Images, structural properties and metal abundances of galaxy clusters observed with Chandra ACIS-I at 0.1<z<1.3

We have assembled a sample of 115 galaxy clusters at 0.1<z<1.3 with archived Chandra ACIS-I observations. We present X-ray images of the clusters and make available region files containing contours of the smoothed X-ray emission. The structural properties of the clusters were investigated and we found a significant absence of relaxed clusters (as determined by centroid shift measurements) at z>0.5. The slope of the surface brightness profiles at large radii were steeper on average by 15% than the slope obtained by fitting a simple beta-model to the emission. This slope was also found to be correlated with cluster temperature, with some indication that the correlation is weaker for the clusters at z>0.5. We measured the mean metal abundance of the cluster gas as a function of redshift and found significant evolution, with the abundances dropping by 50% between z=0.1 and z~1. This evolution was still present (although less significant) when the cluster cores were excluded from the abundance measurements, indicating that the evolution is not solely due to the disappearance of relaxed, cool core clusters (which are known to have enhanced core metal abundances) from the population at z>0.5.Comment: 23 pages, 12 figures. Accepted for publication in ApJS. Updated to match published version. Redshifts of two clusters (RXJ1701 and CL0848) corrected and two observations of MACSJ0744.8 have been combined into one. Conclusions unchanged. A version with images of all of the clusters is available at http://hea-www.harvard.edu/~bmaughan/clusters.htm

A Multi-wavelength Study of the Host Environment of SMBHB 4C+37.11

4C+37.11, at z=0.055 shows two compact radio nuclei, imaged by VLBI at 7mas separation, making it the closest known resolved super-massive black hole binary (SMBHB). An important question is whether this unique object is young, caught on the way to a gravitational in-spiral and merger, or has `stalled' at 7pc. We describe new radio/optical/X-ray observations of the massive host and its surrounding X-ray halo. These data reveal X-ray/optical channels following the radio outflow and large scale edges in the X-ray halo. These structures are promising targets for further study which should elucidate their relationship to the unique SMBHB core.Comment: To appear in the Astrophysical Journa

X-ray Over-Luminous Elliptical Galaxies: A New Class of Mass Concentrations in the Universe?

We detect four isolated, X-ray over-luminous (Lx>2e43 [h/0.5]**-2 erg/s) elliptical galaxies (OLEGs) in our 160 square degree ROSAT PSPC survey. The extent of their X-ray emission, total X-ray luminosity, total mass, and mass of the hot gas in these systems correspond to poor clusters, and the optical luminosity of the central galaxies (M_R<-22.5 + 5 lg h) is comparable to that of cluster cDs. However, there are no detectable fainter galaxy concentrations around the central elliptical. The mass-to-light ratio within the radius of detectable X-ray emission is in the range 250-450 Msun/Lsun, which is 2-3 times higher than typically found in clusters or groups. These objects can be the result of galaxy merging within a group. However, their high M/L values are difficult to explain in this scenario. OLEGs must have been undisturbed for a very long time, which makes them the ultimate examples of systmes in hydrostatic equilibrium. The number density of OLEGs is n=2.4(+3.1-1.2}x10**-7 (h/0.5)**-3 Mpc**-3 at the 90% confidence. They comprise 20% of all clusters and groups of comparable X-ray luminosity, and nearly all galaxies brighter than M_R=-22.5. The estimated contirubution of OLEGs to the total mass density in the Universe is close to that of T>7 keV clusters.Comment: 4 pages, 2 figures, uses emulateapj.sty, submitted to ApJ Letter

CHANDRA observations of the NGC 1550 galaxy group -- implication for the temperature and entropy profiles of 1 keV galaxy groups

