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Hubble Space Telescope spectroscopic observations of the narrow-line region in nearby low-luminosity active galactic nuclei

Walsh, Jonelle L. and Barth, Aaron J. and Ho, Luis C. and Filippenko, Alexei V. and Rix, Hans-Walter and Shields, Joseph C. and Sarzi, Marc and Sargent, Wallace L. W. (2008) Hubble Space Telescope spectroscopic observations of the narrow-line region in nearby low-luminosity active galactic nuclei. Astronomical Journal, 136 (4). pp. 1677-1702. ISSN 0004-6256. doi:10.1088/0004-6256/136/4/1677.

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We present Space Telescope Imaging Spectrograph observations of 14 nearby low-luminosity active galactic nuclei, including 13 LINERs and 1 Seyfert, taken at multiple parallel slit positions centered on the galaxy nuclei and covering the Hα spectral region. For each galaxy, we measure the emission-line velocities, line widths, and strengths to map out the inner narrow-line region structure -— typically within ~100 pc from the galaxy nucleus. There is a wide diversity among the velocity fields: in a few galaxies the gas is clearly in disk-like rotation, while in other galaxies the gas kinematics either appear chaotic or are dominated by radial flows with multiple velocity components. In most objects, the emission-line surface brightness distribution is very centrally peaked. The [S II] line ratio indicates a radial stratification in gas density, with a sharp increase within the inner 10-20 pc, in the majority of the Type 1 (broad-lined) objects. The electron-density gradients of the Type 1 objects exhibit a similar shape that is well fit by a power law of the form ne = n0(r/1 pc)α, where α = –0.60 ± 0.13. We examine how the [N II] λ6583 line width varies as a function of the aperture size over a range of spatial scales, extending from scales comparable to the black hole's sphere of influence to scales dominated by the host galaxy's bulge. For most galaxies in the sample, we find that the emission-line velocity dispersion is largest within the black hole's gravitational sphere of influence, and decreases with increasing aperture size toward values similar to the bulge stellar velocity dispersion measured within ground-based apertures. We construct models of gas disks in circular rotation and show that this behavior can be consistent with virial motion, although for some combinations of disk parameters we show that the line width can increase as a function of aperture size, as observed in NGC 3245. Future dynamical modeling to determine black hole masses for a few objects in this sample may be worthwhile, although disorganized motion will limit the accuracy of the mass measurements.

Item Type:Article
Related URLs:
URLURL TypeDescription
Barth, Aaron J.0000-0002-3026-0562
Ho, Luis C.0000-0001-6947-5846
Filippenko, Alexei V.0000-0003-3460-0103
Rix, Hans-Walter0000-0003-4996-9069
Additional Information:© 2008 The American Astronomical Society. Received 2008 March 10, accepted for publication 2008 July 23. Published 2008 September 12. Print publication: Issue 4 (2008 October). This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. The data presented in this paper were obtained from the Multimission Archive at STScI (MAST); support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NAG5-7584 and by other grants and contracts. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-7403 and GO-7354.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
NASANAS 5-26555
Subject Keywords:galaxies: active; galaxies: bulges; galaxies: kinematics and dynamics; galaxies: nuclei
Issue or Number:4
Record Number:CaltechAUTHORS:WALaj08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11701
Deposited By: Archive Administrator
Deposited On:20 Sep 2008 02:18
Last Modified:08 Nov 2021 22:01

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