A near-infrared excess in the continuum of high-redshift galaxies: a tracer of star formation and circumstellar disks?

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Title: A near-infrared excess in the continuum of high-redshift galaxies: a tracer of star formation and circumstellar disks?
Author(s): Mentuch, Erin; Abraham, Roberto G.; Glazebrook, Karl; McCarthy, Patrick J.; Yan, Haojing; O'Donnell, Daniel V.; Le Borgne, Damien; Savaglio, Sandra; Crampton, David; Murowinski, Richard; Juneau, Stephanie; Carlberg, R. G.; Jorgensen, Inger; Roth, Kathy; Chen, Hsiao-Wen; Marzke, Ronald O.
Abstract: A broad continuum excess in the near-infrared, peaking in the rest frame at 2-5 micron, is detected in a spectroscopic sample of 88 galaxies at 0.5<2.0 taken from the Gemini Deep Deep Survey. Line emission from polycyclic aromatic hydrocarbons (PAHs) at 3.3 micron alone cannot explain the excess, which can be fit by a spectral component consisting of a template of PAH emission lines superposed on a modified blackbody of temperature T~850 K. The luminosity ratio of this near-infrared excess emission relative to the galaxy's stellar emission at 3 micron is found to be related to the specific star formation rate of the galaxy, suggesting that the rest-frame J-L color can potentially be used as a sensitive and nearly extinction-free tracer of star-formation. The origin of the near-infrared excess is explored by examining similar excesses observed locally in massive star forming regions, reflection and planetary nebulae, post-AGB stars and in the galactic cirrus. We conclude that the most likely explanation for the 2-5 micron excess is the contribution from circumstellar disks around massive young stellar objects seen in the integrated light of high-redshift galaxies. Assuming circumstellar disks extend down to lower masses, as they do in our own Galaxy, the excess emission presents us with an exciting opportunity to measure the formation rate of planetary systems at earlier cosmic epochs, at a time when our own Solar System formed.
Publication type: Journal article
Research centre: Swinburne University of Technology. Faculty of Information and Communication Technologies. Centre for Astrophysics and Supercomputing
Source: Astrophysical Journal, Vol. 706, no. 2 (Dec 2009), pp. 1020-1035
Publication year: 2009
FOR Code(s): 0201 Astronomical and Space Sciences; 020103 Cosmology and Extragalactic Astronomy; 020104 Galactic Astronomy; 020110 Stellar Astronomy and Planetary Systems
Keyword(s): Circumstellar matter; Evolution; Galaxy formation; Infrared galaxies; Planetary systems; Protoplanetary disks; Stellar content
Publisher: Institute of Physics Publishing
ISSN: 0004-637X
Publisher URL: http://dx.doi.org/10.1088/0004-637X/706/2/1020
Copyright: Copyright © 2009 the American Astronomical Society. All rights reserved. Publisher does not officially support author/institution self-archiving of either the postprint (final, revised accepted draft) or published version of full text.
Peer reviewed