We present a detailed \chandra study of the galaxy group NGC 1550. For its temperature (1.37$\pm$0.01 keV) and velocity dispersion ($\sim$ 300 km s$^{-1}$), the NGC 1550 group is one of the most luminous known galaxy groups (L$_{\rm bol}$ = 1.65$\times10^{43}$ erg s$^{-1}$ within 200 kpc, or 0.2 \rv). We find that within $\sim 60$ kpc, where the gas cooling time is less than a Hubble time, the gas temperature decreases continuously toward the center, implying the existence of a cooling core. The temperature also declines beyond $\sim$ 100 kpc (or 0.1 \rv). There is a remarkable similarity of the temperature profile of NGC 1550 with those of two other 1 keV groups with accurate temperature determination. The temperature begins to decline at 0.07 - 0.1 \rv, while in hot clusters the decline begins at or beyond 0.2 \rv. Thus, there are at least some 1 keV groups that have significantly different temperature profiles from those of hot clusters, which may reflect the role of non-gravitational processes in ICM/IGM evolution. NGC 1550 has no isentropic core in its entropy profile, in contrast to the predictions of `entropy-floor' simulations. We compare the scaled entropy profiles of three 1 keV groups (including NGC 1550) and three 2 - 3 keV groups. The scaled entropy profiles of 1 keV groups show much larger scatter than those of hotter systems, which implies varied pre-heating levels. We also discuss the mass content of the NGC 1550 group and the abundance profile of heavy elements.Comment: emulateapj5.sty, 18 pages, 11 figures (including 4 color), to appear in ApJ, v598, n1, 20 Nov 200

Hot Gas Structure in the Elliptical Galaxy NGC 4472

We present X-ray spectroscopic and morphological analyses using Chandra ACIS and ROSAT observations of the giant elliptical galaxy NGC 4472 in the Virgo cluster. We discuss previously unobserved X-ray structures within the extended galactic corona. In the inner 2' of the galaxy, we find X-ray holes or cavities with radii of ~2 kpc, corresponding to the position of radio lobes. These holes were produced during a period of nuclear activity that began 1.2 x 10^7 years ago and may be ongoing. We also find an asymmetrical edge in the galaxy X-ray emission 3' (14 kpc) northeast of the core and an ~8' tail (36 kpc) extending southwest of the galaxy. These two features probably result from the interaction of NGC 4472 gas with the Virgo gas, which produces compression in the direction of NGC 4472's infall and an extended tail from ram pressure stripping. Assuming the tail is in pressure equilibrium with the surrounding gas, we compute its angle to our line of sight and estimate that its true extent exceeds 100 kpc. Finally, in addition to emission from the nucleus (first detected by Soldatenkov, Vikhlinin & Pavlinsky), we detect two small extended sources within 10'' of the nucleus of the galaxy, both of which have luminosities of ~7 x 10^38 erg/s.Comment: 25 pages, 11 figures, accepted by Ap

The narrow X-ray tail and double H-alpha tails of ESO 137-002 in Abell 3627

We present the analysis of a deep Chandra observation of a ~2L_* late-type galaxy, ESO 137-002, in the closest rich cluster A3627. The Chandra data reveal a long (>40 kpc) and narrow tail with a nearly constant width (~3 kpc) to the southeast of the galaxy, and a leading edge ~1.5 kpc from the galaxy center on the upstream side of the tail. The tail is most likely caused by the nearly edge-on stripping of ESO 137-002's ISM by ram pressure, compared to the nearly face-on stripping of ESO 137-001 discussed in our previous work. Spectral analysis of individual regions along the tail shows that the gas throughout it has a rather constant temperature, ~1 keV, very close to the temperature of the tails of ESO 137-001, if the same atomic database is used. The derived gas abundance is low (~0.2 solar with the single-kT model), an indication of the multiphase nature of the gas in the tail. The mass of the X-ray tail is only a small fraction (<5%) of the initial ISM mass of the galaxy, suggesting that the stripping is most likely at an early stage. However, with any of the single-kT, double-kT and multi-kT models we tried, the tail is always "over-pressured" relative to the surrounding ICM, which could be due to the uncertainties in the abundance, thermal vs. non-thermal X-ray emission, or magnetic support in the ICM. The H-alpha data from SOAR show a ~21 kpc tail spatially coincident with the X-ray tail, as well as a secondary tail (~12 kpc long) to the east of the main tail diverging at an angle of ~23 degrees and starting at a distance of ~7.5 kpc from the nucleus. At the position of the secondary H-alpha tail, the X-ray emission is also enhanced at the ~2 sigma level. We compare the tails of ESO 137-001 and ESO 137-002, and also compare the tails to simulations. Both the similarities and differences of the tails pose challenges to the simulations. Several implications are briefly discussed.Comment: 15 pages, 6 figures, accepted for publication in Ap

