The ROSAT Deep Cluster Survey: the X-ray Luminosity Function out to z=0.8

We present the X-ray Luminosity Function (XLF) of the ROSAT Deep Cluster Survey (RDCS) sample over the redshift range 0.05-0.8. Our results are derived from a complete flux-limited subsample of 70 galaxy clusters, representing the brightest half of the total sample, which have been spectroscopically identified down to the flux limit of 4*10^{-14} erg/cm^2/s (0.5-2.0 keV) and have been selected via a serendipitous search in ROSAT-PSPC pointed observations. The redshift baseline is large enough that evolutionary effects can be studied within the sample. The local XLF (z < 0.25) is found to be in excellent agreement with previous determinations using the ROSAT All-Sky Survey data. The XLF at higher redshifts, when combined with the deepest number counts constructed to date (f>2*10^{-14} arg/cm^2/s), reveal no significant evolution at least out to z=0.8, over a luminosity range 2*10^{42}-3*10^{44} erg/s in the [0.5-2 keV] band. These findings extend the study of cluster evolution to the highest redshifts and the faintest fluxes probed so far in X-ray surveys. They complement and do not necessarily conflict with those of the Einstein Extended Medium Sensitivity Survey, leaving the possibility of negative evolution of the brightest end of the XLF at high redshifts.Comment: 12 pages, 4 figures, LaTeX (aasms4.sty). To appear in ApJ Letter

Morphology with Light Profile Fitting of Confirmed Cluster Galaxies at z=0.84

We perform a morphological study of 124 spectroscopically confirmed cluster galaxies in the z=0.84 galaxy cluster RX J0152.7-1357. Our classification scheme includes color information, visual morphology, and 1-component and 2-component light profile fitting derived from Hubble Space Telescope riz imaging. We adopt a modified version of a detailed classification scheme previously used in studies of field galaxies and found to be correlated with kinematic features of those galaxies. We compare our cluster galaxy morphologies to those of field galaxies at similar redshift. We also compare galaxy morphologies in regions of the cluster with different dark-matter density as determined by weak-lensing maps. We find an early-type fraction for the cluster population as a whole of 47%, about 2.8 times higher than the field, and similar to the dynamically young cluster MS 1054 at similar redshift. We find the most drastic change in morphology distribution between the low and intermediate dark matter density regions within the cluster, with the early type fraction doubling and the peculiar fraction dropping by nearly half. The peculiar fraction drops more drastically than the spiral fraction going from the outskirts to the intermediate-density regions. This suggests that many galaxies falling into clusters at z~0.8 may evolve directly from peculiar, merging, and compact systems into early-type galaxies, without having the chance to first evolve into a regular spiral galaxy.Comment: 13 pages, 11 figures, accepted for publication in A&

A Deficit of Faint Red Galaxies in the Possible Large-Scale Structures around the RDCS J1252.9-2927 Cluster at z=1.24

(Abridged) We report a discovery of possible large-scale structures around the RDCS J1252.9-2927 cluster at z=1.24 based on photometric redshifts. We carried out multi-band wide-field imaging with Suprime-Cam on the Subaru Telescope and WFCAM on the United Kingdom Infra-Red Telescope (UKIRT). The distribution of photo-z selected galaxies reveals clumpy structures surrounding the central cluster. We compare the observed structure with an X-ray map and find that two of the four plausible clumps show significant X-ray emissions and one with a marginal detection, which strongly suggest that they are dynamically bound systems. Following the discovery of the possible large-scale structure, we carried out deeper SOFI K_s-band imaging with New Technology Telescope on the four plausible clumps. We construct the optical-to-near-infrared colour-magnitude diagrams of the galaxies in the clumps, and find that the colour-magnitude relation (CMR) of the red galaxies in the clumps is sharply truncated below K_s=22. Interestingly, the main cluster shows a clear relation down to K_s=23 (Lidman et al. 2004). We suggest that galaxies follow the 'environment-dependent down-sizing' evolution. Massive galaxies in high density environments first stop forming stars and become red. Less massive galaxies in less dense environments become red at later times. Based on a few assumptions, we predict that the brightest tip of the CMR appears at z~2.5.Comment: 10 pages, 8 figures, accepted for publication in MNRA

The Brera Multi-scale Wavelet (BMW) ROSAT HRI source catalog. I: the algorithm

We present a new detection algorithm based on the wavelet transform for the analysis of high energy astronomical images. The wavelet transform, due to its multi-scale structure, is suited for the optimal detection of point-like as well as extended sources, regardless of any loss of resolution with the off-axis angle. Sources are detected as significant enhancements in the wavelet space, after the subtraction of the non-flat components of the background. Detection thresholds are computed through Monte Carlo simulations in order to establish the expected number of spurious sources per field. The source characterization is performed through a multi-source fitting in the wavelet space. The procedure is designed to correctly deal with very crowded fields, allowing for the simultaneous characterization of nearby sources. To obtain a fast and reliable estimate of the source parameters and related errors, we apply a novel decimation technique which, taking into account the correlation properties of the wavelet transform, extracts a subset of almost independent coefficients. We test the performance of this algorithm on synthetic fields, analyzing with particular care the characterization of sources in poor background situations, where the assumption of Gaussian statistics does not hold. For these cases, where standard wavelet algorithms generally provide underestimated errors, we infer errors through a procedure which relies on robust basic statistics. Our algorithm is well suited for the analysis of images taken with the new generation of X-ray instruments equipped with CCD technology which will produce images with very low background and/or high source density.Comment: 8 pages, 6 figures, ApJ in pres

