Jonelle L. Walsh et al. 2008 The Astronomical Journal 136 1677 doi:10.1088/0004-6256/136/4/1677
Jonelle L. Walsh1, Aaron J. Barth1, Luis C. Ho2, Alexei V. Filippenko3, Hans-Walter Rix4, Joseph C. Shields5, Marc Sarzi6 and Wallace L. W. Sargent7
Show affiliationsWe 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 n e = n 0(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.
galaxies: active; galaxies: bulges; galaxies: kinematics and dynamics; galaxies: nuclei
Issue 4 (2008 October)
Received 2008 March 10, accepted for publication 2008 July 23
Published 2008 September 12
Jonelle L. Walsh et al. 2008 The Astronomical Journal 136 1677
H Araújo et al 2007 J. Phys.: Conf. Ser. 66 012003
2009 Modelling Simul. Mater. Sci. Eng. 17 089901
G Ratel and C Michotte 2003 Metrologia 40 06008
C A DeJoseph Jr et al 2008 J. Phys. B: At. Mol. Opt. Phys. 41 085701
Babak Ebrahimi et al 2009 Smart Mater. Struct. 18 015017
Sara Campos et al 2009 Metrologia 46 01004
E Castaños-Martínez et al 2009 J. Phys. D: Appl. Phys. 42 012003
Jeffrey H Shapiro and Seth Lloyd 2009 New J. Phys. 11 063045
Y Aregbe and P D P Taylor 2009 Metrologia 46 08005