Spitzer and Hubble Constraints on the Physical Properties of the z~7 Galaxy Strongly Lensed by Abell 2218

E. Egami , J. -P. Kneib (1) , G. H. Rieke , R. S. Ellis , J. Richard , J. Rigby , C. Papovich , D. Stark , M. R. Santos , J. -S. Huang , H. Dole , E. Le Floc'H , P. G. Perez-Gonzalez

1 LAM - Laboratoire d'Astrophysique de Marseille

We report the detection of a z~7 galaxy strongly lensed by the massive galaxy cluster Abell 2218 (z=0.175) at 3.6 and 4.5 um using the Spitzer Observatory and at 1.1 um using the Hubble Space Telescope. The new data indicate a refined photometric redshift in the range of 6.6-6.8 depending on the presence of Ly-alpha emission. The spectral energy distribution is consistent with having a significant Balmer break, suggesting that the galaxy is in the poststarburst stage with an age of at least ~50 Myr and quite possibly a few hundred Myr. This suggests the possibility that a mature stellar population is already in place at such a high redshift. Compared with typical Lyman break galaxies at z~3-4, the stellar mass is an order of magnitude smaller (~10^{9} Msun), but the specific star formation rate (star formation rate/M_{star}) is similarly large (> 10^{-9} yr^{-1}), indicating equally vigorous star-forming activity.

Mots clés: Cosmology: Observations; Galaxies: Evolution; Galaxies: Formation; Galaxies: High-Redshift; Cosmology: Gravitational Lensing

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

E. Egami, J. -P. Kneib, G. H. Rieke, R. S. Ellis, J. Richard, et al.. Spitzer and Hubble Constraints on the Physical Properties of the z~7 Galaxy Strongly Lensed by Abell 2218. The Astrophysical Journal, 2005, 618L, pp.5. ⟨10.1086/427550⟩. ⟨hal-00015080⟩