We investigate if the discrepancy between estimates of the total baryon mass fraction obtained from observations of the cosmic microwave background (CMB) and of galaxy groups/clusters persists when a large sample of groups is considered. To this purpose, 91 candidate X-ray groups/poor clusters at redshift 0.1 ≤ z ≤ 1 are selected from the COSMOS 2 deg 2 survey, based only on their X-ray luminosity and extent. This sample is complemented by 27 nearby clusters with a robust, analogous determination of the total and stellar mass inside R 500 . The total sample of 118 groups and clusters with z ≤ 1 spans a range in M 500 of ∼ 10 13 -10 15 M ⊙ . We find that the stellar mass fraction associated with galaxies at R 500 decreases with increasing total mass as M −0.37±0.04 500, independent of redshift. Estimating the total gas mass fraction from a recently derived, high quality scaling relation, the total baryon mass fraction (f stars+gas 500 = f stars 500 + f gas 500 ) is found to increase by ∼ 25% when M 500 increases from M = 5 × 10 13 M ⊙ to M = 7 × 10 14 M ⊙ . After consideration of a plausible contribution due to intra-cluster light (11-22% of the total stellar mass), and gas depletion through the hierarchical assembly process (10% of the gas mass), the estimated values of the total baryon mass fraction are still lower than the latest CMB measure of the same quantity (WMAP5), at a significance level of 3.3σ for groups of M = 5 × 10 13 M ⊙ . The discrepancy decreases towards higher total masses, such that it is 1σ at M = 7 × 10 14 M ⊙ . We discuss this result in terms of non-gravitational processes such as feedback and filamentary heating.

Measurements of X-ray scaling laws are critical for improving cosmological constraints derived with the halo mass function and for understanding the physical processes that govern the heating and cooling of the intracluster medium. In this paper, we use a sample of 206 X-ray selected galaxy groups to investigate the scaling relation between X-ray luminosity (L X ) and halo mass (M 200 ) where M 200 is derived via stacked weak gravitational lensing. This work draws upon a broad array of multiwavelength COSMOS observations including 1.64 degrees 2 of contiguous imaging with the Advanced Camera for Surveys (ACS) to a limiting magnitude of I F814W = 26.5 and deep XMM-Newton/Chandra imaging to a limiting flux of 1.0 × 10 −15 erg cm −2 s −1 in the 0.5-2 keV band. The combined depth of these two data-sets allows us to probe the lensing signals of X-ray detected structures at both higher redshifts and lower masses than previously explored. Weak lensing profiles and halo masses are derived for nine sub-samples, narrowly binned in luminosity and redshift. The COSMOS data alone are well fit by a power law, M 200 ∝ (L X ) α , with a slope of α = 0.66 ± 0.14. These results significantly extend the dynamic range for which the halo masses of X-ray selected structures have been measured with weak gravitational lensing. As a result, tight constraints are obtained for the slope of the M − L X relation. The combination of our group data with previously published cluster data demonstrates that the M − L X relation is well described by a single power law, α = 0.64 ± 0.03, over two decades in mass, M 200 ∼ 10 13.5 -10 15.5 h −1 72 M . These results are inconsistent at the 3.7σ level with the self-similar prediction of α = 0.75. We examine the redshift dependence of the M − L X relation and find little evidence for evolution beyond the rate predicted by self-similarity from z ∼ 0.25 to z ∼ 0.8.

We present a study of the relation between dark matter halo mass and the baryonic content of their host galaxies, quantified through galaxy luminosity and stellar mass. Our investigation uses 154 deg 2 of Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) lensing and photometric data, obtained from the CFHT Legacy Survey. To interpret the weak lensing signal around our galaxies we employ a galaxy-galaxy lensing halo model which allows us to constrain the halo mass and the satellite fraction. Our analysis is limited to lenses at redshifts between 0.2 and 0.4, split into a red and a blue sample. We express the relationship between dark matter halo mass and baryonic observable as a power law with pivot points of 10 11 h −2 70 L ⊙ and 2 × 10 11 h −2 70 M ⊙ for luminosity and stellar mass respectively. For the luminosity-halo mass relation we find a slope of 1.32 ± 0.06 and a normalisation of 1.19 +0.06 −0.07 × 10 13 h −1 70 M ⊙ for red galaxies, while for blue galaxies the best-fit slope is 1.09 +0.20 −0.13 and the normalisation is 0.18 +0.04 −0.05 × 10 13 h −1 70 M ⊙ . Similarly, we find a best-fit slope of 1.36 +0.06 −0.07 and a normalisation of 1.43 +0.11 −0.08 × 10 13 h −1 70 M ⊙ for the stellar mass-halo mass relation of red galaxies, while for blue galaxies the corresponding values are 0.98 +0.08 −0.07 and 0.84 +0.20 −0.16 × 10 13 h −1 70 M ⊙ . All numbers convey the 68% confidence limit. For red lenses, the fraction which are satellites inside a larger halo tends to decrease with luminosity and stellar mass, with the sample being nearly all satellites for a stellar mass of 2 × 10 9 h −2 70 M ⊙ . The satellite fractions are generally close to zero for blue lenses, irrespective of luminosity or stellar mass. This, together with the shallower relation between halo mass and baryonic tracer, is a direct confirmation from galaxy-galaxy lensing that blue galaxies reside in less clustered environments than red galaxies. We also find that the halo model, while matching the lensing signal around red lenses well, is prone to over-predicting the large-scale signal for faint and less massive blue lenses. This could be a further indication that these galaxies tend to be more isolated than assumed.

