbg.fr/simbad/ 3 http://www.gemini.edu/sciops/instruments/midir-resources/ 1 http://www.eso.org/sci/software/gasgano.html imaging-calibrations/fluxmagnitude-conversion 4 Durre´ & Mould

Table 2. NGC 5728 Observation Log

Date Instrument/Filter Exp. Timea/Frames Airmass/ Seeing (00)b Rc FOV (pc)d Program ID/PI Plate Scale (00)e Total Exp. Time (s) Standard Star BCf/∆Vg Sp. Res.h (pc/pixel)

2014 Apr 11 SINFONI J 300/6 1.085/1.3 2400 1500 093.B-0461(A)/Mould 0.25 1800 HIP091038 11.6/53 25

2015 Feb 23 SINFONI H+K 300/6 1.011/1 1560 600 093.B-0057(B)/Davies 0.1 1800 HIP073266 28.3/85 10

2015 Mar 5 SINFONI H+K 300/6 1.012/1.25 1560 600 093.B-0057(B)/Davies 0.1 1800 HIP071451 25.8/85 10

2015 Jun 14 SINFONI H+K 300/6 1.016/1.25 1560 600 093.B-0057(B)/Davies 0.1 1800 HIP078968 -13.9/85 10

2015 Jun 25 SINFONI H+K 300/6 1.203/0.75 1560 600 093.B-0057(B)/Davies 0.1 1800 HIP082670 -21.8/85 10

2016 Apr 3 MUSE V 480/1 1.048/0.66 1800 12800 097.B-0640(A) /Gadotti 0.2 480 . . . i 15.5/70 40 aExposure time (sec) for each on-target frame. b Seeing from the ESO Paranal Astronomical Site Monitoring (VLT) or the Mauna Kea Weather Center DIMM archive (Keck). c Measured spectral resolution. dObserved field of view e SINFONI plate scale is re-binned to half size in the final data cube. fBarycenter correction in km s−1 from ‘Barycentric Velocity Correction’ website http://astroutils.astronomy.ohio-state.edu/ exofast/barycorr.html(Wright & Eastman 2014) gSpectral velocity resolution (km s−1) hSpatial resolution i Data not available pronounced ‘notch’ in the emission line spectrum. This visible in any of the tomograms, presumably because of was corrected by using the IRAF telluric procedure which the combination of cubes over 4 dates. shifts and scales the telluric spectrum to best divide out All the data cubes had some spikes and geometric arti- features from data spectra by minimizing the RMS er- facts, from the data-reduction package (DRP) or other ror. The comparison between the telluric spectrum and noise which is not removed (e.g. cosmic rays). These a spectrum from the cube of the nuclear region showed were manually cleaned by interpolation over the offend- a shift of 0.8 pixels, which, when applied to the data ing pixels, especially over the range of emission lines cube, reduced the feature considerably. wavelengths. The well-known ‘instrumental fingerprint’ in the SIN- To check on the wavelength calibration, the OH sky- FONI J data cube was characterized by PCA tomogra- line wavelengths were measured from the off-target sky phy (Menezes et al. 2014, 2015); this fingerprint is the data cubes. These lines are assumed to be very narrow result of detector array persistence (see George et al. and the wavelengths are published in Rousselot et al. 2016). Over the characteristic broad horizontal stripe, (2000). This showed a wavelength shift of ∼ 0.44 nm, the flux correction was substantial, in places up to equivalent to ∼ 62 km s−1; this value is used in in the ±15%. The correction was applied by interpolation over computation of the systemic velocity of the galaxy. the fingerprint in the y axis direction at each spectral pixel. For the final H+K data cube, no fingerprint was 3. RESULTS 3.1. The Nucleus of NGC 5728 NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 5

The nucleus of NGC 5728 is highly complex, as re- star-forming ring. Masking out all pixels that have a vealed by multi-wavelength images taken at high spatial value >300 mJy (to remove the jet) (bottom left plot), resolution, with evidence of star formation, radio and the SF ring is seen as a string of emission features, each X-ray jets and distorted kinematics. Fig.2 shows the i with roughly the same luminosity (∼2 mJy), which are band image from the MAST Pan-STARRS image cutout probably individual supernova remnants. The VLA 20 facility4, overlaid with the contours of the VLA 20 cm cm high-resolution map presents a very similar struc- large-scale map. It also shows the HST F160W struc- ture (not mapped here). Aligning the 6 cm and 20 cm ture map combined with the VLA 6 cm map. The VLA high-resolution maps allows measurement of the spec- images (Schommer et al. 1988) were acquired from the tral index; this is also plotted in Fig.3. The spectral 5 NRAO Science Data Archive , as set out in Table3. index is computed α = ∆ log(Sν )/∆ log(ν), and is in the There are 2 sets of 20 cm VLA data; large scale with 500 range -1.7 – -0.3, with a median value of -0.8, indicating spaxels and small scale with 000.3144 spaxels; the beam non-thermal (i.e. synchrotron) emission. size given is the half-power beam width for the antenna configuration and frequency (from the NRAO resolution table6). Table 3. VLA observations for NGC 5728 The HST structure map (Pogge & Martini 2002) pro- Obs. Date Wavelength Freq. Pixel Scale Beam Size duces an image defined as: (cm) (GHz) (00)(00)

 I  18 Apr 1994 20 1.4 0.3144 1.3 S = ⊗ P (1) I ⊗ P t 23 Mar 1988 20.1 1.49 5 14 14 Jan 1984 6 4.86 0.3259 1.0 where I is the original image, P is the HST point spread function (PSF) from the TinyTim software7 (Krist et al. 2011), Pt is the transpose of the PSF and ⊗ is the con- volution operator. The structure map enhances the nuclear bar and ring, Fig.4 shows the elliptical model fit to the Pan- with the whole central structure looking like a miniature STARRS image, using the IRAF stsdas.analysis.isophote barred spiral. The spiral aspect appears close to face- ellipse and bmodel tasks. The parameters for the var- on, which is different to the rest of the galaxy. Prada & ious features are given in Table4. The ‘ellipticity’ is Guti´errez(1999) found that the core is counter-rotating  = 1 − b/a, where a is the major and b is the minor with respect to the main galaxy, and considered that it axis size (a smaller value means closer to circular); from was most probably caused by orbital instabilities asso- which, assuming circular symmetry, the inclination i of ciated with the secondary bar; however they could not the ellipse to the LOS can be derived. This will become rule out satellite or gas accretion with negative angular important in determining the inclination to the LOS of momentum. The filamentary dust lanes delineate the the jet. cold-phase fueling flows into the SMBH (see e.g. Sim˜oes Lopes et al. 2007; Mezcua et al. 2015). The 20 cm large-scale map (Fig.2) shows nuclear Table 4. Model fit to features. Col. 2 - the approximate lim- emission combined with two regions coincident with the iting magnitude of the feature. The semi-major axis (SMA), star formation at the end of the galactic bar. At 6 cm, position angle (PA) and ellipticity () are from the ellipse model fit. PA is N=0◦, E=90◦. i=0◦ is face-on, 90◦ is edge- the higher spatial resolution nuclear emission shows an on to LOS. annulus structure, with the highest emission coincident ◦ ◦ with the structure map outer ring/arms. It also shows Feature Mag SMA (pc) PA( )  i( ) a jet in the NW-SE direction, aligned with the ionized Inner Bar 9.0 370 82 0.446 56 gas emission. Inner Ring 10.5 1045 20 0.128 29 Fig.3 displays the VLA 6 cm fluxes at three different Main Disk 12.5 4800 27 0.452 57 intensity scalings, to respectively enhance the jet and Outer Ring 14.0 13200 32 0.580 65

4 https://archive.stsci.edu/ 5 https://archive.nrao.edu/archive/advquery.jsp 6 https://science.nrao.edu/facilities/vla/docs/manuals/oss/ Fig.5 shows the the [O III] MUSE flux image (see referencemanual-all-pages below) overlaid with the Chandra X-ray contours (ac- 7 http://www.stsci.edu/hst/observatory/focus/TinyTim quired from the Chandra Source Catalog, Evans et al. 6 Durre´ & Mould

15

1 0 0 0 0 0 2 14 1 0 0

5 0 10 0 1000 13 0 0 5 5 0 0 0 5 0 2 1 0 0 0 0 0 0 0 0 0 2 0 2 5 0 00 0 0 12 0 0 0 1

1 0 0

0 0

0 2 11

500 10 1 0 0 5 kpc 0 9 500 pc 10" 2" 8

Figure 2. Left panel: Pan-STARRS i image overlaid with VLA 20 cm large-scale flux contours with star-formation at the end of the main bar and nuclear AGN/SF emission. Color values in mag arcsec−2. Right panel: HST F160W structure map overlaid with VLA 6 cm flux contours showing the AGN jet and the SF ring. Contour values in µJy.

15

4 0.5 10 0.25 ) ) y 3 y 5 J

J 0 m ) ( m

c

e x x

s −0.25 0 u c u l r 2 l F a F

( ( −0.5 g m c o

−5 l

6 1 −0.75

−10 1 kpc −1 0 −15 15 −0.4 10 2.5 −0.6

2 x

5 e ) d

y −0.8 ) n J c I

e l m 1.5 s ( a

0 −1 c r r x t a ( c u l e

F 1 −1.2 −5 p S −1.4 0.5 −10 −1.6 0 −15 15 10 5 −5 −10 −1515 10 5 −5 −10 −15 (arcsec) (arcsec) Figure 3. AGN and circumnuclear SF activity from VLA 6 cm images. Top left: linear scaling (to enhance the jet). Top right: logarithmic scaling (to enhance star-forming ring). Bottom left: Jet masked to show point-source supernova remnant emission. All flux values are in mJy. Bottom right: Spectral index derived from 6 cm and 20 cm fluxes; the negative index indicates non-thermal (i.e. synchrotron) emission. NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 7

14 14 .5 15 .5 13.5 13.5 0.4 14 13 13

13 0.2 1 12 1 12 4 4

1 1

2 2

. . 5 12 5 0 11

10 −0.2

5 kpc 9 −0.4 10" 8

12 13 12 0.2

12 11.5 11.5 0.1 11 11

5 5 . 10 11 . 10 0 0 1 1

9 5 9 5 . . 0

9 9 10

−0.1 9

5" = 1 kpc 8 −0.2

Figure 4. Elliptical model fit to the Pan-STARRS isophotes, showing the complex structure of outer disk, inner ring and nuclear bar. Left panel: (top) outer, (bottom) inner parts of the galaxy, showing the centrally disturbed morphology. Right panel: Model residual (image–model); (top) outer, (bottom) inner. All color-bars and contours for isophote models have values in magnitudes arcsec−2. 8 Durre´ & Mould

(2010), using the CSCView tool8), and the VLA 6 cm from the 0.8–2.4 µm atlas of AGN (Riffel et al. 2006) is contours. also plotted (rescaled for clarity). Fig.7 shows the de- tail for the main emission lines of interest. The optical MUSE nuclear spectrum is presented in Fig.8, show- 10 ing the Seyfert 2-like narrow emission lines of hydrogen, 5 oxygen, nitrogen, and sulfur. It also shows smooth flux 10 [ O

