1,198 research outputs found
Luminosity Profiles of Merger Remnants
Using published luminosity and molecular gas profiles of the late-stage
mergers NGC 3921, NGC 7252 and Arp 220, we examine the expected luminosity
profiles of the evolved merger remnants, especially in light of the massive CO
complexes that are observed in their nuclei. For NGC 3921 and NGC 7252 we
predict that the resulting luminosity profiles will be characterized by an
r^{1/4} law. In view of previous optical work on these systems, it seems likely
that they will evolve into normal ellipticals as regards their optical
properties. Due to a much higher central molecular column density, Arp 220
might not evolve such a ``seamless'' light profile. We conclude that
ultraluminous infrared mergers such as Arp 220 either evolve into ellipticals
with anomalous luminosity profiles, or do not produce many low-mass stars out
of their molecular gas complexes.Comment: Final refereed version. Note new title. 4 pages, 2 encapsulated color
figures, uses emulateapj.sty. Accepted to ApJL. Also available at
http://www.cv.nrao.edu/~jhibbard/Remnants/remnants.htm
The Apparent Morphology of Peculiar Galaxies at Intermediate to High Redshifts
We use rest frame ultraviolet (UV), B, and V band images of five nearby
(z<0.02) interacting and/or starbursting galaxies to simulate deep HST
observations of peculiar galaxies at medium to high redshifts. In particular,
we simulate Hubble Deep Field (HDF) observations in the F606W and F814W filters
of starburst galaxies in the redshift range z~0.5---2.5 by explicitly account
for the combined effects of band-shifting and surface brightness dimming. We
find that extended morphological features remain readily visible in the long
exposures typical of the HDF out to redshifts of ~ 1. For systems above z~1.5,
the simulated morphologies look remarkably similar to those of the faint
objects found in the HDF and other deep HST fields. Peculiar starburst galaxies
therefore appear to be the best local analogs to the highest redshift galaxies
in terms of morphology, star formation rates, and spectral energy
distributions. Nevertheless, photometric measurements of the z>1.5 images fail
to recover the true global properties of the underlying systems. This is
because the high-z observations are sensitive to the rest-frame UV emission,
which is dominated by the most active star forming regions. The extended
distribution of starlight from more evolved populations would not be detected.
We conclude that imaging observations in the restframe UV alone cannot reveal
whether high-z systems (z>1.5) are proto-galaxies, proto-bulges, or starbursts
within a pre-existing population. Definitive statements regarding the global
properties and dynamical states of these objects require deep imaging
observations at longer wavelengths.Comment: 15 pages, AAS LaTex macros v4.0, 6 Figs. To appear in The
Astronomical Journal. 1200 kB gzipped encapsulated postscript file of paper
and high-resolution figures is available at
http://www.ifa.hawaii.edu/~hibbard/highZ/ or
http://www.ifa.hawaii.edu/~vacca/highz.htm
NGC 4438: Ram pressure sweeping of a tidally disrupted galaxy
NGC 4438 is the highly HI deficient peculiar spiral in the center of the Virgo cluster. Observations are given of the neutral hydrogen emission obtained with the Very Large Array (VLA) in the D-array configuration. These observations map out the total HI as determined from single dish measurements, and show the hydrogen to be confined to a region about one third the size of the optical disk and displaced to the side of the galaxy opposite M87. The hydrogen content of the galaxy is over an order of magnitude less than that expected for a galaxy of its type. The data suggest that the HI deficiency is a result of ram pressure stripping of the gas in the outer regions of the galaxy by the hot intracluster medium after being tidally perturbed
Mergers, Interactions, and The Fueling of Starbursts
The most active starbursts are found in galaxies with the highest IR
luminosities, with peak star formation rates and efficiencies that are over an
order of magnitude higher than in normal disk systems. These systems are almost
exclusively on-going mergers. In this review I explore the conditions needed
for interactions to experience such a phase by comparing two systems at similar
stages of merging but quite different IR luminosities: NGC 4038/9 and Arp 299.
These observations show that the most intense starbursts occur at the sites
with the highest gas densities, which is a general result for IR luminous
mergers. Observations and theory both suggest that the strength of the merger
induced starburst depends on the internal structure of the progenitors, the
amount and distribution of the gas, and the violence of the interaction. In
particular, interactions involving progenitors with dense bulges, gas-rich
disks, and/or a retrograde spin are expected to preferentially lead to large
amounts of gaseous dissipation, although the interplay between these parameters
is unknown. A major outstanding question is how the effects of feedback alter
these conclusions.Comment: 14 pages, 5 Figs. 816 kB gzipped encapsulated postscript file of
paper and high-resolution figures is available at
http://www.ifa.hawaii.edu/~hibbard/MdConf/ . To appear in the 7th Annual
Astrophysics Conference in Maryland, ``Star Formation, Near and Far'', S.S.
Holt & L.G. Mundy editor
The Neutral Hydrogen Distribution in Merging Galaxies: Differences between Stellar and Gaseous Tidal Morphologies
We have mapped the neutral atomic gas (HI) in the three disk-disk merger
systems NGC 520, Arp 220, and Arp 299. These systems differ from the majority
of the mergers mapped in HI, in that their stellar and gaseous tidal features
do not coincide. In particular, they exhibit large stellar tidal features with
little if any accompanying neutral gas and large gas-rich tidal features with
little if any accompanying starlight. On smaller scales, there are striking
anti-correlations where the gaseous and stellar tidal features appear to cross.
We explore several possible causes for these differences, including dust
obscuration, ram pressure stripping, and ionization effects. No single
explanation can account for all of the observed differences. The fact that each
of these systems shows evidence for a starburst driven superwind expanding in
the direction of the most striking anti-correlations leads us to suggest that
the superwind is primarily responsible for the observed differences, either by
sweeping the features clear of gas via ram pressure, or by excavating a clear
sightline towards the starburst and allowing UV photons to ionize regions of
the tails.Comment: 16 pages, 5 figures, uses emulateapj.sty. To appear in the March 2000
issue of AJ. Version with full resolution figures is available via
http://www.cv.nrao.edu/~jhibbard/HIdisp/HIdisp.htm
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