ben maughan (cfa)chandra fellows symposium 2006 the cluster scaling relations observed by chandra c....

Chandra Fellows Symposium 2006Ben Maughan (CfA)

The cluster scaling relations observed by Chandra

C. Jones, W. Forman, L. Van Speybroeck


Introduction

Galaxy clusters are powerful cosmological probes They are dominated by dark matter and their properties are

sensitive to dark energy Measurements of e.g. mass function, gas fraction and

apparent evolution can place useful cosmological constraints

Provide independent constraints to e.g. CMB, SNIa with different degeneracies and systematics

Best cosmology with clusters requires mass estimates


Measuring Cluster Masses

Clusters are ~85% dark matter and ~15% baryons Baryons are dominated by hot X-ray emitting gas Very luminous so can be detected to z~1.5 Emissivity 2 so projection effects minimised


Measuring Cluster Masses

Clusters are ~85% dark matter and ~15% baryons Baryons are dominated by hot X-ray emitting gas Very luminous so can be detected to z~1.5 Emissivity 2 so projection effects minimised

Use X-rays to measure radial profiles of gas and kT Under assumption of hydrostatic equilibrium, solve for total

gravitating mass However, such detailed measurements require LOTS of

photons – hard for less luminous / more distant clusters


Scaling Relations

Current and future cluster surveys will detect 1000’s of clusters out to high z

Need efficient method to estimate masses from simple properties measured in survey data (e.g. kT, Lx)

Simple self-similar models predict tight scaling relations between basic cluster properties (e.g. LxkT2, MkT3/2)

Observations find relations do exist, but differ from SS predictions (e.g. LxkT3) Indicates importance of non-gravitational processes


Non-Gravitational Processes

Dense gas in cluster cores radiates efficiently and cools Bright, cool cores in many clusters

Scaled temperature profiles from Vikhlinin et. al. (2006)




Large amounts of very cool gas not detected in cores Cooling balanced by energy input

Prime candidate: AGN activity, details uncertain Mergers also important to cluster energetics




Large amounts of very cool gas not detected in cores Cooling balanced by energy input

Prime candidate: AGN activity, details uncertain Mergers also important to cluster energetics

Study of scaling relations gives insight into when, where and how these processes affect cluster properties


The Sample

128 clusters observed with Chandra ACIS-I Includes all such clusters at z>0.1 with published z


Analysis Methods

Use blank sky bg files for spectral and imaging analysis Measure kT within R500 and iterate until stable

Estimate R500 using Vikhlinin et. al. (2006) MT relation R500 radius within which mean is 500crit(z)

Generally exclude central region for kT and Lx measurements

Fit surface brightness profile with projected 3D emission measure profile (Vikhlinin et. al. 2006) Modified -model with core component and steeper

slope at large R Derive gas density profile


Gratuitous Eye Candy

adaptively smoothed, 3Mpc per side, in order of z


Gratuitous Eye Candy

adaptively smoothed, 3Mpc per side, in order of z

Drop z<0.1 for the purposes discussed here (leaves 111)


The L-T Relation

Lx and kT with no correction for cool cores compared with Markevitch (1998) relation for local clusters

Predicted SS evolution removed

CC clusters: kT in core at least 1 cooler than external kT

N.B. local relation corrected for cool cores


The L-T Relation

Plot fractional residuals from local relation against redshift without evolution correction

Solid line marks locus of expected SS evolution Points should

scatter about that


The L-T Relation

Now exclude central 70kpc from Lx and central 0.15 R500 from kT measurements Consistent with method for local relation


The L-T Relation

Finally exclude central 0.15 R500 for Lx too Scatter dominated by core properties Expected SS evolution generally ok

Still some significant deviations from relation


Gas Density Profiles

Compare most significantly deviant clusters with the non-deviant clusters

Plot gas density normalised to crit(z) and radius normalised to R500 (from kT with 0.15 R500 excluded)

Deviant clusters have high gas densities out to ~0.5R500


Deviant Clusters

Two deviants with best data Mass profiles consistent with normal systems Both have striking cold fronts – are these responsible?

MS1455 (z=0.26) ZW3146 (z=0.29)

R500


The Lx-Yx Relation

Yx = product of gas mass and temperature (Kravtsov et al. 2006)

Has more robust, low-scatter relation with total mass than other X-ray observables

kT in Yx is with central 0.15 R500 excluded

Lx is not CC corrected


The Lx-Yx Relation

Excluding central 0.15 R500 for Lx gives very tight relation Lowest scatter of all relations studied here

If Yx good mass proxy, implies Lx outside core is too


The Lx-Yx Relation

Plot fractional residuals from local relation Predicted evolution is strong, but matches data

Data suggests slightly weaker evolution?


Summary and conclusions

Looked at scaling relations in large sample of Chandra clusters

Deviations/scatter dominated by cluster cores Lx-kT deviations also revealed subset of clusters with

elevated gas density out to large radii Related to cool cores & cold fronts?

Surprisingly tight Lx-Yx relation outside core Lx outside core good mass proxy? Lx-kT deviations outside core due to low kT for M?

SS evolution obeyed in all relations Possible weaker evolution in Lx-Yx?

ben maughan (cfa)chandra fellows symposium 2006 the cluster scaling relations observed by chandra c....

Documents

cluster cores

cluster energetics slide

cool gas

cluster scaling relations

cool cores

s of clusters

distant clusters

basic cluster properties