Quantifying the Morphologies and Dynamical Evolution of Galaxy Clusters. II. Application to a Sample of ROSAT Clusters

Abstract

We quantify the morphologies and dynamical states of 59 galaxy clusters using the power-ratio technique of Buote & Tsai applied to ROSAT PSPC X-ray images.The clusters exhibit a particularly strong P 2 =P 0 P 4 =P 0 correlation in the 1h 1 80 Mpc aperture which may be interpreted as an evolutionary track; the location of a cluster on the correlation line indicates the dynamical state of the cluster and the distribution of clusters along this track measures the rate of formation and evolution of clusters in our sample. The power ratios anti-correlate with the cooling-ow rate indicating a reasonable dependence of the ow rate on cluster morphology. The relationship of the power ratios to the optical Bautz-Morgan (BM) Type is more complex. This is because the power ratios are sensitive to unrelaxed regions of clusters within a speci ed scale, whereas BM types are sensitive to unrelaxed regions over many scales. We discuss further astrophysical applications exploiting the relationship between the power ratios and the evolutionary states of clusters. { 2 {From these qualitative measures of \frequency of substructure" in clusters, investigators have attempted to determine (e.g., Richstone et al. 1992) and the power spectrum of primordial density uctuations (e.g., David et al. 1993) by comparison to Press-Schechter (1974) type predictions of the distribution of collapsed (i.e. virialized) objects. However, these comparisons are inherently uncertain because of the unknown relationship between a particular investigator's de nition of \substructure" and the dynamical state of a cluster. Even well de ned and quantitative measures of morphology which employ centroid-shifts and axial ratios (Evrard et al. 1993, Mohr et al. 1995 do not clearly provide any physical connection of these parameters to the dynamical states of clusters.We previously presented a method to quantify the morphologies of galaxy clusters in relation to their dynamical states as given by their gravitational potentials (Buote & Tsai 1995b; hereafter BT). The statistics of this method, i.e. \power ratios", in essence measure the square of the ratio of higher-order multipole moments of the two-dimensional potential to the monopole moment. The power-ratio description of the morphologies of X-ray clusters is intended to classify structure that is obvious to the eye, not subtle substructure that requires more robust techniques (e.g., Bird & Beers 1993); i.e. the signi cance of the substructure is a given, what the structure implies for the aggregate cluster dynamics is our concern.Because of their intimate link to cluster dynamics, power ratios are not only ideal for cosmological studies, but also for studies of clusters themselves. It is our purpose in this paper to create a database of power ratios for testing the predictions of various cosmogonies and to present initial results on the implications of the measured power ratios. We discuss the cluster sample in x2 and the data reduction and analysis in x3. We consider correlations of the various power ratios amo...

Morphology parameters: substructure identification in X-ray galaxy clusters

“…Buote (2001), Schuecker et al (2001), andCassano et al (2010b) show a relation between non-thermal radio sources and X-ray cluster morphology. Buote (2001) notes the linear relation between radio power (P 1.4 GHz ) and power ratio (P 1 /P 0 ) (Buote & Tsai 1995a, 1996 for ROSAT observed X-ray clusters. He concludes that approximately P 1.4 GHz ∝ P 1 /P 0 , which means the clusters that host the powerful radio haloes are experiencing the largest departures from a virialized state.…”

“…These properties also depend strongly on cluster mass and on non-gravitational processes, such as supernovae feedback and central AGN heating (Donnelly et al 1999;Tozzi & Norman 2001;Neumann et al 2003). Buote & Tsai (1996) also compared their power ratio measurements for X-ray clusters with the ICM temperature and luminosity, without finding any strong correlation between sub-clustering and global X-ray properties. In agreement with our conclusion, they pointed out that this lack of correlation is reasonable, since power ratios are a measure of cluster evolution that do not take the cluster mass into account, to which all the other X-ray quantities (e.g.…”

Deep CCD Surface Photometry of Galaxy Clusters. II. Searching for Intracluster Starlight in Non‐cD clusters

“…The possible effect of Virgo's foreground light to our ICL observations will be discussed in x 5.5. Finally, A1914 also has a Rood-Sastry type of L. Its X-ray structure was claimed to be regular and smooth (Buote & Tsai 1996), but Jones et al (2001) subsequently showed that X-ray images showed significant substructure in the core, that a conventional model did not fit the data well, and that the cluster was in the process of merging. A1914 has a high X-ray temperature (10:53 þ0:51 À0:50 keV; White 2000), although Ikebe et al (2002) find a somewhat lower temperature of T ¼ 8:41 þ0:60 À0:58 keV.…”

X-Ray Observations of Cluster Mergers Before 2000 AD

“…Hence, cooling flows are expected to dominate as has been suggested on different grounds (e.g., Arnaud 1988). In fact, it was also shown (Buote & Tsai 1996) that the PRs significantly correlate with the cooling flow mass deposition rate providing for the first time a quantitative description of the anti-correlation of substructure with the strength of a cooling flow. Analysis of this correlation and its large scatter for small cooling flows should shed light on how cooling flows are disrupted by mergers and are subsequently re-established.…”

“…From analysis of the brightest ~ 40 clusters with the ROSAT PSPC Buote & Tsai (1996) showed that the PRs represent a quantitative implementation of the Jones & Forman morphological classification scheme. It was shown quantitatively that the brightest ~ 40 clusters lack young members and are instead dominated by mostly evolved clusters with only small-scale (< 500 kpc) substructure.…”