1,613 research outputs found
A Radio Study of the Seyfert Galaxy IC 5063: Evidence for Fast Gas Outflow
New radio continuum (8 GHz and 1.4 GHz) and HI 21 cm line observations of the
Seyfert 2 galaxy IC 5063 (PKS 2048-572) were obtained with the Australia
Telescope Compact Array (ATCA). The 8 GHz image reveals a linear triple
structure (~4'', 1.5 kpc) oriented perpendicular to the optical polarization
position angle. It is aligned with the inner dust lane and shows strong
morphological association with the narrow emission line region (NLR). At 21 cm,
very broad (~700 km/s) HI absorption is observed against the strong continuum
source. This absorption is almost entirely blueshifted, indicating a fast net
outflow, but a faint and narrow redshifted component is also present. In IC
5063 we see clear evidence for strong shocks resulting from the radio
plasma-ISM interaction in the central few kpc. However, the energy flux in the
radio plasma is an order of magnitude smaller than the energy emitted in
emission lines. Thus, shocks are unlikely to account solely for the global
ionization of the emission line region, particularly at large distances.
The HI emission outlines a warped disk associated with the system of dust
lanes some ~2' (~38 kpc) in radius. The lack of kinematically disturbed gas
outside the central few kpc, coupled with the disk warp and close morphological
connection of the inner dust lanes and the large-scale ionized gas, support the
idea that the gas at large radii is photoionized by the central region, while
shadowing effects are important in defining its X-shaped morphology. The
kinematics of the ionized and of the neutral gas suggests the existence of a
dark halo.Comment: 18 pages, 8 Postscript figures, 3 jpeg figures, Postscript preprint
is available from http://jhufos.pha.jhu.edu/~zlatan/papers.htm
A Radio Study of the Seyfert galaxy Markarian 6: Implications for Seyfert life-cycles
We have carried out an extensive radio study with the Very Large Array on the
Seyfert 1.5 galaxy Mrk 6 and imaged a spectacular radio structure in the
source. The radio emission occurs on three different spatial scales, from ~7.5
kpc bubbles to ~1.5 kpc bubbles lying nearly orthogonal to them and a ~1 kpc
radio jet lying orthogonal to the kpc-scale bubble. To explain the complex
morphology, we first consider a scenario in which the radio structures are the
result of superwinds ejected by a nuclear starburst. However, recent Spitzer
observations of Mrk 6 provide an upper limit to the star formation rate (SFR)
of ~5.5 M_sun/yr, an estimate much lower than the SFR of ~33 M_sun/yr derived
assuming that the bubbles are a result of starburst winds energized by
supernovae explosions. Thus, a starburst alone cannot meet the energy
requirements for the creation of the bubbles in Mrk 6. We show that a single
plasmon model is energetically infeasible, and we argue that a jet-driven
bubble model while energetically feasible does not produce the complex radio
morphologies. Finally, we consider a model in which the complex radio structure
is a result of an episodically-powered precessing jet that changes its
orientation. This model is the most attractive as it can naturally explain the
complex radio morphology, and is consistent with the energetics, the spectral
index and the polarization structure. Radio emission in this scenario is a
short-lived phenomenon in the lifetime of a Seyfert galaxy which results due to
an accretion event.Comment: Accepted for publication in Ap
The Resolved Narrow Line Region in NGC4151
We present slitless spectra of the Narrow Line Region (NLR) in NGC4151 from
the Space Telescope Imaging Spectrograph (STIS) on HST, and investigate the
kinematics and physical conditions of the emission line clouds in this region.
