POLYCYCLIC AROMATIC HYDROCARBON AND MID-INFRARED CONTINUUM EMISSION IN A z > 4 SUBMILLIMETER GALAXY

We report the detection of 6.2 [mu]m polycyclic aromatic hydrocarbon (PAH) and rest-frame 4-7 [mu]m 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. Th...

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Bibliographic Details
Published in:The Astrophysical journal 2014-05, Vol.786 (1), p.1-7
Main Authors: Riechers, Dominik A, Pope, Alexandra, Daddi, Emanuele, Armus, Lee, Carilli, Christopher L, Walter, Fabian, Hodge, Jacqueline, Chary, Ranga-Ram, Morrison, Glenn E, Dickinson, Mark, Dannerbauer, Helmut, Elbaz, David
Format: Article
Language:English
Subjects:
Active galactic nuclei
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Continuums
COSMOLOGY
DETECTION
DUSTS
EMISSION
ENERGY SOURCES
GALAXIES
HARD X RADIATION
Infrared
LUMINOSITY
Nuclear power generation
PHOTONS
Polyallylamine hydrochloride
POLYCYCLIC AROMATIC HYDROCARBONS
RED SHIFT
SPACE
STARS
TELESCOPES
X-rays
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Summary:We report the detection of 6.2 [mu]m polycyclic aromatic hydrocarbon (PAH) and rest-frame 4-7 [mu]m 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 sub([middot in circle]) yr super(-1). We find that this intense starburst powers at least ~1/3 of the faint underlying 6 [mu]m 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 [mu]m 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.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/786/1/31