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

Relating Mass and Light in the COSMOS
J.E. Taylor, R.J. Massey (California Institute of Technology),
J. Rhodes (Jet Propulsion Laboratory)
& the COSMOS Team
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
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
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.
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).
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)
Hamana, Takada & Yoshida 2004 MNRAS 350, 893
Taylor et al. 2006 in preparation
Convergence Bin

similar documents