584 research outputs found
Coma cluster object populations down to M_R~-9.5
This study follows a recent analysis of the galaxy luminosity functions and
colour-magnitude red sequences in the Coma cluster (Adami et al. 2007). We
analyze here the distribution of very faint galaxies and globular clusters in
an east-west strip of arcmin crossing the Coma cluster
center (hereafter the CS strip) down to the unprecedented faint absolute
magnitude of M. This work is based on deep images obtained at the
CFHT with the CFH12K camera in the B, R, and I bands. The analysis shows that
the observed properties strongly depend on the environment, and thus on the
cluster history. When the CS is divided into four regions, the westernmost
region appears poorly populated, while the regions around the brightest
galaxies NGC 4874 and NGC 4889 (NGC 4874 and NGC 4889 being masked) are
dominated by faint blue galaxies. They show a faint luminosity function slope
of -2, very significantly different from the field estimates. Results are
discussed in the framework of galaxy destruction (which can explain part of the
very faint galaxy population) and of structures infalling on to Coma.Comment: To be published in A&
The CFH Optical PDCS survey (COP) I: The Data
This paper presents and gives the COP (COP: CFHT Optical PDCS; CFHT:
Canada-France-Hawaii Telescope; PDCS: Palomar Distant Cluster Survey) survey
data. We describe our photometric and spectroscopic observations with the MOS
multi-slit spectrograph at the CFH telescope. A comparison of the photometry
from the PDCS (Postman et al. 1996) catalogs and from the new images we have
obtained at the CFH telescope shows that the different magnitude systems can be
cross-calibrated. After identification between the PDCS catalogues and our new
images, we built catalogues with redshift, coordinates and V, I and
Rmagnitudes. We have classified the galaxies along the lines of sight into
field and structure galaxies using a gap technique (Katgert et al. 1996). In
total we have observed 18 significant structures along the 10 lines of sight.Comment: 40 pages, 13 figures, accepted in A
A Turn-over in the Galaxy Luminosity Function of the Coma Cluster Core?
Our previous study of the faint end (R21.5) of the galaxy luminosity
function (GLF) was based on spectroscopic data in a small region near the Coma
cluster center. In this previous study Adami et al. (1998) suggested, with
moderate statistical significance, that the number of galaxies actually
belonging to the cluster was much smaller than expected. This led us to
increase our spectroscopic sample. Here, we have improved the statistical
significance of the results of the Coma GLF faint end study (R22.5) by
using a sample of 85 redshifts. This includes both new spectroscopic data and a
literature compilation. The relatively small number of faint galaxies belonging
to Coma that was suggested by Adami et al. (1998) and Secker et al. (1998) has
been confirmed with these new observations. We also confirm that the
color-magnitude relation is not well suited for finding the galaxies inside the
Coma cluster core, close to the center at magnitudes fainter than R19. We
show that there is an enhancement in the Coma line of sight of field galaxies
compared to classical field counts. This can be explained by the contribution
of groups and of a distant cluster along the line of sight. The
result is that the Coma GLF appears to turn-over or at least to become flat for
the faint galaxies. We suggest that this is due to environmental effects.Comment: 8 pages, 6 postscript figures, accepted in A&A, new table 1, updated
figure
Dynamical and content evolution of a sample of clusters from z~0 to z~0.5
In this paper, we present an analysis of the dynamics and segregation of
galaxies in rich clusters from z~0.32 to z~0.48 taken from the CFHT Optical
PDCS (COP) survey and from the CNOC survey (Carlberg et al. 1997). Our results
from the COP survey are based upon the recent observational work of Adami et
al. (2000) and Holden et al. (2000) and use new spectroscopic and photometric
data on six clusters selected from the Palomar Distant Cluster Survey (PDCS;
Postman et al. 1996). We have compared the COP and CNOC samples to the ESO
Nearby Abell Cluster Survey (ENACS: z~0.07). Our sample shows that the z<0.4
clusters have the same velocity dispersion versus magnitude, morphological type
and radius relationships as nearby Abell clusters. The z~0.48 clusters exhibit,
however, departures from these relations. Furthermore, there appears to be a
higher fraction of late-type (or bluer, e.g. Butcher and Oemler, 1984) galaxies
in the distant clusters compared to the nearby ones. The classical scenario in
which massive galaxies virialize before they evolve from late into early type
explain our observations. In such a scenario, the clusters of our sample began
to form before a redshift of ~0.8 and the late-type galaxy population had a
continuous infall into the clusters.Comment: 11 pages, 4 figures, accepted in A&
Velocity Dispersions of CNOC Clusters and the Evolution of the Cluster Abundance
We present the results of the analysis of the internal velocity dispersions,
\sigma_v, for the CNOC sample of distant galaxy clusters, based on an
interlopers removal algorithm, which is different from that originally applied
by Carlberg et al. (1996, C96). We find that the resulting \sigma_v values are
consistent within <10% with the original C96 estimates. This result points in
favor of a substantial robustness of currently applied methods for optical
studies of the internal cluster dynamics. The resulting distribution of
velocity dispersions is used to trace the redshift evolution of the cluster
abundance with the aim of constraining the matter density parameter, \Omega_m.
