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

Autor(en)
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
Abstrakt

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(en)
Institut für Astrophysik
Externe Organisation(en)
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
Band
786
Anzahl der Seiten
7
ISSN
0004-637X
DOI
https://doi.org/10.1088/0004-637X/786/1/31
Publikationsdatum
05-2014
Peer-reviewed
Ja
ÖFOS 2012
103003 Astronomie, 103004 Astrophysik
Schlagwörter
ASJC Scopus Sachgebiete
Astronomy and Astrophysics, Space and Planetary Science
Link zum Portal
https://ucrisportal.univie.ac.at/de/publications/ba8093af-aa98-4d15-b288-6bf52b0e1aa9