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Star Formation Rates in Lyman Break Galaxies: Radio Stacking of LBGs in the COSMOS Field and the Sub-μJy Radio Source Population

Carilli, C. L. and Lee, Nicholas and Capak, P. and Schinnerer, E. and Lee, K.-S. and McCraken, H. and Yun, M. S. and Scoville, N. and Smolčić, V. and Giavalisco, M. and Datta, A. and Taniguchi, Y. and Urry, Megan C. (2008) Star Formation Rates in Lyman Break Galaxies: Radio Stacking of LBGs in the COSMOS Field and the Sub-μJy Radio Source Population. Astrophysical Journal, 689 (2). pp. 883-888. ISSN 0004-637X. doi:10.1086/592319.

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We present an analysis of the radio properties of large samples of Lyman break galaxies (LBGs) at z ~ 3, 4, and 5 from the COSMOS field. The median stacking analysis yields a statistical detection of the z ~ 3 LBGs (U-band dropouts), with a 1.4 GHz flux density of 0:90 ± 0:21 µJy. The stacked emission is unresolved, with a size <1, or a physical size <8 kpc. The total star formation rate implied by this radio luminosity is 31 ± 7Mסּ yr^(-1), based on the radio-FIR correlation in low-redshift star-forming galaxies. The star formation rate derived from a similar analysis of the UV luminosities is 17 Mסּ yr^(-1), without any correction for UV dust attenuation. The simplest conclusion is that the dust attenuation factor is 1.8 at UV wavelengths. However, this factor is considerably smaller than the standard attenuation factor of ~5, normally assumed for LBGs. We discuss potential reasons for this discrepancy, including the possibility that the dust attenuation factor at z ≥ 3 is smaller than at lower redshifts. Conversely, the radio luminosity for a given star formation rate may be systematically lower at very high redshift. Two possible causes for a suppressed radio luminosity are (1) increased inverse Compton cooling of the relativistic electron population due to scattering off the increasing CMB at high redshift or (2) cosmic-ray diffusion from systematically smaller galaxies. The radio detections of individual sources are consistent with a radio-loud AGN fraction of 0.3%. One source is identified as a very dusty, extreme starburst galaxy (a ‘‘submillimeter galaxy’’)

Item Type:Article
Related URLs:
URLURL TypeDescription
Carilli, C. L.0000-0001-6647-3861
Capak, P.0000-0003-3578-6843
Schinnerer, E.0000-0002-3933-7677
McCraken, H.0000-0002-9489-7765
Yun, M. S.0000-0001-7095-7543
Scoville, N.0000-0002-0438-3323
Smolčić, V.0000-0002-3893-8614
Giavalisco, M.0000-0002-7831-8751
Taniguchi, Y.0000-0003-2247-3741
Urry, Megan C.0000-0002-0745-9792
Additional Information:© 2008. The American Astronomical Society. Print publication: Issue 2 (2008 December 20). Received 2008 April 21; accepted 2008 August 1. The HST COSMOS Treasury program was supported through NASA grant HST-GO-09822. We gratefully acknowledge the contributions of the entire COSMOS collaboration consisting of more than 70 scientists. More information on the COSMOS survey is available at C. C. thanks the Max-Planck-Gesellschaft and the Humboldt-Stiftung for support through the Max-Planck-Forschungspreis. We thank the referee for helpful comments. Based on observations in the COSMOS Legacy Survey including those taken on the HST, Keck, NRAO-VLA, Subaru, KPNO 4 m, CTIO 4 m, and CFHT 3.6 m. The Very Large Array of the National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Group:COSMOS, Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Subject Keywords:galaxies: evolution; galaxies: formation; surveys
Issue or Number:2
Record Number:CaltechAUTHORS:20090409-093614140
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13901
Deposited By: Ruth Sustaita
Deposited On:17 Jul 2009 21:52
Last Modified:08 Nov 2021 22:41

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