1,032 research outputs found
Quantitative Morphology of Galaxies in the Hubble Deep Field
We measure quantitative structural parameters of galaxies in the Hubble Deep
Field (HDF) on the drizzled F814W images. Our structural parameters are based
on a two-component surface brightness made up of a S\'ersic profile and an
exponential profile. We compare our results to the visual classification of van
den Bergh et al. (1996) and the classification of Abraham et al. (1996a).
Our morphological analysis of the galaxies in the HDF indicates that the
spheroidal galaxies, defined here as galaxies with a dominant bulge profile,
make up for only a small fraction, namely 8% of the galaxy population down to
m = 26.0. We show that the larger fraction of early-type systems
in the van den Bergh sample is primarily due to the difference in
classification of 40% of small round galaxies with half-light radii <
0\arcsecpoint 31. Although these objects are visually classified as elliptical
galaxies, we find that they are disk-dominated with bulge fractions < 0.5.
Given the existing large dataset of HDF galaxies with measured spectroscopic
redshifts, we are able to determine that the majority of distant galaxies
() from this sample are disk-dominated. Our analysis reveals a subset of
HDF galaxies which have profiles flatter than a pure exponential profile.Comment: 35 pages, LaTeX, 18 Postscript Figures, Tables available at
http://astro.berkeley.edu/~marleau/. Accepted for Publication in The
Astrophysical Journa
Mid-Infrared Galaxy Morphology Along the Hubble Sequence
The mid-infrared emission from 18 nearby galaxies imaged with the IRAC
instrument on Spitzer Space Telescope samples the spatial distributions of the
reddening-free stellar photospheric emission and the warm dust in the ISM.
These two components provide a new framework for galaxy morphological
classification, in which the presence of spiral arms and their emission
strength relative to the starlight can be measured directly and with high
contrast. Four mid-infrared classification methods are explored, three of which
are based on quantitative global parameters (colors, bulge-to-disk ratio)
similar to those used in the past for optical studies; in this limited sample,
all correlate well with traditional B-band classification. We suggest reasons
why infrared classification may be superior to optical classification.Comment: ApJS (in press), Spitzer Space Telescope Special Issue; 13 pages,
LaTeX (or Latex, etc); Figure 1ab is large, color plate; full-resolution
plates in .pdf format available at
http://cfa-www.harvard.edu/irac/publications
A New Concept of Transonic Galactic Outflows in a Cold Dark Matter Halo with a Central Super-Massive Black Hole
We study fundamental properties of isothermal, steady and spherically
symmetric galactic outflow in the gravitational potential of a cold dark matter
halo and a central super-massive black hole. We find that there are two
transonic solutions having different properties: each solution is mainly
produced by the dark matter halo and the super-massive black hole,
respectively. Furthermore, we apply our model to the Sombrero galaxy. In this
galaxy, Chandra X-ray observatory detected the diffuse hot gas as the trace of
galactic outflows while the star-formation rate is low and the observed gas
density distribution presumably indicates the hydrostatic equilibrium. To solve
this discrepancy, we propose a solution that this galaxy has a transonic
outflow, however, the transonic point forms in a very distant region from the
galactic center (? 127 kpc). In this slowly accelerated transonic
outflow, the outflow velocity is less than the sound velocity for most of the
galactic halo. Since the gas density distribution in this subsonic region is
similar to the hydrostatic one, it is difficult to distinguish the wide
subsonic region from hydrostatic state. Such galactic outflows are dfferent
from the conventional supersonic outflows observed in star-forming galaxies.Comment: 7 pages, 3 figures, accepted for publication in JPS Conference
Proceedings. arXiv admin note: substantial text overlap with arXiv:1405.345
Dependence of Spiral Galaxy Distribution on Viewing Angle in RC3
The normalized inclination distributions are presented for the spiral
galaxies in RC3. The results show that, except for the bin of
-, in which the apparent minor isophotal diameters that
are used to obtain the inclinations, are affected by the central bulges, the
distributions for Sa, Sab, Scd and Sd are well consistent with the Monte-Carlo
simulation of random inclinations within 3-, and Sb and Sbc almost, but
Sc is different. One reason for the difference between the real distribution
and the Monte-Carlo simulation of Sc may be that some quite inclined spirals,
the arms of which are inherently loosely wound on the galactic plane and should
be classified to Sc galaxies, have been incorrectly classified to the earlier
ones, because the tightness of spiral arms which is one of the criteria of the
Hubble classification in RC3 is different between on the galactic plane and on
the tangent plane of the celestial sphere. Our result also implies that there
might exist biases in the luminosity functions of individual Hubble types if
spiral galaxies are only classified visually.Comment: 5 pages + 8 figures, LaTe
What are S0 (0) Galaxies?
Among early-type galaxies with almost circular isophotes E0 and E1 galaxies
are, at 99.3% significance, more luminous than face-on objects classified as S0
(0) and S(0) (1). This result supports the view that rotation and "diskiness"
are more important in the outer regions of faint-early type galaxies than they
are for more luminous galaxies of very early morphological type.Comment: 7 pages. 0 figures. Astrophysical Jounral Letters in pres
The CMB Dipole and Circular Galaxy Distribution
The validity of Hubble's law defies the determination of the center of the
big bang expansion, even if it exists. Every point in the expanding universe
looks like the center from which the rest of the universe flies away. In this
article, the author shows that the distribution of apparently circular galaxies
is not uniform in the sky and that there exists a special direction in the
universe in our neighborhood. The data is consistent with the assumption that
the tidal force due to the mass distribution around the universe center causes
the deformation of galactic shapes depending on its orientation and location
relative to the center and our galaxy. Moreover, the cmb dipole data can also
be associated with the center of the universe expansion, if the cmb dipole at
the center of our supercluster is assumed to be due to Hubble flow. The
location of the center is estimated from the cmb dipole data. The direction to
the center from both sets of data is consistent and the distance to the center
is computed from the cmb dipole data.Comment: 9 pages, 3 figures (10 figure captions), 1 tabl
The Arecibo Dual-Beam Survey: The HI Mass Function of Galaxies
We use the HI-selected galaxy sample from the Arecibo Dual-Beam Survey
(Rosenberg & Schneider 2000) to determine the shape of the HI mass function of
galaxies in the local universe using both the step-wise maximum likelihood and
the 1/V_tot methods. Our survey region spanned all 24 hours of right ascension
at selected declinations between 8 and 29 degrees covering ~430 deg^2 of sky in
the main beam. The survey is not as deep as some previous Arecibo surveys, but
it has a larger total search volume and samples a much larger area of the sky.
