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

Abstract

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-fit by a model which is a power-law at large radii and approaches a constant value at small radii: K(r) = K 0 + K 100 (r/100 kpc) α , where K 0 quantifies the typical excess of core entropy above the best fitting power-law found at larger radii. We also show that the K 0 distributions of both the full archival sample and the primary HIFLUGCS sample of Reiprich (2001) are bimodal with a distinct gap between K 0 ≈ 30 − 50 keV cm 2 and population peaks at K 0 ∼ 15 keV cm 2 and K 0 ∼ 150 keV cm 2 . The effects of PSF smearing and angular resolution on best-fit K 0 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 K 0 is also considered, and we find no indication K 0 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 For completeness, we include previously unpublished optical spectroscopy of Hα and [N II] emission lines discussed in Cavagnolo et al.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.Abell 119 (z = 0.0442): This is a highly diffuse cluster without a prominent cool core. The large core region and slowly varying surface brightness made deprojection highly unstable. We have excluded a small source at the very center of the BCG. The exclusion region for the source is ≈ 2.2 ′′ in radius which at the redshift of the cluster is ∼ 2 kpc. This cluster required a double β-model.Abell 160 (z = 0.0447): The highly asymmetric, low surface brightness of this cluster resulted in a noisy surface brightness profile that could not be deprojected. This cluster required a double β-model. The BCG hosts a compact X-ray source. The exclusion region for the compact source has a radius of ∼ 5 ′′ or ∼ 4.3 kpc. The BCG for this cluster is not coincident with the X-ray centroid and hence is not at the zero-point of our radial analysis.Abell 193 (z = 0.0485): This cluster has an azimuthally symmetric and a very diffuse ICM centered on a BCG which is interacting with a companion galaxy. In Fig. 1 one can see that the central three bins of this cluster's surface brightness profile are highly discrepant from the best-fit β-model. This is a result of the BCG being coincident with a bright, compact X-ray source. As we have concluded in 3.5, compact X-ray sources are excluded from our analysis as they are not the focus of our study here. Hence we have used the best-fit β-model in d...

STAR-FORMING BRIGHTEST CLUSTER GALAXIES AT 0.25 < z < 1.25: A TRANSITIONING FUEL SUPPLY

“…and for those harboring the 80% most passive BCGs. At z<0.3, we show clusters from the ACCEPT sample (Cavagnolo et al 2009), where the SFRs are inferred from archival infrared data (z<0.1; Fraser-McKelvie et al 2014) or the Hα line luminosity (z>0.1; Crawford et al 1999). We recomputed the central entropy in a 15 kpc aperture (∼0.015R 500 ) for clusters at z<0.3 to match our more coarse, high-z aperture, and to avoid resolution bias (e.g., Panagoulia et al 2014).…”

“…In order to test whether this trend was established at high-z, we require estimates of the core entropy and cooling rate for each cluster. Given that we only have ∼2000 X-ray counts per cluster, modeling the central entropy (e.g., Cavagnolo et al 2009) or estimating the spectroscopically derived cooling rate (e.g., Voigt & Fabian 2004) is not feasible. Instead, we compute spectroscopic quantities (bolometric luminosity, temperature) from a circular aperture with a radius of 0.075 R 500 (where R 500 was derived based on the Y X -M 500 relation of Vikhlinin et al 2009), which should roughly correspond to the deprojected core temperature (see e.g., McDonald et al 2014a).…”

“…McDonald et al, in preparation) and X-ray-selected (Donahue et al 1992Hoffer et al 2012;Rawle et al 2012;Fraser-McKelvie et al 2014;Donahue et al 2015) clusters, and are being compared here to an SZ-selected sample. For the ACCEPT (Cavagnolo et al 2009) and CLASH ) samples, we apply a small correction because both of these cluster samples are biased toward cool core clusters. This bias correction assumes that the true, underlying fraction of cool core clusters is 30% (Haarsma et al 2010;Hudson et al 2010;McDonald et al 2013b) and that non-cool cores do not have star-forming BCGs at z0.5 (Cavagnolo et al 2008;O'Dea et al 2008;McDonald et al 2010).…”

“…Numerous studies have found evidence for ultraviolet (UV) and infrared (IR) continuum (e.g., McNamara & O'Connell 1989;Hicks & Mushotzky 2005;O'Dea et al 2008;McDonald et al 2011b;Hoffer et al 2012;Rawle et al 2012;Fraser-McKelvie et al 2014;Donahue et al 2015), warm, ionized gas (e.g., Hu et al 1985;Johnstone et al 1987;Heckman et al 1989;Crawford et al 1999;Edwards et al 2007;Hatch et al 2007;McDonald et al 2010McDonald et al , 2011a, and both warm and cold molecular gas (e.g., Jaffe & Bremer 1997;Donahue et al 2000;Edge 2001;Edge et al 2002;Edge & Frayer 2003;Salomé & Combes 2003;Hatch et al 2005;Jaffe et al 2005;Johnstone et al 2007;Oonk et al 2010;McDonald et al 2012c)-all of which are indicative of ongoing or recent star formation. Star-forming BCGs were found preferentially in galaxy clusters with "cool cores," as identified by a central density enhancement in the ICM (e.g., Vikhlinin et al 2007;Santos et al 2008;Hudson et al 2010) or low central entropy/cooling time (e.g., Cavagnolo et al 2008Cavagnolo et al , 2009Hudson et al 2010). These and other works established a link between the cooling ICM and the presence of multiphase gas, suggesting that cooling flows may indeed be fueling star formation in BCGs.…”

Interplay Among Cooling, Agn Feedback, and Anisotropic Conduction in the Cool Cores of Galaxy Clusters

“…Entropy profiles of observed CC clusters also appear to follow a baseline profile predicted by the precipitationregulated feedback model . However, we note that there exist discrepancies between the entropy profiles of the above-mentioned work (based on the work of Cavagnolo et al 2009) and those derived from a different group (Panagoulia et al 2014). Moreover, it is still unresolved how exactly the cold gas is channeled to the SMBH and what the roles of angular momentum transport, self-gravity, and cloudcloud collisions are (Pizzolato & Soker 2010;Gaspari et al 2013).…”