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Register a new userImages, structural properties and metal abundances of galaxy clusters observed with Chandra ACIS-I at 0.1<z<1.3
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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.
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We present the analysis of the temperature and metallicity profiles of 12 galaxy clusters in the redshift range 0.1--0.3 selected from the Chandra archive with at least ~20,000 net ACIS counts and kT>6 keV. We divide the sample between 7 Cooling-Core (CC) and 5 Non-Cooling-Core (NCC) clusters according to their central cooling time. We find that single power-laws can describe properly both the temperature and metallicity profiles at radii larger than 0.1 r_180 in both CC and NCC systems, showing the NCC objects steeper profiles outwards. A significant deviation is only present in the inner 0.1 r_180. We perform a comparison of our sample with the De Grandi & Molendi BeppoSAX sample of local CC and NCC clusters, finding a complete agreement in the CC cluster profile and a marginally higher value (at ~1sigma) in the inner regions of the NCC clusters. The slope of the power-law describing kT(r) within 0.1 r_180 correlates strongly with the ratio between the cooling time and the age of the Universe at the cluster redshift, being the slope >0 and tau_c/tau_age<=0.6 in CC systems.
A software package able to simulate imaging observations of galaxy clusters by the Chandra X-ray telescope is here presented. We start from high resolution N-body hydrodynamical simulations of galaxy clusters and assign to each gas particle a spectrum of emissivity, after assuming the MeKaL model. We then construct spatial images of the source differential flux which are used to create lists of incoming X-ray photons, preserving information on photon direction and energy. The photon lists are passed on to the Chandra simulator (MARX) to produce the final observation events. Background events are added to complete the simulation. Data analysis is currently in progress and simulated observations by other telescopes will become available in the future.
We present measurements of the X-ray observables of the intra-cluster medium (ICM), including luminosity $L_X$, ICM mass $M_{ICM}$, emission-weighted mean temperature $T_X$, and integrated pressure $Y_X$, that are derived from XMM-Newton X-ray observations of a Sunyaev-Zeldovich Effect (SZE) selected sample of 59 galaxy clusters from the South Pole Telescope SPT-SZ survey that span the redshift range of $0.20 < z < 1.5$. We constrain the best-fit power law scaling relations between X-ray observables, redshift, and halo mass. The halo masses are estimated based on previously published SZE observable to mass scaling relations, calibrated using information that includes the halo mass function. Employing SZE-based masses in this sample enables us to constrain these scaling relations for massive galaxy clusters ($M_{500}geq 3 times10^{14}$ $M_odot$) to the highest redshifts where these clusters exist without concern for X-ray selection biases. We find that the mass trends are steeper than self-similarity in all cases, and with $geq 2.5{sigma}$ significance in the case of $L_X$ and $M_{ICM}$. The redshift trends are consistent with the self-similar expectation, but the uncertainties remain large. Core-included scaling relations tend to have steeper mass trends for $L_X$. There is no convincing evidence for a redshift-dependent mass trend in any observable. The constraints on the amplitudes of the fitted scaling relations are currently limited by the systematic uncertainties on the SZE-based halo masses, however the redshift and mass trends are limited by the X-ray sample size and the measurement uncertainties of the X-ray observables.
We present a pilot X-ray study of the five most massive ($M_{500}>5 times 10^{14} M_{odot}$), distant (z~1), galaxy clusters detected via the Sunyaev-Zeldovich effect. We optimally combine XMM-Newton and Chandra X-ray observations by leveraging the throughput of XMM to obtain spatially-resolved spectroscopy, and the spatial resolution of Chandra to probe the bright inner parts and to detect embedded point sources. Capitalising on the excellent agreement in flux-related measurements, we present a new method to derive the density profiles, constrained in the centre by Chandra and in the outskirts by XMM. We show that the Chandra-XMM combination is fundamental for morphological analysis at these redshifts, the Chandra resolution being required to remove point source contamination, and the XMM sensitivity allowing higher significance detection of faint substructures. The sample is dominated by dynamically disturbed objects. We use the combined Chandra-XMM density profiles and spatially-resolved temperature profiles to investigate thermodynamic quantities including entropy and pressure. From comparison of the scaled profiles with the local REXCESS sample, we find no significant departure from standard self-similar evolution, within the dispersion, at any radius, except for the entropy beyond 0.7$R_{500}$. The baryon mass fraction tends towards the cosmic value, with a weaker dependence on mass than observed in the local Universe. We compare with predictions from numerical simulations. The present pilot study demonstrates the utility and feasibility of spatially-resolved analysis of individual objects at high-redshift through the combination of XMM and Chandra observations. Observations of a larger sample will allow a fuller statistical analysis to be undertaken, in particular of the intrinsic scatter in the structural and scaling properties of the cluster population. (abridged)
We study a sample of 48127 galaxies selected from the SDSS MPA-JHU catalogue, with $log M_{star}/M_{odot} = 10.73 - 11.03$ and $z<0.1$. Local galaxies in this stellar mass range have been shown to have systematically shorter assembly times within their inner regions ($<0.5~R_{50}$) when compared to that of the galaxy as a whole, contrary to lower or higher mass galaxies which show consistent assembly times at all radii. Hence, we refer to these galaxies as Inside-Out Assembled Galaxy (IOAG) candidates. We find that the majority of IOAG candidates with well-detected emission lines are classified as either AGN (40%) or composite (40%) in the BPT diagram. We also find that the majority of our sources are located below the main sequence of star formation, and within the green valley or red sequence. Most BPT-classified star-forming IOAG candidates have spiral morphologies and are in the main sequence, whereas Seyfert 2 and composites have mostly spiral morphologies but quiescent star formation rates (SFRs). We argue that a high fraction of IOAG candidates seem to be in the process of quenching, moving from the blue cloud to the red sequence. Those classified as AGN have systematically lower SFRs than star-forming galaxies suggesting that AGN activity may be related to this quenching. However, the spiral morphology of these galaxies remains in place, suggesting that the central star-formation is suppressed before the morphological transformation occurs.
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