481 research outputs found
Stellar Velocity Dispersion in Dissipative Galaxy Mergers with Star Formation
In order to better understand stellar dynamics in merging systems, such as
NGC 6240, we examine the evolution of central stellar velocity dispersion
(\sig) in dissipative galaxy mergers using a suite of binary disk merger
simulations that include feedback from stellar formation and active galactic
nuclei (AGNs). We find that undergoes the same general stages of
evolution that were observed in our previous dissipationless simulations:
coherent oscillation, then phase mixing, followed by dynamical equilibrium. We
also find that measurements of that are based only upon the youngest
stars in simulations consistently yield lower values than measurements based
upon the total stellar population. This finding appears to be consistent with
the so-called " discrepancy," observed in real galaxies. We note that
quasar-level AGN activity is much more likely to occur when is near
its equilibrium value rather than during periods of extreme .
Finally, we provide estimates of the scatter inherent in measuring
in ongoing mergers.Comment: 17 pages, 10 figures, accepted for publication in Ap
Star Formation in QSO Host Galaxies
Many of the conditions that are necessary for starbursts appear to be
important in the triggering of QSOs. However, it is still debatable whether
starbursts are ubiquitously present in galaxies harboring QSOs. In this paper
we review our current knowledge from observations of the role of starbursts in
different types of QSOs. Post-starburst stellar populations are potentially
present in the majority of QSO hosts. QSOs with far-infrared colors similar to
those of ultraluminous infrared galaxies invariably reside in merging galaxies
that have interaction-induced starbursts of a few hundred Myr or less. Similar,
but dramatically more luminous post-starburst populations are found in the
recently discovered class of QSOs known as post-starburst QSOs, or Q+A's. Both
of these classes, however, comprise only a small fraction (10-15%) of the total
QSO population. The so-called "red" QSOs generally suffer from strong
extinction at optical wavelengths, making them ideal candidates for the study
of hosts. Their stellar populations typically show a post-starburst component
as well, though with a larger range of ages. Finally, optical "classical" QSO
hosts show traces of major star formation episodes (typically involving >10% of
the mass of the stellar component) in the more distant past (1-2 Gyr). These
starbursts appear to be linked to past merger events. It remains to be
determined whether these mergers were also responsible for triggering the QSO
activity that we observe today.Comment: 8 pages, 5 figures, invited review for "QSO Host Galaxies: Evolution
and Environment", held at the Lorentz Center, Universiteit Leiden, August,
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Spectacular Shells in the Host Galaxy of the QSO MC2 1635+119
We present deep HST/ACS images and Keck spectroscopy of MC2 1635+119, a QSO
hosted by a galaxy previously classified as an undisturbed elliptical. Our new
images reveal dramatic shell structure indicative of a merger event in the
relatively recent past. The brightest shells in the central regions of the host
are distributed alternately in radius, with at least two distinct shells on one
side of the nucleus and three on the other, out to a distance of ~13 kpc. The
light within the five shells comprises ~6% of the total galaxy light. Lower
surface brightness ripples or tails and other debris extend out to a distance
of ~65 kpc. A simple N-body model for a merger reproduces the inner shell
structure and gives an estimate for the age of the merger between ~30 Myr and
~1.7 Gyr, depending on a range of reasonable assumptions. While the inner shell
structure is suggestive of a minor merger, the total light contribution from
the shells and extended structures are more indicative of a major merger. The
spectrum of the host galaxy is dominated by a population of intermediate age
(~1.4 Gyr), indicating a strong starburst episode that may have occurred at the
time of the merger event. We speculate that the current QSO activity may have
been triggered in the recent past by either a minor merger, or by debris from
an older (~Gyr) major merger that is currently ``raining'' back into the
central regions of the merger remnant.Comment: 14 pages, 5 figures. Accepted for publication in the Astrophysical
Journa
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