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Aims. Based on XMM-Newton, Chandra, and optical DR10-SDSS data, we investigate the metal enrichment history of the group NGC 4325 (z = 0.026). To complete the analysis we used chemical evolution models and studied the optical spectrum of the central dominant galaxy through its stellar population analysis and emission line diagnostics to analyse its role in the metal enrichment of the intra-group medium. Methods. We used X-ray 2D spectrally resolved maps to resolve structure in temperature and metallicity. We also derived gas and total masses within r2500 and r500 assuming hydrostatic equilibrium and spherical symmetry. To perform stellar population analysis we applied the spectral fitting technique with STARLIGHT to the optical spectrum of the central galaxy. We simulated the chemical evolution of the central galaxy. Results. While the temperature, pseudo-pressure, and pseudo-entropy maps showed no inhomogeneities, the spatial distribution of the metallicity shows a filamentary structure in the core of this group, which is spatially correlated with the central galaxy, suggesting a connection between the two. The analysis of the optical spectrum of the central galaxy showed no contribution by any recent AGN activity. Using the star formation history as input to chemical evolution models, we predicted the iron and oxygen mass released by supernovae (SNe) winds in the central galaxy up to the present time. Conclusions. Comparing the predicted amount of mass released by the NGC 4325 galaxy to the ones derived through X-ray analysis we conclude that the winds from the central galaxy alone play a minor role in the IGM metal enrichment of this group inside r2500. The SNe winds are responsible for no more than 3% of it and of the iron mass and 21% of the oxygen mass enclosed within r2500. Our results suggest that oxygen has been produced in the early stages of the group formation, becoming well mixed and leading to an almost flat profile. Instead, the iron distribution is centrally peaked, indicating that this element is still being added to the IGM specifically in the core by the SNIa. A possible scenario to explain the elongated metal-rich structure in the core of the NGC 4325 is a past AGN activity, in which our results suggest an episode older than ~107-108 yrs and younger than 5 × 108. Through the overall distribution of the galaxies, we found no signs of recent merger in the group centre that could explain the metal-rich structure. [ABSTRACT FROM AUTHOR]

Aims. Based on XMM-Newton, Chandra, and SDSS data, we investigate the baryon distribution in groups and clusters and its use as a cosmological constraint. For this, we considered a sample of 123 systems with temperatures kT500 = 1.0-9.0 keV, total masses in the mass range M500 = (∼1013-4 × 1015) h-1 70 M☉, and redshifts 0.02 < z < 1.3. Methods. The gas masses and total masses are derived from X-ray data under the assumption of hydrostatic equilibrium and spherical symmetry. The stellar masses are based on SDSS-DR8 optical photometric data. For the 37 systems out of 123 that had both optical and X-ray data available, we investigated the gas, stellar, and total baryon mass fractions inside r2500 and r500 and the differential gas mass fraction within the spherical annulus between r2500 and r500, as a function of total mass. For the other objects, we investigated the gas mass fraction only. Results. We find that the gas mass fraction inside r2500 and r500 depends on the total mass. However, the differential gas mass fraction does not show any dependence on total mass for systems with M500 > 1014 M☉. The stellar mass fraction inside r2500 and r500 increases towards low-mass systems more steeply than the fgas decrease with total mass. Adding the gas and stellar mass fractions to obtain the total baryonic content, we find it to increase with cluster mass, reaching the WMAP-7 value for clusters with M500 ∼ 1014 M☉. This led us to investigate the contribution of the intracluster light to the total baryon budget for lower mass systems, but we find that it cannot account for the difference observed. Conclusions. The gas mass fraction dependence on total mass observed for groups and clusters could be due to the difficulty of low-mass systems to retain gas inside the inner region (r < r2500). Because of their shallower potential well, non-thermal processes are more effective in expelling the gas from their central regions outwards. Since the differential gas mass fraction is nearly constant, it provides better constraints for cosmology. Moreover, we find that the gas mass fraction does not depend on redshift at a 2σ level. Using our total fb estimates, our results imply Ωm < 0.55, and taking the highest significant estimates for fb, Ωm > 0.22. [ABSTRACT FROM AUTHOR]

A correction to the article "Star-formation efficiency and metal enrichment of the intracluster medium in local massive clusters of galaxies," by Y.-Y. Zhang and colleagues that was published in the 2011 issue is presented.