Ben Maughan (CfA)Chandra Fellows Symposium 2006 The cluster scaling relations observed by Chandra C. Jones, W. Forman, L. Van Speybroeck

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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. Lx  kT 2, M  kT 3/2 )  Observations find relations do exist, but differ from SS predictions (e.g. Lx  kT 3 )  Indicates importance of non-gravitational processes

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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)

Ben Maughan (CfA)Chandra Fellows Symposium 2006 Non-Gravitational Processes  Dense gas in cluster cores radiates efficiently and cools  Bright, cool cores in many clusters  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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 Non-Gravitational Processes  Dense gas in cluster cores radiates efficiently and cools  Bright, cool cores in many clusters  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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 The Sample  128 clusters observed with Chandra ACIS-I  Includes all such clusters at z>0.1 with published z

Ben Maughan (CfA)Chandra Fellows Symposium 2006 Analysis Methods  Use blank sky bg files for spectral and imaging analysis  Measure kT within R 500 and iterate until stable  Estimate R 500 using Vikhlinin et. al. (2006) MT relation  R 500 radius within which mean  is 500  crit(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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 Gratuitous Eye Candy adaptively smoothed, 3Mpc per side, in order of z

Ben Maughan (CfA)Chandra Fellows Symposium 2006 Gratuitous Eye Candy adaptively smoothed, 3Mpc per side, in order of z Drop z<0.1 for the purposes discussed here (leaves 111)

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 The L-T Relation  Now exclude central 70kpc from Lx and central 0.15 R500 from kT measurements  Consistent with method for local relation

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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

Ben Maughan (CfA)Chandra Fellows Symposium 2006 The Lx-Yx Relation  Plot fractional residuals from local relation  Predicted evolution is strong, but matches data  Data suggests slightly weaker evolution?

Ben Maughan (CfA)Chandra Fellows Symposium 2006 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?