The AGN, Star-Forming, and Morphological Properties of Luminous IR-Bright-Optically-Faint Galaxies - Astrophysics > Cosmology and Nongalactic AstrophysicsReportar como inadecuado




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Abstract: We present the AGN, star-forming, and morphological properties of a sample of13 MIR-luminous f24 > 700uJy IR-bright-optically-faint galaxies IRBGs,f24-fR > 1000. While these z~2 sources were drawn from deep Chandra fieldswith >200 ks X-ray coverage, only 7 are formally detected in the X-ray and fourlack X-ray emission at even the 2 sigma level. Spitzer IRS spectra, however,confirm that all of the sources are AGN-dominated in the mid-IR, although halfhave detectable PAH emission responsible for ~25% of their mid-infrared fluxdensity. When combined with other samples, this indicates that at least 30-40%of luminous IRBGs have star-formation rates in the ULIRG range ~100-2000Msun-yr. X-ray hardness ratios and MIR to X-ray luminosity ratios indicatethat all members of the sample contain heavily X-ray obscured AGN, 80% of whichare candidates to be Compton-thick. Furthermore, the mean X-ray luminosity ofthe sample, log L2-10 keVergs-s=44.6, indicates that these IRBGs are Type 2QSOs, at least from the X-ray perspective. While those sources most heavilyobscured in the X-ray are also those most likely to display strong silicateabsorption in the mid-IR, silicate absorption does not always accompany X-rayobscuration. Finally, ~70% of the IRBGs are merger candidates, a rateconsistent with that of sub-mm galaxies SMGs, although SMGs appear to bephysically larger than IRBGs. These characteristics are consistent with theproposal that these objects represent a later, AGN-dominated, and more relaxedevolutionary stage following soon after the star-formation-dominated onerepresented by the SMGs.



Autor: J. L. Donley, G. H. Rieke, D. M. Alexander, E. Egami, P. G. Perez-Gonzalez

Fuente: https://arxiv.org/







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