INTRACLUSTER MEDIUM ENTROPY PROFILES FOR A CHANDRA ARCHIVAL SAMPLE OF GALAXY CLUSTERS

By K. Cavagnolo, M. Donahue, G. Mark Voit, Ming Sun. 2009

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We present radial entropy profiles of the intracluster medium (ICM) for a collection of 239 clusters taken from the Chandra X-ray Observatory's Data Archive. Entropy is of great interest because it controls ICM global properties and records the thermal history of a cluster. Entropy is therefore a useful quantity for studying the effects of feedback on the cluster environment and investigating any breakdown of cluster self-similarity. We find that most ICM entropy profiles are well fitted by a model which is a power law at large radii and approaches a constant value at small radii: K(r) = K0 + K100(r/100 kpc)α, where K0 quantifies the typical excess of core entropy above the best-fitting power law found at larger radii. We also show that the K0 distributions of both the full archival sample and the primary Highest X-Ray Flux Galaxy Cluster Sample of Reiprich (2001) are bimodal with a distinct gap between K0 ≈ 30–50 keV cm2 and population peaks at K0 ∼ 15 keV cm2 and K0 ∼ 150 keV cm2. The effects of point-spread function smearing and angular resolution on best-fit K0 values are investigated using mock Chandra observations and degraded entropy profiles, respectively. We find that neither of these effects is sufficient to explain the entropy-profile flattening we measure at small radii. The influence of profile curvature and number of radial bins on best-fit K0 is also considered, and we find no indication that K0 is significantly impacted by either. For completeness, we include previously unpublished optical spectroscopy of Hα and [N ii] emission lines discussed in Cavagnolo et al. (2008a). All data and results associated with this work are publicly available via the project Web site.

Subfields: Astronomy and Astrophysics

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ON THE CLUSTER PHYSICS OF SUNYAEV–ZEL'DOVICH AND X-RAY SURVEYS. I. THE INFLUENCE OF FEEDBACK, NON-THERMAL PRESSURE, AND CLUSTER SHAPES ON Y–M SCALING RELATIONS (2011, background): “Energetic feedback In many clusters the ICM cooling times are much shorter than a Hubble time (Fabian 1994; Cavagnolo et al. 2009), which should cause extremely high star formation rates that are well beyond what is observed.”
Weak Lensing Measurement of the Mass--Richness Relation of SDSS redMaPPer Clusters (2016, methodology): “Specifically, we compute the distribution of positional offsets R of galaxy clusters shared between redMaPPer and two high-resolution X-ray external data sets, the XCS DR1 (Mehrtens et al. 2012) and ACCEPT (Cavagnolo et al. 2009) cluster catalogues.”
CAUSE AND EFFECT OF FEEDBACK: MULTIPHASE GAS IN CLUSTER CORES HEATED BY AGN JETS (2011, background): “The entropy is elevated to 30 keV cm2 at 10 kpc – still within observational bounds (Cavagnolo et al. 2009) – while the total gas mass is decreased only by 8%.”
SEARCH FOR COSMIC-RAY-INDUCED GAMMA-RAY EMISSION IN GALAXY CLUSTERS (2013, methodology): “For this purpose we use the classification presented in Hudson et al. (2010) or follow recommendations by Cavagnolo et al. (2009).”
Simulating the effect of active galactic nuclei feedback on the metal enrichment of galaxy clusters (2009, background): “Early observational results on the presence of entropy cores (e.g., Ponman et al. 1999) have been more recently revised, in the light of higher quality data from Chandra (e.g., Cavagnolo et al. 2009) and XMM–Newton (e.g., Johnson et al. 2009) observations.”
A RELATIONSHIP BETWEEN AGN JET POWER AND RADIO POWER (2010, background): “The assumed background pressure is based on the mean value ob- 4 K. W. Cavagnolo et al. served in the outskirts of clusters and groups (Cavagnolo et al. 2009).”
Towards a realistic population of simulated galaxy groups and clusters (2013, methodology): “Detailed studies of the radial structure of the gas with Chandra and XMM-Newton have suggested that there may be a bimodality in the central entropy (Cavagnolo et al. 2009; Pratt et al. 2010), although this has been called into question recently (Panagoulia, Fabian & Sanders 2014).”
Radiative efficiency, variability and Bondi accretion on to massive black holes: the transition from radio AGN to quasars in brightest cluster galaxies (2012, neutral): “Cavagnolo et al. 2009).”
Formation of Galaxy Clusters (2012, background): “This is at odds with the entropy and pressure profiles of real clusters which exhibit smoothly declining entropy down tor ∼ 10 − 20 kpc (e.g., Arnaud et al. 2010, Cavagnolo et al. 2009).”
The case for AGN feedback in galaxy groups (2009, background): “In the case of massive galaxy clusters, for example, the central entropy varies by more than an order of magnitude at fixed halo mass (Cavagnolo et al. 2009).”
The cool-core bias in X-ray galaxy cluster samples - I. Method and application to HIFLUGCS (2010, background): “Recent observational works have shown that the population of clusters is bimodal (Cavagnolo et al. 2009), which could support this scenario because of the lack of intermediate objects.”
AGN wind scaling relations and the co-evolution of black holes and galaxies (2017, background): “Interestingly, only the brightest central galaxies (BCGs) in clusters/groups with low inner entropy (short cooling time) have an active nucleus, and are actively forming stars (Cavagnolo et al. 2008, 2009).”
X-ray spectroscopy of galaxy clusters: studying astrophysical processes in the largest celestial laboratories (2009, methodology): “The diagnostics of entropy profiles has now been pursued in detail for larger cluster amples by Cavagnolo et al. (2009) and representative cluster samples by Prat et al. (2009, in preparation) providing a more detailed picture, the proper interpretation of which has to be assisted by simulations.”
Thermal instability and the feedback regulation of hot haloes in clusters, groups and galaxies (2011, methodology): “We initialize the ICM in hydrostatic equilibrium with an entropy profile1 K(r) ≡ TkeV n 2/3 e = K0 +K100 ( r r100 )α , (5) where r100 = 100 kpc for our fiducial run (C10) and scales with M 1/3 0 for other halo masses (Cavagnolo et al. 2009).”
Gas entropy in a representative sample of nearby X-ray galaxy clusters (REXCESS): relationship to gas mass fraction (2009, methodology): “Observed profiles are also found generally to have similar external slopes (e.g., Pratt et al. 2006; Sunet al. 2009) and to flatten in the central regions in high resolution Chandra observations (Donahue et al. 2006; Sanderson et al. 2009; Cavagnolo et al. 2009).”