1,493 research outputs found
Cluster Galaxy Morphologies: The Relationship among Structural Parameters, Activity and the Environment
We use an approach to estimate galaxy morphologies based on an ellipticity
(e) vs. Bulge-to-Total ratio (B/T) plane. We have calibrated this plane by
comparing with Dressler's classifications. With the aid of our calibration, we
have classified 635 galaxies in 18 Abell clusters (0.02 < z < 0.08). Our
approach allowed us to recover the Kormendy's relation. We found that
ellipticals and Spirals are slightly brighter than S0 in R band. As S0 bulges
are brighter than spirals bulges, we believe that ram pressure is not the main
mechanism to generate S0s. In our sample, cluster radio galaxies morphologies
cover the range S0-E-cD and their bulges have absolutes magnitudes distributed
within -21 mag < M < -24.5 mag. If we believe Ferrarese & Merrit's relation,
these radio sources have 10^8-10^9 M black hole mass.Comment: Originally published in the proceedings of the conference "The
Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters", AIP
Conference Proceedings, Volume 1201 edited by Sebastian Heinz and Eric
Wilcots. This version contains slight modification
Optical BVI Imaging and HI Synthesis Observations of the Dwarf Irregular Galaxy ESO 364-G 029
As part of an effort to enlarge the number of well-studied Magellanic-type
galaxies, we obtained broadband optical imaging and neutral hydrogen radio
synthesis observations of the dwarf irregular galaxy ESO 364-G 029. The optical
morphology characteristically shows a bar-like main body with a one-sided
spiral arm, an approximately exponential light distribution, and offset
photometric and kinematic centers. The HI distribution is mildly asymmetric
and, although slightly offset from the photometric center, roughly follows the
optical brightness distribution, extending to over 1.2 Holmberg radii (where
mu_B = 26.5 mag/arcsec^2). In particular, the highest HI column densities
closely follow the bar, one-arm spiral, and a third optical extension. The
rotation is solid-body in the inner parts but flattens outside of the optical
extent. The total HI flux F_HI = 23.1 pm 1.2 Jy km/s, yielding a total HI mass
M_HI= (6.4 pm 1.7) x 10^8 Msun (for a distance D = 10.8 pm 1.4 Mpc) and a total
HI mass-to-blue-luminosity ratio M_HI/L_B = (0.96 pm 0.14) Msun / Lsun,B
(distance independent). The HI data suggest a very complex small-scale HI
structure, with evidence of large shells and/or holes, but deeper observations
are required for a detailed study. Follow-up observations are also desirable
for a proper comparison with the Large Magellanic Cloud, where despite an
optical morphology very similar to ESO 364-G 029 the HI bears little
resemblance to the optical.Comment: 10 pages, 11 figures, accepted by A&
A Region of Violent Star Formation in the Irr Galaxy IC 10: Structure and Kinematics of Ionized and Neutral Gas
We have used observations of the galaxy IC 10 at the 6-m telescope of the
Special Astrophysical Observatory with the SCORPIO focal reducer in the
Fabry-Perot interferometer mode and with the MPFS spectrograph to study the
structure and kinematics of ionized gas in the central region of current
intense star formation. Archive VLA 21-cm observations are used to analyze the
structure and kinematics of neutral gas in this region. High-velocity wings of
the H-alpha and [SII] emission lines were revealed in the inner cavity of the
nebula HL 111 and in other parts of the complex of violent star formation. We
have discovered local expanding neutral-gas shells around the nebulae HL 111
and HL 106.Comment: 22 pages, 10 figures; accepted in Astronomy Report
Gas-Rich Companions of Isolated Galaxies
We have used the VLA to search for gaseous remnants of the galaxy formation
process around six extremely isolated galaxies. We found two distinct HI clouds
around each of two galaxies in our sample (UGC 9762 & UGC 11124). These clouds
are rotating and appear to have optical counterparts, strongly implying that
they are typical dwarf galaxies. The companions are currently weakly
interacting with the primary galaxy, but have short dynamical friction
timescales (~1 Gyr) suggesting that these triple galaxy systems will shortly
collapse into one massive galaxy. Given that the companions are consistent with
being in circular rotation about the primary galaxy, and that they have small
relative masses, the resulting merger will be a minor one. The companions do,
however, contain enough gas that the merger will represent a significant
infusion of fuel to drive future star formation, bar formation, or central
activity, while building up the mass of the disk thus making these systems
important pieces of the galaxy formation and evolution process.Comment: Corrected dynamical friction calculation error. Revised discussion &
conclusions. 7 pages, 4 tables, 6 figures, to appear in May 1999 Astronomical
Journa
High Resolution H I Distributions and Multi-Wavelength Analyses of Magellanic Spirals NGC 4618 and NGC 4625
We present a detailed analysis of high resolution H I observations of the
Magellanic spiral galaxies NGC 4618 and NGC 4625. While the H I disk of NGC
4625 is remarkably quiescent with a nearly uniform velocity dispersion and no
evidence of H I holes, there is a dynamic interplay between star formation and
the distribution of neutral hydrogen in NGC 4618. We calculate the critical
density for widespread star formation in each galaxy and find that star
formation proceeds even where the surface density of the atomic gas is well
below the critical density necessary for global star formation. There are
strong spatial correlations in NGC 4618 between UV emission, 1.4 GHz radio
continuum emission, and peaks in the H I column density. Despite the apparent
overlap of the outer disks of the two galaxies, we find that they are
kinematically distinct, indicating that NGC 4618 and NGC 4625 are not
interacting. The structure of NGC 4618 and, in particular, the nature of its
outer ring, are highly suggestive of an interaction, but the timing and nature
of such an interaction remain unclear
Molecular Gas in the Low Metallicity, Star Forming Dwarf IC 10
We present a complete survey of CO 1->0 emission in the Local Group dwarf
irregular IC 10. The survey, conducted with the BIMA interferometer, covers the
stellar disk and a large fraction of the extended HI envelope with the
sensitivity and resolution necessary to detect individual giant molecular
clouds (GMCs) at the distance of IC 10 (950 kpc). We find 16 clouds with a
total CO luminosity of 1 x 10^6 K km s^-1 pc^2, equivalent to 4 x 10^6 Msun of
molecular gas using the Galactic CO-to-H2 conversion factor. Observations with
the ARO 12m find that BIMA may resolve out as much as 50% of the CO emission,
and we estimate the total CO luminosity as 2.2 x 10^6 K km s^-1 pc^2. We
measure the properties of 14 GMCs from high resolution OVRO data. These clouds
are very similar to Galactic GMCs in their sizes, line widths, luminosities,
and CO-to-H2 conversion factors despite the low metallicity of IC 10 (Z ~ 1/5
Zsun). Comparing the BIMA survey to the atomic gas and stellar content of IC 10
we find that most of the CO emission is coincident with high surface density
HI. IC 10 displays a much higher star formation rate per unit molecular (H2) or
total (HI+H2) gas than most galaxies. This could be a real difference or may be
an evolutionary effect - the star formation rate may have been higher in the
recent past.Comment: 21 pages, 14 figures, Accepted to Ap
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