Risa Wechsler - Astronomy and Astrophysics

M 200
Lensing Mass
r200 [h !1 Cluster Mpc] Size
10 14
10 13
10 12
2.0
1.0
0.9
0.8
0.7
0.6
0.5
S
M200 = A Ngal A= 2.1±0.4 ×10 11
S= 1.56±0.07
χ 2 = 11.1 DOF=10
0.4
6 8 10 20 40 60 80 100
N gals
lensing mass
Sigma diff
1000
several ways to
measure the
scaling between
cluster richness
and “mass”
Real Data
• need to understand velocity bias (as a function of radius & L)
1
Sheldon et al 2005 (in prep)
• can measure scatter
10 100
cluster sizes
100
1 10
McKay et al 2005 (in prep)
100 1000
Ngals Hansen et al 2005,
ApJ in press
Velocity Dispersion
• well understood theoretically
• selection biases and centering effects need to be understood
• no direct method to measure scatter
cluster velocity dispersions
• need additional data (spectra), which is typically redshift dependent
1000.0
• depends on galaxy background, degenerate with cosmology
cluster-cluster correlation function
• no direct method to measure scatter
ξ(r)
Cluster Correlation
Function
100.0
10.0
• uncertainties in redshifts can bias measurements
probably have more scatter than Lx, SZ,
1.0
but order of magnitude easier to find
0.1
1 10 100
r [Mpc/h]