Monday 01/27/2013

Cosmic Ray Heating of the Warm Ionized Medium Joshua Wiener, Ellen G. Zweibel, S. Peng Oh (Submitted on 18 Jan 2013)

Observations of line ratios in the Milky Way’s warm ionized medium (WIM) suggest that photoionization is not the only heating mechanism present. For the additional heating to explain the discrepancy it would have to have a weaker dependence on the gas density than the cooling rate, $\Lambda n_e^2$. \cite{reynolds99} suggested turbulent dissipation or magnetic field reconnection as possible heating sources. We investigate here the viability of MHD-wave mediated cosmic ray heating as a supplemental heating source. This heating rate depends on the gas density only through its linear dependence on the Alfv\’en speed, which goes as $n_e^{-1/2}$. We show that, scaled to appropriate values of cosmic ray energy density, cosmic ray heating can be significant. Furthermore, this heating is stable to perturbations. These results should also apply to warm ionized gas in other galaxies.

Subjects: Galaxy Astrophysics (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)
Cite as: arXiv:1301.4445 [astro-ph.GA]
(or arXiv:1301.4445v1 [astro-ph.GA] for this version)

Ultraviolet properties of Galactic globular clusters with GALEX E. Dalessandro, R. P. Schiavon, F. R. Ferraro, S. T. Sohn, B. Lanzoni, R. W. O’ Connell (Submitted on 18 Jan 2013)

We present ultraviolet (UV) integrated colors of 44 Galactic globular clusters (GGCs) observed with the Galaxy Evolution Explorer (GALEX) in both FUV and NUV bands. We find for the first time that GCs associated with the Sagittarius dwarf galaxy have (FUV-V) colors systematically redder than GGCs with the same metallicity. M31 GCs show almost the same UV colors as GGCs, while M87 are systematically bluer. We speculate about the presence of an interesting trend, suggesting that the UV color of GCs may be correlated with the mass of the host galaxy, in the sense that more massive galaxies possess bluer clusters.

Comments: 4 pages, 2 figures, proceedings of the meeting "Reading the book of globular clusters with the lens of stellar evolution", Rome, Nov. 26-28, 2012, to be published in Memorie della Societa’ Astronomica Italiana
Subjects: Galaxy Astrophysics (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:1301.4329 [astro-ph.GA]
(or arXiv:1301.4329v1 [astro-ph.GA] for this version)
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