339 research outputs found

    Ultra-Luminous Sources in Nearby Galaxies

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    I briefly review much of the X-ray and optical data on the nature of the ULXs in nearby galaxies. I present new results on radio emission, finding that the radio is usually rather luminous and extended. I review the X-ray data on timing and spectra. There is no direct evidence in the X-ray data for either geometric or relativistic beaming and in 4 objects direct evidence against beaming. I argue that the X-ray timing and spectral properties of these objects are, in general, not good analogs of AGN or galactic black holes and that the ULX may represent a new mode of accretion only rarely seen in other objects.Comment: 18 pages, 4 figure

    Tracing Star Formation in Cool Core Clusters with GALEX

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    We present recent results from a GALEX investigation of star formation in 16 cooling core clusters of galaxies, selected to span a broad range in both redshift and central cooling time. Initial results demonstrate clear UV excesses in most, but not all, brightest cluster galaxies in our sample. This UV excess is a direct indication of the presence of young massive stars and, therefore, recent star formation. We report on the physical extent of UV emission in these objects as well as their FUV-NUV colors, and compare GALEX inferred star formation rates to central cooling times, H-alpha and IR luminosities for our sample.Comment: 4 pages, 4 figures; to appear in proceedings of The Monster's Fiery Breath: Feedback in Galaxies, Groups, and Clusters (AIP conference series

    Supernovae Types Ia/II and Intracluster Medium Enrichment

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    We re-examine the respective roles played by supernovae (SNe) Types Ia and II in enriching the intracluster medium (ICM) of galaxy clusters, in light of the recent downward shift of the ASCA abundance ratios of alpha-elements to iron favoured by Ishimaru & Arimoto (1997, PASJ, 49, 1). Because of this shift, Ishimaru & Arimoto conclude that >50% of the ICM iron must have originated from within Type Ia SNe progenitors. A point not appreciated in their study, nor in most previous analyses, is the crucial dependence of such a conclusion upon the adopted massive star physics. Employing several alternative Type II SN yield compilations, we demonstrate how uncertainties in the treatment of convection and mass-loss can radically alter our perception of the relative importance of Type Ia and II SNe as ICM polluters. If mass-loss of the form favoured by Maeder (1992, A&A, 264, 105) or convection of the form favoured by Arnett (1996, Supernovae and Nucleosynthesis) is assumed, the effect upon the oxygen yields would lead us to conclude that Type Ia SNe play no part in polluting the ICM, in contradiction with Ishimaru & Arimoto. Apparent dichotomies still exist (e.g. the mean ICM neon-to-iron ratio implies a 100% Type II Fe origin, while the mean sulphur ratio indicates a 100% Type Ia origin) that cannot be reconciled with the currently available yield tables.Comment: 6 pages (incl 1 PostScript figure), LaTeX, also available at http://msowww.anu.edu.au/~gibson/publications.html, MNRAS, in pres
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