We conducted extensive tests on all aspects of the galaxy detection process,
allowing us to empirically correct for our sensitivity limits, unlike the
previous surveys. The mass function for the entire sample is quite steep, with
a power-law slope of \alpha ~ -1.5. We find indications that the slope of the
HI mass function is flatter near the Virgo cluster, suggesting that
evolutionary effects in high density environments may alter the shape of the HI
mass function. These evolutionary effects may help to explain differences in
the HI mass function derived by different groups. We are sensitive to the most
massive sources (log M > 5x10^10 M\solar) over most of the declination range,
\~1 sr, and do not detect any massive low surface brightness galaxies. These
statistics restrict the population of Malin 1-like galaxies to <5.5x10^-6
Mpc^-3.Comment: ApJ accepted, 12 page
Dependence of Galaxy Shape on Environment in the Sloan Digital Sky Survey
Using a sample of galaxies from the Sloan Digital Sky Survey (SDSS) Data
Release 4, we study the trends relating surface brightness profile type and
apparent axis ratio to the local galaxy environment. We use the SDSS parameter
`fracDeV' to quantify the profile type. We find that galaxies with M_r > -18
are mostly described by exponential profiles in all environments. Galaxies with
-21 < M_r < -18 mainly have exponential profiles in low density environments
and de Vaucouleurs profiles in high density environments. The most luminous
galaxies, with M_r < -21, are mostly described by de Vaucouleurs profiles in
all environments. For galaxies with M_r < -19, the fraction of de Vaucouleurs
galaxies is a monotonically increasing function of local density, while the
fraction of exponential galaxies is monotonically decreasing. For a fixed
surface brightness profile type, apparent axis ratio is frequently correlated
with environment. As the local density of galaxies increases, we find that for
-20 < M_r < -18, galaxies of all profile types become slightly rounder, on
average; for -22 < M_r < -20, galaxies with exponential profiles tend to become
flatter, while galaxies with de Vaucouleurs profiles become rounder; for M_r <
-22, galaxies with exponential profiles become flatter, while the de
Vaucouleurs galaxies become rounder in their inner regions, yet exhibit no
change in their outer regions. We comment on how the observed trends relate to
the merger history of galaxies.Comment: 23 pages, 7 figures, accepted by Ap
Disentangling Morphology, Star Formation, Stellar Mass, and Environment in Galaxy Evolution
We present a study of the spectroscopic and photometric properties of
galaxies in six nearby clusters. We perform a partial correlation analysis on
our dataset to investigate whether the correlation between star formation rates
in galaxies and their environment is merely another aspect of correlations of
morphology, stellar mass, or mean stellar age with environment, or whether star
formation rates vary independently of these other correlations. We find a
residual correlation of ongoing star formation with environment, indicating
that even galaxies with similar morphologies, stellar masses, and mean stellar
ages have lower star formation rates in denser environments. Thus, the current
star formation gradient in clusters is not just another aspect of the
morphology-density, stellar mass-density, or mean stellar age-density
relations. Furthermore, the star formation gradient cannot be solely the result
of initial conditions, but must partly be due to subsequent evolution through a
mechanism (or mechanisms) sensitive to environment. Our results constitute a
true ``smoking gun'' pointing to the effect of environment on the later
evolution of galaxies.Comment: 31 pages, including 5 figures; accepted for publication in Ap
Constraints on the Massive Supernova Progenitors
Generally accepted scheme distinguishes two main classes of supernovae (SNe):
Ia resulting from the old stellar population (deflagration of a white dwarf in
close binary systems), and SNe of type II and Ib/c whose ancestors are young
massive stars (died in a core-collapse explosion). Concerning the latter, there
are suggestions that the SNe II are connected to early B stars, and SNe Ib/c to
isolated O or Wolf-Rayet (W-R) stars. However, little or no effort was made to
further separate SNe Ib from Ic. We have used assumed SN rates for different SN
types in spiral galaxies in an attempt to perform this task. If isolated
progenitor hypothesis is correct, our analysis indicates that SNe Ib result
from stars of main-sequence mass , while the progenitors of SNe Ic are more
massive stars with .
Alternatively, if the majority of SNe Ib/c appear in close binary systems
(CBs) then they would result from the same progenitor population as most of the
SNe II, i.e. early B stars with initial masses of order . Future observations of SNe at high-redshift () and
their rate will provide us with unique information on SN progenitors and
star-formation history of galaxies. At higher- (deeper in the cosmic past)
we expect to see the lack of type Ia events, i.e. the dominance of
core-collapse SNe. Better understanding of the stripped-envelope SNe (Ib/c),
and their potential use as distance indicators at high-, would therefore be
of great practical importance.Comment: 11 pages, 2 figures, accepted for publication in IJMP
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