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The optical spectra of Spitzer 24 micron galaxies in the COSMOS field: II. Faint infrared sources in the zCOSMOS-bright 10k catalogue | | K. I. Caputi
; S. J. Lilly
; H. Aussel
; E. Le Floc'h
; D. Sanders
; C. Maier
; D. Frayer
; C. M. Carollo
; T. Contini
; J.-P. Kneib
; O. Le Fevre
; V. Mainieri
; A. Renzini
; M. Scodeggio
; N. Scoville
; G. Zamorani
; S. Bardelli
; M. Bolzonella
; A. Bongiorno
; G. Coppa
; O. Cucciati
; S. de la Torre
; L. de Ravel
; P. Franzetti
; B. Garilli
; O. Ilbert
; A. Iovino
; P. Kampczyk
; J. Kartaltepe
; C. Knobel
; K. Kovac
; F. Lamareille
; J.-F. Le Borgne
; V. Le Brun
; M. Mignoli
; Y. Peng
; E. Perez-Montero
; E. Ricciardelli
; M. Salvato
; J. Silverman
; J. Surace
; M. Tanaka
; L. Tasca
; L. Tresse
; D. Vergani
; E. Zucca
; U. Abbas
; D. Bottini
; P. Capak
; A. Cappi
; P. Cassata
; A. Cimatti
; M. Elvis
; G. Hasinger
; A. M. Koekemoer
; A. Leauthaud
; D. Maccagni
; C. Marinoni
; H. McCracken
; P. Memeo
; B. Meneux
; P. Oesch
; R. Pello
; C. Porciani
; L. Pozzetti
; R. Scaramella
; C. Scarlata
; D. Schiminovich
; Y. Taniguchi
; M. Zamojski
; | | Date: |
30 Oct 2009 | | Abstract: | We have used the zCOSMOS-bright 10k sample to identify 3244 Spitzer/MIPS
24-micron-selected galaxies with 0.06< S(24um)< 0.50 mJy and I(AB)<22.5, over
1.5 deg^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 around
80% of our infrared (IR) sources, within the error bars. For up to 16% of
objects, instead, the Halpha/Hbeta ratios are too high for their IR/UV
attenuations, which is probably a consequence of inhomogenous 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 ~22% 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 Hdelta
equivalent-width versus Dn(4000) diagram for 1722 faint and bright 24um
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 ~40% of the less luminous sources. Our results suggest a
transition in the possible modes of star formation at total IR luminosities
L(TIR)=(3 +/-2)x10^11 Lsun. | | Source: | arXiv, 0910.5824 | | Services: | Forum | Review | PDF | Favorites | |
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