I

5 I continuity with the NIR spectrum. I ]

F l u x

) ( c 4 * 3.3. Continuum Emission 1

e 10 0 s

0 - c 1 r 6

a

e We can examine the nuclear structure, stellar popu- ( r g /

c lations, and obscuring dust using continuum imagery. m 2 /

−5 1000 s As the J band cube has poorer observational resolution ) (000.25 with no AO), we will only use the H+K cube (000.05 with AO). The H and K continuum magnitude −10 1 kpc 100 images are derived from the cube by measuring the av- 10 5 0 −5 −10 erage flux over 10 nm around the 2MASS filter effective (arcsec) wavelengths (H = 1662 nm, K = 2159 nm), converting −2 Figure 5. Chandra+VLA+[O III]. [O III] flux image (loga- to mag arcsec for each pixel, and deriving the color rithmic scaling) from MUSE data (flux values as per color- H − K. Fig.9 presents the magnitude and color maps bar), showing photo-ionized and shocked gas in the cones. for the central 300.8 (760 × 760 pc). Chandra (0.5–7 keV) smoothed flux contours (blue) with val- The dust-lane (starting at ∆RA=+100, ∆Dec=000, ues of 0.1, 0.2, 0.5, 1, 2, and 5 × 10−6 photons cm−2 s−1; ending at ∆RA=-000.5, ∆Dec=-000.5) shows up well in this shows the reflected AGN emission plus production from the H -band magnitude map; as expected, it is less shocked gas. VLA 6 cm contours (green) flux levels at 0.2, prominent in the K -band. The central region is very 0.5, 1 and 2 mJy, delineating the synchrotron emission from the relativistic jet. The X-ray, radio, and emission-line gas red, H − K = 0.6 mag. The location of the peak of the 00 structures are clearly aligned. central object appears to shift by ∼0 .085 between H and K. This is because of the increased dust penetra- tion at longer wavelengths. The AGN is presumed to The X-ray and [O III] fluxes are co-spatial. The X-ray be located behind this dust lane; the precise location is data have been smoothed by a Gaussian with a 2 pixel described in Paper II and is plotted in this paper. FWHM, to prevent pixellation. The X-ray orientation The H − K image shows a broad bar aligned at PA has the highest flux in the SE direction, counter to the = 40◦–220◦, roughly 90◦ to the line of the cones. This radio jet; this can be explained by obscuration of the is caused by the hot dust in the equatorial plane of the NW X-ray jet, plus relativistic beaming of the NW ra- AGN, which also is the source of the very red colors at dio jet over the SE counter-jet. Rodr´ıguez-Ardilaet al. the nucleus; this is the equatorial toroidal obscuration (2017), studying NGC 1368, deduce that the extended component. The H − K image also shows reduced ob- X-ray emission in that object is caused by shocks greater scuration in the SE and NW quadrants; the edges of −1 than 200 km s producing free-free emission; as will be these (at < 0.2 mag) align with the edges of the cones seen in Paper II, the outflow velocities of NGC 5728 (as revealed by the channel maps presented in Paper II), certainly exceed that value. especially in the SE. Fig. 10 (left panel) shows the structure map for the 3.2. The NIR and Optical Nuclear Spectrum central 1600 of the HST F814W image, clearly showing The nuclear spectrum was obtained by integrating the the feeding filaments in the inner spiral structure. The 00 flux in a circular aperture of radius 0 .5 around the right panel then overlays the K -band magnitudes con- brightest pixel in the continuum image for the SINFONI tour over the central 300.8. The dark lanes are seen as and MUSE data cubes. Fig.6 gives the spectra for the extension into the center of the feeding filaments. the whole NIR wavelength range, showing the good flux calibration between the data cubes, taken at different 3.4. Gas Line Emission dates and instruments. For comparison, the spectrum Emission lines diagnose various physical parameters in the interstellar medium, including star formation and 8 http://cda.cfa.harvard.edu/cscview/, Dataset ID outflow dynamics, as well as the physical processes of ADS/Sa.CXO#CSC/Reg/4077-1-P-2-0003 excitation. Table5 shows the flux (with uncertainty) NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 9

) 120 J - SINFONI ] I ) m ] I I I ?

H+K - SINFONI ] ] I ( I I

n

I V I

/ e

V α

P F a

IR Atlas i [ C [ s 2 100 a / S C ] ] P [ [ H I I 2 I

I I γ β X

) ) )

I 2 e 2 2

e 0 1 2 e a a m - - - H H H H S F ] P H [ [ P I 2 3 4 I c ( ( (

/ δ γ e 2 2 2 2 2 O O O 2 r r g 80 F [ B H H H B H H C C C H r e

6 1 -

0 60 1 * (

y t i 40 s n e D

20 x u l F 0 1200 1400 1600 1800 2000 2200 2400 λ (nm)

Figure 6. Nuclear spectrum from central 100 from SINFONI (J and H+K ), plus the NIR atlas of (Riffel et al. 2006). Emission lines and CO absorption band-heads are marked. The NIR atlas spectrum is rescaled and offset for clarity. All spectra are reduced to rest-frame. 80 ) m n

/ 70 s / 2

m 60 c / g ] ] r I I β X

e

I H2 [Si VI] a

e

6 50 P S F 1 [ [ -

0 H2 1 *

( 40

H2 y

t Brγ i H2 s H2

n 30 [Ca VIII] e D

x 20 u l

F CO 10 1240 1260 1280 1300 1930 1950 1970 1990 2100 2200 2250 2300 2350 2400 λ (nm) λ (nm) λ (nm)

Figure 7. Enlarged SINFONI spectra from Fig.6, showing the main lines. Spectra are reduced to rest-frame.

00 −1 for the observed emission lines in the central 1 of the 150–250 km s over systemic. The H2 lines, which are nucleus, from the J, H+K and MUSE cubes. It will not kinematically or spatially associated with the ion- be noted that the observed central wavelengths do not ization cones, have wavelengths closer to the systemic exactly correspond to the red-shifted air wavelengths, values. especially in the NIR. This comes from the biased wave- We derive maps of the gas emission fluxes from the lengths of the multiple kinematic components, where the velmap (velocity map) procedure in QFitsView on the receding gas dominates over the approaching gas; with SINFONI data cubes (J and H+K ). This procedure fits the ionized species lines in the cones (hydrogen recom- a Gaussian curve for every spaxel at the estimated cen- bination, [Fe II], and [Si VI]) show a recession velocity tral wavelength and full width half maximum (FWHM). 10 Durre´ & Mould ] I ) I ]

I I ] N I I m [

] I I

I n O

] ] S [ / ] I I [ ] I ] I I ] I ] N I ] I ] I I I I I [ s I I I T I I I I

/ r r β α a 2 O N A O S S O A S H [ [ [ [ H [ [ [ [ C [ m c / 1000 g r e

6 1 - 0 1 * (

y t i s

n 100 e D

x u l F 500 600 700 800 900 λ (nm)

Figure 8. MUSE spectra of central 100, showing the main lines. The spectrum is reduced to rest-frame. The flux is log-scale plotted because of the large dynamic range and to enhance weak lines. The [S II] (679 nm) and the [O II] (740 nm) are doublets. The Ca triplet (CaT) is also indicated.

H K H-K 14 14 0.6 1.5 13.75 0.5 1 13.5 13.5 0.4 ) c e

s 0 13.25 13 c 0.3 r a ( 13 0.2 −1 12.5 12.75 100pc 0.1 −1.5 12.5 12 1.5 1 0.5 0 −0.5 −1 −1.5 1.5 1 0.5 0 −0.5 −1 −1.5 1.5 1 0.5 0 −0.5 −1 −1.5 (arcsec) (arcsec) (arcsec) Figure 9. H and K surface magnitude and H − K color map, as labeled. The magnitude colors are plotted with square-root scaling, to enhance contrast. The color-bar values are in mag arcsec−2. The H − K plot shows the AGN equatorial obscuration. This generates maps of the best fit continuum level (C), ponent for Seyfert 1.9 classifications, where misclassifi- height (H), central wavelength (λ), and FWHM. These cation is caused by the presence of strong, AGN-driven, are readily converted to the dispersion (σ), the flux (F ) outflows. and the emission equivalent width (EW ). Maps were Map values are accepted or rejected based on ranges obtained for the species Pa β (1282 nm), Br γ (2166 on each of the derived parameters produced by the pro- nm), [Fe II] (1257 and 1644 nm), H2 (2121 nm) and cedure, based on visual inspection of the fluxes and kine- [Si VI] (1964 nm). We note that the Br γ and [Si VI] matic structures i.e. the derived values of continuum, maps have already been presented in Shimizu et al. line flux, LOS velocity or dispersion have to be within (2018), in the context of reevaluating the broad H α com- certain values. Single pixels may be rejected because ] ] I I I T T I

a a S O [ [ C C NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 11

7.5 1.5 4 1 .8 13 14 5 13 .8 1 1 3.4 2.5 1 0.5 3.2 12.9 ) ) c c

1 e e 2 12.5 6 . s s

.

0 0 7 c c 3 r r 1 a a ( ( −0.5 −2.5

−1 −5 1 3.8 −1.5 14 −7.5 7.5 5 2.5 0 −2.5 −5 −7.5 1.5 1 0.5 0 −0.5 −1 −1.5 (arcsec) (arcsec) Figure 10. Left panel: HST F814W structure map, showing the feeding spirals, the bright central nucleus, and the star-forming regions (bright points aligned with the outer edges of the dust lanes). The light green rectangles are the fields of view of the SINFONI H+K (inner) and J (outer) observations. Right panel: Central 300.8 (760 pc) of the structure map overlaid with the K magnitude contours; the H − K obscuration matches the feeding filament. of large excursions from their neighbors; the source of were masked to a minimum flux level for each species anomalous values is usually noise spikes in the data or and to remove the bright star some 1900NE of the nu- low flux values, causing poor model fits. Rejected pix- cleus. els are then interpolated over from neighbors or masked 3.4.1. Emission-line Morphology out, as appropriate. The [Si VI] maps were difficult to produce due to the Figs. 11, 12, 13 and 14 shows the flux and EW for close and strong H2 (1957 nm) line; since the range of each species. The J -band maps have a spatial extent of velocities over the whole field is fairly large, the velmap 700.5 square, as against the H+K -band of 300 (1.5 vs. 0.6 routine was ‘locking on’ to the wrong line in places. This kpc) (the FOV of H+K is overplotted on the Pa β flux was solved by creating the maps for the H2 line, then map.). The hydrogen recombination emission, [Fe II] subtracting a Gaussian fit at each spaxel from the fitted and coronal [Si VI] lines all show similar structure of a ◦ parameters; this had the effect of removing the H2 line biconal outflow with a PA = 140–320 ; the equivalent from the data cube. Additionally the fitting procedure width maps show this clearly (the EW is invariant to was done independently for the north and south halves obscuration), displaying a distinct ‘waist’ at the cone of the data cube and then combined, as the H2 velocity intersections ; this shows that there is significant stellar field is oriented in that direction. The [Si VI] line was continuum in front of the emission and obscuration along then fitted successfully. our LOS.. By contrast, the H2 is spatially distinct, pre- We also obtained emission-line maps from the MUSE senting as a disk oriented roughly NS with ‘arms’ trailing data cube in a similar manner. To increase the signal-to- to the NW and SE. As we will show in Paper II, it is noise ratio (S/N), especially in the outer regions were the also kinematically distinct. gas emission is weak, we use the ‘Weighted Voronoi Tes- The MUSE H α and [O III] maps show a similar pic- sellation’ (WVT) method (Cappellari & Copin 2003), ture, with a greater FOV of 3000 × 3000 (6 × 6 kpc) (Fig. using the voronoi procedure in QfitsView. This aggre- 13). The ionization cones can easily be traced with the gates spatial pixels in a region to achieve a target S/N. [O III] emission up to 2.5 kpc from the nucleus. The H α This needs both signal and noise maps; these are ob- emission also clearly shows the star-forming ring. Many tained at each spaxel by the data and the square root of H II regions are visible in a ring of approximately 7 kpc the variance from the MUSE data cube, both averaged radius around the nucleus; these trace the faint spiral along the spatial axis. After some experimentation, the arms from the outer ring to where they join the nuclear target S/N was set to 60. We obtained maps of the structure, especially SE of the SF ring, where there is a species H α,H β, [O III] (500.7 nm), [S II] (671.6, 673.1 short extension pointing SW. nm), [N II](654.8 nm) and [O I] (630.0 nm). These maps 3.4.2. Coronal Line Emission 12 Durre´ & Mould

Flux (x10-16 erg/cm2/s) Eq. Width (nm) 4 4

1 1 2 2 P a

0.8 0.8 β

( ) ) 1 c c e e 2

s + s + 0.6 0 0.6 0 8 c c r r 2 a a ( (

0.4 n 0.4 m −2 −2 ) 0.2 0.2 200pc −4 −4 0 4 4 1.2 1.25

1 [ 2 2 F 1 e

I

0.8 I ]

) ) ( c c 1

e e 0.75 2 s 0 + s 0 + c 0.6 c 5 r r a a 7 ( (

0.5 n

0.4 m

−2 −2 ) 0.2 0.25

0 0 −4 −4 4 2 0 −2 −4 4 2 0 −2 −4 (arcsec) (arcsec)

Figure 11. Ionization cone structure as shown by the flux and equivalent width values for Pa β and [Fe II] (1257 nm). Flux values (shown in color-bar) in units of 10−16 erg cm−2 s−1. Contours are 10, 25, 50, 75 and 90% of the maximum flux. Equivalent width values in nm. Blue circles on the Pa β EW map are the locations for SF age measurement. The outer ring in the Pa β maps traces the star-forming ring around the nucleus, [Fe II] traces the ionization cone boundaries. The blue rectangle on the Pa β flux map shows the FOV of the SINFONI H+K filter observations.

