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Published January 1, 2008 | Published
Journal Article Open

The faint-end slopes of galaxy luminosity functions in the COSMOS field


We examine the faint-end slope of the rest-frame V-band luminosity function (LF), with respect to galaxy spectral type, of field galaxies with redshift z < 0.5, using a sample of 80,820 galaxies with photometric redshifts in the 2 deg^2 Cosmic Evolution Survey (COSMOS) field. For all galaxy spectral types combined, the LF slope ranges from –1.24 to –1.12, from the lowest redshift bin to the highest. In the lowest redshift bin (0.02 < z < 0.1), where the magnitude limit is MV ≾ − 13, the slope ranges from α ~ − 1.1 for galaxies with early-type spectral energy distributions (SEDs) to α ~ − 1.9 for galaxies with low-extinction starburst SEDs. In each galaxy SED category (early-type, Sbc, Scd+Irr, and starburst), the faint-end slopes grow shallower with increasing redshift; in the highest redshift bin (0.4 < z < 0.5), α ~ − 0.5 and –1.3 for early types and starbursts, respectively. The steepness of α at lower redshifts could be qualitatively explained by LF evolution, or by large numbers of faint dwarf galaxies, perhaps of low surface brightness, that are not detected at higher redshifts.

Additional Information

© 2008 The American Astronomical Society. Received 2006 August 11; accepted 2007 August 9. The HST COSMOS Treasury program was supported through NASA grant HST-GO-09822. We wish to thank Tony Roman, Denise Taylor, and David Soderblom for their assistance in the planning and scheduling of the extensive COSMOS observations. We gratefully acknowledge the contributions of the entire COSMOS collaboration, which contains more than 70 scientists. More information on the COSMOS survey is available at http:// www.astro.caltech.edu/~cosmos. It is a pleasure to acknowledge the excellent services provided by the NASA IPAC/IRSA staff (Anastasia Laity, Anastasia Alexov, Bruce Berriman, and John Good) in providing online archive and server capabilities for the COSMOS data sets. The COSMOS Science meeting in 2005 May was supported in part by the NSF through grant OISE- 0456439. We thank Paris Bogdanos and James Cohen for image processing and data formatting assistance. C. Liu, T. Paglione, and S. Tribiano gratefully acknowledge support from a City University of New York CCIR grant, as well as the hospitality and support of the Hayden Planetarium and Department of Astrophysics at the American Museum of Natural History. Facilities: HST (ACS), Subaru, KPNO, CTIO, CFHT.

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