We find that constraints on \Omega_m are very sensitive to the adopted value of
\sigma_8, as obtainable from the local cluster abundance: as \sigma_8 varies
from 0.5 to 0.6 (for Omega_m=1), the best fitting Omega_m varies in the range
0.3-1.0.Comment: 11 pages, 8 figures, 1 table, LateX, uses apj.sty, ApJ, corrected
some typo
Geometrical tests of cosmological models. I. Probing dark energy using the kinematics of high redshift galaxies
We suggest to use the observationally measured and theoretically justified correlation between size and rotational velocity of galactic discs as a viable method to select a set of high redshift standard rods which may be used to explore the dark energy content of the universe via the classical angular-diameter test. Here we explore a new strategy for an optimal implementation of this test.We propose to use the rotation speed of high redshift galaxies as a standard size indicator and show how high resolution multi-object spectroscopy and ACS/HST high quality spatial images, may be combined to measure the amplitude of the dark energy density parameter ΩQ, or to constrain the cosmic equation of state parameter for a smooth dark energy component (w = p/Ï, â1 †w < â1/3). Nearly 1300 standard rods with high velocity rotation in the bin V = 200 ± 20 km sâ1 are expected in a field of 1 sq. degree and over the
redshift baseline 0 < z < 1.4. This sample is sufficient to constrain the cosmic equation of state parameter w at a level of 20% (without priors in the [Ωm,ΩQ] plane) even when the [OII]λ3727 Ă
linewidth-diameter relationship is calibrated with a scatter of âŒ40%. We evaluate how systematics may affect the proposed tests, and find that a linear standard rod evolution, causing galaxy dimensions
to be up to 30% smaller at z = 1.5, can be uniquely diagnosed, and will minimally bias the confidence level contours in the [ΩQ, w] plane. Finally, we show how to derive, without a priori knowing the specific functional form of disc evolution, a cosmologyevolution diagram with which it is possible to establish a mapping between different cosmological models and the amount of galaxy
disc/luminosity evolution expected at a given redshift
Redshifts and Velocity Dispersions of Galaxy Clusters in the Horologium-Reticulum Supercluster
We present 118 new optical redshifts for galaxies in 12 clusters in the
Horologium-Reticulum supercluster (HRS) of galaxies. For 76 galaxies, the data
were obtained with the Dual Beam Spectrograph on the 2.3m telescope of the
Australian National University at Siding Spring Observatory. After combining 42
previously unpublished redshifts with our new sample, we determine mean
redshifts and velocity dispersions for 13 clusters, in which previous
observational data were sparse. In six of the 13 clusters, the newly determined
mean redshifts differ by more than 750 km/s from the published values. In the
case of three clusters, A3047, A3109, and A3120, the redshift data indicate the
presence of multiple components along the line of sight. The new cluster
redshifts, when combined with other reliable mean redshifts for clusters in the
HRS, are found to be distinctly bi-modal. Furthermore, the two redshift
components are consistent with the bi-modal redshift distribution found for the
inter-cluster galaxies in the HRS by Fleenor et al. (2005).Comment: 13 pages, 3 figures, Accepted to A
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