Emission lines of highly ionized species (e.g. [Si VI], driven by the radio jet, and that shock mechanisms [Ca VIII], and [S IX]) trace the direct photo-ionization were favored over photo-ionization. A similar conclu- either from EUV and soft X-rays from the AGN accre- sion was deduced for NGC 1368 by Rodr´ıguez-Ardila tion disk, or by fast shocks. These species have ion- et al.(2017). ization potentials (IP) up to several hundred eV, and Apart from the [Si VI] emission, we also detect weak are called coronal lines (CLs) and the emission loca- [S IX] and [Ca VIII] coronal lines. This is in contrast tions are called coronal line regions (CLRs). This emis- to Rodr´ıguez-Ardilaet al.(2011), who reported no de- sion has the advantage of not being contaminated by tectable flux for those species for NGC 5728, in their photo-ionization from star formation i.e. it is diagnos- coronal line study of 54 local AGN. We constructed flux tic of AGN activity. For coronal species with an IP of maps these species by averaging the data cube along the ∼ 100 − 150 eV, the emission exhibits a similar mor- spectral axis over the emission line profile, then sub- phology and kinematics to lower ionization lines such tracting the average continuum in a neighboring fea- as [O III]; however for species with IP > 250 eV, the tureless spectral region; the result was multiplied by the emission is very compact. line profile width to produce the flux. The weakness of Mazzalay et al.(2013a) found for NGC 1068 that the the flux precluded using the standard velmap procedure. morphology and kinematics were consistent with being Fig. 15 plots the flux maps; the weakness of the lines NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 13

Flux (*10-16 erg/cm2/s) Eq. Width (nm)

1.5 1.5 0.2 1.5

1 1 1.25 0.15 0.5 0.5 1 ) ) c c e e γ s s r 0 0 c c

r r 0.75 B + 0.1 + a a ( ( −0.5 −0.5 0.5 −1 0.05 −1 0.25 −1.5 100pc −1.5 0 0

1.5 1.5 12.5 1.5

) 1 1 10

m 1.25 n

0.5 0.5 6 ) ) . c 1 c 7.5 5 e e s s 7 0 0 c c r r 8 + + a a

( 0.75 ( 1 ( −0.5 −0.5 5 α

a 0.5

P −1 −1 2.5 0.25 −1.5 −1.5 0 2 1.5 0.3 1.5

) 1 0.25 1 1.5 m n 0.5 0.2 0.5 4 ) ) c c 4 e e 6 s 0 s 0 c c

1 1 r 0.15 r

( + + a a

( ( ] I I

−0.5 −0.5

e 0.1 F

[ 0.5 −1 −1 0.05 −1.5 −1.5 0 0

1.5 0.8 1.5

4

) 1 1

m 0.6 n 0.5 0.5 4

) ) 3 c c 6 e e 9 s 0 s 0 c c 1 r r

( + 0.4 + a a

( ( ]

I 2 −0.5 −0.5 V

i S

[ 0.2 −1 −1 1

−1.5 −1.5 0 0

1.5 1.5 0.4 3

1 0.35 1 2.5 ) 0.3 m 0.5 0.5 n ) ) 2 c c

1 0.25 e e s s 2 0 0 c c r r 1 + + a 0.2 a 1.5 ( ( 2 (

2 −0.5 0.15 −0.5

H 1 −1 0.1 −1 0.5 0.05 −1.5 −1.5 0 1.5 1 0.5 0 −0.5 −1 −1.5 1.5 1 0.5 0 −0.5 −1 −1.5 (arcsec) (arcsec)

Figure 12. As for Fig. 11, but for Br γ, Pa α,H2 (2121 nm), [Fe II] (1644 nm), and [Si VI]. The [Si VI] has nearly the same extent as the hydrogen recombination emission. The star-forming ring is outside the scale of the maps. 14 Durre´ & Mould

Flux (x10-16 erg/cm2/s) Equiv. Width (nm)

5 10 10 H

104 α

( 6

1 5 6 . 1000 3

n m

0.1 ) 100

104 10 H

β

( 4

1000 8 6 . 1

n 1 m 100 )

30

20 5

10 [ 100 O

I I

10 I ]

4 ( ) 10 5 c e 0 s

0 10 0 c r . a 7 (

1000 n

−10 m

1 ) −20 100 1000 pc −30 30 20 10 0 −10 −20 −30 (arcsec)

Figure 13. MUSE flux and EW maps for H α,H β and [O III]. The star-forming ring is prominent in H II but is absent in [O III]. The flux values are plotted with logarithmic scale to enhance details. The ionization cones (most prominent in [O III]) can be traced up to 2.5 kpc from the nucleus. NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 15

Flux (x10-16 erg/cm2/s) Equiv. Width (nm)

105 [ N

I I ]

4

10 ( 6

1 5 8 . 3

1000 n m )

100 0.1

4

10 [ 10 S I I ]

( 6

1000 7 8 . 3

n m

100 ) 1

10 30 10 104 20 [ O

10 I ]

(

) 1000 6 c 3 e s

0 0 c r . a 0 ( 1 n −10 100 m )

−20 1000 pc 10 −30 30 20 10 0 −10 −20 −30 (arcsec)

Figure 14. MUSE flux and EW maps for [N II], [S II] and [O I]. The star-forming ring is prominent in H II but is absent in [O III]. The flux values are plotted with logarithmic scale to enhance details. The ionisation cones (most prominent in [O III]) can easily be traced up to 2.5 kpc from the nucleus. 16 Durre´ & Mould

Table 5. Integrated flux for emission lines for the central will cause some uncertainties, so the flux values should 00 00 1 (0 .5 radius) aperture, with their respective uncertainties not be taken as very accurate, however the structure is −16 −2 −1 (∆F). Flux values are in 10 erg cm s . Measurements clear. are grouped by data source.

Data Source [S IX] Flux Species λ (Obs) λ (Air) F ∆F 4 1.6 MUSE

H β 491.1 486.1 75.72 3.11 2 1.4 [O III] 500.9 495.9 349.15 20.90 )

[O III] 505.8 500.7 1039.59 53.67 c 1.2 e + s 0 c

[N I] 525.0 519.8 11.99 1.60 r a

( 1 [Ar III] 615.1 608.9 12.91 1.27 [O I] 636.3 630.0 41.17 1.40 −2 0.8 [S II] 642.8 636.0 13.07 0.94 0.6 [N II] 661.4 654.8 129.80 12.0 200pc H α 662.9 656.3 357.30 13.31 −4 4 2 −2 −4 [N II] 664.9 658.3 462.6 12.3 (arcsec) [Ca VIII] Flux [S II] 678.3 671.6 103.63 3.23

[S II] 679.3 673.1 101.66 2.97 1.5 0.175 [Ar III] 720.8 713.8 36.57 1.78 1 [O II] 739.3 732.0 5.81 0.88 0.15 [O II] 740.4 733.0 11.81 1.16 0.5 0.125 ) c

[Ar III] 783.0 775.0 10.49 0.78 e s 0 + 0.1 c r

[S III] 916.1 906.9 128.00 6.20 a ( −0.5 0.075 SINFONI J 0.05 Pa γ 1105.3 1094.1 13.94 1.01 −1 0.025 He II 1197.2 1185.5 7.78 1.28 −1.5 100pc [P II] 1201.3 1188.6 19.01 2.20 1.5 1 0.5 −1 −1.5 C I (?) 1216.7 1204.9 9.77 0.98 (arcsec) [Fe II] 1269.4 1256.7 39.47 2.57 Figure 15. [S IX] and [Ca VIII] emission line flux. [S IX] Pa β 1295.3 1282.2 40.88 1.64 contour levels at 0.2, 0.5, and 1, [Ca VIII] contour levels at −15 −2 −1 SINFONI H+K 0.02, 0.05, and 0.1; all units are 10 erg cm s . The AGN is not marked on the [Ca VIII] map, as it is located [Fe II] 1660.4 1643.6 35.88 3.97 at the flux maximum. Note that the plots are at different H2 2-1 S(5) 1964.2 1944.9 8.26 2.06 spatial scales. The very high excitation species are confined H2 1-0 S(3) 1976.3 1957.6 48.96 2.18 around the AGN. [Si VI] 1983.5 1964.1 77.10 2.72

H2 1-0 S(2) 2053.2 2033.8 18.10 0.62 He I 2078.8 2059.5 7.45 0.71 The CLR, as delineated by the [Si VI] emission, ex-

H2 2-1 S(3) 2093.3 2073.5 3.27 0.60 tends almost to full length of the NLR, out to 300 pc in

H2 1-0 S(1) 2142.1 2121.8 45.56 2.13 each direction from the AGN. This indicates strongly

H2 2-1 S(2) 2174.5 2154.2 4.37 1.12 collimated hard UV–soft X-ray flux from the AGN. Br γ 2187.3 2166.1 17.94 1.09 While the [Si VI] flux scales reasonably well with the Br γ flux, there is an impression from the morphology H2 3-2 S(3) 2221.5 2201.4 0.56 0.25 that the production mechanism is different between the H2 1-0 S(0) 2244.5 2223.5 10.58 0.90 two cones; the SE emission is in a conal form, as would H2 2-1 S(1) 2269.1 2247.7 6.44 0.51 be expected from direct ionization from the AGN EUV H2 1-0 Q(1) 2429.6 2406.6 41.15 1.79 field. By contrast, the NW emission outlines, rather H 1-0 Q(2) 2435.6 2413.4 7.80 1.36 2 than infills, the cone; this is clearer in the equivalent H 1-0 Q(3) 2446.8 2423.7 36.49 1.82 2 width plots rather than the flux plots. This indicates that shock mechanisms predominate in the NW. NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 17

The [S IX] emission (IP = 379 eV, λ = 83.3 nm) et al.(2015), where approaching clouds preferen- showing a small extension along the line of the SW cone, tially show their non-ionized face to the observer; while the [Ca VIII] (IP = 147 eV, λ = 8.4 nm) exhibits thus their line emission is attenuated by dust em- a more compact structure around the AGN location, bedded in the cloud and the average velocity mea- with a possible extension along the NW cone; both of sured for the blue-shifted clouds is skewed toward these extensions are close to the observational resolution smaller values. limits. Neither of these species shows the same spatial extent as [Si VI]; in the case of [Ca VIII] (which has a We deduce the position of the AGN by 3 different similar IP to [Si VI]), the low line strength means that methods, each of which is plotted on Fig. 16, which 00 the flux level drops below the detectable threshold; in shows the magnified central region (1 = 20 pixels a the case of [S IX] an additional factor could be that the side). These are derived from: ISM fully absorbs the ionizing radiation closer to the • The centroid/maximum of the H2 flux, assuming AGN. We can also posit that the higher IP species are this is kinematically cold and settled around the ionized directly by the AGN, while the [Si VI] emission center of mass of the nucleus. The [Fe II] (1644 is also generated by shock excitation in the ionization nm), H2 and Br γ flux maxima locations are also cones, which do not have enough energy to excite the plotted for comparison. higher IP species. • The [Si VI] flux is presumably generated by direct 3.5. Locating the AGN photo-ionization from the AGN, and thus the peak In Seyfert 2-type galaxies, the AGN is obscured by value will be on the AGN location. the dusty torus, so the small, unresolved BLR is not • The H+K -band flux ratio of [Fe II] and Br γ shows visible; this torus can extend from 0.1 to tens of parsecs that the [Fe II] jackets the Br γ, thus defining the (Hopkins & Hernquist 2006; Netzer 2015; Elitzur 2008), edges of the cones. The cone edges are plotted depending on AGN luminosity. The position of the AGN as lines; these are derived from the [Fe II] zero is usually taken as the brightest pixel in the continuum velocity channel map (see Paper II). (on the assumption that there is a nuclear cluster), but in this case there is a dust lane that obscures this loca- • The continuum centroid positions are plotted for tion, as seen on the H−K color map (Paper I). This lane H+K wavelengths at 1460 nm, then in 100 nm in- is in addition to the supposedly compact dusty torus, as crements from 1600–2400 nm. This assumes that it extends across the field for ∼ 400 pc, and connects to the flux peak moves closer to the AGN as the ob- the spiral feeding filaments. scuration becomes less important at longer wave- Presumably, the ionization cones have their origin lengths. (both positionally and kinematically) at the AGN cen- tral engine; however there are issues that will affect the • The lines that joins the peaks of the velocity ex- symmetry of the observed flux and velocity fields: trema (maximum and minimum) for [Fe II] (1644 nm) and Br γ are also plotted - there is some un- • Obscuration; the dust lane is on the approaching certainty in defining these lines, as the extrema side; this will reduce the flux (and corresponding locations are not well defined. flux-weighted velocity). All points are assumed to have a positional error of • ISM impact; the SW velocity field shows an in- ±1 pixel. The H2 flux, the continuum centroid trajec- crease out from the AGN to a maximum of about tory and the outflow edges all seem to align to within 350 km s−1 at 300 pc from the AGN and then a ±2 pixels. The final AGN location is taken to be the deceleration to 150 km s−1 at 760 pc (projected centroid of the locations of the H2, Br γ and [Si VI] flux distances); if the outflow encounters a more dense maxima centroids and the [Fe II] bicone center, plus the ISM (associated with increased obscuration), this location of the maximum of the image at 2400 nm; this will both reduce the distance to and the velocity is marked as the yellow star in Fig. 16. We did not in- of the maximum. clude the [Fe II] flux maximum, as this is only excited in low ionization regions, i.e. away from the central AGN • Velocity bias; even without obscuration, an out- source. If we assume the AGN location is the same flow that has a significant component of velocity as the Chandra compact, 2–7 keV X-ray source, this is along the LOS will have the approaching veloc- RA = 14h 420 23.88300, DEC = -17◦ 150 11.2500 (Evans ities biased towards zero, as described by Lena et al. 2010, with typical 000.6 precision). 18 Durre´ & Mould

