WEAK GRAVITATIONAL LENSING OF X-RAY GROUPS
Alexie Leauthaud Chamberlain Fellow Lawrence Berkeley National Lab & Berkeley Center for Cosmological Physics
Kevin Bundy, Matt George, Melody Wolk, Yen-Ting Lin, Stefania Giodini, Masayuki Tanaka Jean-Paul Kneib, Alexis Finoguenov, Jeremy Tinker, Richard Massey, James Taylor, Jason Rhodes, Peter Capak, Olivier Ilbert & the COSMOS Collaboration The cosmos X-ray group sample
Aim of this work: study the Dark Matter properties of a sample of ~150 groups/clusters detected via extended XMM emission in the COSMOS survey
This is one of the largest samples of it’s kind and is comprised of groups with halo masses 13 13 M200 ~ 10 Msun to 10 Msun .
Lensing constraints on halo centers and group members (Matt George)
Statistical nature of BCGs (Melody Wolk & Yen Ting Lin)
Assembly history of groups and BCGs 2 1.3 deg (Kevin Bundy) COSMOS survey CHANDRA + XMM Baryon fraction (Stefania Giodini) A. Finoguenov et al. 2007 Alexie Leauthaud Motivations for pushing down to the low end of the mass function
I. Constraints on cosmological parameters can be improved by extending measurements down to the low end of the mass function (on condition that masses can be measured correctly for groups).
Most massive systems: - low numbers The growth of the Dark Matter Mass Function over - mergers/ non relaxed cosmic time - Heitmann et al. 2006 - triaxiality Alexie Leauthaud Motivations for pushing down to the low end of the mass function
I. Constraints on cosmological parameters can be improved by extending measurements down to the low end of the mass function (on condition that masses can be measured correctly for groups).
II. Understanding the scaling relations of galaxy groups will lead to a better handle on the slope and amplitude of the scaling relations of more massive systems.
The growth of the Dark Matter Mass Function over cosmic time - Heitmann et al. 2006 Alexie Leauthaud Motivations for pushing down to the low end of the mass function
I. Constraints on cosmological parameters can be improved by extending measurements down to the low end of the mass function (on condition that masses can be measured correctly for groups).
II. Understanding the scaling relations of galaxy groups will lead to a better handle on the slope and amplitude of the scaling relations of more massive systems.
III. Galaxy groups may play in key role in processes of galaxy formation (low velocity dispersions ⇒ galaxies are more likely to merge?). Groups are the building blocks of clusters (in terms of The growth of the Dark Matter Mass Function over cosmic time - Heitmann et al. 2006 mass if not in terms of galaxy numbers). Alexie Leauthaud The cosmos group sample
Alexie Leauthaud The M200 - Lx relation In this project, we have looked into the calibration of the X-ray Luminosity (Lx) - Halo mass (M200) relation. Nevertheless, the method outlined here can be applied to other mass proxies such as Temperature, Richness, Velocity Dispersion, etc.
Lx - M200 T - M200 N200 - M200 σdyn - M200 MSZ - M200
A better understanding of each of these scaling relations is necessary for DE studies but will also shed light on the the underlying physical processes within groups & clusters.
The X-ray luminosity of groups and clusters is considered a reasonable tracer of halo mass with a logarithmic scatter of roughly 20% to 30% (Stanek et al. 2006, Maughan 2007, Pratt et al. 2008 Rozo et al. 2008, Rykoff et al. 2008, Vikhlinin et al. 2009).
Although more tightly correlated mass tracers have been found - such indicators require the measurement of an X-ray spectrum which is not possible for most surveys where count rates are low. Lx is a simple X-ray observable, accessible with survey quality data, and the only one that can be easily measured at high-z. slope α * Form of the M " E(z) $ L " E(z)#1' 200 = A " X M200 - LX relation: & ) M0 % L0 ( Alexie Leauthaud
! « m-Lx » is not the same as « lx-M » !
P(M|Lx)
For e.g see P(Lx|M) appendix in Leauthaud et al. 2010
Also mentioned by Gus Evrard.
