206 research outputs found
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
Discovery of a 7 mHz X-Ray Quasi-periodic Oscillation from the most Massive Stellar-mass Black Hole IC 10 X-1
We report the discovery with XMM-Newton of an approximately 7 mHz X-ray
(0.3-10.0 keV) quasi-periodic oscillation (QPO) from the eclipsing,
high-inclination black hole binary IC 10 X-1. The QPO is significant at > 4.33
sigma confidence level and has a fractional amplitude (% rms) and a quality
factor, Q, of approximately 11 and 4, respectively. The overall X-ray (0.3-10.0
keV) power spectrum in the frequency range 0.0001 - 0.1 Hz can be described by
a power-law with an index of -2, and a QPO at 7 mHz. At frequencies > 0.02 Hz
there is no evidence for significant variability. The fractional amplitude
(rms) of the QPO is roughly energy-independent in the energy range of 0.3-1.5
keV. Above 1.5 keV the low signal to noise ratio of the data does not allow us
to detect the QPO. By directly comparing these properties with the wide range
of QPOs currently known from accreting black hole and neutron stars, we suggest
that the 7 mHz QPO of IC 10 X-1 may be linked to one of the following three
categories of QPOs: (1) the "heartbeat" mHz QPOs of the black hole sources GRS
1915+105 and IGR J17091-3624, or (2) the 0.6-2.4 Hz "dipper QPOs" of
high-inclination neutron star systems, or (3) the mHz QPOs of Cygnus X-3.Comment: Published in ApJ Letter
Oxygen Abundances in the Milky Way Using X-ray Absorption Measurements Towards Galaxy Clusters
We present measurements of the oxygen abundance of the Milky Way's ISM by
observing the K-shell X-ray photoionization edge towards galaxy clusters. This
effect is most easily observed towards objects with galactic columns (n_H) of a
few times 1e21 cm^-2. We measure X-ray column densities towards 11 clusters and
find that at high galactic columns above approximately 1e21 cm^-2 the X-ray
columns are generally 1.5--3.0 times greater than the 21 cm H II columns,
indicating that molecular clouds become an important contributor to n_H at
higher columns. We find the average ISM oxygen abundance to be (O/H) = (4.85
+/- 0.06) x 10^-4, or 0.99 solar when using the most recent solar photospheric
values. Since X-ray observations are sensitive to the total amount of oxygen
present (gas + dust), these results indicate a high gas to dust ratio. Also,
the oxygen abundances along lines of sight through high galactic columns (n_H)
are the same as abundances through low columns, suggesting that the composition
of denser clouds is similar to that of the more diffuse ISM.Comment: submitted to Ap
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