18 research outputs found
Two-Color Surface Photometry of Brightest Cluster Members
The Gunn g, r and i CCD images of a representative sample of 17 Brightest
Cluster Galaxies (BCM) have been analyzed in order to derive surface brightness
and color profiles, together with geometrical parameters like eccentricity and
position angle. The sample includes both X-ray and optically selected clusters,
ranging in redshift from z=0.049 to z=0.191. We find that BCMs are
substantially well described by de Vaucouleurs' law out to radii of kpc, and that color gradients are generally absent. Only in two cases we
find a surface brightness excess with respect to the law, which for
A150 is coupled with a change in the color. The rest frame colors of BCMs
do not show any intrinsic dispersion. By parametrizing the environment with the
local galaxy number density, we find that it is correlated with the BCM
extension, i.e. BCMs with larger effective radii are found in denser
environments.Comment: accepted for publication in Aj, May 1997, 25 pages LaTeX format (aas
style files), including tables, plus 6 figures (postscript
The zCOSMOS 10k-Bright Spectroscopic Sample
We present spectroscopic redshifts of a large sample of galaxies with I_(AB) < 22.5 in the COSMOS field, measured from spectra of 10,644 objects that have been obtained in the first two years of observations in the zCOSMOS-bright redshift survey. These include a statistically complete subset of 10,109 objects. The average accuracy of individual redshifts is 110 km s^(–1), independent of redshift. The reliability of individual redshifts is described by a Confidence Class that has been empirically calibrated through repeat spectroscopic observations of over 600 galaxies. There is very good agreement between spectroscopic and photometric redshifts for the most secure Confidence Classes. For the less secure Confidence Classes, there is a good correspondence between the fraction of objects with a consistent photometric redshift and the spectroscopic repeatability, suggesting that the photometric redshifts can be used to indicate which of the less secure spectroscopic redshifts are likely right and which are probably wrong, and to give an indication of the nature of objects for which we failed to determine a redshift. Using this approach, we can construct a spectroscopic sample that is 99% reliable and which is 88% complete in the sample as a whole, and 95% complete in the redshift range 0.5 < z < 0.8. The luminosity and mass completeness levels of the zCOSMOS-bright sample of galaxies is also discussed
The XMM-LSS survey. Survey design and first results
We have designed a medium deep large area X-ray survey with XMM - the XMM
Large Scale Structure survey, XMM-LSS - with the scope of extending the
cosmological tests attempted using ROSAT cluster samples to two redshift bins
between 0<z<1 while maintaining the precision of earlier studies. Two main
goals have constrained the survey design: the evolutionary study of the
cluster-cluster correlation function and of the cluster number density. The
results are promising and, so far, in accordance with our predictions as to the
survey sensitivity and cluster number density. The feasibility of the programme
is demonstrated and further X-ray coverage is awaited in order to proceed with
a truly significant statistical analysis. (Abridged)Comment: Published in Journal of Cosmology and Astroparticle Physic
Lyman-alpha Forest Tomography from Background Galaxies: The First Megaparsec-Resolution Large-Scale Structure Map at z>2
We present the first observations of foreground Lyman- forest
absorption from high-redshift galaxies, targeting 24 star-forming galaxies
(SFGs) with within a region of the COSMOS
field. The transverse sightline separation is
comoving, allowing us to create a tomographic reconstruction of the 3D
Ly forest absorption field over the redshift range . The resulting map covers in the transverse plane and
along the line-of-sight with a spatial resolution of , and is the first high-fidelity map of large-scale
structure on scales at . Our map reveals significant
structures with extent, including several
spanning the entire transverse breadth, providing qualitative evidence for the
filamentary structures predicted to exist in the high-redshift cosmic web.
Simulated reconstructions with the same sightline sampling, spectral
resolution, and signal-to-noise ratio recover the salient structures present in
the underlying 3D absorption fields. Using data from other surveys, we
identified 18 galaxies with known redshifts coeval with our map volume enabling
a direct comparison to our tomographic map. This shows that galaxies
preferentially occupy high-density regions, in qualitative agreement with the
same comparison applied to simulations. Our results establishes the feasibility
of the CLAMATO survey, which aims to obtain Ly forest spectra for SFGs over of the COSMOS field, in order to map
out IGM large-scale structure at over a large
volume .Comment: Accepted for publication in Astrophysical Journal Letters; 8 pages
and 5 figure
Mass and environment as drivers of galaxy evolution in SDSS and zCOSMOS and the origin of the Schechter function
We explore the inter-relationships between mass, star-formation rate and
environment in the SDSS, zCOSMOS and other surveys. The differential effects of
mass and environment are completely separable to z ~ 1, indicating that two
distinct processes are operating, "mass-quenching" and "environment-quenching".
Environment-quenching, at fixed over-density, evidently does not change with
epoch to z ~ 1, suggesting that it occurs as large-scale structure develops in
the Universe. The observed constancy of the mass-function shape for
star-forming galaxies, demands that the mass-quenching of galaxies around and
above M*, must be proportional to their star-formation rates at all z < 2. We
postulate that this simple mass-quenching law also holds over a much broader
range of stellar mass and epoch. These two simple quenching processes, plus
some additional quenching due to merging, then naturally produce (a) a
quasi-static Schechter mass function for star-forming galaxies with a value of
M* that is set by the proportionality between the star-formation and
mass-quenching rates, (b) a double Schechter function for passive galaxies with
two components: the dominant one is produced by mass-quenching and has exactly
the same M* as the star-forming galaxies but an alpha shallower by +1, while
the other is produced by environment effects and has the same M* and alpha as
the star-forming galaxies, and is larger in high density environments.
Subsequent merging of quenched galaxies modifies these predictions somewhat in
the denser environments, slightly increasing M* and making alpha more negative.
All of these detailed quantitative relationships between the Schechter
parameters are indeed seen in the SDSS, lending strong support to our simple
empirically-based model. The model naturally produces for passive galaxies the
"anti-hierarchical" run of mean ages and alpha-element abundances with mass.Comment: 66 pages, 19 figures, 1 movie, accepted for publication in ApJ. The
movie is also available at
http://www.exp-astro.phys.ethz.ch/zCOSMOS/MF_simulation_d1_d4.mo