337 research outputs found
Ultra-Luminous Sources in Nearby Galaxies
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
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
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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