Tuesday 9/25/2012

GOODS-Herschel: Impact of Active Galactic Nuclei and Star Formation Activity on Infrared Spectral Energy Distributions at High Redshift

Authors: Allison Kirkpatrick, et al.
(Submitted on 21 Sep 2012)
Abstract: We explore the effects of active galactic nuclei (AGN) and star formation activity on the infrared (0.3-1000 microns) spectral energy distributions of luminous infrared galaxies from z = 0.5 to 4.0. We have compiled a large sample of 151 galaxies selected at 24 microns (S24 > 100 uJy) in the GOODS-N and ECDFS fields for which we have deep Spitzer IRS spectroscopy, allowing us to decompose the mid-IR spectrum into contributions from star formation and AGN activity. A significant portion (~25%) of our sample is dominated by an AGN in the mid-IR. Based on the mid-IR classification, we divide our full sample into four sub-samples: z~1 star-forming (SF) sources; z~2 SF sources; AGN with clear 9.7 micron silicate absorption; and AGN with featureless mid-IR spectra. From our large spectroscopic sample and wealth of multi-wavelength data, including deep Herschel imaging at 100, 160, 250, 350, and 500 microns, we use 95 galaxies with complete spectral coverage to create a composite spectral energy distribution (SED) for each sub-sample. We then fit a two-temperature component modified blackbody to the SEDs. We find that the IR SEDs have similar cold dust temperatures, regardless of the mid-IR power source, but display a marked difference in the warmer dust temperatures. We calculate the average effective temperature of the dust in each sub-sample and find a significant (~20 K) difference between the SF and AGN systems. We compare our composite SEDs to local templates and find that local templates do not accurately reproduce the mid-IR features and dust temperatures of our high redshift systems. High redshift IR luminous galaxies contain significantly more cool dust than their local counterparts. We find that a full suite of photometry spanning the IR peak is necessary to accurately account for the dominant dust temperature components in high redshift IR luminous galaxies.

Comments: Accepted for publication in ApJ. 24 pages, 11 figures. High resolution version of the figures, and composite SEDs presented in the paper, are available at this http URL
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1209.4902 [astro-ph.CO]

Radial Metallicity Distribution Breaks at Corotation Radius in Spiral GalaxiesAuthors: Sergio Scarano Jr, Jacques R. D. Lépine
(Submitted on 23 Sep 2012)
Abstract: We analyzed the relation between the corotation radii and the galactic radii at which breaks or changes of slope of the metallicity gradients occur in spiral galaxies. With this purpose we compiled the results from the literature on rotation curves, corotation radii and radial metallicity distributions of 27 galaxies, of which 16 were considered qualified to be studied in the context of this work. We re-scaled all references of each galaxy to a same framework in order to compare the results and to identify the radii where breaks and changes of slopes are found, when non-linear models fit the radial metallicities better than a linear model. In most galaxies we have found minima and breaks in radial metallicity near the corotation radius, revealing a significant correlation between these two radii, as it occurs in our Galaxy. The results are interpreted as a consequence of long-lived spiral structures, in which the star-formation rate depends on the distance to the corotation radius, producing secular effects in the observed radial metallicity distributions.

Comments: 20 pages, 5 figures, 4 tables. Accepted for publication in MNRAS. (MN-12-0359-MJ.R2)
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA)
Cite as: arXiv:1209.5031 [astro-ph.CO]
(or arXiv:1209.5031v1 [astro-ph.CO] for this version)

Complete Ionisation of the Neutral Gas in High Redshift Radio Galaxies and QuasarsAuthors: S. J. Curran, M. T. Whiting
(Submitted on 24 Sep 2012)
Abstract: Cool neutral gas provides the raw material for all star formation in the Universe, and yet, from a survey of the hosts of high redshift radio galaxies and quasars, we find a complete dearth of atomic (HI 21-cm) and molecular (OH, CO, HCO+ & HCN) absorption at redshifts z > 3. Upon a thorough analysis of the optical photometry, we find that all of our targets have ionising ultra-violet continuum luminosities of logL > 23 W/Hz. We therefore attribute this deficit to the traditional optical selection of targets biasing surveys towards the most ultra-violet luminous objects, where the intense radiation excites the neutral gas to the point where it cannot engage in star formation. However, this hypothesis does not explain why there is a critical luminosity, rather than a continuum where the detections gradually become fewer and fewer as the harshness of the radiation increases. We show that by placing a quasar within a galaxy of gas there is always a finite ultra-violet luminosity above which all of the gas is ionised. This demonstrates that these galaxies are probably devoid of star-forming material rather than this being at abundances below the sensitivity limits of current radio telescopes.

Comments: To appear in Molecular Gas, Dust and Star Formation in Galaxies. Proceedings IAU Symposium No. 292
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1209.5136 [astro-ph.CO]
(or arXiv:1209.5136v1 [astro-ph.CO] for this version)
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