5 research outputs found
Joint Analysis of Cluster Observations: II. Chandra/XMM-Newton X-ray and Weak Lensing Scaling Relations for a Sample of 50 Rich Clusters of Galaxies
We present a study of multiwavelength X-ray and weak lensing scaling
relations for a sample of 50 clusters of galaxies. Our analysis combines
Chandra and XMM-Newton data using an energy-dependent cross-calibration. After
considering a number of scaling relations, we find that gas mass is the most
robust estimator of weak lensing mass, yielding 15 +/- 6% intrinsic scatter at
r500 (the pseudo-pressure YX has a consistent scatter of 22%+/-5%). The scatter
does not change when measured within a fixed physical radius of 1 Mpc. Clusters
with small BCG to X-ray peak offsets constitute a very regular population whose
members have the same gas mass fractions and whose even smaller <10% deviations
from regularity can be ascribed to line of sight geometrical effects alone.
Cool-core clusters, while a somewhat different population, also show the same
(<10%) scatter in the gas mass-lensing mass relation. There is a good
correlation and a hint of bimodality in the plane defined by BCG offset and
central entropy (or central cooling time). The pseudo-pressure YX does not
discriminate between the more relaxed and less relaxed populations, making it
perhaps the more even-handed mass proxy for surveys. Overall, hydrostatic
masses underestimate weak lensing masses by 10% on the average at r500; but
cool-core clusters are consistent with no bias, while non-cool-core clusters
have a large and constant 15-20% bias between r2500 and r500, in agreement with
N-body simulations incorporating unthermalized gas. For non-cool-core clusters,
the bias correlates well with BCG ellipticity. We also examine centroid shift
variance and and power ratios to quantify substructure; these quantities do not
correlate with residuals in the scaling relations. Individual clusters have for
the most part forgotten the source of their departures from self-similarity.Comment: Corrects an error in the X-ray luminosities (erratum
submitted)---none of the other results are affected. Go to
http://sfstar.sfsu.edu/jaco for an electronic fitter and updated quick data
download link
Evolution of the Red Sequence Giant to Dwarf Ratio in Galaxy Clusters out to z ~ 0.5
We analyze deep g' and r' band data of 97 galaxy clusters imaged with MegaCam
on the Canada-France-Hawaii telescope. We compute the number of luminous
(giant) and faint (dwarf) galaxies using criteria based on the definitions of
de Lucia et al. (2007). Due to excellent image quality and uniformity of the
data and analysis, we probe the giant-to-dwarf ratio (GDR) out to z ~ 0.55.
With X-ray temperature (Tx) information for the majority of our clusters, we
constrain, for the first time, the Tx-corrected giant and dwarf evolution
separately. Our measurements support an evolving GDR over the redshift range
0.05 < z < 0.55. We show that modifying the (g'-r'), m_r' and K-correction used
to define dwarf and giant selection do not alter the conclusion regarding the
presence of evolution. We parameterize the GDR evolution using a linear
function of redshift (GDR = alpha * z + beta) with a best fit slope of alpha =
0.88 +/- 0.15 and normalization beta = 0.44 +/- 0.03. Contrary to claims of a
large intrinsic scatter, we find that the GDR data can be fully accounted for
using observational errors alone. Consistently, we find no evidence for a
correlation between GDR and cluster mass (via Tx or weak lensing). Lastly, the
data suggest that the evolution of the GDR at z < 0.2 is driven primarily by
dry merging of the massive giant galaxies, which when considered with previous
results at higher redshift, suggests a change in the dominant mechanism that
mediates the GDR.Comment: 20 pages, 15 figures. Accepted to MNRA
Halo mass - concentration relation from weak lensing
We perform a statistical weak lensing analysis of dark matter profiles around
tracers of halo mass from galactic- to cluster-size halos. In this analysis we
use 170,640 isolated ~L* galaxies split into ellipticals and spirals, 38,236
groups traced by isolated spectroscopic Luminous Red Galaxies (LRGs) and 13,823
MaxBCG clusters from the Sloan Digital Sky Survey (SDSS) covering a wide range
of richness. Together these three samples allow a determination of the density
profiles of dark matter halos over three orders of magnitude in mass, from
10^{12} M_{sun} to 10^{15} M_{sun}. The resulting lensing signal is consistent
with an NFW or Einasto profile on scales outside the central region. We find
that the NFW concentration parameter c_{200b} decreases with halo mass, from
around 10 for galactic halos to 4 for cluster halos. Assuming its dependence on
halo mass in the form of c_{200b} = c_0 [M/(10^{14}M_{sun}/h)]^{\beta}, we find
c_0=4.6 +/- 0.7 (at z=0.22) and \beta=0.13 +/- 0.07, with very similar results
for the Einasto profile. The slope (\beta) is in agreement with theoretical
predictions, while the amplitude is about two standard deviations below the
predictions for this mass and redshift, but we note that the published values
in the literature differ at a level of 10-20% and that for a proper comparison
our analysis should be repeated in simulations. We discuss the implications of
our results for the baryonic effects on the shear power spectrum: since these
are expected to increase the halo concentration, the fact that we see no
evidence of high concentrations on scales above 20% of the virial radius
suggests that baryonic effects are limited to small scales, and are not a
significant source of uncertainty for the current weak lensing measurements of
the dark matter power spectrum. [ABRIDGED]Comment: 17 pages, 5 figures, accepted to JCAP pending minor revisions that
are included in v2 here on arXi
Framing the nation Languages of `modernity' in India
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