4. DISCUSSION 0.4 4.1. Gaseous Excitation 4.1.1. Infrared Diagnostics Excitation mechanisms broadly fall into two categories 0.2 (1) photo-ionization by a central, spectrally hard radia- tion field (from an AGN accretion disk) or by young, ) "

( hot stars (UV ionization and recombination or colli-

c

e 0 sional heating) or (2) thermal heating, which can be D either by shocks (from AGN outflows, supernova rem- Δ nants, star formation, asymptotic giant branch stellar −0.2 winds or radio jet interaction) or UV/X-ray heating of gas masses. H2 is also excited by UV pumping and flu- orescence (Black & van Dishoeck 1987). The emission line spectra flux ratios enable determination of the par- −0.4 20pc ticular or mixture of mechanisms. We derive excitation mode diagnostic diagrams from the emission line ratios 0.4 0.2 0 −0.2 −0.4 [Fe II] 1257 nm/Pa β and H2/Br γ. Nuclear activity for AGN Δ RA (") NIR emission line objects can be categorized by a di- H2 Centroid agnostic diagram (Larkin et al. 1998; Rodr´ıguez-Ardila Brγ Centroid [Fe II] Centroid et al. 2005), where the log of the flux ratio of H2/Br γ [Si VI] Centroid is plotted against that of [Fe II](1257 nm)/Pa β. This is [Fe II] Outflow Edges & Centroid analogous to the BPT diagrams (Baldwin et al. 1981) H+K Cont. Centroid J Cont. Centroid commonly used in the optical regime (e.g. Kewley et al. [Fe II] Velocity Extrema Axis 2006). Following the updated limits from Riffel et al. Brγ Velocity Extrema Axis (2013a), the diagram is divided into three regimes for star-forming (SF) or starburst (SB) (dominated by H II Figure 16. AGN location derived by different methods: see regions), AGN i.e. subjected to the radiation field from text for explanation. The outflow edges as delineated by the accretion disk and low-ionization nuclear emission the [Fe II] zero velocity channel maps are shown as black line region (LINER) excitations, where shocks from SN dotted lines, with the centroid shown as the cyan diamond. and evolved stellar outflows dominate. Transition Ob- The centroids for the flux maxima for H+K and J cubes jects (TOs) have a mixture of excitations, and can be with wavelength are shown as read and black trajectories, respectively. The axes are the data cube spatial pixels; 1 sub-divided by the diagnostic ratios into those where pixel = 10 pc = 000.05 projected distance; the grid lines are [Fe II] dominates and those where H2 dominates. 1 pixel. The (0,0) position in RA, DEC is the brightest pixel As we do not have the J - and K -band data at the of the H+K image from the wavelength collapsed cube. The same spatial scale, the J -band diagnostic ratio ([Fe II] AGN location is taken as the average of the centroids of the 1257 nm/Pa β) is re-calibrated to the ratio ([Fe II] 1644 H2, Br γ, [Si VI] and continuum flux peaks, plus the outflow nm/Br γ) in the H+K -band, using the ratios ([Fe II] boundary intersection. 1257/1644) and (Pa β/Br γ) as given in Table6. The

We can match the AGN location on the J -band data Table 6. Infrared excitation mode diagnostic diagram cube by following the trajectory of the flux peak with regimes flux ratios. wavelength. This is plotted at 1140 nm, then in 50 nm increments from 1200–1350 nm. We equate the contin- Excitation Mode H2/Br γ [Fe II]/Pa β [Fe II]/Br γ uum centroid at 1350 nm in J as the same as 1460 nm (1257 nm) (1644 nm) in H+K, displaced to follow the trend of the trajectory SF/SB < 0.4 < 0.6 < 2.6 with wavelength. These positions are shown on previous AGN 0.4 – 6 0.6 – 2 2.6 – 8.6 and subsequent maps with a ‘+’ symbol. LINER > 2 > 2 > 8.6 Further support for the determination of the AGN lo- cation is given by the close alignment with the stellar velocity kinematics and the maximum velocity gradient diagnostic emission lines are convenient; the pairs are of the gas kinematics. close together in wavelength, removing the dependency on calibration accuracy and differential extinction. The NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 19 table has been supplemented with the expected ratio be either photo-ionization by young hot stars (UV) or regimes for [Fe II] 1644 nm/Br γ for H and K com- accretion disk radiation (EUV/soft X-rays). In the bined spectra, taking the ratios Pa β/Br γ = 5.88 and [Fe II]1644 nm/Br γ ratio plots, the cones shows low [Fe II] 1257/1644 nm = 1.36. If this ratio is used, the ratios, however these are not generated by hot, young fluxes must be corrected for extinction. stars, but by the AGN radiation field, as shown by the The H+K -band diagnostic ratios are shown in Fig. 17 [Si VI] flux. [Si VI] has an IP = 167 eV (extreme UV/X- (top left and right panels). Normally, extinction correc- ray – 7.4 nm), which fully ionizes [Fe II] to [Fe III] (which tion is not required as the line pairs are close together, has an IP 16.2 eV), therefore the ratio of [Fe II]/Pa β will however the [Fe II] 1644 nm flux values must be multi- be reduced in the ionization cones, which is exposed di- plied by 1.17 to correct for the extinction relative to Br γ rectly to the AGN radiation. This is also illustrated by in this case, taking a value of AV = 2.6 from Section 4.2, the X-ray image (Fig.5). below. Fig. 17 also shows (bottom right) the density of We distinguish between excitation sources at a partic- all pixels that have a measurement of both ratios on the ular location by examination of the continuum and emis- excitation diagnostic diagram; the labels correspond to sion line maps, as well as the diagnostic ratios. From the locations on the [Fe II] 1644 nm/Br γ map, i.e. the Fig. 17 (panel 1), for the [Fe II]/Pa β ratios, we can nucleus(‘N’), the two cones (‘1’ and ‘2’) and an off-axis see that there is almost no ‘pure’ star formation, ex- location (‘3’). cept in the ring around the edge of the field (the 1.6 kpc Overall, the excitation mode diagram show no ‘pure’ ring). The ionization cones, unsurprisingly, show mainly photo-ionization/SF mode, with the vast majority of AGN excitation, with a mixture of AGN and LINER pixels in the AGN mode region, with some LINER and excitation surrounding it. The actual mode in the pe- TO excitation. Fig. 17 (bottom left) shows the predom- riphery will be somewhat uncertain, as the flux values inating mode at each spatial location, as defined by the are low, with correspondingly larger uncertainties. By regions outlined in the bottom right panel. The colors contrast, the H2/Br γ ratios have a different structure; denote the mode, as defined in the caption; the ‘TO’ this is due to the molecular hydrogen being decoupled regions have been divided into that which is dominated both spatially and kinematically from the cones. This by excess H2 and that dominated by excess [Fe II] emis- is also shown by the velocity and dispersion histograms; sion. The plot shows the predominance of the AGN the [Fe II] and hydrogen recombination absolute velocity mode, with a TO ([Fe II] excess)/LINER at the cone and dispersions peaks are higher than H2(these results end caps and TO (H2 excess) at the ‘waist’. will be presented in Paper II). The correlation between the two sets of ratios on a We can use the forbidden lines [Fe II] and [Si VI] as 2 spaxel-by-spaxel basis is weak or non-existent (R = diagnostics for density, as above a critical density (ncr) 0.044), unlike that found for e.g. IC 630 (Durr´eet al. for each species the emission is suppressed because of 2017) and for IC 4687, but similar to NGC 7130 (both rapid collisional de-excitation (Rodr´ıguez-Ardila et al. 5 −3 Colina et al. 2015). This is due to the multi-component 2011). For [Fe II], this is of the order ncr = 10 cm ; 8 −3 nature of this object; IC 630 is a starburst galaxy for [Si VI] this is ncr = 6.3 × 10 cm . This indicates and IC 4687 a prototype star-forming luminous in- that the densities inside and outside the cones could be frared galaxy (LIRG), whereas NGC 7130 has a mix- different by several orders of magnitude. ture of star-forming regions and compact AGN excita- tion. Davies et al.(2016) have presented computations 4.1.2. Optical Diagnostics of AGN and star-forming mixing ratio for NGC 5728 We also constructed BPT diagrams diagrams from the from WiFeS optical observations on a 100 scale (the S7 MUSE data cube optical emission-line maps (see Section survey), where there is a clear trajectory of excitation. 3.4.1). The pixel excitation density maps for [N II]/H α, From our observations, this diagnostic is not possible [S II]/H α and [O I]/H α vs. [O III]/H β are shown in Fig. for the nuclear region from infrared observations at high 18 (top row). We use the classification lines from Kewley resolution because of the mixture of ionizing and ther- et al.(2006), dividing up the diagrams into H II-region- mal processes at any one LOS. like, Seyferts, LINERs, and composite H IIAGN types. The standard division of the NIR excitation diagram The tight distribution of the points shows a smooth tran- into H II regions, AGNs, LINERs, and TOs is a little sition of star formation to AGN excitation. Following misleading, as what is being plotted is excitation mech- Davies et al.(2014a,b), this is parameterized on each anism, i.e. photo-ionization and recombination versus diagram using a star-formation/AGN mixing ratio mea- thermal processes (heating plus shocks). Especially in sure, where the 0 and 100% AGN fraction is assigned the bottom-left corner of the diagram, the source can to the extrema of the measured mixing sequence. The 20 Durre´ & Mould

Log(H2/Brγ) Log([Fe II] 1644 nm/Brγ) 1.5

1.5 1.5 1.25 R R

E 1 E

N 2 N 1 I 1 I L L 1 0.5 0.5 0.5 ) )

c c 0.75 e e s s 0 N 0 N N c + 0 c r r G G a a A A

( ( 3 −0.5 −0.5 0.5 −0.5

−1 I −1 I I 1 I 0.25 100pc H −1 H −1.5 −1.5 0 −1.5 1.5 1 0.5 0 −0.5 −1 −1.5 1.5 1 0.5 0 −0.5 −1 −1.5 (arcsec) (arcsec) Spatial Excitation Mode Excitation Mode 2

1.5 LINER TO 1.5 1 ) γ r B /

0.5 m n

) 1 c 4 e 4

s 1 0 6 c AGN 1 r

] a I (

I 3

−0.5 e F [ (

g 2 TO o −1 l N 0 HII −1.5

−0.5 1.5 1 0.5 0 −0.5 −1 −1.5 −1 −0.5 0 0.5 1 1.5

(arcsec) log(H2/Brγ)

Figure 17. Excitation diagnostic maps from SINFONI H+K data. Top left: H2/Br γ flux ratio map (log ratio). Black contours are K -band continuum flux, normalized to 10, 30, 50, 70, and 90% of the maximum. Color-bar labels show the excitation mode (H II–AGN–LINER). Top right: [Fe II]1644 nm/Br γ flux ratio, corrected for reddening, black contours are the Br γ flux; normalized to 10, 30, 50, 70, and 90% of the maximum. Bottom left: Spatial excitation mode; colors are red-AGN, green-LINER, orange-TO (H2 predominating), purple-TO ([Fe II] predominating). Bottom right: Excitation pixel density map for log(H2/Br γ) vs. log([Fe II] 1644 nm/Br γ). Contour levels at 1, 5, 10, and 50% of maximum. The labels (‘N’,‘1’,‘2’,‘3’) correspond to locations on the [Fe II]/Br γ ratio plot, as described in the text.

