BAAA, Vol. 59, 2017 Asociaci´onArgentina de Astronom´ıa P. Benaglia, H. Muriel, R. Gamen & M. Lares, eds. Bolet´ınde art´ıculoscient´ıficos

Central structures of Seyfert NGC 1672 Firpo V.1,2, D´ıazR.2,3, Dottori H.4, Aguero M.P.5, Bosch G.6,7, H¨ageleG.6,7, Cardaci M.6,7, Dors O.8 1 Departamento de F´ısica y Astronom´ıa,Universidad de La Serena, Chile 2 Gemini observatory, La Serena, Chile 3 Instituto de Ciencias Astron´omicas, de la Tierra y del Espacio, CONICET-UNSJ, Argentina 4 Instituto de F´ısica, Universidade Federal do Rio Grande do Sul, Brasil 5 Observatorio Astron´omico de C´ordoba, UNC, Argentina 6 Facultad de Ciencias Astron´omicas y Geof´ısicas, UNLP, Argentina 7 Instituto de Astrof´ısica de La Plata, CONICET, Argentina 8 Universidade do Vale do Paraiba, Brasil

Contact / VF: [email protected]

Resumen / Presentamos el campo de velocidad interno 4”( 350 pc) de NGC 1672, observado con Gemini GMOS/IFU con un muestreo espacial de 0.2”, resoluci´onespacial∼ de 0.4” y resoluci´onespectral 6000. Determi- namos un l´ımitesuperior para la masa del SMBH en el n´ucleoLINER utilizando el campo de∼ velocidad radial del gas ionizado, y confirmamos que el n´ucleogal´acticoactivo est´adesplazado con respecto al centro de simetr´ıa rotacional del disco circumnuclear.

Abstract / We present the velocity field of the inner 4”( 350 pc) of NGC 1672, observed with Gemini GMOS/IFU with a spatial sampling of 0.2”, spatial resolution of 0.4”,∼ and spectral resolution 6000. We determine an upper limit for the mass of the SMBH in the LINER core using the ionized gas radial velocity∼ field, and we confirmed that the is located off-center respect to the circumnuclear disk rotation symmetry center.

Keywords / : nuclei — galaxies: Seyfert — galaxies: kinematics and dynamics

1. Introduction The ASCA data (de Naray et al., 2000) showed no ev- idence of significant hard (2-10 keV) emission from the NGC 1672 is a late-type barred NGC 1672 nuclear source, so it was concluded that if an active nu- (SB(r)bc) located at 18.5 Mpc (3 K CMB corrected, cleus is present in NGC 1672, it must be Compton-thick, 24 2 NED). The galaxy has a circumnuclear ring of for- with NH>2x10 cm− . The latest work on the sub- mation (S´ersic& Pastoriza, 1965) and a nucleus with ject (Jenkins et al., 2011) showed via spatially resolved low level activity (Veron-Cetty & Veron, 1986) (see multi-wavelength photometry that the nuclear source is Fig. 1, first and second images). Its scale of 89 pc/arcsec a low-luminosity active galactic nucleus (LLAGN), but and moderately low inclination angle (i=34◦; (de Vau- with activity very close to the central couleurs, 1991)) make it an ideal target for kinematical black hole. studies and 3D spectroscopy to unveil the nature of its nuclear activity and its fueling mechanisms. The galaxy has a strong bar (length 2.2’ 12 kpc), There has been some controversy about the AGN many Hii regions in its four spiral arms, plus∼ vigor- classification of the nucleus, dating from the first de- ous star formation at the ends of the bar Brandt et tailed observations. Spatially resolved studies by (Veron al. (1996), and references therein). It has a high IR et al., 1981) detected possible broadening of [Oiii]( 300 luminosity (log LFIR/L = 10.2) and a global star for- 1 1∼ 1 km s− ) compared to Hβ lines ( 150 km s− ) in mation rate (SFR) of 2.7 M yr− (Kewley et al., 2000). the central 2”x4”, which they suggested∼ was evidence Therefore the bar seems to be acting as the main global of a composite Hii/Seyfert 2 nucleus. Garcia-Vargas fueling mechanism. However, there is no morpholog- et al. (1990) performed a high-spatial-resolution spec- ical evidence of strong asymmetries at radii more in- tral analysis of the nucleus, and found a strong increase ternal than the circumnuclear ring of 11”x9” (1.0x0.8 in the [Oii]/Hβ ratio in the central 1” compared to kpc). There is no evidence of lopsidedness∼ or a nu- its immediate surroundings. However, both lines had clear mini-bar which could account for angular momen- the same FWHM of 300 km/s, and the authors clas- tum removal and AGN feeding. A detailed study of sified the nucleus as∼ a LINER. According to Brant et the velocity field at 1.5” resolutions (D´ıazet al., 1999) al. 1996, the brightest X-ray source is located at the nu- showed a rotational pattern with a velocity gradient of 1 1 cleus, which has a soft X-ray spectrum consistent with 50 km s− arcsecs− in the inner 6 arcsec, indicating a thermal emission with a temperature of 0.68 keV, and mass of 9x108 M inside a radius of 125 pc, a relatively 39 1 a soft X-ray luminosity of 7x10 erg s− (0.2-2 keV). high central mass concentration for spiral galaxy, only However, these studies could not determine whether the matched by the active galaxy NGC 4959 (Kormendy et bulk of the soft emission came from a starburst or AGN. al., 1996). D´ıazet al. (1999) found that the nucleus as

