882 research outputs found
Evolution of Cluster Ellipticals at 0.2 < z < 1.2 from Hubble Space Telescope Imaging
Two-dimensional surface photometry derived from Hubble Space Telescope
imaging is presented for a sample of 225 early-type galaxies (assumed to be
cluster members) in the fields of 9 clusters at redshifts .
The 94 luminous ellipticals (; selected by morphology alone with
no reference to color) form tight sequences in the size-luminosity plane. The
position of these sequences shifts, on average, with redshift so that an object
of a given size at z=0.55 is brighter by mag than
its counterpart (measured with the same techniques) in nearby clusters. At
z=0.9 the shift is mag. If the relation between
size and luminosity is universal so that the local cluster galaxies represent
the evolutionary endpoints of those at high redshift, and if the
size-luminosity relation is not modified by dynamical processes then this
population of galaxies has undergone significant luminosity evolution since z=1
consistent with expectations based on models of passively evolving, old stellar
populations.Comment: 7 pages, 3 figures, and 1 Tabl
The host galaxy of GRB010222: The strongest damped Lyman-alpha system known
Analysis of the absorption lines in the afterglow spectrum of the gamma-ray
burst GRB010222 indicates that its host galaxy (at a redshift of z=1.476) is
the strongest damped Lyman-alpha (DLA) system known, having a very low
metallicity and modest dust content. This conclusion is based on the detection
of the red wing of Lyman-alpha plus a comparison of the equivalent widths of
ultraviolet Mg I, Mg II, and Fe II lines with those in other DLAs. The column
density of H I, deduced from a fit to the wing of Lyman-alpha, is (5 +/- 2)
10^22 cm^-2. The ratio of the column densities of Zn and Cr lines suggests that
the dust content in our line of sight through the galaxy is low. This could be
due to either dust destruction by the ultraviolet emission of the afterglow or
to an initial dust composition different to that of the diffuse interstellar
material, or a combination of both.Comment: Submitted to MNRAS 12 page
Ram pressure and dusty red galaxies - key factors in the evolution of the multiple cluster system Abell 901/902
We present spectroscopic observations of 182 disk galaxies (96 in the cluster
and 86 in the field environment) in the region of the Abell 901/902 multiple
cluster system, which is located at a redshift of . The presence
of substructures and non-Gaussian redshift distributions indicate that the
cluster system is dynamically young and not in a virialized state. We find
evidence for two important galaxy populations. \textit{Morphologically
distorted galaxies} are probably subject to increased tidal interactions. They
show pronounced rotation curve asymmetries at intermediate cluster-centric
radii and low rest-frame peculiar velocities. \textit{Morphologically
undistorted galaxies} show the strongest rotation curve asymmetries at high
rest-frame velocities and low cluster-centric radii. Supposedly, this group is
strongly affected by ram-pressure stripping due to interaction with the
intra-cluster medium. Among the morphologically undistorted galaxies, dusty red
galaxies have particularly strong rotation curve asymmetries, suggesting ram
pressure is an important factor in these galaxies. Furthermore, dusty red
galaxies on average have a bulge-to-total ratio higher by a factor of two than
cluster blue cloud and field galaxies. The fraction of kinematically distorted
galaxies is 75% higher in the cluster than in the field environment. This
difference mainly stems from morphological undistorted galaxies, indicating a
cluster-specific interaction process that only affects the gas kinematics but
not the stellar morphology. Also the ratio between gas and stellar scale length
is reduced for cluster galaxies compared to the field sample. Both findings
could be best explained by ram-pressure effects.Comment: Electronic version published in Astronomy and Astrophysics Volume
549, Page 0; 19 pages, 21 figure
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Tully-Fisher analysis of the multiple cluster system Abell 901/902
We derive rotation curves from optical emission lines of 182 disk galaxies
(96 in the cluster and 86 in the field) in the region of Abell 901/902 located
at . We focus on the analysis of B-band and stellar-mass
Tully-Fisher relations. We examine possible environmental dependencies and
differences between normal spirals and "dusty red" galaxies, i.e. disk galaxies
that have red colors due to relatively low star formation rates. We find no
significant differences between the best-fit TF slope of cluster and field
galaxies. At fixed slope, the field population with high-quality rotation
curves (57 objects) is brighter by \Delta M_{B}=-0\fm42\pm0\fm15 than the
cluster population (55 objects). We show that this slight difference is at
least in part an environmental effect. The scatter of the cluster TFR increases
for galaxies closer to the core region, also indicating an environmental
effect. Interestingly, dusty red galaxies become fainter towards the core at
given rotation velocity (i.e. total mass). This indicates that the star
formation in these galaxies is in the process of being quenched. The
luminosities of normal spiral galaxies are slightly higher at fixed rotation
velocity for smaller cluster-centric radii. Probably these galaxies are
gas-rich (compared to the dusty red population) and the onset of ram-pressure
stripping increases their star-formation rates. The results from the TF
