THE OPTICAL SPECTRA OF SPITZER 24 mum GALAXIES IN THE COSMIC EVOLUTION SURVEY FIELD. II. FAINT INFRARED SOURCES IN THE zCOSMOS-BRIGHT 10k CATALOG

Journal Article · Sun Dec 20 00:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/707/2/1387· OSTI ID:21392556

Caputi, K I; Lilly, S J; Maier, C; Carollo, C M ^[1]; Aussel, H; Floc'h, E Le ^[2]; Sanders, D ^[3]; Frayer, D ^[4]; Contini, T ^[5]; Kneib, J -P; Le Fevre, O ^[6]; Mainieri, V ^[7]; Renzini, A ^[8]; Scodeggio, M ^[9]; Scoville, N ^[10]; Zamorani, G; Bardelli, S; Bolzonella, M; Coppa, G ^[11]; Bongiorno, A ^[12]

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1. Institute of Astronomy, Swiss Federal Institute of Technology (ETH), Wolfgang-Pauli-Strasse 27, CH-8093 Zuerich (Switzerland)
2. CEA/DSM-CNRS, Universite Paris Diderot, DAPNIA/SAp, Orme des Merisiers, 91191 Gif-sur-Yvette (France)
3. Institute for Astronomy, University of Hawaii, Honololu, HI (United States)
4. Spitzer Science Center, California Institute of Technology, Pasadena, CA (United States)
5. Laboratoire d'Astrophysique de Toulouse-Tarbes, Universite de Toulouse, 14 avenue Edouard Belin, Toulouse (France)
6. Laboratoire d'Astrophysique de Marseille, 38 rue Frederic Joliot-Curie, Marseille (France)
7. European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching (Germany)
8. Dipartimento di Astronomia, Universita di Padova, Padova (Italy)
9. INAF-IASF Milano, via E. Bassini 15, 20133 Milan (Italy)
10. California Institute of Technology, Pasadena, CA (United States)
11. INAF Osservatorio Astronomico di Bologna, Bologna (Italy)
12. Max Planck Institut fuer Extraterrestrische Physik, Garching (Germany)

We have used the zCOSMOS-bright 10k sample to identify 3244 Spitzer/MIPS 24 mum-selected galaxies with 0.06 mJy < S{sub 24{sub m}}u{sub m} approx< 0.50 mJy and I{sub AB} < 22.5, over 1.5 deg{sup 2} of the COSMOS field, and studied different spectral properties, depending on redshift. At 0.2 < z < 0.3, we found that different reddening laws of common use in the literature explain the dust extinction properties of approx80% of our infrared (IR) sources, within the error bars. For up to 16% of objects, instead, the Halpha lambda6563/Hbeta lambda4861 ratios are too high for their IR/UV attenuations, which is probably a consequence of inhomogeneous dust distributions. In only a few of our galaxies at 0.2 < z < 0.3, the IR emission could be mainly produced by dust heated by old rather than young stars. Besides, the line ratios of approx22% of our galaxies suggest that they might be star-formation/nuclear-activity composite systems. At 0.5 < z < 0.7, we estimated galaxy metallicities for 301 galaxies: at least 12% of them are securely below the upper-branch mass-metallicity trend, which is consistent with the local relation. Finally, we performed a combined analysis of the H{sub d}elta equivalent width versus D{sub n} (4000) diagram for 1722 faint and bright 24 mum galaxies at 0.6 < z < 1.0, spanning two decades in mid-IR luminosity. We found that, while secondary bursts of star formation are necessary to explain the position of the most luminous IR galaxies in that diagram, quiescent, exponentially declining star formation histories can well reproduce the spectral properties of approx40% of the less luminous sources. Our results suggest a transition in the possible modes of star formation at total IR luminosities L{sub TIR} approx (3 +- 2) x 10{sup 11} L{sub sun}.

• OSTI ID: 21392556
• Journal Information: Astrophysical Journal, Vol. 707, Issue 2; Other Information: DOI: 10.1088/0004-637X/707/2/1387; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABUNDANCE
ATTENUATION
CATALOGS
DUSTS
GALACTIC EVOLUTION
GALAXIES
LUMINOSITY
RED SHIFT
SPECTRA
STARS
UNIVERSE
DOCUMENT TYPES
EVOLUTION
OPTICAL PROPERTIES
PHYSICAL PROPERTIES