Discovery of a possibly old galaxy at $z=6.027$, multiply imaged by the massive cluster Abell 383

Дата и время публикации : 2011-02-24T21:00:02Z

Авторы публикации и институты :
Johan Richard (CRAL/Lyon, Dark Cosmology Centre)
Jean-Paul Kneib (LAM/OAMP)
Harald Ebeling (U.Hawaii)
Dan Stark (IoA, Cambdrige)
Eiichi Egami (Steward Observatory)
Andrew K. Fiedler (Steward Observatory)

Ссылка на журнал-издание: Ссылка на журнал-издание не найдена
Коментарии к cтатье: 6 pages, 3 figures, MNRAS in press, replaced with accepted version including minor comments
Первичная категория: astro-ph.CO

Все категории : astro-ph.CO

Краткий обзор статьи: We report the discovery of a unique $z=6.027$ galaxy, multiply imaged by the cluster Abell 383 and detected in new Hubble Space Telescope ACS and WFC3 imaging, as well as in Warm Spitzer observations. This galaxy was selected as a pair of i-dropouts; its suspected high redshift was confirmed by the measurement of a strong Lyman-alpha line in both images using Keck/DEIMOS. Combining Hubble and Spitzer photometry after correcting for contamination by line emission (estimated to be a small effect), we identify a strong Balmer break of 1.5 magnitudes. Taking into account the magnification factor of 11.4+/-1.9 (2.65+/-0.17 mag) for the brightest image, the unlensed AB magnitude for the source is 27.2+/-0.05 in the H band, corresponding to a 0.4 L* galaxy, and 25.7+/-0.08 at 3.6 um. The UV slope is consistent with beta~2.0, and from the rest-frame UV continuum we measure a current star formation rate of 2.4+/-1.1 Msol/yr. The unlensed half-light radius is measured to be 300 pc, from which we deduce a star-forming surface density of ~10 Msol/yr/kpc2. The Lyman-alpha emission is found to be extended over ~3" along the slit, corresponding to ~5 kpc in the source plane. This can be explained by the presence of a much larger envelope of neutral hydrogen around the star-forming region. Finally, fitting the spectral energy distribution using 7 photometric data points with simple SED models, we derive the following properties: very little reddening, an inferred stellar mass of M*=6e9 Msol, and an inferred age of ~800 Myrs (corresponding to a redshift of formation of ~18). The star-formation rate of this object was likely much stronger in the past than at the time of observation, suggesting that we may be missing a fraction of galaxies at z~6 which have already faded in rest-frame UV wavelengths.

Category: Physics