Volume 518, July-August 2010
Herschel: the first science highlights
|Number of page(s)||7|
|Published online||16 July 2010|
Letter to the Editor
Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach 1312, 85741 Garching, Germany e-mail: email@example.com
2 Herschel Science Centre, ESAC, Villanueva de la Cañada, 28691 Madrid, Spain
3 Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot, IRFU/Service d'Astrophysique, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
4 ESO, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
5 INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
6 Instituto de Astrofísica de Canarias, 38205 La Laguna, Spain
7 Departamento de Astrofísica, Universidad de La Laguna, Spain
8 Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
9 INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
10 INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Italy
11 Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 3, 35122 Padova, Italy
Accepted: 21 April 2010
The constituents of the cosmic IR background (CIB) are studied at its peak wavelengths (100 and 160 μm) by exploiting Herschel/PACS observations of the GOODS-N, Lockman Hole, and COSMOS fields in the PACS evolutionary probe (PEP) guaranteed-time survey. The GOODS-N data reach 3σ depths of ~3.0 mJy at 100 μm and ~5.7 mJy at 160 μm. At these levels, source densities are 40 and 18 beams/source, respectively, thus hitting the confusion limit at 160 μm. Differential number counts extend from a few mJy up to 100-200 mJy, and are approximated as a double power law, with the break lying between 5 and 10 mJy. The available ancillary information allows us to split number counts into redshift bins. At z ≤ 0.5 we isolate a class of luminous sources (LIR ~ 1011 ), whose SEDs resemble late-spiral galaxies, peaking at ~130 μm restframe and significantly colder than what is expected on the basis of pre-Herschel models. By integrating number counts over the whole covered flux range, we obtain a surface brightness of 6.36±1.67 and 6.58±1.62 [ nW m-2 sr-1] at 100 and 160 μm, resolving ~45% and ~52% of the CIB, respectively. When stacking 24 μm sources, the inferred CIB lies within 1.1σ and 0.5σ from direct measurements in the two bands, and fractions increase to 50% and 75%. Most of this resolved CIB fraction was radiated at z ≤ 1.0, with 160 μm sources found at higher redshift than 100 μm ones.
Key words: infrared: diffuse background / infrared: galaxies / cosmic background radiation / galaxies: statistics / galaxies: evolution
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Table 1 and Appendix A are only available in electronic form at http://www.aanda.org
© ESO, 2010
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