Mapping the Kinematics of the Narrow-Line Region in the Seyfert Galaxy NGC 4151

Abstract

Using The Hubble Space Telescope's Space Telescope Imaging Spectrograph (HST's STIS ), observations of the [O III] emission from the narrow-line region (NLR) of NGC 4151 were obtained and radial velocities determined. Five orbits of HST time were used to obtain spectra at five parallel slit configurations, at a position angle of 58 o , with spatial resolution 0 ′′ .2 across and 0 ′′ .1 along each slit. A spectral resolving power (∆λ/λ) of ∼9,000 with the G430M grating gave velocity measurements accurate to ∼34 km s −1 . A kinematic model was generated to match the radial velocities, for comparison to previous kinematic models of biconical radial outflow developed for low-dispersion spectra at two slit positions. The new high-resolution spectra permit the measurement of accurate velocity dispersions for each radial-velocity component. The full-width at half-maximum (FWHM) reaches a maximum of 1000 km s −1 near the nucleus, and generally decreases with increasing distance to about 100 km s −1 in the Based on observations made with the NASA/ESA Hubble Space Telescope. STScI is operated bt the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with proposal GTO-8473

Velocity Offsets Due to Mass Outflows in Active Galaxies

“…The unsmoothed profiles in Figures 2 and 3 show significant structure with multiple peaks. From our analysis of the resolved STIS spectra, it is clear that this structure is due to the superposition of velocity profiles from the numerous emission-line knots seen in Figures 2 and 3, with each knot having its own peculiar radial velocity with respect to the general outflow pattern (Das et al 2005(Das et al , 2006. To simulate low-resolution ground-based spectra at at R =1000, we convolved the unsmoothed spectra with a Gaussian with a FWHM = 500 km s −1 (representing the line-spread function) and rebinned them to one-half of a resolution element.…”

“…We have found that the kinematics of the NLR are dominated by radial outflow in the four nearby Seyferts that we have studied to date: NGC 4151 (Hutchings et al 1998;Das et al 2005), NGC 1068 (Crenshaw & Kraemer 2000;Das et al 2006), Mrk 3 (Ruiz et al 2001), and Mrk 573 (T. Fischer et al, in preparation; see also Schlesinger et al 2009). In order to compare our results with those from previous groundbased spectra, we use HST/STIS long-slit spectra that cover most of the NLR in NGC 1068 (Cecil et al 2002;Das et al 2006) and NGC 4151 (Das et al 2005).…”

“…In order to compare our results with those from previous groundbased spectra, we use HST/STIS long-slit spectra that cover most of the NLR in NGC 1068 (Cecil et al 2002;Das et al 2006) and NGC 4151 (Das et al 2005). Spectra were Figure 1.…”

“…In order to determine the three-dimensional geometry of the outflows and extinction, we combined our parameters from the biconical outflow models with the observed parameters of the host galaxy disks (Das et al 2005(Das et al , 2006. In Figure 4, we show the geometry of the biconical outflow and the host galaxy disk for NGC 1068 and NGC 4151.…”

“…The left-hand side shows the view from Earth, and the right-hand side shows a viewpoint in which the bicone axis is in the plane of the sky and the galactic disk is edge-on, to show the true angle between the bicone and the disk (see the figure captions for more details). The parallel lines on either side of the galactic midplane show the dust scale height if we assume a typical value of ∼200 pc for spiral galaxies (Xilouris et al 1999) and a length of ∼800 pc for each bicone along its axis (Das et al 2005(Das et al , 2006.…”