0% mixing ratio point is shown on each plot as a green .50%), with Seyfert/AGN excitation coded yellow and symbol, with the green dotted contour lines delineating red (with the mixing ratio &50%). the mixing percentage along the sequence. The excitation values for several representative loca- The bottom row of Fig. 18 shows the excitation mode tions were computed for a 100diameter aperture; the flux maps for each diagnostic set, color-coded by the mixing values (with errors) were measured by Gaussian fits to ratio of each spaxel; there is complete consistency be- the emission line. These locations are at the nucleus, two tween the plots. Star-formation/composite excitation is in the SE and three in the NW ionization cones, three coded as blue, cyan and green (with the mixing ratio on the star-forming ring, and two in the spiral arm that NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 21

Table 7. Basis locations for SF/AGN mixing ratios.

log([N II]/H α) log([S II]/H α) log([O I]/H α)

Basis Point SF (-0.5,-0.8) (-0.7,-0.7) (-2.0,-0.75) Basis Point AGN (0.2,1.45) (0.05,1.45) (0.7,1.45) intersects the SF ring from the south (one near the in- • UV photons (fluorescence) from star formation tersection point and one at a star forming site ∼2600SW and/or AGN continuum emission (Black & van of the nucleus). The values are given in Table8. For the Dishoeck 1987). nucleus, where the line of sight intersect both approach- ing and receding gas, a multi-component Gauss fit was • Shocks from supernovae, AGN outflows or star- required to de-blend the 6 overlapping components (two formation winds (Hollenbach & McKee 1989). each for H α and [N II] λλ 654.9, 658.3 nm). These locations are shown as numbers on the [N II]/H α mix- • X-rays from the AGN irradiating and heating ing ratio map; each location is plotted on the respective dense gas (Maloney et al. 1996). excitation density map (red numbers). In reality, all these different mechanisms occur together; The electron density N (Acker & Jaschek 1986) and e however, the dominating mechanism can be estimated temperature T (Osterbrock & Ferland 2006) can also e and the contributing fractions of different mechanisms be estimated from optical diagnostics, using the [N II] can be constrained (Busch et al. 2017). and [S II] emission lines for the MUSE spectrum. The Following the method outlined in Wilman et al. relationships are: 5 −3 (2005), for gas with density nT > 10 cm , the ther- mal (collisional) temperatures can be estimated. The

RN = I(λ654.8 + λ658.4)/I(λ575.4) (2) occupation numbers of the excited ro-vibrational levels of the H2 molecule will be in thermal equilibrium at a RS = I(λ671.7)/I(λ673.1) (3) temperature T equal to the kinetic temperature of 25000 exc Te = (4) the gas. This leads to the relationship: ln (RN /8.3)     2 RS − 1.49 Fi λi Ti Ne = 10 Te (5) ln = constant − (6) 5.62 − 12.8RS Ai gi Texc where R is the ratio for the [N II] lines and R is the N S where Fi is the flux of the ith H2 line, λi is its wave- ratio for the [S II] lines. The alternate diagnostic for T e length, Ai is the spontaneous emission coefficient, gi is using the [O III] lines (Kwok 2007) is not available in the the statistical weight of the upper level of the transition MUSE spectral range. For the SF-dominated regions and Ti is the energy of the level expressed as a temper- (locations ‘7’ to ‘11’), the [N II]λ575.4 was not mea- ature. The left-hand side of this equation is equivalent surable; we used an estimated temperature of T =8000 e to ln(Nupper), the occupation number of the upper level K, somewhat lower than the AGN-dominated locations. of the H2 transition. This relation is valid for thermal The calculated values are given in Table8; while the excitation, under the assumption of an ortho:para abun- electron temperatures are reasonably consistent (with dance ratio of 3:1. The Ai, gi, and Ti for each line was error bars of the order of 5-10%) in the AGN-dominated obtained from on-line data ‘Molecular Hydrogen Tran- regions, the electron density has larger errors (from 25 sition Data’9. to 70%, mainly due to the uncertainties in the flux of At a particular location, plotting ln(Nupper) vs. the weak [N II]λ575.4 nm line), but there is a clear trend Ti gives a linear relationship, where the negative in- with lower density being at a greater distance from the verse slope is the excitation temperature Texc. AGN. N linearly scales with a lower assumed T . e e The H2 2-1 S(3) (2073.5 nm) is diagnostic for X-ray

4.1.3. H2 Excitation excitation, which is expected to suppress the line, as the upper level of this transition is depopulated by a Molecular hydrogen (H ) is very important in the star- 2 resonance with photons around the wavelength of Lyα formation context of AGN activity, since it is the ba- at 1216 A,˚ which are readily generated by X-ray heating sic building block for stars. In the K band, there are a whole series of rotational-vibrational emission lines, which can be used to examine the excitation mechanism 9 www.astronomy.ohio-state.edu/∼depoy/research/observing/ molhyd.htm for H2, which can be either: 22 Durre´ & Mould

[N II]/Hα vs. [O III]/Hβ [S II]/Hα vs. [O III]/Hβ [O I]/Hα vs. [O III]/Hβ 1.5 1 00 80 1 Seyfert 8 1 Seyfert 1 80 4 0 4 4 1 3 6 3 6 63 2 2 2 60 60 650 5 5 ) β H / ]

I 4 4 I 0 0 I 40 O [

( 0 AGN g o l 170 170 107 HII 9 209 2 9 20 0 8 HII 8 LINER 8 LINER −0.5 11 11 11

Comp HII −1

−2 −1.5 −1 0 0.5 1 −1 0.5 −2 −1.5 −0.5 0 log([NII]/Hα) log([SII]/Hα) log([OI]/Hα)

100 100 100

20

80 80 80

10

6 ) ) ) % % %

7 ( ( ( 60 60 60 o o o i i i t t t

) 5

4 a a a c R R R e 1 9 s g g g

0 n n n c 2 3 i i i r x x x i i i a (

8 M M M

N 40 N 40 N 40 G G G A A A 10 −10

20 20 20

−20 1000 pc 11 0 0 0 20 10 0 −10 −20 20 10 0 −10 −20 20 10 0 −10 −20 (arcsec) (arcsec) (arcsec)

Figure 18. Optical excitation (BPT) diagnostic diagrams from MUSE data. Top row: Excitation pixel density map for log([N II]/H α), log([S II]/H α) and log([O I]/H α) vs. log([O III]/H β). Contour levels at 1, 5, 10, and 50% of maximum density. The labels (‘1’..‘11’) correspond to the representative locations, as described in the text. The basis point for the star-formation/AGN mixing ratio is plotted as a green symbol, with the ratio shown by green dotted contours. Bottom row: Spatial excitation mode for each set of diagnostics, color-coded by star-formation/AGN mixing distance. (Black & van Dishoeck 1987; Krabbe et al. 2000; Davies The results for the derived parameters are given in Table et al. 2005). 9 for the excitation temperatures. The flux for the H2 K -band lines was measured at Independently, the rotational and vibrational temper- several locations, P1–P6, as shown in Fig. 20 (top left atures can be determined from two ortho/para lines panel). The spectrum at each location was taken from that belong to the same vibrational level, e.g. 1–0 S(0) a circular region 4 pixels wide and the flux measured (2223.5 nm) and 1–0 S(2) (2033.8 nm), whereas the vi- from a Gaussian fit to the line, using QFitsView fitting brational excitation temperature can be determined by facility. The locations were chosen to be the nucleus connecting two transitions with same J but from consec- and 000.5 N and S, in line with the rotation, plus other utive ν levels, e.g. 2–1 S(1) (2247.7 nm), and 1–0 S(1) features visible in the flux map. (2121.8 nm) (Riffel et al. 2014; Busch et al. 2017). The We could measure all of the low excitation lines (ν = formulas are: 1 − 0); however the high excitation line fluxes (ν = 2 − 1 and ν = 3 − 2) were more uncertain. At location P4, only the 2–1 S(3) line could be measured (see Fig. 19). NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 23

Table 8. Excitation diagnostic values and estimated electron temperature and density at locations plotted in Fig. 18. Locations are labeled as “IC” - ionization cone, “SFR” - star-forming ring and “S Arm” - southern spiral arm.

Location log([O III]/H β) log([N II]/H α) log([S II]/H α) log([O I]/H α)Te Ne 1 - Nucleus 1.13 ± 0.04 0.13 ± 0.02 -0.22 ± 0.03 -0.90 ± 0.03 8045 ± 361 50450 ± 12958 2 - IC SE 1 0.89 ± 0.02 -0.02 ± 0.02 -0.35 ± 0.02 -1.13 ± 0.02 9080 ± 802 21590 ± 10430 3 - IC SE 2 1.04 ± 0.01 -0.12 ± 0.02 -0.42 ± 0.02 -1.04 ± 0.02 9559 ± 659 15280 ± 7516 4 - IC NW 1 1.10 ± 0.03 0.14 ± 0.03 -0.16 ± 0.04 -0.88 ± 0.04 8059 ± 307 37473 ± 14909 5 - IC NW 2 0.61 ± 0.02 -0.17 ± 0.01 -0.41 ± 0.01 -1.37 ± 0.02 8042 ± 853 15422 ± 5327 6 - IC NW 3 1.05 ± 0.01 0.02 ± 0.02 -0.20 ± 0.02 -1.05 ± 0.04 8311 ± 790 9262 ± 6604 7 - SFR 1 -0.18 ± 0.04 -0.29 ± 0.01 -0.48 ± 0.01 -1.70 ± 0.05 8000* 11605 ± 3374 8 - SFR 2 -0.38 ± 0.04 -0.30 ± 0.01 -0.47 ± 0.01 -1.57 ± 0.04 8000* 10562 ± 3670 9 - SFR 3 -0.23 ± 0.03 -0.29 ± 0.01 -0.57 ± 0.01 -1.73 ± 0.03 8000* 19503 ± 3589 10 - S Arm 1 -0.15 ± 0.02 -0.30 ± 0.01 -0.50 ± 0.01 -1.77 ± 0.07 8000* 8874 ± 3931 11 - S Arm 2 -0.51 ± 0.02 -0.38 ± 0.01 -0.70 ± 0.01 -2.17 ± 0.08 8000* 6963 ± 2788

∗Estimated temperature.

Table 9. H2 excitation temperatures. Table 10. H2 rotational and vibrational temperatures.

Location TRot (K) TV ib (K) Location Name Texc (K) Texc (K) Texc (K) ν = 1 − 0 ν = 2 − 1/3 − 2 All P1 1450 ± 10 2210 ± 72

P1 Nucleus 1375 ± 35 4165 ± 510 2155 ± 30 P2 1870 ± 394 2262 ± 152 P2 000.5 S 1685 ± 160 4445 ± 445 2840 ± 50 P3 2007 ± 463 2270 ± 198 P3 000.5 N 1700 ± 100 1960 ± 560 2060 ± 80 P4 1542 ± 515 2512 ± 289 P4 SE 1775 ± 210 . . . * 1830 ± 165 P5 1604 ± 674 2384 ± 379 P5 NW 1800 ± 185 2275 ± 400 7040 ± 310 P6 2225 ± 973 2050 ± 147 P6 W 2085 ± 60 5620 ± 875 2840 ± 75

We calculate the excitation temperatures from the ∗No slope could be determined; only 1 data point inverse slope of the low-excitation (ν = 1 − 0), high- excitation (ν = 2 − 1/3 − 2), and all lines, respectively. These are given in Table9. The low-excitation tem- 1113K peratures are very similar (1740±50K), except for the T = (7) nucleus and location P6. It can be hypothesized that rot(ν=1) F  1.130 + ln 1−0S(0) the H in the line of sight of the nucleus is shielded from F 2 1−0S(2) the some of the heating effect of the AGN by the circum- 5594K T = (8) nuclear torus or dusty bar that is visible in the H − K vib F  0.304 + ln 1−0S(1) magnitude maps (Fig.9). The radio jet impact on the F2−1S(1) ISM at location P6 could increase the excitation in that region. The computed values are given in Table 10. Fig. 19 If we include all the lines, the derived temperatures shows the excitation temperature plot derived from the increase somewhat; however the high-excitation flux val- method of Wilman et al.(2005) and Fig. 20 (bottom ues are more uncertain. These temperatures now com- panel) shows the rotation and vibrational temperatures patible with results for other Seyfert galaxies in the lit- plotted on the Mouri(1994) excitation mechanism dia- erature, in the range 2100–2700 K (e.g. Riffel et al. 2015; gram. These results show that the gas is close to the Storchi-Bergmann et al. 2009; Riffel et al. 2014; Riffel & local thermodynamic equilibrium (LTE) line, indicating Storchi-Bergmann 2011; Riffel et al. 2010). The tem- predominantly thermal processes. The 2-1 S(3) line is perature derived for P5 for all lines is would seem to be present at all locations, however in most locations (P1, unphysical, being above the disassociation temperature P2, P3, and P6) it is below the fitted line, indicating for H2. However, Davies et al.(2003, 2005) shows that that X-rays make up a minor component of the exci- the lower ν = 1 − 0 levels may be thermalised, but the tation (e.g. Krabbe et al. 2000, for NGC 1275), with ν = 2 − 1 and ν = 3 − 2 levels can be overpopulated shocks probably the main contributor to the excitation. due to fluorescent excitation by far-ultraviolet photons. 24 Durre´ & Mould

