217,036 research outputs found
A Study of 3CR Radio Galaxies from z = 0.15 to 0.65. II. Evidence for an Evolving Radio Structure
Radio structure parameters were measured from the highest quality radio maps
available for a sample of 3CR radio galaxies in the redshift range 0.15 < z <
0.65. Combined with similar data for quasars in the same redshift range, these
morphology data are used in conjunction with a quantification of the richness
of the cluster environment around these objects (the amplitude of the
galaxy-galaxy spatial covariance function, Bgg) to search for indirect evidence
of a dense intracluster medium (ICM). This is done by searching for confinement
and distortions of the radio structure that are correlated with Bgg.
Correlations between physical size and hot spot placement with Bgg show
evidence for an ICM only at z 0.4,
suggesting an epoch of z ~ 0.4 for the formation of an ICM in these Abell
richness class 0-1, FR2-selected clusters. X-ray selected clusters at
comparable redshifts, which contain FR1 type sources exclusively, are
demonstrably richer than the FR2-selected clusters found in this study. The
majority of the radio sources with high Bgg values at z < 0.4 can be described
as ``fat doubles'' or intermediate FR2/FR1s. The lack of correlation between
Bgg and bending angle or Bgg and lobe length asymmetry suggests that these
types of radio source distortion are caused by something other than interaction
with a dense ICM. Thus, a large bending angle cannot be used as an unambiguous
indicator of a rich cluster around powerful radio sources. These results
support the hypothesis made in Paper 1 that cluster quasars fade to become
FR2s, then FR1s, on a timescale of 0.9 Gyrs (for H0 = 50 km s^-1 Mpc^-1).Comment: 44 pages, 8 figures, 2 tables; to be published in the September 2002
issue of The Astronomical Journa
The evolution of the cluster optical galaxy luminosity function between z=0.4 and 0.9 in the DAFT/FADA survey
We compute optical galaxy luminosity functions (GLFs) in the B, V, R, and I
rest-frame bands for one of the largest medium-to-high-redshift (0.4 < z < 0.9)
cluster samples to date in order to probe the abundance of faint galaxies in
clusters. We also study how the GLFs depend on cluster redshift, mass, and
substructure, and compare the GLFs of clusters with those of the field. We
separately investigate the GLFs of blue and red-sequence (RS) galaxies to
understand the evolution of different cluster populations. We find that the
shapes of our GLFs are similar for the B, V, R, and I bands with a drop at the
red GLF faint end that is more pronounced at high-redshift: alpha(red) ~ -0.5
at 0.40 0.1 at 0.65 < z < 0.90. The blue GLFs have
a steeper faint end (alpha(blue) ~ -1.6) than the red GLFs, that appears to be
independent of redshift. For the full cluster sample, blue and red GLFs
intersect at M(V) = -20, M(R) = -20.5, and M(I) = -20.3. A study of how galaxy
types evolve with redshift shows that late type galaxies appear to become early
types between z ~ 0.9 and today. Finally, the faint ends of the red GLFs of
more massive clusters appear to be richer than less massive clusters, which is
more typical of the lower redshift behaviour. Our results indicate that our
clusters form at redshifts higher than z = 0.9 from galaxy structures that
already have an established red sequence. Late type galaxies then appear to
evolve into early types, enriching the red-sequence between this redshift and
today. This effect is consistent with the evolution of the faint end slope of
the red-sequence and the galaxy type evolution that we find. Finally, faint
galaxies accreted from the field environment at all redshifts might have
replaced the blue late type galaxies that converted into early types,
explaining the lack of evolution in the faint end slopes of the blue GLFs.Comment: accepted for publication in A&
The Red-Sequence Luminosity Function in Galaxy Clusters since z~1
We use a statistical sample of ~500 rich clusters taken from 72 square
degrees of the Red-Sequence Cluster Survey (RCS-1) to study the evolution of
~30,000 red-sequence galaxies in clusters over the redshift range 0.35<z<0.95.
