86 research outputs found
Apparent and actual galaxy cluster temperatures
The redshift evolution of the galaxy cluster temperature function is a
powerful probe of cosmology. However, its determination requires the
measurement of redshifts for all clusters in a catalogue, which is likely to
prove challenging for large catalogues expected from XMM--Newton, which may
contain of order 2000 clusters with measurable temperatures distributed around
the sky. In this paper we study the apparent cluster temperature, which can be
obtained without cluster redshifts. We show that the apparent temperature
function itself is of limited use in constraining cosmology, and so concentrate
our focus on studying how apparent temperatures can be combined with other
X-ray information to constrain the redshift. We also briefly study the
circumstances in which non-thermal spectral features can give redshift
information.Comment: 7 pages LaTeX file with 13 figures incorporated (uses mn.sty and
epsf). Minor changes to match MNRAS accepted versio
The Butcher-Oemler Effect in High Redshift X-ray Selected Clusters
We are engaged in a wide-field, multi-colour imaging survey of X-ray selected
clusters at intermediate and high redshift. We present blue fractions for the
first 8 out of 29 clusters, covering almost a factor of 100 in X-ray
luminosity. We find no correlation of blue fraction with redshift or X-ray
luminosity. The lack of a correlation with L, places strong constraints
on the importance of ram-pressure stripping as a driver of the Butcher-Oemler
effect.Comment: 4 pages, 4 figures, to be puplished in the proceedings of the ''Sesto
2001-Tracing Cosmic Evolution with Galaxy Clusters'', Sesto 3-6 July 2001,
Italy, eds, Stefano Borgan
Simulation tests of galaxy cluster constraints on chameleon gravity
We use two new hydrodynamical simulations of Lambda cold dark matter (LambdaCDM) and f(R) gravity to test the methodology used by Wilcox et al. (W15) in constraining the effects of a fifth force on the profiles of clusters of galaxies. We construct realistic simulated stacked weak lensing and X-ray surface brightness cluster profiles from these cosmological simulations, and then use these data projected along various lines of sight to test the spherical symmetry of our stacking procedure. We also test the applicability of the NFW profile to model weak lensing profiles of clusters in f(R) gravity. Finally, we test the validity of the analytical model developed in W15 against the simulated profiles. Overall, we find our methodology is robust and broadly agrees with these simulated data. We also apply our full Markov Chain Monte Carlo analysis from W15 to our simulated X-ray and lensing profiles, providing consistent constraints on the modified gravity parameters as obtained from the real cluster data, e.g. for our LambdaCDM simulation we obtain |fR0| < 8.3 × 10-5 (95 per cent CL), which is in good agreement with the W15 measurement of |fR0| < 6 × 10-5. Overall, these tests confirm the power of our methodology which can now be applied to larger cluster samples available with the next generation surveys
The Butcher-Oemler Effect at Moderate Redshift
We present the results of Butcher-Oemler-style analysis of three moderate-
redshift (0.1<z<0.2) clusters which have bimodal X-ray surface brightness
profiles. We find that at least two of these clusters exhibit unusually high
fractions of blue galaxies as compared to clusters at comparable redshifts
studied by Butcher and Oemler (1984). This implies that star formation is
occurring in a high fraction of the galaxies in the two clusters. Our results
are consistent with hierarchical clustering models in which subcluster-
subcluster mergers create shocks in the intracluster medium. The shocks, in
turn, induce simultaneous starbursts in a large fraction of cluster galaxies.
Our study therefore lends weight to the hypothesis that the Butcher-Oemler
effect is an environmental, as well as evolutionary, phenomenon.Comment: 22 pages, 8 figures; accepted for publication in A
The XMM Cluster Survey: The Dynamical State of XMMXCS J2215.9-1738 at z=1.457
We present new spectroscopic observations of the most distant X-ray selected
galaxy cluster currently known, XMMXCS J2215.9-1738 at z=1.457, obtained with
the DEIMOS instrument at the W. M. Keck Observatory, and the FORS2 instrument
on the ESO Very Large Telescope. Within the cluster virial radius, as estimated
from the cluster X-ray properties, we increase the number of known
spectroscopic cluster members to 17 objects, and calculate the line of sight
velocity dispersion of the cluster to be 580+/-140 km/s. We find mild evidence
that the velocity distribution of galaxies within the virial radius deviates
from a single Gaussian. We show that the properties of J2215.9-1738 are
inconsistent with self-similar evolution of local X-ray scaling relations,
finding that the cluster is underluminous given its X-ray temperature, and that
the intracluster medium contains ~2-3 times the kinetic energy per unit mass of
the cluster galaxies. These results can perhaps be explained if the cluster is
observed in the aftermath of an off-axis merger. Alternatively, heating of the
intracluster medium through supernovae and/or Active Galactic Nuclei activity,
as is required to explain the observed slope of the local X-ray
luminosity-temperature relation, may be responsible.Comment: 13 pages, 6 figures, accepted for publication in Ap
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