Using medium resolution (~0.5 Angstrom) slitless spectra at two roll angles and
narrow band undispersed images, we have mapped the NLR velocity field from 1.2
kpc to within 13 pc (H_o=75 km/s/Mpc) of the nucleus. The inner biconical cloud
distribution exhibits recessional velocities relative to the nucleus to the NE
and approaching velocities to the SW of the nucleus. We find evidence for at
least two kinematic components in the NLR. One kinematic component is
characterized by Low Velocities and Low Velocity Dispersions (LVLVD clouds: |v|
< 400 km/s, and Delta_v < 130 km/s). This population extends through the NLR
and their observed kinematics may be gravitationally associated with the host
galaxy. Another component is characterized by High Velocities and High Velocity
Dispersions (HVHVD clouds: 400 130 km/s). This
set of clouds is located within 1.1 arcsec (~70pc) of the nucleus and has
radial velocities which are too high to be gravitational in origin, but show no
strong correlation between velocity or velocity dispersion and the position of
the radio knots. Outflow scenarios will be discussed as the driving mechanism
for these HVHVD clouds.Comment: 38 pages, 14 figures, accepted by ApJ. For higher resolution images
see http://www.pha.jhu.edu/~kaiser
Direct measurement of the jet geometry in Seyfert galaxies
We demonstrate that, by combining optical, radio and X-ray observations of a
Seyfert, it is possible to provide a direct measurement of the angle
between the direction of the radio jet and the normal to the plane of the
spiral host galaxy. To do so, we make the assumptions that the inner radio jet
is perpendicular to the X-ray observed inner accretion disk, and that the
observed jet (or the stronger component, if the jet is two-sided) is physically
closer to Earth than the plane of the galaxy. We draw attention to the
possibility of measurement producing a result which is not self-consistent, in
which case for that galaxy, one of the assumptions must fail.Comment: 11 pages, 1 figure, accepted for publication in The Astrophysical
Journal Letter
A Hubble Space Telescope Survey of Extended [OIII]5007A Emission in a Far-Infrared Selected Sample of Seyfert Galaxies: Results
We present the results of a Hubble Space Telescope (HST) survey of extended
[OIII] emission in a sample of 60 nearby Seyfert galaxies (22 Seyfert 1's and
38 Seyfert 2's), selected by mostly isotropic properties. The comparison
between the semi major axis size of their [OIII] emitting regions (R_Maj) shows
that Seyfert 1's and Seyfert 2's have similar distributions, which seems to
contradict Unified Model predictions. We discuss possible ways to explain this
result, which could be due either to observational limitations or the models
used for the comparison with our data. We show that Seyfert 1 Narrow Line
Regions (NLR's) are more circular and concentrated than Seyfert 2's, which can
be attributed to foreshortening in the former. We find a good correlation
between the NLR size and luminosity, following the relation R_Maj propto
L([OIII])^0.33, which is flatter than a previous one found for QSO's and
Seyfert 2's. We discuss possible reasons for the different results, and their
implications to photoionization models. We confirm previous results which show
that the [OIII] and radio emission are well aligned, and also find no
correlation between the orientation of the extended [OIII] emission and the
host galaxy major axis. This agrees with results showing that the torus axis
and radio jet are not aligned with the host galaxy rotation axis, indicating
that the orientation of the gas in the torus, and not the spin of the black
hole, determine the orientation of the accretion disk, and consequently the
orientation of the radio jet.Comment: 17 pages including 12 figures, to appear in Ap
HST FOC spectroscopy of the NLR of NGC 4151. I. Gas kinematics
We present the results from a detailed kinematic analysis of both
ground-based, and Hubble Space Telescope/Faint Object Camera long-slit
spectroscopy at sub-arcsec spatial resolution, of the narrow-line region of NGC
4151. In agreement with previous work, the extended emission gas (R > 4") is
found to be in normal rotation in the galactic plane, a behaviour that we were
able to trace even across the nuclear region, where the gas is strongly
disturbed by the interaction with the radio jet, and connects smoothly with the
large scale rotation defined by the neutral gas emission. The HST data, at
0.029" spatial resolution, allow us for the first time to truly isolate the
kinematic behaviour of the individual clouds in the inner narrow-line region.
We find that, underlying the perturbations introduced by the radio ejecta, the
general velocity field can still be well represented by planar rotation down to
a radius of ~ 0.5" (30 pc), distance at which the rotation curve has its
turnover.
The most striking result that emerges from our analysis is that the galaxy
potential derived fitting the rotation curve changes from a "dark halo" at the
ENLR distances to dominated by the central mass concentration in the NLR, with
an almost Keplerian fall-off in the 1"< R < 4" interval. The observed velocity
of the gas at 0.5" implies a mass of M ~ 10E9 M(sol) within the inner 60 pc.
The presence of a turnover in the rotation curve indicates that this central
mass concentration is extended. The first measured velocity point (outside the
region saturated by the nucleus) would imply an enclosed mass of ~ 5E7 M(sol)
within R ~ 0.15" (10 pc) which represents an upper limit to any nuclear point
mass.Comment: 30 pages (aaspp4.sty), 14 figures. Fig. 1, 2 and 4 available by
anonymous FTP at 143.54.2.51 (cd /pub/winge) as GIF files; or upon request to
[email protected]. Accepted for publication in the Astrophysical Journal
(part 1
STIS Longslit Spectroscopy Of The Narrow Line Region Of NGC 4151. I. Kinematics and Emission Line Ratios
Longslit spectra of the Seyfert galaxy NGC 4151 from the UV to near infrared
have been obtained with STIS to study the kinematics and physical conditions in
the NLR. The kinematics show evidence for three components, a low velocity
system in normal disk rotation, a high velocity system in radial outflow at a
few hundred km/s relative to the systemic velocity and an additional high
velocity system also in outflow with velocities up to 1400 km/s, in agreement
with results from STIS slitless spectroscopy (Hutchings et al., 1998, Kaiser et
al., 1999, Hutchings et al., 1999) We have explored two simple kinematic models
and suggest that radial outflow in the form of a wind is the most likely
explanation. We also present evidence indicating that the wind may be
decelerating with distance from the nucleus.
