University of Kentucky UKnowledge Physics and Astronomy Faculty Publications Physics and Astronomy 8-2000 The aN rrow-Line Region in the Seyfert 2 Galaxy NGC 3393 Andrew J. Cooke University of Edinburgh, UK J. A. Baldwin Cerro Tololo Inter-American Observatory, Chile Gary J. Ferland University of Kentucky, [email protected] Hagai Netzer Tel Aviv University, Israel Andrew S. Wilson University of Maryland - College Park Right click to open a feedback form in a new tab to let us know how this document benefits oy u. Follow this and additional works at: https://uknowledge.uky.edu/physastron_facpub Part of the Astrophysics and Astronomy Commons, and the Physics Commons Repository Citation Cooke, Andrew J.; Baldwin, J. A.; Ferland, Gary J.; Netzer, Hagai; and Wilson, Andrew S., "The aN rrow-Line Region in the Seyfert 2 Galaxy NGC 3393" (2000). Physics and Astronomy Faculty Publications. 143. https://uknowledge.uky.edu/physastron_facpub/143 This Article is brought to you for free and open access by the Physics and Astronomy at UKnowledge. It has been accepted for inclusion in Physics and Astronomy Faculty Publications by an authorized administrator of UKnowledge. For more information, please contact [email protected]. The Narrow-Line Region in the Seyfert 2 Galaxy NGC 3393 Notes/Citation Information Published in The Astrophysical Journal Supplement Series, v. 129, no. 2, p. 517-545. © 2000. The American Astronomical Society. All rights reserved. The opc yright holder has granted permission for posting the article here. Digital Object Identifier (DOI) http://dx.doi.org/10.1086/313422 This article is available at UKnowledge: https://uknowledge.uky.edu/physastron_facpub/143 THE ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 129:517È545, 2000 August ( 2000. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE NARROW-LINE REGION IN THE SEYFERT 2 GALAXY NGC 3393 ANDREW J. COOKE1,2 Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK; andrew=intertrader.com J. A. BALDWIN Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile3,4; baldwin=pa.msu.edu G. J. FERLAND Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40503; gary=cloud9.pa.uky.edu HAGAI NETZER School of Physics and Astronomy, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel; netzer=wise.tau.ac.il AND ANDREW S. WILSON Department of Astronomy, University of Maryland, College Park, MD 20742; and Space Telescope Science Institute; wilson=astro.umd.edu Received 1999 November 24; accepted 2000 March 7 ABSTRACT The narrow-line region (NLR) of the Seyfert 2 galaxy NGC 3393 is dominated by a symmetric struc- ture which appears as S-shaped arms in Hubble Space Telescope (HST ) images. These arms, which occupy the central few arcseconds of the nucleus, border a linear, triple-lobed radio source. We use HST imaging and spectra, ground-based optical images, long-slit spectra, Fabry-Perot imaging spectroscopy, and VLA radio data to perform a detailed investigation of the kinematics and ionization of the line- emitting gas in NGC 3393 and of its relationship with the relativistic gas responsible for the radio emis- sion. The excitation map [O III] j5007/(Ha ] [N II] jj6548, 6584) shows a biconical structure, consistent with the anisotropic nuclear ionizing radiation expected in the uniÐed scheme. Extrapolation to ionizing frequencies of our upper limit to the 2100A Ñux of the nuclear source provides a factor º3 ] 104 too few ionizing photons to account for the recombination line emission, which also suggests that the nuclear ionizing source radiates anisotropically. However, the kinetic energy of the outÑow is sufficient to power the line emission via photoionizing shocks, and a tentative detection of extended UV emission is consistent with this model. Furthermore, the broad component of the emission lines has a similar orientation and spatial extent as the triple radio source. Nevertheless, other tests are inconsistent with the photoionizing shock modelÈthere is no correlation between local velocity dispersion, surface bright- ness, and excitation, and the gaseous abundances of [Ca II], Al II], and Mg II are much lower than expected if these species have been liberated into the gas phase through grain destruction by shocks. We conclude that the radio lobes appear to have created denser regions of gas on their leading edges, thus forming the S-shaped arms, but that the ionization is most likely due to photoionization by an obscured central source. Subject headings: galaxies: active È galaxies: individual (NGC 3393) È galaxies: nuclei È galaxies: Seyfert 1. INTRODUCTION emitted by a central source is made anisotropic by the pres- ence of some sort of