Polycyclic Aromatic Hydrocarbon and Mid-Infrared Continuum Emission in a z > 4 Submillimeter Galaxy

Author(s)
Dominik A. Riechers, Alexandra Pope, Emanuele Daddi, Helmut Dannerbauer, L. Armus, Chris Carilli, F Walter, J. A. Hodge, Ranga-Ram Chary, Glenn Morrison, Mark Dickinson, David Elbaz
Abstract

We report the detection of 6.2 μm polycyclic aromatic hydrocarbon (PAH) and rest-frame 4-7 μm continuum emission in the z = 4.055 submillimeter galaxy GN20, using the Infrared Spectrograph on board the Spitzer Space Telescope. This represents the first detection of PAH emission at z > 4. The strength of the PAH emission feature is consistent with a very high star formation rate of ∼1600 M

odot; yr

-1. We find that this intense starburst powers at least ∼1/3 of the faint underlying 6 μm continuum emission, with an additional, significant (and perhaps dominant) contribution due to a power-law-like hot dust source, which we interpret to likely be a faint, dust-obscured active galactic nucleus (AGN). The inferred 6 μm AGN continuum luminosity is consistent with a sensitive upper limit on the hard X-ray emission as measured by the Chandra X-Ray Observatory if the previously undetected AGN is Compton-thick. This is in agreement with the finding at optical/infrared wavelengths that the galaxy and its nucleus are heavily dust-obscured. Despite the strong power-law component enhancing the mid-infrared continuum emission, the intense starburst associated with the photon-dominated regions that give rise to the PAH emission appears to dominate the total energy output in the infrared. GN20 is one of the most luminous starburst galaxies known at any redshift, embedded in a rich protocluster of star-forming galaxies. This investigation provides an improved understanding of the energy sources that power such exceptional systems, which represent the extreme end of massive galaxy formation at early cosmic times.

Organisation(s)
Department of Astrophysics
External organisation(s)
University of Massachusetts, Amherst, Université Paris VII - Paris-Diderot, Cornell University, California Institute of Technology (Caltech), Max-Planck-Institut für Astronomie, Canada-France-Hawaii Telescope, National Radio Astronomy Observatory Socorro, University of Hawaii, National Optical Astronomy Observatory, Tucson
Journal
The Astrophysical Journal
Volume
786
No. of pages
7
ISSN
0004-637X
DOI
https://doi.org/10.1088/0004-637X/786/1/31
Publication date
05-2014
Peer reviewed
Yes
Austrian Fields of Science 2012
103003 Astronomy, 103004 Astrophysics
Keywords
ASJC Scopus subject areas
Astronomy and Astrophysics, Space and Planetary Science
Portal url
https://ucrisportal.univie.ac.at/en/publications/ba8093af-aa98-4d15-b288-6bf52b0e1aa9