We construct red-sequence luminosity functions (RSLFs) for a well-defined,
homogeneously selected, richness limited sample. The RSLF at higher redshifts
shows a deficit of faint red galaxies (to M_V=> -19.7) with their numbers
increasing towards the present epoch. This is consistent with the `down-sizing`
picture in which star-formation ended at earlier times for the most massive
(luminous) galaxies and more recently for less massive (fainter) galaxies. We
observe a richness dependence to the down-sizing effect in the sense that, at a
given redshift, the drop-off of faint red galaxies is greater for poorer (less
massive) clusters, suggesting that star-formation ended earlier for galaxies in
more massive clusters. The decrease in faint red-sequence galaxies is
accompanied by an increase in faint blue galaxies, implying that the process
responsible for this evolution of faint galaxies is the termination of
star-formation, possibly with little or no need for merging. At the bright end,
we also see an increase in the number of blue galaxies with increasing
redshift, suggesting that termination of star-formation in higher mass galaxies
may also be an important formation mechanism for higher mass ellipticals. By
comparing with a low-redshift Abell Cluster sample, we find that the
down-sizing trend seen within RCS-1 has continued to the local universe.Comment: ApJ accepted. 11 pages, 5 figure
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The role of quality ladders in a Ricardian model of trade with nonhomothetic preference.
The literature on North-South trade has explored conditions under which international trade might be a factor magnifying income disparities between the advanced North and the backward South. Little attention has yet been placed on the effect of trade on countries that do not display substantial dissimilarities concerning capital endowments. We show that even when no single country is technologically more advanced than any other one and productivity changes are uniform and identical in all countries, international trade may still be a source of income divergence. Income divergence will be experienced when comparative advantages induce patterns of specialisation that, although optimal for each country at some initial point in time, do not offer the same scope for improvements in terms of subsequent quality upgrading of final products
Carbon Stars and other Luminous Stellar Populations in M33
The M33 galaxy is a nearby, relatively metal-poor, late-type spiral. Its
proximity and almost face-on inclination means that it projects over a large
area on the sky, making it an ideal candidate for wide-field CCD mosaic
imaging. Photometry was obtained for more than 10^6 stars covering a 74' x 56'
field centered on M33. Main sequence (MS), supergiant branch (SGB), red giant
branch (RGB) and asymptotic giant branch (AGB) populations are identified and
classified based on broad-band V and I photometry. Narrow-band filters are used
to measure spectral features allowing the AGB population to be further divided
into C and M-star types. The galactic structure of M33 is examined using star
counts, colour-colour and colour-magnitude selected stellar populations. We use
the C to M-star ratio to investigate the metallicity gradient in the disk of
M33. The C/M-star ratio is found to increase and then flatten with increasing
galactocentric radius in agreement with viscous disk formation models. The
C-star luminosity function is found to be similar to M31 and the SMC,
suggesting that C-stars should be useful distance indicators. The ``spectacular
arcs of carbon stars'' in M33 postulated recently by Block et al. (2004) are
found in our work to be simply an extension of M33's disk.Comment: 20 pages, 20 figures. Accepted for publication in The Astronomical
Journa
SDSS superclusters: morphology and galaxy content
We compare the galaxy populations in superclusters of different morphology in
the nearby Universe (180 < d < 270 Mpc) to see whether the inner structure and
overall morphology of superclusters are important in shaping galaxy properties
in superclusters. Supercluster morphology has been found with Minkowski
functionals. We analyse the probability density distributions of colours,
morphological types, stellar masses, star formation rates (SFR) of galaxies,
and the peculiar velocities of the main galaxies in groups in superclusters of
filament and spider types, and in the field. We show that the fraction of red,
early-type, low SFR galaxies in filament-type superclusters is higher than in
spider-type superclusters; in low-density global environments their fraction is
lower than in superclusters. In all environments the fraction of red, high
stellar mass, and low SFR galaxies in rich groups is higher than in poor
groups. In superclusters of spider morphology red, high SFR galaxies have
higher stellar masses than in filament-type superclusters. Groups of equal
richness host galaxies with larger stellar masses, a larger fraction of
early-type and red galaxies, and a higher fraction of low SFR galaxies, if they
are located in superclusters of filament morphology. The peculiar velocities of
the main galaxies in groups from superclusters of filament morphology are
higher than in those of spider morphology. Groups with higher peculiar
velocities of their main galaxies in filament-type superclusters are located in
higher density environment than those with low peculiar velocities. There are
significant differences between galaxy populations of the individual richest
superclusters. Therefore both local (group) and global (supercluster)
environments and even supercluster morphology play an important role in the
formation and evolution of galaxies.Comment: Comments: 14 pages, 11 figures, accepted for publication in Astronomy
and Astrophysic
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