If we fit just the ν = 2 − 1 and ν = 3 − 2 levels, we can the nuclear region, plus uncertainties in the flux mea- see that the P5 location has a very high temperature surements. (∼ 7000 K); this is in the NW ionization cone at the hy- 0.5 pothesized point of impact of the radio jet with the ISM 1.5 0.4 and is also presumably illuminated by the accretion disk P5 0.4 1 ) 0.35 s / m 2 n

radiation field where the fluorescent excitation is high- m

0.3 1 c / 0.5 P3 2 g 1

r 0.3 ) est. Alternately, there may be a component of much 2 / e c

0.25 7 6 e 1 s 4 0 - c P1 2 0 r P6 hotter gas close to the H dissociation temperature of 2 1 2 a

0.2 ( * 2 (

0.2 H x

−0.5 u

P2 o

∼ 4000 K, or there is non-thermal emission due to ex- l 0.15 i t F

a 2 R citation of the molecule by secondary electrons deep in −1 H 0.1 0.1 P4 the cloud. 0.05 −1.5 100pc 100pc 0 P1 1.5 1 0.5 0 −0.5 −1 −1.5 1.5 1 0.5 0 −0.5 −1 −1.5 (arcsec) (arcsec) 5 P2 Tvib°K P3 1500 2000 2500 3000 3500 2.5 P4 4000 ) P5 s t i P6 2.25 n U

3000 3000 y

r 0

a 2

r X-ray t ) i 0 ( b S r P 6 T 0 - A r o 1

2000 t ( ° / P )

1.75 K 3 2000 2 ) (

p P

S 2 p

u 0 - 1 N

( P 1.5 5 n P 4 1500 L P Shock 1

1.25 −7.5

1000 1 1000 6 8 10 12 14 16 18 20 0 0.05 0.1 0.15 0.2 0.25 2-1 S(1)/1-0 S(1)

EUpp (x1000 K) Figure 20. Left panel: H2 measurement locations on flux ) ) ) ) ) ) ) ) ) ) ) 1 2 3 0 1 2 3 1 2 3 5 ( ( ( ( ( ( ( ( ( ( (

Q S Q S Q S S S S S S map. Contours are at 5, 10, 30, and 50 % of maximum

0 0 0 0 0 0 0 1 1 1 1 ------

1 1 1 1 1 1 1 2 2 2 2 flux. Right panel: H2 2248/2121 nm flux ratio. Over-plotted

contours are H 2 2121 nm flux, at levels of 5, 10, 20, and 50% of maximum. Thermal processes dominate at high H2 Figure 19. H2 temperature plots. The value of the inverse flux, with an increasing contribution from UV fluorescence slope of the relationship between ln(Nupper) and Eupper is the at lower fluxes. Bottom panel: Diagnostic diagram (Mouri excitation temperature of H2 for LTE. The values are plotted 1994) for H2 locations. The green trajectory is for gas at for each location, each with an offset for clarity. The transi- LTE with the temperature indicated. The values for points tions are labeled below the plot. The ν = 1−0 transition fits P1–P6 are plotted. Thermal processes (X-ray heating and are plotted with solid lines, the ν = 2 − 1 and ν = 3 − 2 fits shocks) predominate. are plotted with dotted lines, those for all transitions with dashed lines. Including the higher-excitation increases the derived temperatures, but these may not be in LTE. It is noted that there is a difference between the optical and IR excitation diagnostic diagrams, with the optical diagram showing a tight relationship along the mixing The flux ratio for the 2–1 S(1) (2247.7 nm) and 1– sequence, but the IR diagram shows a broad spread. 0 S(1) (2121.8 nm) lines is diagnostic for excitation by This difference can be ascribed to the use of H2 in the IR soft-UV photons (from star formation) vs. thermal pro- diagnostic, which incorporates different excitation mech- cesses (from shocks or X-ray heating), with a value of anisms (X-ray heating and UV fluorescence) to the that ∼ 0.1 − 0.2 for thermal and ∼ 0.55 for fluorescent pro- of the metal ions (AGN power-law radiation field). cesses (following Riffel et al. 2014, in their excitation study of NGC 1068). Fig. 20 (top right panel) shows 4.1.4. Other Diagnostics this plot; where there is strong H2 flux, the ratios indi- The [Fe II] and [P II] 1188.6 nm emission lines cate purely thermal processes. Higher values at the pe- can be used to diagnose the relative contribution of riphery reflect an increasing contribution of excitation photo-ionization and shocks (Oliva et al. 2001; Storchi- by hot stars away from the X-ray heating and shocks in Bergmann et al. 2009), where ratios ∼ 2 indicate photo- NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 25 ionization (as the [Fe II] is locked into dust grains), with the Cardelli et al.(1989) empirical relationships to de- higher values indicating shocked release of the [Fe II] rive the αλ1,λ2 values. The hydrogen line ration are from from the grains (up to 20 for SNRs). This ratio was de- Hummer & Storey(1987), assuming Case B recombina- 00 4 termined at three locations with a 1 aperture; the AGN tion, an electron temperature Te = 10 K and a density 3 −3 (5.9 ± 1.2), the SE cone maximum flux (5.8 ± 1.6), and ne = 10 cm . The [Fe II] ratios in the literature are the NW cone maximum flux (3.9 ± 0.7). This shows the discrepant, we will use the commonly accepted value of excitation is a mixture of shock and photo-ionization, 1.36 (see the discussion in Durr´eet al. 2017). with the latter predominating. This result is confirmed by the diagnostics from Mouri Table 11. Extinction constants for Equation9. et al.(2000), who calculated photo-ionization and shock heating models, and generated diagnostic diagrams for Line Pair λ1 λ2 αλ1,λ2 Rλ1,λ2 the ratios of [Fe II] 1257 nm/Pa β vs. [O I]/H α for Pa β–Br γ 1282.2 2166.1 6.07 5.88 both power-law and blackbody photo-ionization, as well [Fe II] 1256.7 1643.6 8.22 1.36 as shock heating models. From Table5 values, the ra- Pa γ–Pa β 1094.1 1282.2 10.24 0.55 tios within the inner 100 are [Fe II] 1644 nm/Br γ = 2.0 Pa α–Br γ 1875.6 2166.1 26.55 12.15 (which translates to [Fe II] 1257 nm/Pa β = 0.46) and H β–H α 486.1 656.3 2.33 2.86 [O I]/H α = 0.115 (from the MUSE data). These values are compatible with both power-law photo-ionization and shock models (favoring photo-ionization), where the For this object, the [Fe II] 1257/1644 nm ratio will metal abundances are sub-solar and the ionization pa- be somewhat uncertain, even with the corrected telluric rameter is high, U ≥ 10−1.5 (see Fig. 3 of Mouri et al. feature in the 1257 nm emission line. The Pa γ/Pa β 2000). ratio has the advantage that it is measured in the same We attempted to measure the electron density from band, but the Pa γ gas kinematics are of poor quality the [Fe II] line ratio, from the methods described in due to the line being near the short end of the spectrum Storchi-Bergmann et al.(2009), from the ratios of H - and close to the edge of the atmospheric window. An band emission lines for [Fe II] 1533/1644, 1600/1644, attempt at calculating the extinction using this ratio 1664/1644, and/or 1677/1644 nm. However, all fluxes, produced unphysical values over the whole field. We other than the 1644 nm line, were all very weak even at also suspect that there is some telluric contamination, the location of the peak [Fe II] 1644 nm flux. The only as the line width is broader than Pa β. The Pa β/Br γ one that could be measured with reasonable certainty ratio can only be mapped over part of the whole central (the 1533 nm line) gave a low flux ratio (0.062 ± 0.01) ring feature, as the H+K -band observations are at a which indicated a low electron density (< 1000 cm−3). smaller scale than the J -band ones; uncertainties are This is a firm upper limit, as the 1644 nm flux is strong. also introduced by the rescaling and any flux calibration This low density is measured in the partially ionized uncertainties. The Pa α/Br γ ratio has the advantage [Fe II] line emitting region, and not close to the central that it is in the one data cube; however the Pa α line engine, where it would be much higher. is in the atmospheric absorption region between the H 4.2. Extinction and K bands. On examination of the cube, it was seen that the Pa α line is very strong, and the continuum We can derive the extinction by dust from emission is piece-wise smooth between the bands, so a definitive line flux ratios, where the known ratio of a pair of emis- measurement can be made. sion lines is compared against observations and extrap- We derived the extinction value A from the flux olated to the B−V extinction and A (the absolute V V maps of Pa α and Br γ, with the constants as given in extinction in the V band). In general, the formulae are Table 11; unphysical values are masked out. This is as follows: shown in Fig. 21, where the left panel shows the color   Rλ1,λ2 map of the Br γ and the contour giving the Pa α flux; E(B − V ) = αλ1,λ2 log (9) Fλ1 /Fλ2 the extinction map is plotted in the right panel. The AV values range up to 19 magnitudes, and the extinction is AV = E(B − V ) × RV (10) strongly concentrated around the AGN, presenting as a where Rλ1,λ2 is the intrinsic emissivity ratio of the two roughly elliptical region or bar of size 64 × 28 pc (where lines and αλ1,λ2 extrapolates from the emission line the extinction is > 16 mag), aligned at right angles to wavelengths to B−V . RV is the total-to-selective ex- the ionization cones. This is comparable in size to the tinction ratio; we use the fiducial value of 3.1. We use obscuring dust bar found for NGC 2110 at 55 × 27 pc 26 Durre´ & Mould

-16 2 (Durr´e& Mould 2014). The average extinction over all Paα/Brγ Fluxes (*10 erg/cm /s) Av (Paα / Brγ) valid pixels is 3.7 magnitudes. 1.5 20 Determining the extinction from the [Fe II] line ratio 1 . 0.1 0 1 0 0 . was more difficult, given the uncertainties mentioned .1 2 15 0.5 0.1

) 1 above. The J flux map was sub-sampled to the same c .

0 0.5 2

. e

0 s 0 1 10 c + + scale and aligned to the H+K map by matching the r a 0.01 ( −0.5 flux maxima; the fluxes of the lines are shown in Fig. 21 0 .1 5 (left panel - color map is [Fe II] 1257 nm flux, contours −1 100pc 1644 nm flux). The values range up to 15 magnitudes of −1.5 10−3 0 extinction, and the morphology is comparable with the 1.5 1 0.5 0 −0.5 −1 −1.5 1.5 1 0.5 0 −0.5 −1 −1.5 Pa α/Br γ maps, with some differences (Fig. 23, right (arcsec) (arcsec) panel). The peak location is for [Fe II] extinction is Figure 21. Extinction map from hydrogen recombination not on located on the AGN, but somewhat to the SE (Pa α–Br γ). Left panel: Pa α and Br γ fluxes; color map (∼ 30 pc). The morphology is also more even, with the and color-bar is Br γ flux, contours and labels are Pa α flux, interiors of the ionization cones having greater extinc- both in units of 10−16 erg cm−2 s−1. Right panel: Visual tion than the Pa α/Br γ extinction. These values and extinction AV in magnitudes. conclusions should be treated with some caution, as it depends on the exact alignment of the two [Fe II] flux [Fe II] 1257/1644 Fluxes (*10-16 erg/cm2/s) A ([Fe II] 1257/1644 nm) maps (e.g. a 2-pixel shift in the RA co-ordinate places V the peak extinctions at the same location). 1.5 0.1 The extinction was also measured by taking a spec- 1 12.5

0

. 5 0 00 0 0.5 0 . 2 10 trum from the data cubes in an aperture of 1 diameter .02 0 ) c 0.05 0.1 e 0.2 s 0 0.05 7.5 around the AGN location, showing A = 14.9 mag for c + +

