Monday 11/26/2012

Title: Integrated Spectroscopy of the Herschel Reference Survey. The spectral line properties of a volume-limited, K-band selected sample of nearby galaxies
Authors: Boselli, A.; Hughes, T.; Cortese, L.; Gavazzi, G.; Buat, V.
Publication: eprint arXiv:1211.5262
Publication Date: 11/2012
Origin: ARXIV
Keywords: Astrophysics – Cosmology and Extragalactic Astrophysics
Comment: Accepted for publication on A&A; The full set of data (tables and images) are available on the dedicated database:
Bibliographic Code: 2012arXiv1211.5262B


We present long-slit integrated spectroscopy of 238 late-type galaxies belonging to the Herschel Reference Survey, a volume limited sample representative of the nearby universe. This sample has a unique legacy value since ideally defined for any statistical study of the multifrequency properties of galaxies spanning a large range in morphological type and luminosity. The spectroscopic observations cover the spectral range 3600-6900 A at a resolution R ~ 1000 and are thus suitable for separating the underlying absorption from the emission of the Hbeta line as well as the two [NII] lines from the Halpha emission. We measure the fluxes and the equivalent widths of the strongest emission lines ([OII], Hbeta, [OIII], [NII], Halpha, and [SII]). The data are used to study the distribution of the equivalent width of all the emission lines, of the Balmer decrement C(Hbeta) and of the observed underlying Balmer absorption under Hbeta in this sample. Combining these new spectroscopic data with those available at other frequencies, we also study the dependence of C(Hbeta) and E.W.Hbeta_{abs} on morphological type, stellar mass and stellar surface density, star formation rate, birthrate parameter and metallicity in galaxies belonging to different environments (fields vs. Virgo). The distribution of the equivalent width of all the emission lines, of C(Hbeta) and E.W.Hbeta_{abs} are systematically different in cluster and field galaxies. The Balmer decrement increases with stellar mass, stellar surface density, metallicity and star formation rate of the observed galaxies, while it is unexpectedly almost independent from the column density of the atomic and molecular gas. The dependence of C(Hbeta) on stellar mass is steeper than that previously found in other works. The underlying Balmer absorption does not significantly change with any of these physical parameters.

Title: Extended Hot Halos Around Isolated Galaxies Observed in the ROSAT All-Sky Survey
Authors: Anderson, Michael E.; Bregman, Joel N.; Dai, Xinyu
Publication: eprint arXiv:1211.5140
Publication Date: 11/2012
Origin: ARXIV
Keywords: Astrophysics – Cosmology and Extragalactic Astrophysics
Comment: 23 pages, 21 figures, 4 tables. Accepted for publication in ApJ
Bibliographic Code: 2012arXiv1211.5140A


We place general constraints on the luminosity and mass of hot X-ray emitting gas residing in extended "hot halos" around nearby massive galaxies. We examine stacked images of 2165 galaxies from the 2MASS Very Isolated Galaxy Catalog (2MVIG), as well as subsets of this sample based on galaxy morphology and K-band luminosity. We detect X-ray emission at high confidence (ranging up to nearly 10\sigma) for each subsample of galaxies. The average L_X within 50 kpc is 1.0\pm0.1 (statistical) \pm0.2 (systematic) x10^40 erg/s, although the early-type galaxies are more than twice as luminous as the late-type galaxies. Using a spatial analysis, we also find evidence for extended emission around five out of seven subsamples (the full sample, the luminous galaxies, early-type galaxies, luminous late-type galaxies, and luminous early-type galaxies) at 92.7%, 99.3%, 89.3%, 98.7%, and 92.1% confidence, respectively. Several additional lines of evidence also support this conclusion and suggest that about 1/2 of the total emission is extended, and about 1/3 of the extended emission comes from hot gas. For the sample of luminous galaxies, which has the strongest evidence for extended emission, the average hot gas mass is 4×10^9 Msun within 50 kpc and the implied accretion rate is 0.4 Msun/yr.

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