Issue |
A&A
Volume 533, September 2011
|
|
---|---|---|
Article Number | A119 | |
Number of page(s) | 26 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/201117239 | |
Published online | 13 September 2011 |
GOODS–Herschel: an infrared main sequence for star-forming galaxies⋆
1
Laboratoire AIM-Paris-Saclay, CEA/DSM/Irfu, CNRS, Université Paris
Diderot,
Saclay, pt courrier 131,
91191
Gif-sur-Yvette,
France
e-mail: delbaz@cea.fr
2
National Optical Astronomy Observatory,
950 North Cherry
Avenue, Tucson,
AZ
85719,
USA
3
Department of Physics and Institute of Theoretical &
Computational Physics, University of Crete, 71003
Heraklion,
Greece
4
Max-Planck-Institut für Extraterrestrische Physik (MPE),
Postfach 1312,
85741, Garching,
Germany
5
Institut d’Astrophysique de Paris, UMR 7095, CNRS,
UPMC Univ. Paris 06, 98bis
boulevard Arago, 75014
Paris,
France
6
Spitzer Science Center, California Institute of Technology,
Pasadena,
CA
91125,
USA
7
IESL/Foundation for Research and Technology, Hellas, 71110,
Heraklion, Greece and Chercheur Associé, Observatoire de Paris,
75014
Paris,
France
8
Herschel Science Centre, European Space Astronomy Centre,
Villanueva de la Cañada, 28691
Madrid,
Spain
9
Astronomy Department, Universidad de Concepción,
Casilla 160-C, Concepción, Chile
10
IPAC, California Institute of Technology,
Pasadena,
CA, 91125, USA
11
Department of Physics and Astronomy, Durham
University, South
Road, Durham,
DH1 3LE,
UK
12
Laboratoire d’Astrophysique de Marseille, OAMP, Université
Aix-Marseille, CNRS, 38 rue
Frédéric Joliot-Curie, 13388
Marseille Cedex 13,
France
13
INAF – Osservatorio Astronomico di Bologna, via Ranzani 1,
40127
Bologna,
Italy
14
UK Astronomy Technology Centre, Royal Observatory,
Blackford Hill,
Edinburgh
EH9 3HJ,
UK
15
Institute for Astronomy, University of Edinburgh, Royal
Observatory, Blackford
Hill, Edinburgh
EH9 3HJ,
UK
16
Steward Observatory, University of Arizona,
933 North Cherry
Avenue, Tucson,
AZ
85721,
USA
17
Institute for Astronomy, University of Hawaii,
Honolulu,
HI
96822,
USA
18
Canada-France-Hawaii Telescope, Kamuela, HI
96743,
USA
19
Department of Astronomy, University of
Massachusetts, Amherst,
MA
01003,
USA
20
Department of Physics & Astronomy, University of
British Columbia, 6224 Agricultural
Road, Vancouver, BC
V6T 1Z1,
Canada
21
Institut d’Astrophysique Spatiale (IAS), bâtiment 121, Université
Paris-Sud 11 and CNRS (UMR 8617), 91405
Orsay,
France
22
Jet Propulsion Laboratory, California Institute of
Technology, 4800 Oak Grove
Drive, Pasadena,
CA
91109,
USA
23
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD
21228,
USA
24
National Radio Astronomy Observatory, PO Box 2, Green Bank,
WV24944, USA
25
Department of Physics and Astronomy, Texas A&M
University, College
Station, TX
77845-4242,
USA
26
George P. and Cynthia Woods Mitchell Institute for Fundamental
Physics and Astronomy, Texas A&M University, College Station, TX
77845-4242,
USA
Received:
11
May
2011
Accepted:
3
August
2011
We present the deepest 100 to 500 μm far-infrared observations obtained with the Herschel Space Observatory as part of the GOODS-Herschel key program, and examine the infrared (IR) 3–500 μm spectral energy distributions (SEDs) of galaxies at 0 < z < 2.5, supplemented by a local reference sample from IRAS, ISO, Spitzer, and AKARI data. We determine the projected star formation densities of local galaxies from their radio and mid-IR continuum sizes.
We find that the ratio of total IR luminosity to rest-frame 8 μm luminosity, IR8 (≡ LIRtot), follows a Gaussian distribution centered on IR8 = 4 (σ = 1.6) and defines an IR main sequence for star-forming galaxies independent of redshift and luminosity. Outliers from this main sequence produce a tail skewed toward higher values of IR8. This minority population (<20%) is shown to consist of starbursts with compact projected star formation densities. IR8 can be used to separate galaxies with normal and extended modes of star formation from compact starbursts with high–IR8, high projected IR surface brightness (ΣIR > 3 × 1010 L⊙ kpc-2) and a high specific star formation rate (i.e., starbursts). The rest-frame, UV-2700 Å size of these distant starbursts is typically half that of main sequence galaxies, supporting the correlation between star formation density and starburst activity that is measured for the local sample.
Locally, luminous and ultraluminous IR galaxies, (U)LIRGs (LIRtot), are systematically in the starburst mode, whereas most distant (U)LIRGs form stars in the “normal” main sequence mode. This confusion between two modes of star formation is the cause of the so-called “mid-IR excess” population of galaxies found at z > 1.5 by previous studies. Main sequence galaxies have strong polycyclic aromatic hydrocarbon (PAH) emission line features, a broad far-IR bump resulting from a combination of dust temperatures (Tdust ~ 15–50 K), and an effective Tdust ~ 31 K, as derived from the peak wavelength of their infrared SED. Galaxies in the starburst regime instead exhibit weak PAH equivalent widths and a sharper far-IR bump with an effective Tdust ~ 40 K. Finally, we present evidence that the mid-to-far IR emission of X-ray active galactic nuclei (AGN) is predominantly produced by star formation and that candidate dusty AGNs with a power-law emission in the mid-IR systematically occur in compact, dusty starbursts. After correcting for the effect of starbursts on IR8, we identify new candidates for extremely obscured AGNs.
Key words: galaxies: active / infrared: galaxies / galaxies: evolution / galaxies: starburst
© ESO, 2011
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