An overdensity of galaxies at z=5.9 +/-0.2 in the Ultra Deep Field confirmed using the ACS grism

Malhotra, S
Rhoads, J E
Pirzkal, N
Haiman, Z
Xu, C
Daddi, E
Yan, H
Bergeron, L E
Wang, J
Ferguson, H A
Koekemoer, A M
Moustakas, L A
Panagia, N
Stiavelli, M
Walsh, J
Windhorst, R A
Pasquali, A
Gronwall, C
Kümmel, M
Alighieri, S S

Publication date

January 2005

Abstract

We present grism spectra taken with the Advanced Camera for Surveys to identify 29 red sources with (i'-z') > 0.9 in the Hubble Ultra Deep Field (HUDF). Of these 23 are found to be galaxies at redshifts between z=5.4 and 6.7, identified by the break at 1216 angstrom due to IGM absorption; two are late type dwarf stars with red colors; and four are galaxies with colors and spectral shape similar to dust reddened or old galaxies at redshifts z~1-2. This constitutes the largest uniform, flux-limited sample of spectroscopically confirmed galaxies at such faint fluxes z'<27.5. Many are also among the most distant spectroscopically confirmed galaxies (at redshifts up to z=6.7). We find a significant overdensity of galaxies at redshifts z=5.9 +/- ...