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Register a new userOn the Iron content in rich nearby Clusters of Galaxies
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In this paper we study the iron content of a sample of 22 nearby hot clusters observed with BeppoSAX. We find that the global iron mass of clusters is tightly related to the cluster luminosity and that the relatively loose correlation between the iron mass and the cluster temperature follows from the combination of the iron mass vs. luminosity and luminosity vs. temperature correlations. The iron mass is found to scale linearly with the intracluster gas mass, implying that the global iron abundance in clusters is roughly constant. This result suggests that enrichment mechanisms operate at a similar rate in all clusters. By employing population synthesis and chemical enrichment models, we show that the iron mass associated to the abundance excess which is always found in the centre of cool core clusters can be entirely produced by the brightest cluster galaxy (BCG), which is always found at the centre of cool core clusters. The iron mass associated to the excess, the optical magnitude of the BCG and the temperature of the cluster are found to correlate with one another suggesting a link between the properties of the BCG and the hosting cluster. These observational facts lends strength to current formation theories which envisage a strong connection between the formation of the giant BCG and its hosting cluster.
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Besides giant elliptical galaxies, a number of low-mass stellar systems inhabit the cores of galaxy clusters, such as dwarf elliptical galaxies (dEs/dSphs), ultra-compact dwarf galaxies (UCDs), and globular clusters. The detailed morphological examination of faint dwarf galaxies has, until recently, been limited to the Local Group (LG) and the two very nearby galaxy clusters Virgo and Fornax. Here, we compare the structural parameters of a large number of dEs/dSphs in the more distant clusters Hydra I and Centaurus to other dynamically hot stellar systems.
We derive here the mean temperature profile for a sample of hot, medium distant clusters recently observed with XMM-Newton, whose profiles are available from the literature, and compare it with the mean temperature profile found from BeppoSAX data. The XMM-Newton and BeppoSAX profiles are in good agreement between 0.05 and 0.25 r_180. From 0.25 to about 0.5 r_180 both profiles decline, however the BeppoSAX profile does so much more rapidly than the XMM-Newton profile.
We report results from the analysis of 21 nearby galaxy clusters, 11 with cooling flow (CF) and 10 without cooling flow, observed with BeppoSAX. The temperature profiles of both CF and non-CF systems are characterized by an isothermal core extending out to 0.2 r_180; beyond this radius both CF and non-CF cluster profiles rapidly decline. Our results differ from those derived by other authors who either found continuously declining profiles or substantially flat profiles. Neither the CF nor the non-CF profiles can be modeled by a polytropic temperature profile, the reason being that the radius at which the profiles break is much larger than the core radius characterizing the gas density profiles. For r > 0.2 r_180, where the gas can be treated as a polytrope, the polytropic indices derived for CF and non-CF systems are respectively 1.20 +/- 0.06 and 1.46 +/- 0.06. The former index is closer to the isothermal value, 1, and the latter to the adiabatic value, 5/3. Published hydrodynamic simulations do not reproduce the peculiar shape of the observed temperature profile, probably suggesting that a fundamental ingredient is missing.
We present the UV composite luminosity function for galaxies in the Virgo, Coma and Abell 1367 clusters. The luminosity function (LF) is well fitted by a Schechter function with M*(UV} - 5*log h(75) = -20.75 +/- 0.40 and alpha = -1.50 +/- 0.10 and does not differ significantly from the local UV luminosity function of the field. This result is in agreement with recent studies carried out in the Halpha and B-bands which find no difference between the LFs of star forming galaxies in clusters and in the field. This indicates that, whatever mechanisms are responsible for quenching the star formation in clusters, they influence similarly the giant and the dwarf populations, leaving the shape of the LF unchanged and only modifying its normalization.
We report the results of spectroscopic observations, obtained with the GEMINI Multi-Object Spectrograph, of 8 planetary nebulae (PNe) in the dwarf spheroidal (dSph) galaxy NGC147, a companion of M31. The physico-chemical properties of the six brightest PNe (Corradi et al. 2005) were derived using both the empirical ICF method and photoionization modelling with CLOUDY. Different aspects of the evolution of low and intermediate mass stars in a low-metallicity environment are analysed using relationships between chemical abundances. In addition, certain features of the chemical evolution of NGC147 were examined. In particular, the mean metallicity of PNe, O/H=8.06 (corresponding to [Fe/H](PNe)~-0.97), is close to the metallicity of the old stellar population, [Fe/H]=-1.0 (Butler & Martinez-Delgado), suggesting a negligible chemical enrichment during a substantial amount of time. Finally, the luminosity-metallicity relationship for the dwarf galaxies of the Local Group is discussed. The location in the luminosity-metallicity diagram of dSphs does not exclude their formation from old dwarf irregular (dIrs) galaxies, but it does exclude their formation from the present time dIrs, since the differences between their metallicities are already present in their older populations. The offset in the luminosity-metallicity relationship indicates a faster enrichment of dSphs, and together with the different average abundance ratio [O/Fe] demonstrates the different star formation histories for these two types of galaxies.
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