analysis are consistent with and complement our previous findings. Dusty red
galaxies might be an intermediate stage in the transformation of infalling
field spiral galaxies into cluster S0s, and this might explain the well-known
increase of the S0 fraction in galaxy clusters with cosmic time.Comment: Accepted for publication in Astronomy and Astrophysics; 16 pages, 14
figure
A Rich Cluster of Galaxies Near the Quasar B2 1335+28 at z=1.1: Color Distribution and Star-Formation Properties
We previously reported a significant clustering of red galaxies (R-K=3.5--6)
around the radio-loud quasar B2 1335+28 at z=1.086. In this paper, we establish
the existence of a rich cluster at the quasar redshift, and study the
properties of the cluster galaxies through further detailed analysis of the
photometric data. The color distribution of the galaxies in the cluster is
quite broad and the fraction of blue galaxies (\sim 70%) is much larger than in
intermediate-redshift clusters. Using evolutionary synthesis models, we show
that this color distribution can be explained by galaxies with various amounts
of star-formation activity mixed with the old stellar populations. Notably,
there are about a dozen galaxies which show very red optical-NIR colors but
also show significant UV excess with respect to passive-evolution models. They
can be interpreted as old early-type galaxies with a small amount of star
formation. The fact that the UV-excess red galaxies are more abundant than the
quiescent red ones suggests that a large fraction of old galaxies in this
cluster are still forming stars to some extent. However, a sequence of
quiescent red galaxies is clearly identified on the R-K versus K
color-magnitude (C-M) diagram. The slope and zero point of their C-M relation
appear to be consistent with those expected for the precursors of the C-M
relation of present-day cluster ellipticals when observed at z=1.1. We estimate
the Abell richness class of the cluster to be R \sim 1. New X-ray data
presented here place an upper limit of L_x < 2 10^{44} erg s^{-1} for the
cluster luminosity. Inspections of the wider optical images reveal some lumpy
structure, suggesting that the whole system is still dynamically young.Comment: 54 pages including 13 Postscript figures, 1 jpg figure, and 1 table,
uses aasms4.sty and epsf.sty. Accepted for publication in ApJ: Replaced as
the older verison was missed to include the figure 2c, 2d, and figure
NICMOS Snapshot Survey of Damped Lyman Alpha Quasars
We image 19 quasars with 22 damped Lyman alpha (DLA) systems using the F160W
filter and the Near-Infrared Camera and Multiobject Spectrograph aboard the
Hubble Space Telescope, in both direct and coronagraphic modes. We reach 5
sigma detection limits of ~H=22 in the majority of our images. We compare our
observations to the observed Lyman-break population of high-redshift galaxies,
as well as Bruzual & Charlot evolutionary models of present-day galaxies
redshifted to the distances of the absorption systems. We predict H magnitudes
for our DLAs, assuming they are producing stars like an L* Lyman-break galaxy
(LBG) at their redshift. Comparing these predictions to our sensitivity, we
find that we should be able to detect a galaxy around 0.5-1.0 L* (LBG) for most
of our observations. We find only one new possible candidate, that near
LBQS0010-0012. This scarcity of candidates leads us to the conclusion that most
DLA systems are not drawn from a normal LBG luminosity function nor a local
galaxy luminosity function placed at these high redshifts.Comment: 31 pages, 8 figures, Accepted for Feb. 10 issue of Ap
An Optical/Near-Infrared Study of Radio-Loud Quasar Environments II. Imaging Results
We use optical and near-IR imaging to examine the properties of the
significant excess population of K>=19 galaxies found in the fields of 31 z=1-2
radio-loud quasars by Hall, Green & Cohen (1998). The excess occurs on two
spatial scales: a component at <40'' from the quasars significant compared to
the galaxy surface density at >40'' in the same fields, and a component roughly
uniform to ~100'' significant compared to the galaxy surface density seen in
random-field surveys in the literature. The r-K color distributions of the
excess galaxy populations are indistinguishable and are significantly redder
than the color distribution of the field population.
The excess galaxies are consistent with being predominantly early-type
galaxies at the quasar redshifts, and there is no evidence that they are
associated with intervening MgII absorption systems. The average excess within
0.5 Mpc (~65'') of the quasars corresponds to Abell richness class ~0 compared
to the galaxy surface density at >0.5 Mpc from the quasars, and to Abell
richness class ~1.5 compared to that from the literature.
We discuss the spectral energy distributions (SEDs) of galaxies in fields
with data in several passbands. Most candidate quasar-associated galaxies are
consistent with being 2-3 Gyr old early-types at the quasar redshifts of z~1.5.
However, some objects have SEDs consistent with being 4-5 Gyr old at z~1.5, and
a number of others are consistent with ~2 Gyr old but dust-reddened galaxies at
the quasar redshifts. These potentially different galaxy types suggest there
may be considerable dispersion in the properties of early-type cluster galaxies
at z~1.5. There is also a population of galaxies whose SEDs are best modelled
by background galaxies at z>2.5.Comment: Accepted to ApJ; 54 pages including 30 figures; 2 color GIF files
available separately; also available from
http://www.astro.utoronto.ca/~hall/thesis.htm
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