Relating Mass and Light in the COSMOS Field J.E. Taylor, R

Report
Relating Mass and Light in the COSMOS
Field
J.E. Taylor, R.J. Massey (California Institute of Technology),
J. Rhodes (Jet Propulsion Laboratory)
& the COSMOS Team
Introduction
3-D Analysis
The COSMOS survey (Scoville et al. 2006) provides an unprecedented
combination of sensitive gravitational lensing maps, high-resolution Xray imaging, and multi-band optical observations over a 2-square
degree field.
This unique data set can be used to trace the growth of structure on a
wide range of spatial scales, and from the local universe to high
redshift. In particular, independent lensing and X-ray information can be
used to determine the mass, age, and thermodynamic state for a large
sample of groups and clusters. It also serves as a testing ground for
new methods of reconstructing the full 3-dimensional matter distribution,
and characterizing the dependence of galaxy properties on local
environment.
The COSMOS data set will eventually include spectroscopic redshifts for 50000
objects. We can already use the multi-band photometry to estimate approximate
redshifts for 1 Million or more galaxies. While less accurate, these photometric
redshifts are well suited to lensing studies, where statistical averages over
hundreds of galaxies are required to obtain reasonable signal-to-noise. We
illustrate an initial use of information in the third dimension below.
Lensing Peaks vs. X-ray
Clusters
Galaxy clusters are strong X-ray sources, visible out to moderate redshift, and
should also appear as peaks in the weak lensing mass maps. The abundance of
clusters at high redshift is a sensitive test of cosmology which many future surveys
hope to exploit. We can test how X-ray emission and cluster mass are related in the
COSMOS field, by comparing objects in the X-ray group and cluster catalogue
(Finoguenov et al. 2006) with a map of weak lensing convergence. Even in
projection, roughly 60% of the lensing peaks correspond to massive systems in the
X-ray catalogue, confirming recent predictions (Hamana et al. 2004).
Mean tangential shear vs. angular diameter
distance, along lines of sight around peaks in the
2-D map. Increasing positive shear beyond a
particular distance indicates the presence of a
cluster at that distance
Galaxy Properties vs.
Environment
log(Stellar Mass)
Morphological T
The weak lensing measurement of projected mass (convergence) opens up a whole new
range of parameter space for studies of environmental dependence in galaxy properties.
As an initial indication, we can bin galaxies by the local convergence in a medium-redshift
lensing mass (sensitive to mass between z ~ 0.2 and 0.9), and see how galaxy properties
change in denser regions.
Convergence Bin
Correspondence between lensing mass map (background
image) and X-ray groups and clusters (circles, scaled to
R500,with redshift).
References
See COSMOS 2006 Ap.J. Special Issue papers, especially:
Scoville et al. 2006 (survey); Rhodes et al. 2006, Massey et al 2006, Leauthaud et al
2006 (weak lensing); Capak et al. 2006; Mobasher et al. 2006, Tasca et al. 2006
(photometry and redshifts); Finoguenov et al. 2006 (X-ray catalogue)
Also:
Hamana, Takada & Yoshida 2004 MNRAS 350, 893
Taylor et al. 2006 in preparation
Convergence Bin

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