Monday, Feb. 8, 2013

Sorry it’s late. I thought I sent this out, but it was the hotter topics email.

Testing For Azimuthal Abundance Gradients In M101 Authors: Yanxia Li, Fabio Bresolin, Robert C. Kennicutt Jr
(Submitted on 1 Feb 2013)

Abstract: New optical spectra of 28 H II regions in the M101 disk have been obtained, yielding 10 new detections of the [O III]{\lambda}4363 auroral line. The oxygen abundance gradient measured from these data, combined with previous observations, displays a local scatter of 0.15+/-0.03 dex along an arc in the west side of the galaxy, compared with a smaller scatter of 0.08+/-0.01 dex in the rest of the disk. One of the H I I regions in our sample (H27) has a significantly lower oxygen abundance than surrounding nebulae at a similar galactocentric distance, while an additional, relatively nearby one (H128) was already known to have a high oxygen abundance for its position in the galaxy. These results represent marginal evidence for the existence of moderate deviations from chemical abundance homogeneity in the interstellar medium of M101. Using a variety of strong-line abundance indicators, we find no evidence for significant large-scale azimuthal variations of the oxygen abundance across the whole disk of the galaxy.

Comments: 16 pages, 13 figures, accepted for publication in The Astrophysical Journal
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1302.0094 [astro-ph.CO]
(or arXiv:1302.0094v1 [astro-ph.CO] for this version)

Role of AGNs in the Ultra-Luminous Infrared Galaxy phase since z ~ 3 Authors: Ming-Yi Lin, Sebastien Foucaud, Yasuhiro Hashimoto
(Submitted on 1 Feb 2013)

Abstract: In order to understand the mutual influence between active galactic nuclei (AGN) and star formation during the evolution of galaxies, we investigate 142 galaxies detected in both X-ray and 70{\mu}m observations in the COSMOS (Cosmic Evolution Survey) field. All of our data are obtained from archive, X-ray point source catalogs from Chandra and XMM-Newton observation; far-infrared 70{\mu}m point source catalog from Spitzer-MIPS observation. Although the IRAC colors of our samples indicate the existence of star formation, the ratio of rest frame 2-10 keV luminosity to total infrared luminosity (8-1000{\mu}m) shows that AGN predominates the spectral energy distribution (SED). We identify obscured AGN in these 70{\mu}m luminous galaxies as characterized by a larger hardness ratio. The higher X-ray obscuration fraction indicates an extra contribution from the star formation in the host galaxy in addition to the usual AGN dusty torus. If AGN feedback occurs in their host galaxies, the star formation must be quenched and dust in host galaxy will be dispersed. However, our temperature fitting shows there is no significant dust temperature enhancement in far-infrared wavelength, suggesting the thermal radiative feedback is absent from the AGN to the galaxy.

Comments: 12 pages, 7 figures and 3 Tables
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1302.0113 [astro-ph.CO]
(or arXiv:1302.0113v1 [astro-ph.CO] for this version)

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