Mid-Infrared Spectroscopy of High Redshift Submillimeter Galaxies: First Results
Blain, Andrew W.
Alexander, Dave M.
Chapman, Scott C.
Ivison, Rob J.
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We present mid-infrared spectra of 5 submillimeter galaxies at z=0.65-2.38 taken with the Spitzer Space Telescope. Four of these sources, at z<1.5, have strong PAH features and their composite spectrum is well fitted by an M82-like spectrum with an additional power-law component consistent with that expected from AGN activity. Based on a comparison of the 7.7-micron PAH equivalent width and the PAH-to-infrared luminosity ratio of these galaxies with local templates, we conclude that these galaxies host both star-formation and AGN activity, with star-formation dominating the bolometric luminosity. The source at z=2.38 displays a Mrk231-type broad feature at restframe ~8 micron that does not conform to the typical 7.7/8.6 micron PAH complex in starburst galaxies, suggesting a more substantial AGN contribution.
Menéndez-Delmestre, Karín, Andrew W. Blain, Dave M. Alexander, Ian Smail, et al. 2007. "Mid-Infrared Spectroscopy of High Redshift Submillimeter Galaxies: First Results." The Astrophysical Journal 655(2): 65-L68