Evolution of the Cluster X-ray Luminosity Function

We report measurements of the cluster X-ray luminosity function out to z=0.8 based on the final sample of 201 galaxy systems from the 160 Square Degree ROSAT Cluster Survey. There is little evidence for any measurable change in cluster abundance out to z~0.6 at luminosities less than a few times 10^44 ergs/s (0.5-2.0 keV). However, between 0.6 < z < 0.8 and at luminosities above 10^44 ergs/s, the observed volume densities are significantly lower than those of the present-day population. We quantify this cluster deficit using integrated number counts and a maximum-likelihood analysis of the observed luminosity-redshift distribution fit with a model luminosity function. The negative evolution signal is >3 sigma regardless of the adopted local luminosity function or cosmological framework. Our results and those from several other surveys independently confirm the presence of evolution. Whereas the bulk of the cluster population does not evolve, the most luminous and presumably most massive structures evolve appreciably between z=0.8 and the present. Interpreted in the context of hierarchical structure formation, we are probing sufficiently large mass aggregations at sufficiently early times in cosmological history where the Universe has yet to assemble these clusters to present-day volume densities.Comment: 15 pages, 10 figures, accepted for publication in Ap

Stormy weather in 3C 196.1: nuclear outbursts and merger events shape the environment of the hybrid radio galaxy 3C 196.1

We present a multi-wavelength analysis based on archival radio, optical and X-ray data of the complex radio source 3C 196.1, whose host is the brightest cluster galaxy of a $z=0.198$ cluster. HST data show H$\alpha$+[N II] emission aligned with the jet 8.4 GHz radio emission. An H$\alpha$+[N II] filament coincides with the brightest X-ray emission, the northern hotspot. Analysis of the X-ray and radio images reveals cavities located at galactic- and cluster- scales. The galactic-scale cavity is almost devoid of 8.4 GHz radio emission and the south-western H$\alpha$+[N II] emission is bounded (in projection) by this cavity. The outer cavity is co-spatial with the peak of 147 MHz radio emission, and hence we interpret this depression in X-ray surface brightness as being caused by a buoyantly rising bubble originating from an AGN outburst $\sim$280 Myrs ago. A \textit{Chandra} snapshot observation allowed us to constrain the physical parameters of the cluster, which has a cool core with a low central temperature $\sim$2.8 keV, low central entropy index $\sim$13 keV cm$^2$ and a short cooling time of $\sim$500 Myr, which is $<0.05$ of the age of the Universe at this redshift. By fitting jumps in the X-ray density we found Mach numbers between 1.4 and 1.6, consistent with a shock origin. We also found compelling evidence of a past merger, indicated by a morphology reminiscent of gas sloshing in the X-ray residual image. Finally, we computed the pressures, enthalpies $E_{cav}$ and jet powers $P_{jet}$ associated with the cavities: $E_{cav}\sim7\times10^{58}$ erg, $P_{jet}\sim1.9\times10^{44}$ erg s$^{-1}$ for the inner cavity and $E_{cav}\sim3\times10^{60}$ erg, $P_{jet}\sim3.4\times10^{44}$ erg s$^{-1}$ for the outer cavity.Comment: 14 pages, 4 figures, ApJ accepte