XMM-Newton Observation of a Distant X-ray Selected Cluster of Galaxies at z=1.26 with Possible Cluster Interaction

We report on the XMM-Newton (XMM) observation of RXJ1053.7+5735, one of the most distant (z = 1.26) X-ray selected clusters of galaxies, which also shows an unusual double-lobed X-ray morphology, indicative of possible cluster-cluster interaction. The cluster was discovered during our ROSAT deep pointings in the direction of the Lockman Hole. The XMM observations were performed with the European Photon Imaging Camera (EPIC) during the performance verification phase. Total effective exposure time was ~ 100 ksec. The best fit temperature based on a simultaneous fit of spectra from the all EPIC cameras is 4.9(+1.5/-0.9) keV. Metallicity is poorly constrained even using the joint fit of all spectra, with an upper limit on the iron abundance of 0.62 solar. Using the best fit model parameters, we derived a bolometric luminosity of L(bol) = 3.4x10^44 h_{50}^-2 erg /s. Despite the fact that it was observed at fairly large off-axis angle, the temperature errors are much smaller compared with those of typical measurements based on ASCA or Beppo-Sax observations of z > 0.6 clusters, demonstrating the power of the XMM for determining the X-ray temperature for high-z clusters. The measured temperature and luminosity show that one can easily reach the intrinsically X-ray faint and cool cluster regime comparable with those of z ~ 0.4 clusters observed by past satellites. The new cluster temperature and L(bol) we have measured for RXJ1053.7+5735 is consistent with a weak/no evolution of the L(bol) - Tx relation out to z ~ 1.3, which lends support to a low Omega universe, although more data-points of z > 1 clusters are required for a more definitive statement. The caution has to be also exercised in interpreting the result, because of the uncertainty associated with the dynamical status of this cluster.Comment: Accepted for pubblication in A&A. 7 figures (One color figure is changed to black and white.

On the Fe abundance peak formation in cool-core clusters of galaxies: hints from cluster WARPJ1415.1+3612 at z=1.03

We present a detailed study of the iron content of the core of the high-redshift cluster WARPJ1415.1+3612 (z=1.03). By comparing the central Fe mass excess observed in this system, M_Fe^exc = (1.67 +/- 0.40) x 10^9 M_sun, with those measured in local cool-core systems, we infer that the bulk of the mass excess was already in place at z=1, when the age of the Universe was about half of what it is today. Our measures point to an early and intense period of star formation most likely associated with the formation of the BCG. Indeed, in the case of the power-law delay time distribution with slope -1, which reproduces the data of WARPJ1415.1+3612 best, half of the supernovae explode within 0.4 Gyr of the formation of the BCG. Finally, while for local cool-core clusters the Fe distribution is broader than the near infrared light distribution of the BCG, in WARPJ1415.1+3612 the two distributions are consistent, indicating that the process responsible for broadening the Fe distribution in local systems has not yet started in this distant cluster.Comment: 10 pages, accepted for publication in A&A, minor language corrections added in v

CLASH-VLT: Is there a dependence in metallicity evolution on galaxy structures?

We investigate the environmental dependence of the mass-metallicty (MZ) relation and it's connection to galaxy stellar structures and morphologies. In our studies, we analyze galaxies in massive clusters at z~0.4 from the CLASH (HST) and CLASH-VLT surveys and measure their gas metallicities, star-formation rates, stellar structures and morphologies. We establish the MZ relation for 90 cluster and 40 field galaxies finding a shift of ~-0.3 dex in comparison to the local trends seen in SDSS for the majority of galaxies with logM<10.5. We do not find significant differences of the distribution of 4 distinct morphological types that we introduce by our classification scheme (smooth, disc-like, peculiar, compact). Some variations between cluster and field galaxies in the MZ relation are visible at the high mass end. However, obvious trends for cluster specific interactions (enhancements or quenching of SFRs) are missing. In particular, galaxies with peculiar stellar structures that hold signs for galaxy interactions, are distributed in a similar way as disc-like galaxies - in SFRs, masses and O/H abundances. We further show that our sample falls around an extrapolation of the star-forming main sequence (the SFR-M* relation) at this redshift, indicating that emission-line selected samples do not have preferentially high star-formation rates (SFRs). However, we find that half of the high mass cluster members (M*>10^10Msun) lie below the main sequence which corresponds to the higher mass objects that reach solar abundances in the MZ diagram.Comment: Proceedings of IAU Symposium 309, Vienna, ed. B.L. Ziegler, F. Combes, H. Dannerbauer, M. Verdug