Poster - September 2016 127 NGC 1672 observed in the R-band appears displaced 60 pc towards the SE respect to the kinematic center defined by the rotational symmetry of the velocity field. This could explain the presence of non-circular motions in the in- terstellar medium leading to the active nucleus fueling and deserves further investigation using state of the art 3D spectroscopic techniques.

Figure 2: Panel a) shows the red pure continuum Hα emis- sion. Panel b) shows radial velocity map derived from single Gaussian to Hα emission line profile. Panel c) shows disper- sion velocity map. See text for details.

Figure 1: On left to right: HST F658 image of the galaxy where the cyan square shows the central region of NGC 1672; FLUXER to individual Hα emission line profile. Fig. the central region where the red square is the FoV (3.5”x5”) 2, panel b), shows the Hα velocity map where the axes of GMOS/IFU; HST F814w image convolved with a 0.4 arc- with greatest difference in radial velocity (at PA 90◦) sec seeing; and GMOS/IFU image at 9300A.˚ and that with the greatest amplitude in radial velocity ∼ within the sampled circumnuclear region were marked. The Fig. 2, panel c) shows the velocity dispersion map derived from the Gaussian fitting. The black circle rep- 2. Observations resent the red pure continuum emission peak. It can be seen that the nucleus is located within the region of gas We obtained high spatial resolution data with the turbulence. Gemini Multi-Object Spectrograph (GMOS), at Gem- ini South in its Integral Field Spectroscopy (IFU) 1-slit mode with a spatial sampling of 0.2”, spatial resolution 5. Kinematics of 0.4” and spectral resolution 6000. ∼ 2 The circumnuclear nuclear velocity field shows a strong The used IFU FoV is 3.5”x5” ( 315x450 pc at the distortion in the kinematical minor axis, the major axis distance of NGC 1672, see Fig. 1,∼ red square), and dif- changes from about PA 130◦ to PA 90◦ in the innermost ferent optical spectral ranges were observed combining nuclear region. There is a remarkably change in the line blue (B1200) and red (R400) gratings. The observing of nodes from radii 3 arcsec respect to the inner line conditions were excellent, with an average of 0.4”-0.5” of nodes at r<2 arcsec∼ (see Fig. 3, top panel). In order seeing. to report a preliminary value for the mass of the cen- tral object we used the innermost resolved radial veloc- 3. Hα emission and continuum images ity measurements, at 0.4 arcseconds radii from the red pure continuum emission peak. The inclination value The high S/N and spectral resolution of our GMOS- that we used in this preliminary work is 40◦, as mea- IFU data allowed us to build the continuum Hα image sured by D´ıazet al. (1999) in the whole central region and the flux distribution of the Hα emission line. The of the galaxy. In further versions of this work we plan red pure continuum emission image was obtained after to fit a 2D model in order to derive the best value from median averaging along the red spectrum range close the observed high resolution velocity field parameters. to Hα emission line (5965A˚ to 6300A˚ plus 7000A˚ to A keplerian approach yields a mass of 1x107 M for 7100A),˚ which enhances the continuum contribution to the unresolved central mass (see Fig. 3, bottom panel), the observed spectra (see Fig. 2, panel a). which is within the range of values expected for a large The black cross shows the symmetry center of the spiral galaxy. velocity field (see Fig. 2) implying that the center of Fig. 4 shows the rotation curve obtained along the the rotational symmetry of the velocity field is dis- PA 90◦ assuming an inclination for the inner disc of 40◦ placed respect to the continuum emission peak (black (D´ıazet al., 1999). The clear points correspond to the circle Fig. 2). To compare our sub-arcsecond resolution velocities adapted from D´ıazet al. (1999) that were in- GMOS/IFU image with the HST image, we convolved cluded in order to extend the rotation curve beyond the the HST image at the GMOS resolution. In the Fig. 1, turn-over, which allows us to infer more precisely the third and fourth images show the HST at F814 vs. con- mass distribution. To reproduce observed velocities we tinuum image obtained after median averaging along the considered different mass distributions including spher- more red spectrum range (from 9140A˚ to 9540A).˚ ical and discoid distributions. The best fit to the rotation curve (see Fig. 4, solid 4. Velocity field and velocity dispersion map line) includes two components: an homogeneous sphere that rotates as solid body, and a second mass compo- We build preliminary radial velocity and velocity disper- nent that follows a law of densities of Satoh (Satoh, sion maps, both derived from single Gaussian fits using 1980). We assigned greater weight to the East-side ve-