We find that the emission line ratios along our slits are all entirely
consistent with photoionization from the nuclear continuum source. A decrease
in the [OIII]5007/H-beta and [OIII]5007/[OII]3727 ratios suggests that the
density decreases with distance from the nucleus. This trend is borne out by
the [SII] ratios as well. We find no strong evidence for interaction between
the radio jet and the NLR gas in either the kinematics or the emission line
ratios in agreement with the results of Kaiser et al. (1999) who find no
spatial coincidence of NLR clouds and knots in the radio jet. These results are
in contrast to other recent studies of nearby AGN which find evidence for
significant interaction between the radio source and the NLR gas.Comment: 32 pages, 13 figures, accepted for publication in The Astrophysical
Journa
Mapping the Kinematics of the Narrow-Line Region in the Seyfert Galaxy NGC 4151
Using The Hubble Space Telescope's Space Telescope Imaging Spectrograph HST's
STIS, observations of the OIII 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 degrees, with spatial resolution 0.2 arcseconds across and
0.1 arcseconds along each slit. A spectral resolving power of ~ 9,000 with the
G430M grating gave velocity measurements accurate to ~ 34 km/s. 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
near the nucleus, and generally decreases with increasing distance to about 100
km/s in the extended narrow-line region (ENLR), starting at about 6 arcseconds
from the nucleus. In addition to the bright emission knots, which generally fit
our model, there are faint high velocity clouds which do not fit the biconical
outflow pattern of our kinematic model. These faint clouds occur at the
turnover points of the outflowing bright clouds. We suggest possible scenarios
that could explain these rogue clouds: (1) backflow resulting from shocks and
(2) outflow outside of the bicones, although the latter does not explain how
the knots are ionized and accelerated. A comparison of our observations with a
high-resolution radio map shows that there is no evidence that the kinematics
of the NLR clouds are affected by the radio lobes that comprise the inner jet.Comment: 30 pages, 15 figures (some color), accepted for publication in the
Astronomical Journal. Downloadable versions of the paper with high resolution
figures/images are available here:
http://www.chara.gsu.edu/~crenshaw/NGC4151_kinematics.pdf <--PDF Version
http://www.chara.gsu.edu/~crenshaw/NGC4151_kinematics.ps <--PS Versio
The Sub-parsec Scale Radio Properties of Southern Starburst Galaxies. I. Supernova Remnants, the Supernova Rate, and the Ionised Medium in the NGC 253 Starburst
Wide-field, very long baseline interferometry (VLBI) observations of the
nearby starburst galaxy NGC 253, obtained with the Australian Long Baseline
Array (LBA), have produced a 2.3 GHz image with a maximum angular resolution of
15 mas (0.3 pc). Six sources were detected, all corresponding to sources
identified in higher frequency (>5 GHz) VLA images. One of the sources,
supernova remnant 5.48-43.3, is resolved into a shell-like structure
approximately 90 mas (1.7 pc) in diameter. From these data and data from the
literature, the spectra of 20 compact radio sources in NGC 253 were modelled
and found to be consistent with free-free absorbed power laws. Broadly, the
free-free opacity is highest toward the nucleus but varies significantly
throughout the nuclear region (tau_0 ~ 1->20), implying that the overall
structure of the ionised medium is clumpy. Of the 20 sources, nine have flat
intrinsic spectra associated with thermal radio emission and the remaining 11
have steep intrinsic spectra, associated with synchrotron emission from
supernova remnants. A supernova rate upper limit of 2.4 yr^-1 is determined for
the inner 320 pc region of the galaxy at the 95% confidence level, based on the
lack of detection of new sources in observations spanning almost 17 years and a
simple model for the evolution of supernova remnants. A supernova rate of >0.14
(v/10^4) yr^-1 is implied from estimates of supernova remnant source counts,
sizes and expansion rates, where v is the radial expansion velocity of the
supernova remnant in km s^-1. A star formation rate of 3.4 (v/10^4) <
SFR(M<=5Msun) < 59 Msun yr^-1 has been estimated directly from the supernova
rate limits and is of the same order of magnitude as rates determined from
integrated FIR and radio luminosities.Comment: Accepted by the Astronomical Journal. 34 pages, 6 figures; fixed
typos in assumed expansion velocit
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