Deep GALEX Imaging of the HST/COSMOS Field: A First Look at the Morphology of z~0.7 Star-forming Galaxies

M. A. Zamojski , David Schiminovich , Robert Michael Rich , B. Mobasher , A. M. Koekemoer , P. Capak , Y. Taniguchi , S. S. Sasaki (1) , H. J. Mccracken (2) , Y. Mellier (2, 3) , E. Bertin (4, 2) , H. Aussel , D. B. Sanders , O. Le Fevre (5) , O. Ilbert (5) , M. Salvato , D. J. Thompson , J. S. Kartaltepe , N. Scoville , Tom Barlow (6) , Karl Forster (6) , Peter Friedman (6) , Christopher Martin (6) , Patrick Morrisey , Susan Gale Neff , Mark Seibert , Todd Small , Ted Wyder , Luciana Bianchi (7) , José Donas (5) , Timothy M. Heckman (8) , Young-Wook Lee (9, 10) , Barry Madore (2, 5, 11) , Bruno Milliard (5) , Alex Szalay , B. Y. Welsh , S. K. Yi

1 LPS - Laboratoire de Physique Statistique de l'ENS
2 IAP - Institut d'Astrophysique de Paris
3 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
4 LABSAD - Laboratoire de Statistiques et Analyse des Données
5 LAM - Laboratoire d'Astrophysique de Marseille
6 CALTECH - California Institute of Technology
7 CAS - Center for Astrophysical Sciences [Baltimore]
8 Department of Physics and Astronomy [Baltimore]
9 POSTECH - Pohang University of Science and Technology
10 Center for Space Astrophysics [Seoul]
11 Observatories [Carnegie Institution]

We present a study of the morphological nature of redshift z~0.7 star-forming galaxies using a combination of HST/ACS, GALEX and ground-based images of the COSMOS field. Our sample consists of 8,146 galaxies, 5,777 of which are detected in the GALEX near-ultraviolet band down to a limiting magnitude of 25.5 (AB). We make use of the UV to estimate star formation rates, correcting for the effect of dust using the UV-slope, and compute, from the ACS F814W images, the C,A,S,G,M20 morphological parameters for all objects in our sample. We observe a morphological bimodality in the galaxy population and show that it has a strong correspondence with the FUV - g color bimodality. We conclude that UV-optical color predominantly evolves concurrently with morphology. We observe many of the most star-forming galaxies to have morphologies approaching that of early-type galaxies, and interpret this as evidence that strong starburst events are linked to bulge growth and constitute a process through which galaxies can be brought from the blue to the red sequence while simultaneously modifying their morphology accordingly. We conclude that the red sequence has continued growing at z~<0.7. We also observe z~0.7 galaxies to have physical properties similar to that of local galaxies, except for higher star formation rates. Whence we infer that the dimming of star-forming galaxies is responsible for most of the evolution in the star formation rate density of the Universe since that redshift, although our data are also consistent with a mild number evolution. [abridged]

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]

M. A. Zamojski, David Schiminovich, Robert Michael Rich, B. Mobasher, A. M. Koekemoer, et al.. Deep GALEX Imaging of the HST/COSMOS Field: A First Look at the Morphology of z~0.7 Star-forming Galaxies. 2007. ⟨hal-00131463⟩