V r a (

Pa α/Br γ, and 6.45 mag for [Fe II]. The lower values, −0.5 2 5 .0 0 in general, supports the conclusion that the [Fe II] flux −1 2.5 originates from a skin around the ionization cones, and 100pc −1.5 0.01 0 thus the extinction does not probe the full depth of the 1.5 1 0.5 0 −0.5 −1 −1.5 1.5 1 0.5 0 −0.5 −1 −1.5 cones. (arcsec) (arcsec) Apart from the high extinction around the AGN, there is an indication that the hydrogen recombination extinc- Figure 22. Extinction map from [Fe II]. Left panel: [Fe II] fluxes; color map and color-bar is 1257 nm flux, contours and tion also traces the boundaries of the ionization cones; labels are 1644 nm flux, both in units of 10−16 erg cm−2 s−1. one can hypothesize that the dust (which causes the Right panel: Visual extinction AV in magnitudes. extinction) is sublimated in the AGN radiation field. To check this, the [Si VI] flux (which traces the high- mentioned hypothesis of dust sublimation in the ioniza- ionization region and outflow shock boundaries) is plot- tion cone; the star-forming ring (which has extinction ted with the extinction from hydrogen recombination values in the range 2–5) obscures the NW cone. The (Fig. 23, left panel); the extinction traces the bound- high values near the center have some uncertainties, aries of the [Si VI], providing support for the hypothesis. caused by errors in the flux measurements associated Around the AGN, the obscuring dusty toroidal structure with the multiple kinematic components. overlays the [Si VI] emission along our LOS. We also note the increased extinction that borders the The extinction can also be calculated at a broader star-forming ring; this will produce the drop in EW for scale from the H α/H β ratio, using the MUSE data. the ionized gas species in the NW ionization cone, as The intrinsic ratio for AGN NLRs is quoted as 3.1 ring is in front of the cone along our line of sight. (Davies et al. 2017, following) instead of the fiducial The obscuration caused by the dust lane is seen in Fig. value of 2.86. The extinction map (Fig. 24) uses this 9 in the H-K map and Fig. 11 in the equivalent width value where the AGN mixing ratio is greater than 50%. maps. Since the EW measure is supposedly independent (Section 4.1.2). The two values produces a difference of obscuration, we posit that there is significant stellar of ∼ 0.27 mag in the calculated A . We subtract V continuum in front of the gas emission and obscuration the foreground galactic extinction of 0.279 (Schlafly & along our LOS. In the same manner, the H emission is Finkbeiner 2011). 2 also in front of this obscuration. The striking feature of this map is the low extinction in the SE ionization cone. This supports the previously 4.3. Gas Masses NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 27

Br γ [Fe II] 1644 nm of 1.4, we thus derive the relationship: 2 −2 σGas = 22.1 AV M pc (11) )

" 1 (

n The extinction value towards the AGN implies a cold gas o i t i −2 s 0

o column density of 420 M pc , equivalent to NH = 4× P

t 22 −2 i l 10 cm . Davies et al.(2015) give the column density S −1 24 −2 based on X-ray modeling as NH = 1.6 × 10 cm , a c p

−2 0 factor of 40 times higher. This absorption is likely to 0 2 be at the parsec scale in the broad-line region (BLR)

[Si VI] 1964 nm H2 2121 nm (Burtscher et al. 2016), i.e. it is probing a very narrow 2 LOS, while the recombination lines are measured over a much more extended area; also, these lines will not )

" 1 (

n penetrate very deep into the obscuration, as the high o i t i

s 0

o extinction will attenuate the emission lines so much that P

t i l they will not contribute to the measured total. S −1 We also derive the ionized hydrogen plus warm/hot −2 and cold H gas masses, using the formulae from Riffel 1 1.5 2 2.5 3 2 et al.(2013b, 2015): −600 −400 −200 0 200 400 600 −600 −400 −200 0 200 400 600 17 2 Velocity (km/s) Velocity (km/s) MHII ≈ 3 × 10 FBrγ D M (12) 13 2 Figure 23. Left panel: Ionization cone extinction, as shown MH2 (W arm) ≈ 5.0776 × 10 FH2 D M (13) by AV from Pa β/Br γ(color map - values given in color-bar) M compared with [Si VI] flux (contours at 1, 2, 5, 10, 20, and MH2 (Cold) ≈ RLH2 L 50% of maximum). Right panel: AV from [Fe II] 1257/1644 16 2 (color map - values given in color-bar) compared to AV from ≈ 3.12 × 10 RFH2 D M (14) Pa α/Br γ (contours at 2, 7, 12, and 17 mag). where D is the distance in Mpc and F is measured in −2 −1 5 erg cm s . which gives MCold/MW arm as 7.2 × 10 and 2.7 × 106, respectively. For the Br γ emission, a

-16 2 4 Hα/Hβ Fluxes (*10 erg/cm /s) Av (Hα / Hβ) standard electron temperature T = 10 K and density 30 n = 100 cm−3 is assumed. The H flux is that of the 6 e 2 20 4 2121 nm line. 1 10 0 5 0 1 000 The constant R is given variously as 1174 (Mazzalay 10 0 0 4 1 100 ) 00

c et al. 2013b) for 6 local galaxies, or 4000 (M¨ullerS´anchez e 1000 10000 100 s 0 3 c r

a et al. 2006) from 17 LIRG/ULIRG galaxies; these give ( 1 0 0 1 2 5 6 0 0 −10 100 0 MCold/MW arm as 7.2 × 10 and 2.7 × 10 , respectively. 1 The Mazzalay et al.(2013b) value is originally derived −20 100

10 0 0 1000 pc 0 from the observed CO radio emission with estimates of 1 −30 5 7 20 10 0 −10 −20 20 10 0 −10 −20 CO/H2 ratios (which can vary over a range 10 to 10 ). (arcsec) (arcsec) At the centers of galaxies hosting AGN, this ratio could Figure 24. Extinction map from hydrogen recombination be substantially overestimated, as a greater proportion (H α–H β). Left panel: H α and H β fluxes; color map and of the gas will be excited. Given this uncertainty, we color-bar is H β flux, contours and labels are H α flux, both in will use the Mazzalay et al.(2013b) value of R = 1174. units of 10−16 erg cm−2 s−1. Right panel: Visual extinction Table 12 presents the results. The surface density val- AV in magnitudes. ues for the inner 100 pc radius are within the ranges of the results from Sch¨onellet al.(2017) who summarize The cold gas column density can be derived from results for 5 Seyfert 1, 4 Seyfert 2 and 1 LINER galaxies the visual extinction value. The gas-to-extinction ra- observed by the AGNIFS group; the range of H II sur- 2 tio, NH /AV , varies from 1.8 (Predehl & Schmitt 1995) face densities is 1.5–125 M /pc and of H2 (cold+warm) 21 −2 2 to 2.2 × 10 cm (Ryter 1996). Zhu et al.(2017) surface densities is 526–9600 M /pc . Star formation finds the Milky Way ratio for solar abundances to be rates and supernova rates have not been calculated, as ∼ 2.1× 1021 cm−2; this increases to ∼ 2.5× 1021 cm−2 it is clear that both the hydrogen and [Fe II] excitation for sub-solar abundances. We will use a value of 2.0 × is caused by the AGN photo-ionizing source plus asso- 1021 cm−2. Using an average atomic/molecular weight ciated outflow shocks, rather than star formation. 28 Durre´ & Mould

Table 12. Gas masses for the cold ISM, H II, and H2, in the pixel with greatest flux/extinction and within a radius of 100 and 200 pc from the center and over the whole observed field (600×600 pc), plus the 100 and 200 pc radius surface densities. The extinction/ISM is not measured outside the 100 pc radius.

−2 −2 Max Pixel M M M M pc M pc −2 M pc 100 pc 200 pc (Total) 100 pc 200 pc

6 ISM (σGas) 420 4.9 × 10 ······ 155 ··· H II 110.0 7.93 × 105 1.31 × 106 1.92 × 106 25.2 10.4 −2 −2 −3 H2 (warm) 3.83 × 10 388.5 695.6 957.2 1.24 × 10 5.54 × 10

The mass of warm H2 over the whole observed field 0-0.1" 0-0.25" 0.25-0.5" (∼ 960 M ) compares well with that found derived by 0.5-0.75" 0.75-1" Rodr´ıguez-Ardilaet al.(2005) (900 M ); the estimated Ref. 8 9 o i total (cold) H2 mass is 7×10 − 2.6×10 M . Combes t a R

& Leon(2002), from radio observations of CO(1-0), de- x u l 9 F duced a total H2 mass of 3.1 × 10 M , which covers the whole galactic disk, including the extended nuclear region and the SF loci at the tips of the main bar.

4.4. AGN Torus Properties 1400 1600 1800 2000 2200 2400 Wavelength (nm) AGN tori typically have hot (∼ 600 − 1000 K) dust Fit Nuclear Spectrum Ref Spectrum emission; this can be seen as an increase in the contin- BB Spectrum @ 870K ) s t uum slope towards the end of the K band. Fig. 25 i n U

. shows the ratio of the spectrum in annuli around the b r A (

AGN location to that of a reference spectrum located x u l 100.3 NW of the nucleus, which is presumably represen- F tative of the underlying stellar population. This ratio is

normalized at the shortest wavelength in the spectrum . d i s e

(1453 nm). The changing continuum slope is indicative R 2100 2150 2200 2250 2300 2350 2400 2450 of an increasing hot dust contribution at smaller radii. It Wavelength (nm) should be emphasized that the actual continuum slopes are always negative; the inner slopes are relatively less Figure 25. Hot dust contribution to the nuclear spectrum. Top panel: Ratio of continuum in annuli around the nu- negative. cleus to a non-nuclear reference spectrum, showing the long- The inner torus directly around the AGN is encom- wavelength rise indicative of hot nuclear dust. The first and passed within the central pixel; we can find the temper- second plots are apertures of radius 000.1 and 000.25, then in ature by fitting the K -band spectrum for this pixel with annuli of 000.25 up to 100, around the nucleus. The reference a linear combination of the reference spectrum described spectrum is also plotted for comparison. The ratios have above and a black-body spectrum: been offset for clarity. Bottom panel: Fit to nuclear flux from reference spectrum and black-body spectrum at 870 K. SC = α SR + β SBB(T ) + γ (15) See text for an explanation of the fitting process. The verti- cal axis is in arbitrary flux units. The emission lines in the where SC is the central pixel spectrum, SR is the ref- nuclear spectrum have been masked out. The residual flux erence spectrum, and SBB(T ) is a black-body spectrum is also plotted at the same scale. at temperature T ; α, β, and γ are fitting constants. The equation was solved for T using the generalized 4.5. High-Ionization Emission reduced gradient algorithm (‘GRG Nonlinear’) imple- Murayama & Taniguchi(1998) proposed a model of mented in the MS-Excel add-on Solver. The emission a clumpy CLR associated with the NLR, where the in- lines have been masked out from the central pixel spec- dividual clumps are ‘matter-bounded’, i.e. the whole trum. The best fit black-body spectrum is at a temper- cloud is ionized and its extent is simply that of the gas ature of 870 K; this is shown in Fig. 25, bottom panel. cloud itself. Since, under this model, receding outflows Burtscher et al.(2015) report median hot dust temper- (presumably the far side of the AGN) would preferen- atures of 1292 K for Seyfert 1 and 887 K for Seyfert 2 tially show the highly-ionized face towards the observer, types for 51 local AGN; the value for NGC 5728 is in the emission should be more prominent on that side. good agreement with this range. NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 29

VI However, our observations of the flux ratio [Si ]/Br γ, 1.5 as displayed in Fig. 27 do not show significant difference 0.1 .2 0.3 1 0 0. 5 ) between the two ionization cones. s /