obscuring torus and, in radio-loud 1.1. T he Narrow-L ine Region and the UniÐed Model objects, by beamed synchrotron emission (Antonucci 1993; The geometry and ionization mechanism of the narrow Urry & Padovani 1995). The di†erent observed types of emission line regions (NLRs) that are associated with most AGNs are then caused mainly by di†erent viewing angles. active galactic nuclei (AGNs) have been the principal focus QSOs and Seyfert 1 galaxies are those AGNs which are of a number of detailed observational studies over the past viewed from within the solid angle subtended by a bicone of several years. The general goal has been not only to try to ionizing radiation, while Seyfert 2Ïs are those viewed from determine on a galaxy-by-galaxy basis the spatial and kine- outside the bicone. If there are no additional complications matic layout of the NLR, but also to compare those results (the uniÐed model does not describe the distribution of with the predictions of the ““ uniÐed model ÏÏ of AGNs. NLR gas), this predicts that the extended NLR in most or The uniÐed model supposes that all AGNs have basically all Seyfert 2Ïs should have the shape of two opposed cones, the same structure, in which the Ðeld of ionizing radiation each with its apex at the active nucleus. The NLR structure in many Seyfert 2Ïs can at least loosely be described in these terms (e.g., Pogge 1988; Wilson et al. 1993; Tadhunter & 1 Present address: 65 Cavendish Road, Leicester LE2 7PL, UK. Tsvetanov 1989). 2 Cerro Tololo Inter-American Observatory.4 However, in some objects the spatial structure of the 3 CTIO is operated by AURA, Inc., under cooperative agreement with the National Science Foundation. NLR is so closely associated with that of radio jets that the 4 Present address: Department of Physics and Astronomy, Michigan symmetry in the ionized volume may easily be due to pro- State University, East Lansing, MI 48824-1116. cesses other than just an anisotropic Ðeld of ionizing radi- 517 518 COOKE ET AL. Vol. 129 ation from a central source (Bower et al. 1994; Pogge & De TABLE 1 Robertis 1995; Capetti et al. 1995). NGC 3393 is such a GROUND-BASED IMAGING galaxy, and in this paper we try to determine to what extent the radio jets are important in a†ecting the structure, kine- FILTER matics, and ionization state of its NLR. Center j Width EXPOSURE TELESCOPE (A )(A )LINE (s) 1.2. NGC 3393 NGC 3393 is a nearby (z \ 0.0125), bright(m \ 13.1; de 0.9m...... 6649 76 Ha ] [N II]2] 1200 B 0.9m...... 6563 78 Continuum 2 ] 1200 Vaucouleurs et al. 1991) Seyfert 2 galaxy (also known as ] AM 1045[245, E501[G100) located on the outer fringes 1.5m...... 5257 44 Continuum 3 600 1.5m...... 5081 44 [O III] j5007 3 ] 600 of the Hydra cluster. It is the only Seyfert 2 galaxy besides 1.5m...... 4905 44 Hb 2 ] 600 NGC 1068 that has emission lines sufficiently bright that a decent IUE spectrum could be obtained. It is an early type barred spiral (SBa(rs), with an ““ outer pseudo-ring,ÏÏ accord- after scaling it so that the brighter stars would have the ing to de Vaucouleurs et al. 1991) seen nearly face on, cover- same number of counts in each image. ing over an arcminute on the sky. The redshift implies a These images are used in the large-scale plots throughout ~1 ~1 \ ~1 ~1 this paper. They are analyzed in ° 3.1. scale of 180 h pc arcsec (h H0/100 km s Mpc ), HST so images will show very Ðne detail. For all these 2.2. L ong-Slit Spectra reasons NGC 3393 was chosen for the detailed study of its NLR, which we describe in this paper. Grids of long-slit spectra were taken at the CTIO 4 m ] A pre-HST investigation of NGC 3393 was carried out Blanco Telescope, using a GEC 385 576 CCD on the RC by Diaz, Prieto, & Wamsteker (1988), who used a com- spectrograph (Table 2). A grating with 10A resolution (600 ~1 bination of optical and IUE spectra to study the integrated km s at 5000A) and wavelength coverage from 3700 - Ñux from the nuclear region. Using the low-resolution mode 6900A was used on 1990 March 2, while one giving 50 km ~1 of IUE and its large aperture (20@@ ] 10@@), they detected a s resolution over the wavelength range 4850-5140A was ] ~15 used on 1990 March 3. Both nights were photometric and strong, Ñat UV continuum source(Fj B 1.7 10 ergs cm~2 s~1 A~1) and a rich emission-line spectrum. Compar- the spectra were calibrated using standard stars from Stone ing the IUE measurement of He II j1640 with a ground- & Baldwin (1983); LTT 2415, LTT 2511, and EG 274 on the based measurement of He II j4686 taken through a 4@@ ] 4@@ Ðrst night, and Hiltner 600 and CD -32¡9927 on the second aperture, they deduced that there is essentially no reddening night.