We present the results of a search for galaxy clusters in the first 36 XMM-Newton pointings on the Cosmic Evolution Survey (COSMOS) field. We reach a depth for a total cluster flux in the 0.5Y2 keV band of 3 ; 10 À15 ergs cm À2 s À1 , having one of the widest XMM-Newton contiguous raster surveys, covering an area of 2.1 deg 2 . Cluster candidates are identified through a wavelet detection of extended X-ray emission. Verification of the cluster candidates is done based on a galaxy concentration analysis in redshift slices of thickness 0.1Y0.2 in redshift, using the multiband photometric catalog of the COSMOS field and restricting the search to z < 1:3 and i AB < 25. We identify 72 clusters and derive their properties based on the X-ray cluster scaling relations. A statistical description of the survey in terms of the cumulative log (N > S )-log S distribution compares well with previous results, although yielding a somewhat higher number of clusters at similar fluxes. The X-ray luminosity function of COSMOS clusters matches well the results of nearby surveys, providing a comparably tight constraint on the faint-end slope of ¼ 1:93 AE 0:04. For the probed luminosity range of (8 ; 10 42 )Y(2 ; 10 44 ) ergs s À1 , our survey is in agreement with and adds significantly to the existing data on the cluster luminosity function at high redshifts and implies no substantial evolution at these luminosities to z ¼ 1:3. Subject headingg s: cosmology: observations -dark matter -large-scale structure of universe -surveys

Well-calibrated scaling relations between the observable properties and the total masses of clusters of galaxies are important for understanding the physical processes that give rise to these relations. They are also a critical ingredient for studies that aim to constrain cosmological parameters using galaxy clusters. For this reason much effort has been spent during the last decade to better understand and interpret relations of the properties of the intra-cluster medium. Improved X-ray data have expanded the mass range down to galaxy groups, whereas SZ surveys have openened a new observational window on the intracluster medium. In addition, continued progress in the performance of cosmological simulations has allowed a better understanding of the physical processes and selection effects affecting the observed scaling relations. Here we review the recent literature on various scaling relations, focussing on the latest observational measurements and the progress in our understanding of the deviations from self similarity.

We present a detailed study of a peculiar source detected in the COSMOS survey at z=0.359. Source CXOC J100043.1+020637, also known as CID-42, presents two compact optical sources embedded in the same galaxy. The distance between the two, measured in the HST/ACS image, is 0.495"±0.005" that, at the redshift of the source, corresponds to a projected separation of 2.46±0.02 kpc. A large (∼1200 km/s) velocity offset between the narrow and broad components of Hβ has been measured in three different optical spectra from the VLT/VIMOS and Magellan/IMACS instruments. CID-42 is also the only X-ray source in COSMOS having in its X-ray spectra a strong redshifted broad absorption iron line, and an iron emission line, drawing an inverted P-Cygni profile. The Chandra and XMM-Newton data show that the absorption line is variable in energy by ∆E=500 eV over 4 years and that the absorber has to be highly ionized, in order not to leave a signature in the soft X-ray spectrum. That these features, the morphology, the velocity offset and the inverted P-Cygni profile, occur in the same source is unlikely to be a coincidence. We envisage two possible explanations, both exceptional, for this system: (1) a gravitational wave recoiling black hole (BH), caught 1-10 Myr after merging, (2) a Type 1/ Type 2 system in the same galaxy where the Type 1 is recoiling due to slingshot effect produced by a triple BH system. The first possibility gives us a candidate gravitational waves recoiling BH with both spectroscopic and imaging signatures. In the second case, the Xray absorption line can be explained as a BAL-like outflow from the foreground nucleus (a Type 2 AGN) at the rearer one (a Type 1 AGN), which illuminates the otherwise undetectable wind, giving us the first opportunity to show that fast winds are present in obscured AGN, and possibly universal in AGNs. Subject headings:

We review the methods adopted to reconstruct the mass profiles in X-ray luminous galaxy clusters. We discuss the limitations and the biases affecting these measurements and how these mass profiles can be used as cosmological proxies.

We introduce our survey of galaxy groups at 0.85 < z < 1, as an extension of the Group Environment and Evolution Collaboration. Here we present the first results, based on Gemini GMOS-S nod-and-shuffle spectroscopy of seven galaxy groups selected from spectroscopically confirmed, extended XMM detections in COSMOS. We use photometric redshifts to