1 2 m

1.5 c Rodr´ıguez-Ardilaet al.(2004b) deduced that photo- 0.5 2 / g

3 r e

) 4 6 c 1 - 1 ionization alone is not enough to generate coronal lines e

5 . 0 s 0

0 1 c * r

+ (

a ( at the distances and velocities from the source that x u l F

−0.5 ] our observations show. In 5 of the 6 objects studied, I V

i S

.2 [ the coronal line emission was significantly broader and −1 0

1 asymmetric towards the blue than low-ionization lines. . 0 −1.5

In contrast to their findings, the [Si VI] FWHM for our 1 0 . 0 observations is virtually identical to that of Br γ, both 1.5 1 0.5 0 −0.5 −1 −1.5 over the whole field and specifically along the the out- (arcsec) flow axis. Figure 26. [Si VI] emission-line flux (color map) overlaid The X-ray jet observed by Chandra (especially in the by the Chandra X-ray flux (contours). The color map is soft X-rays) can contribute to the photo-ionization of CL log scaled to bring out faint details; the X-ray flux contours species. The X-rays can be generated by several mech- are labeled, in units of 10−6 photons cm−2 s−1. Note the anisms; direct photo-ionization from the AGN, shocks alignment of of the highly-ionized gas and the X-ray jet. with velocities >200 km s−1 (Rodr´ıguez-Ardila et al. 2017), and inverse Compton scattering of relativistic [Fe II] becomes relatively stronger towards the end and electrons associated with the radio jet. From the gas around the edges of the outflow. The [Si VI] is more kinematics, velocities of the required magnitude are cer- concentrated near the AGN, however it is present the tainly present, and are aligned with the [Si VI] emis- full length of the outflow. The H2 emission is centrally sion generated by shocks. Fig. 26 shows this alignment, concentrated, but as we will see, is kinematically disas- where the color map shows the [Si VI] flux and the over- sociated from the outflow and ionized species. This will laid contours show the X-ray emission. The plots were be explored in Sections 3.4.2 and 4.1. aligned by equating the derived AGN location on the 4.6. The Star-Forming Ring [Si VI] flux map with the a Gaussian fit to the location of the central peak of the smoothed X-ray flux map. The stellar age in the SF ring was determined from the The absence of an X-ray jet in the NW ionization cone Pa β EW, using the STARBURST99 models of Leitherer is most probably caused by higher gas column densities; et al.(1999). These produce EW data for a range of this is certainly the region of the dust lane. metallicities and initial mass functions; all showing a Rodr´ıguez-Ardilaet al.(2017) examined the power- static EW until about 3–5 Myr, then a rapid decrease ful outflows in NGC 1386, and found that the [Si VI] to about 10 Myr. Three locations in the ring, but out of and [Ca VIII] emission extended ∼ 150 pc in one direc- the line of the outflows, were used, as shown in Fig. 11 tion from the nucleus. A similar result was found by top right panel (circles); the EW was averaged within a M¨uller-S´anchez et al.(2011) for 7 Seyfert 1.5 – 2 galax- radius of 3 pixels. These values were in the range 0.16 ies; the [Si VI] emission had radial extents from the nu- – 0.42 nm, which is equivalent to 7.4 – 8.4 Myr for the cleus ranging from 80–150 pc. The largest CLR so far model a Solar metallicity, a mass cutoff of 100 M , and is that of NGC 5135 (Bedregal et al. 2009) of ∼ 600 pc. an IMF slope of 2.35. The CLR of NGC 5728 certainly approaches that size. We can obtain a measure of the SF rate in the ring, Overall, the CLR is generated by a complex mixture of using the H α flux and the Kennicutt et al.(2009) rela- photo-ionization (both directly from the AGN and from tionship. We estimate the true, non-AGN contaminated shock-generated X-rays further along the outflow cone) flux by selecting pixels with the AGN mixing ratio < and shocks. The morphology and kinematics of CLR 50%. We also select pixels where the Balmer decrement- species for each galaxy will depend on the AGN proper- derived extinction is less than 4 mag, as the derived ex- ties; photo-ionizing flux from the accretion disk, outflow tinction is probably uncertain over that value. We then dynamics and collimation to generate shocks and sec- correct the flux at each pixel by the formula:

0.4 Av k(λ) ondary X-rays produced by those shocks. F (Hα)C = F (Hα)O × 10 (16) Assuming a uniform ISM, the [Fe II]/Br γ and where F (Hα) and F (Hα) are the observed and cor- [Si VI]/Br γ ratios plot the relative ionizing conditions O C rected H α fluxes, respectively, and k(λ) = A /A . For for those species. Fig. 27 plots the flux ratio of [Fe II] λ v H α, k(λ) = 0.818, from the Cardelli et al.(1989) for- (1644 nm), H , and [Si VI] to Br γ. This shows that 2 mulation. 30 Durre´ & Mould

[Fe II]/Brγ H2/Brγ [Si VI]/Brγ 10 10 10 1.5 1 8 8 8 F l u ) x

c 6 6 6

e R s 0 c + + + a r a t ( 4 4 4 i o

−1 2 2 2 100pc −1.5 0 0 0 1.5 1 0.5 0 −0.5 −1 −1.5 1.5 1 0.5 0 −0.5 −1 −1.5 −1.5 −1 −0.5 0 0.5 1 1.5 (arcsec) (arcsec) (arcsec)

Figure 27. Flux ratios of [Fe II], H2, and [Si VI] to Br γ, showing relative excitation. Contours on the [Fe II]/Br γ plot are the K -band normalized flux, at 10, 25, 50, 75, and 90% of the maximum flux. [Fe II] is on the outflow boundaries, [Si VI] is more prominent closer to the AGN, and H2 and Br γ emissions are disjoint. Fig. 28 show the H α observed and corrected fluxes 5. CONCLUSION 00 and the extinction map for the nuclear region (10 - note We have examined the nuclear region of NGC 5728 the scale). The average H α flux for the selected pixels using data at multiple wavelengths and methods (X- −16 −2 −1 38 is 7.41 × 10 erg cm s (L(Hα) = 1.5 × 10 ray, optical and NIR IFU spectra, and radio), reveal- −1 erg s at 41.1 Mpc), which gives a star-formation rate ing a highly complex object showing gas with multiple −1 −2 00 of ∼ 0.029 M yr arcsec (0 .2/pixel). We can esti- morphologies and excitation modes, driven by a pow- mate the SF ring size by assuming an annular geometry erful AGN. We have presented and analyzed emission 00 around the nucleus; this is measured at ∼ 3 .2 for the line morphologies and excitation diagnostics, estimat- 00 inner and 7 for the outer radii. The total SFR over the ing stellar populations and ages and obscuration from −1 ring is thus ∼ 3.5 M yr . continuum emission and line ratios and also determined We can also estimate the stellar ages from the H β gas column densities. EW, using the same method as for Pa β, above. The In summary, the nuclear region has the following fea- H β EWs for the flux peaks around the ring (interpreted tures: as individual star clusters), is in the range 0.78 to 1.43 nm; this equates to stellar ages 6.15–6.45 Myr (broadly • Dust lanes and spiraling filaments feed the nucleus, compatible with the values derived from H β). as revealed by the HST structure maps. If the total VLA 6 cm flux, as shown in Fig.3 (bot- • A star-forming ring with a stellar age of 7.4 – 8.4 tom left panel), is summed on the NE sector of the circle −1 Myr, with a SFR ' 3.5 M yr . (since the jet interferes with the SW sector), a value of ∼ 70 mJy is obtained. At the distance of 41.1 Mpc, this • A one-sided radio jet, impacting on the ISM at translates to a luminosity of ∼ 1.4 × 1022 W Hz−1. Us- about 200 pc from the nucleus, combined with ra- ing the indicator of Condon(1992) (their equation 18) dio emission from the SN remnants in the SF ring. where ν = 5 GHz and α = − 0.8, this is equiva- • Biconal ionization, traced by gas emission of H II, lent to a supernova rate of ∼0.4 yr−1; this value may [Fe II], and [Si VI], extending off the edges of the well be high, as the jet emission may be contributing to observed field. MUSE [O III] data shows that the the measured flux. The individual supernova remnant full extent of the cones is over 2.5 kpc from the (SNR) luminosities are ∼ 4.4 × 1020 W m−2; again the nucleus. unmasked jet emission will contribute some of this lu- minosity. This can be compared to the SNRs in M82, • The AGN and BLR is hidden by a dust bar of which have luminosities in the range 0.02 − 1.7 × 1020 size 64 × 28 pc, with up to 19 magnitudes of vi- W m−2 (Muxlow et al. 1994). The spacing of the SNRs sual extinction, with an estimated dust tempera- is reminiscent of the nuclear rings of star clusters; ex- ture at the nuclear position of ∼ 870 K. Extinction amples are cited in Brandl et al.(2012) and Pan et al. maps derived from both hydrogen recombination (2013) for NGC 7552 and B¨oker et al.(2008) for 5 nearby and [Fe II] emission lines show similar structures, spiral galaxies. with some indication that [Fe II]-derived extinc- tion does not probe the full depth of the ionization NGC 5728 Ionization Cones : I - Excitation and Nuclear Structure 31

Observed Hα Flux Extinction A(Hα) Corrected Hα Flux

4 3 25 250

2 x x

1 2.5 1 20 M 200 0 0 a - - 1 1 ) g 6 6 c

n e e e i r r s t

g 150 g 0 15 u c 2 / / r d c c a e m m ( s 2 2 / / 10 s 100 s −2 1.5 5 50 1 −4 200 pc 0 0 4 2 0 −2 −4 4 2 0 −2 −4 4 2 0 −2 −4 (arcsec) (arcsec) (arcsec)

Figure 28. Star-forming ring H α flux for central 1000(note the scale in left panel). Left panel: observed flux. Middle panel: A(H α) extinction (magnitudes). Right panel: corrected flux; the blue dashed circles show the annulus used to estimate the total SF rate. Flux values in units of 10−16 erg cm−2 s−1.

cones. There is some evidence for dust being sub- the cold H I gas mass (from extinction calcula- 6 limated in the outflows, reducing the extinction. tions) is 4.9 × 10 M ; however this could be un- This is supported by extinction measures derived derestimated due to dust sublimation in the out- from MUSE H α/H β emission, which show a de- flows. creased absorption in the ionization cones. To understand the complex nature of AGNs, their as- sociated nuclear gas and stars must be studied at the • An extended coronal-line region traced by [Si VI], highest resolution possible using multi-messenger obser- out to ∼ 300 pc from the nucleus. This is excited vations. ALMA observations, revealing the cool dust by direct photo-ionization from the AGN, plus component, would add materially to the physical map shocks from the high-velocity outflows. Higher- we have constructed here. ionization species ([Ca VIII] and [S IX]) are closely confined around the AGN. This study is based on observations made with ESO • Line-ratio active galaxy diagnostics show mostly Telescopes at the Paranal Observatory. The respective AGN-type activity, with small regions of LINER program IDs are given in section2 above. and TO modes at the peripheries of the out- This research has made use of the NASA/IPAC In- flows and where the dusty torus obscures the di- frared Science Archive, which is operated by the Jet rect photo-ionization from the BH. MUSE opti- Propulsion Laboratory, California Institute of Tech- cal diagnostics (BPT diagrams) show a clean star- nology, under contract with the National Aeronautics formation/AGN mixing sequence. and Space Administration. The SIMBAD Astronomi- cal Database is operated by CDS, Strasbourg, France.

• The H2 gas is dynamically and spatially indepen- IRAF is distributed by the National Optical Astronomy dent of the outflows, concentrated in an equatorial Observatories, which is operated by the Association of disk in the star-forming ring, but also showing en- Universities for Research in Astronomy, Inc. (AURA) trainment along the sides of the bicone. The warm under cooperative agreement with the National Science H2 has a mass of 960 M in the central 600 × 600 Foundation. The National Radio Astronomy Observa- 8 pc, with an estimated 6×10 M of cold H2 in the tory is a facility of the National Science Foundation op- field of view. Line-ratio diagnostics indicate that erated under cooperative agreement by Associated Uni- the gas is excited by thermal processes (shocks and versities, Inc. radiative heating of gas masses) to temperatures The Pan-STARRS1 Surveys (PS1) and the PS1 public in the range 1400– 2100 K, with an increased ratio science archive have been made possible through contri- of fluorescent excitation towards the SF ring. butions by the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max- • With 100 pc of the nucleus, the ionized gas mass Planck Society and its participating institutes, the Max 5 (derived from the Br γ emission) is 8×10 M and Planck Institute for Astronomy, Heidelberg and the Max 32 Durre´ & Mould

Planck Institute for Extraterrestrial Physics, Garching, (ELTE), the Los Alamos National Laboratory, and the The Johns Hopkins University, Durham University, the Gordon and Betty Moore Foundation. University of Edinburgh, the Queen’s University Belfast, We would like to thank our Triplespec colleagues at the Harvard-Smithsonian Center for Astrophysics, the Caltech for their ongoing support of our survey. We Las Cumbres Observatory Global Telescope Network acknowledge the continued support of the Australian Incorporated, the National Central University of Tai- Research Council (ARC) through Discovery project wan, the Space Telescope Science Institute, the National DP140100435. M.D. dedicates this paper (and Pa- Aeronautics and Space Administration under Grant No. per II) to the memory of Dr. Ross McGregor Mitchell NNX08AR22G issued through the Planetary Science Di- (1954-2018), atmospheric scientist and astrophysicist. vision of the NASA Science Mission Directorate, the Facilities: VLT:Yepun (SINFONI, MUSE) National Science Foundation Grant No. AST-1238877, the University of Maryland, Eotvos Lorand University Software: TinyTim(Kristetal.2011),QFitsView(Ott 2012), gasgano (ESO 2012)

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