128 BAAA 59 (2016) Firpo et al.

Innermost rotation curve 210 180 150 120 90 60 30 0 -550 -350 -150 -30 50 250 450 -60

Circular velocity [km/s] velocity Circular -90 -120 -150 -180 -210 -240

Radius [pc]

Figure 4: Rotation curve obtained along the PA 90◦ assum- ing an inclination for the inner disk of 40◦. The origin of distances is located at the nucleus, defined as the continuum emission peak in the spectra.

Programa de Astronom´ıa+ Fondo GEMINI-CONICYT, convo- catoria Research Fellow 2015.

References Brandt W. N., Halpern J. P., Iwasawa K., 1996, MNRAS, 281, 687 de Naray P. J., et al., 2000, AJ, 119, 612 Figure 3: Top panel: the innermost rotation curve show- de Vaucouleurs G., 1991, MNRAS, 249, 28P ing the gas circular velocity projected on the plane of the D´ıazR., et al., 1999, ApJ, 512, 623 galaxy. Bottom panel: cumulative mass distribution in solar Garcia-Vargas M. L., et al., 1990, Ap&SS, 171, 65 masses as a function of radius (keplerian approach). The Jenkins L. P., et al., 2011, ApJ, 734, 33 vertical axis is in logarithmic scale and the spatial resolu- Kewley L. J., et al., 2000, ApJ, 530, 704 tion is 35 pc. The plot shows a mass of 1x107 M for the ∼ ∼ Kormendy J., et al., 1996, ApJL, 473, L91 unresolved central mass in NGC 1672. Satoh C., 1980, PASJ, 32, 41 S´ersicJ. L., Pastoriza M., 1965, PASP, 77, 287 Veron-Cetty M.-P., Veron P., 1986, A&AS, 66, 335 locities, since the West-side in the velocity field presents Veron M. P., Veron P., Zuiderwijk E. J., 1981, A&A, 98, 34 greater kinematic perturbations. The model yielded to- tal masses of 2x109 M , with 50% of this mass inside the 200 pc radius.∼

6. Conclusions We confirm that the nucleus is off-center respect to the larger scale rotating-disk. However the morphology in- dicates that part of the off-centering might be due to the high extinction towards the nucleus. In that case, NIR spectroscopy is needed in order to get more accurate kinematics of the galactic core, as well as to increase the chances of detecting the broad component in the re- combination emission lines (e.g. observing Brγ in the K-band). We continue the analysis of this field using the different emission lines present in our cube to deter- mine, e.g. the presence of shocks, multiple kinematical components, chemical abundances, etc.

Acknowledgements: This work was supported by CONICYT +

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