The Birmingham--CfA cluster scaling project -- I.Gas fraction and the M--TX relation

Abstract

We have assembled a large sample of virialized systems, comprising 66 galaxy clusters, groups and elliptical galaxies with high‐quality X‐ray data. To each system we have fitted analytical profiles describing the gas density and temperature variation with radius, corrected for the effects of central gas cooling. We present an analysis of the scaling properties of these systems and focus in this paper on the gas distribution and M–TX relation. In addition to clusters and groups, our sample includes two early‐type galaxies, carefully selected to avoid contamination from group or cluster X‐ray emission. We compare the properties of these objects with those of more massive systems and find evidence for a systematic difference between galaxy‐sized haloes and groups of a similar temperature. We derive a mean logarithmic slope of the M–TX relation within R200 of 1.84 ± 0.06, although there is some evidence of a gradual steepening in the M–TX relation, with decreasing mass. We recover a similar slope using two additional methods of calculating the mean temperature. Repeating the analysis with the assumption of isothermality, we find the slope changes only slightly, to 1.89 ± 0.04, but the normalization is increased by 30 per cent. Correspondingly, the mean gas fraction within R200 changes from (0.13 ± 0.01) h −3/2 70 to (0.11 ± 0.01) h −3/2 70, for the isothermal case, with the smaller fractional change reflecting different behaviour between hot and cool systems. There is a strong correlation between the gas fraction within 0.3R200 and temperature. This reflects the strong (5.8σ) trend between the gas density slope parameter, β, and temperature, which has been found in previous work. These findings are interpreted as evidence for self‐similarity breaking from galaxy feedback processes, active galactic nuclei heating or possibly gas cooling. We discuss the implications of our results in the context of a hierarchical structure formation scenario.

ChandraX‐Ray Analysis of the Massive High‐Redshift Galaxy Clusters Cl J1113.1−2615 and Cl J0152.7−1357

“…To allow a comparison of our results with those from the low-redshift study of Sanderson et al (2003), who compute cluster gas mass fractions at 0:3r v , we also derived the gas mass fraction of our clusters at this radius (slightly larger than our spectral radii) in our ÃCDM cosmology (this is consistent with the values of H 0 ¼ 70 km s À1 Mpc À1 assumed by Sanderson and coworkers). The results are plotted, along with the data of Sanderson et al (2003), in Figure 15. The loci of our high-redshift clusters do not deviate significantly from the low-redshift data, suggesting that, for this cosmology, the composition of at least some galaxy clusters does not change significantly from z $ 0:8 to 0.1.…”

“…Finally, our new high-redshift data are plotted as diamonds, and we plot mass within 0.3R 200 against emission-weighted temperatures (under our assumption of isothermality, the emission-weighted temperature is the same as the massweighted temperature and constant with radius, although the errors quoted do not include any systematic uncertainties in the masses due to this assumption). Note that 0.3R 200 is very close to R 2500 (see, e.g., Sanderson et al 2003), so the different scales used are consistent.…”

“…Finally, we compare the mass-temperature relation found in the local sample of Sanderson et al (2003) with the properties measured for our high-redshift clusters and for the intermediate-redshift sample of Allen, Schmidt, & Fabian (2001). This intermediate-redshift sample provides a useful comparison since it has secure mass measurements within R 2500 derived from Chandra temperature profiles and corroborated by weak-lensing measurements.…”

“…A more detailed comparison awaits better data. Note.-From the local M-T relation of the Sanderson et al 2003 data above 4 keV and the predicted offset, 1=EðzÞ, based on the assumption of a single redshift of formation for each cluster that is the same as the observation redshift. The local offset excludes AWM 7, the point far below the relation at %5.8 keV.…”

The bow shock, cold fronts and disintegrating cool core in the merging galaxy group RX J0751.3+5012

“…From the global temperature of each group and the masstemperature relation (e.g. Finoguenov, Reiprich & Böhringer 2001;Sanderson et al 2003;Vikhlinin et al 2006), we estimate that the SW group is roughly three times more massive than the NE group. The global temperature of the NE group is likely to have been underestimated as ram pressure stripping has removed most of the warmer, lower density gas.…”