Alexie Leauthaud The Weak Lensing signals around groups ] -2 pc n su M
72 [ h
Delta Sigma
Physical transverse distance [ Mpc h72-1 ]
Radial mass profile of X-ray groups in nine Lx bins. Alexie Leauthaud The M200 - Lx relation
Form of the M200 - LX relation:
* M " E(z) $ L " E(z)#1' 200 = A "& X ) M0 % L0 (
We find a slope : α ~ 0.64 Msun) -1 ! in good agreement with 72
h Stanek et al. 2007 and Rykoff 1 - et al. 2008. .E(z)
200 Cluster data alone can be
( M misleading : Bardeau et al. 10 2007 find α ~ 1.2! Log
Current relation is limited by measurement of cluster masses. Leauthaud et al. 2010 -1 -2 -1 Log10( Lx.E(z) h72 ergs s ) ApJ, 709, 97-114 Alexie Leauthaud Combining Groups and clusters
COSMOS COSMOS + Hoekstra et al. 2007
Alexie Leauthaud REDSHIFT EVOLUTION in Lx-M ?
$ #1'* M200 " E(z) LX " E(z) + = - 0.07 0.9 = A "& ) E(z) γ ± M0 % L0 (
$ #1'* ! M200 " E(z) LX " E(z) + = - 0.14 0.8 = A "& ) (1+ z) δ ± M0 % L0 (
! COSMOS results are consistent with self-similar redshift evolution but the data are not very constraining. Additional group and cluster data with weak lensing masses are required at 0.6 Alexie Leauthaud The slope of the M200 - Lx relation Lensing X-rays Alexie Leauthaud An algorithm to select group members See Poster by Matt George ) ) phot phot P(z P(z mF814W=22.9 mF814W=23.9 , , z=0.99 z=0.83 Pmem=0.80 Pmem=0.52 dN/dz (field) dN/dz (field) dN/dz (group), dN/dz (group), z z Identify members using photoz probability distribution + measured field/group densities Alexie Leauthaud WHERE IS THE CENTER OF THE DARK MATTER? See Poster by Matt George X-ray center Centroid of stellar mass Centroid of light Most massive galaxy near centroid of mass Most massive galaxy near center of light X-ray contours. The stacked weak lensing signal is maximized when the chosen center is closest to the center of the dark matter halo. Alexie Leauthaud Preliminary weak lensing results See Poster by Matt George ‣ Define several “centers” ‣ Calculate typical separations # of groups ‣ Measure stacked WL signal ‣ Study inner profile Transverse separation [Mpc] Preferred center Luminosity centroid ) -2 ] -2 pc ⊙ pc ⊙ M M [ (h ΔΣ ΔΣ RR [ Mpc[Mpc] ] R [Mpc] Preliminary weak lensing results See Poster by Matt George ‣ Define several “centers” ‣ Calculate typical separations # of groups ‣ Measure stacked WL signal ‣ Study inner profile Transverse separation [Mpc] Preferred center Luminosity centroid ) -2 ] -2 Measuring the mass-concentration relation pc ⊙ pc Accurate calibrations of mass-observable relations ⊙ M M Understanding the profiles of dark matter halos [ (h ΔΣ ΔΣ RR [ Mpc[Mpc] ] R [Mpc] The colors and properties of « BCG’’s » (MMGG) ] The (lack of a) cooling flow problem: -1 I. Lack of the detection of X-ray iron lines (e.g. s ergs 40 Peterson et al. 2003) [10 α II. Lack of blue massive galaxies in cluster centers H L Nevertheless: moderate amounts of star formation can still Ko [Kev cm2] exist in the Central Galaxies of Clusters (also Cavagnolo et al. 2008 mentioned by Eiichi Egami’s …): Abell 1835 SFR ~ 100 solar masses yr-1 Abell 2204 SFR ~ 1 solar masses yr-1 tot b Source of gas to fuel star formation: M I. Cooling from ICM II. Merger activity Roff [kpc] Bildfell et al. 2008 The colors and properties of « BCG’’s » (MMGG) Preliminary ! ‘Wet’ merging ‘Dry’ merging ?? Cooling gas Alexie Leauthaud conclusions We observe a striking relation between Lx and halo mass over several decades in mass and luminosity. These are encouraging results in view of calibrating mass- observable relations for dark energy studies and to gain a better understanding of cluster and galaxy physics. The slope that we measure (α ~ 0.64 ) is inconsistent at the 3.7 sigma level with simple models of self-similar evolution which predict α = 0.75. Deeper X-ray data would enable calibration of T - M200 Extending halo mass measurements down to the group regime is necessary in order to obtain an accurate determination of the slope of the Lx-M relation. Galaxy formation as a function of halo mass: ⇒ Where is the center of the dark matter? (Matt George) ⇒ galaxy and AGN properties within groups as a function of halo mass ⇒ the assembly of the most massive galaxies, the central BCG’s (Kevin Bundy) BOSS spectroscopic program to obtain ~ 3000 spectra for BCGs in Stripe 82 + 170 deg2 of CFHT data for lensing.