Orientation of the Narrow-Line Region in local Seyfert galaxies,
using Hubble Space Telescope (HST) STIS spectroscopy and WFPC2 imaging
data.
We have developed a software tool to simulate 3D geometry
of the NLR outflow. This tools can be used to visualize the
orientation of host galaxy disks in relation to orientation of
accretion disk around the central supermassive black hole.
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The above image shows geometry of the nuclear disk and narrow-line
region outflow in Mrk 3, a Seyfert 2 galaxy.
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A study of nuclear dust spirals (scales of ~ 10-500 pc) in local Seyfert galaxies.
We studied 91 Seyfert host galaxies imaged in the optical
using WFPC2 from the Hubble Space Telescope. We showed that a
class of Seyfert galaxies called Narrow-line Seyfert 1s (NLS1)
are more likely to host two-armed nuclear dust spirals. These
two-armed nuclear spirals (a spiral inside the main spiral of
the host galaxy disk) are driven by the gravitational
potential of the large-scale stellar bar in the early-type
host galaxy. Although these spirals are also seen in normal
(non-AGN) galaxies, existence of these spirals along with
active star formation in resonance rings in narrow-line
Seyfert 1s suggests active fueling of the supermassive black
hole via these pathways. This study also suggests that nuclear
activity follows episodes of gas accretion and star formation
in centers of early-type massive host galaxies. NLS1s could
thus be part of an AGN evolutionary sequence.
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A bar driven nuclear spiral in central kiloparsec of galaxy
TOL-2327-027. The large-scale stellar bar is vertical in the image.
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A study of infrared spectra of Seyfert galaxies.
We studied Spitzer/IRS infrared spectra of Seyfert galaxies.
Our primary focus in this study was to observe the 9.7 micron feature in the
spectra of Seyfert 1.8/1.9 galaxies. But instead we found the spectra to be
dominated by starburst features (the famous Polycyclic Aromatic Hydrocarbon
(PAH) features). It had been suggested that the 9.7 micron feature is a
measure of the equatorial dusty obscuration in AGN. However, previous
observations with the Infrared Space Observatory had shown it to be weaker
than predictions of early torus models, further suggesting that the torus
material may be clumpy. Using Spitzer spectra, we showed that the very strong
9.7 micron absorption features originate in the dust of the host galaxy rather
than close to the central engine. Further, we showed that 9.7 micron silicate
emission features likely arise from dust close to the central engine
and study of these features will probe the dust distribution close to the
central engine.
It has been suggested previously that in Seyfert 1.8/1.9
galaxies, our line of sight (LOS) to the central engine grazes the torus
atmosphere. If, this is indeed the case, then in the mid-IR, where the
obscuration due to the torus atmosphere should be little, these
objects should show mid-IR spectra similar to Seyfert 1s (i.e. dominated by
intrinsic AGN continuum). This is not observed. This shows that although
orientation of LOS is key to the observed nature of the central source, it is
not the complete answer. Further, we show that these Seyfert 1.8/1.9 galaxies
all of which were selected to be face-on (to avoid contamination from dust in
the host galaxy disk), show prominent star formation features. This suggests
that circum-nuclear starburst is dominating over the AGN continuum in these
systems.
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A collection of Spitzer/IRS spectra of Seyfert galaxies.
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