Search

In this contribution I will review the current status of cosmological constraints based on the determination of the mass function of galaxy groups and clusters, and its redshift evolution. After describing the approaches to calibrate an analytical expression for the cosmological mass function of collapsed dark matter halos, I will discuss the methods, based on X-ray observations, to compute cluster masses. I will then critically discuss the constraints on cosmological parameters, which have been derived so far, and the future perspectives from upcoming surveys from Sunyaev-Zeldovich and X-ray observations. [ABSTRACT FROM AUTHOR]

We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies at z > 0.3, which cover a temperature range of 3 > kT > 15 keV. Our analysis is aimed at measuring the iron abundance in the ICM out to the highest redshift probed to date. We find that the emission-weighted iron abundance measured within (0.15 - 0.3)Rvir in clusters below 5 keV is, on average, a factor of ∼ 2 higher than in hotter clusters, following Z(T) ≃ 0.88 T-0.47Z⊙, which confirms the trend seen in local samples. We made use of combined spectral analysis performed over five redshift bins at 0.3 > z > 1.3 to estimate the average emission weighted iron abundance.We find a constant average iron abundance ZFe ≃ 0.25 Z⊙ as a function of redshift, but only for clusters at z > 0.5. The emission-weighted iron abundance is significantly higher (ZFe ≃ 0.4 Z⊙) in the redshift range z ≃ 0.3-0.5, approaching the value measured locally in the inner 0.15Rvir radii for a mix of coolcore and non cool-core clusters in the redshift range 0.1 > z > 0.3. The decrease in ZFe with z can be parametrized by a power law of the form ∼ (1 + z)-1.25. The observed evolution implies that the average iron content of the ICM at the present epoch is a factor of ∽ 2 larger than at z ≃ 1.2. We confirm that the ICM is already significantly enriched (ZFe ≃ 0.25 Z⊙) at a look-back time of 9 Gyr. Our data provide significant constraints on the time scales and physical processes that drive the chemical enrichment of the ICM [ABSTRACT FROM AUTHOR]

We present first results of the survey of the Chandra Deep Field South from 130 ks of x-ray observations in the .5 - 10 kev range obtained with the Advanced CCD Imaging Spectrometer in the Chandra X-ray Observatory. We observe a total of 160 sources to limiting fluxes of 2 x 10-16 erg s-1 cm-2 in the .5 - 2 kev soft band and 2 x 10-15 erg s-1 cm-2 in the 2 - 10 kev hard band. We discuss the spectra of the x-ray sources, the Log N-Log S relationship and the discrete source contribution to the integrated sky flux in the two bands. For purposes of identification of the optical counterparts we use observations obtained at the VLT with FORS-1 in the VRI bands complete to $R \le 26$ in a large fraction of the x-ray field, supplemented with data from the ESO Imaging Survey (EIS) in the UBJK bands and the ESO Wide Field Imager Survey (WFI) in the B band. Positional accuracy of about $1^{\prime\prime}$ is obtained for the x-ray sources and about 90% of them can be readily identified with optical candidate objects. Optical spectra have been obtained for 12 sources. Among the outstanding early results are the resolution of the XRB in the 2 - 10 kev range into discrete sources at a level of 60 to 80% of the total; the determination of the hardening of the x-ray spectra of sources at low fluxes which makes them consistent with that of the XRB, and the detection of low x-ray luminosity galaxies in the soft band at $Z \sim 2$. [ABSTRACT FROM AUTHOR]

In this contribution the ongoing effort to build a statistical sample of clusters of galaxies over a wide range of redshifts to study the evolution of clusters and member galaxies is reviewed. The starting point for this project has been the list of candidate clusters identified from the I-band EIS-WiDE survey data. Since the completion of this survey, new optical/infrared observations have become available and have been used to confirm some of these candidates using the photometric data alone or in combination with the results of follow-up spectroscopic observations. Our preliminary results show that the yield of real physical associations from the original catalog is conservatively $\gtrsim 60\%$ and that a large sample of clusters in the southern hemisphere, extending to high-redshifts, is within reach. [ABSTRACT FROM AUTHOR]

The dependence of iron abundance on cluster temperature is subject to continuous debate. There are some evidences of decreasing abundances from ~0.7 to ~0.3 times the solar metallicity in the temperature range of ~3 — 10 keV [1], while a roughly constant value of ~0.3 times solar is claimed [2]. Physical interpretation of these ambiguous observational results calls for robust theoretical models that can predict systematic trends for the enrichment of clusters of different masses. [ABSTRACT FROM AUTHOR]