An overdensity of galaxies at z=5.9 +/- 0.2 in the hubble ultra deep field confirmed using the ACS grism

作者：Malhotra S; Rhoads JE; Pirzkal N; Haiman Z; Xu C; Daddi E; Yan H; Bergeron LE; Wang J; Ferguson HC; Gronwall C^*; Koekemoer A; Kuemmel M; Moustakas LA; Panagia N; Pasquali A; Stiavelli M; Walsh J; Windhorst RA; Alighieri SD

来源：Astrophysical Journal, 2005, 626(2): 666-679.

DOI：10.1086/430047

• galaxies : evolution
• galaxies : formation
• galaxies : high-redshift
• galaxies : luminosity function
• mass function
• intergalactic medium

We present grism spectra taken with the Advanced Camera for Surveys ( ACS) to identify 29 red sources with (i(775) - z(850)) >= 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 intergalactic medium (IGM) absorption; two are late-type dwarf stars with red colors; and four are galaxies with colors and spectral shapes similar to dust-reddened or old galaxies at redshifts z approximate to 1-2. This constitutes the largest uniform, flux-limited sample of spectroscopically confirmed galaxies at such faint fluxes (z(850) <= 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 +/- 0.2. Nearly two-thirds of the galaxies in our sample (15/23) belong to this peak. Taking into account the selection function and the redshift sensitivity of the survey, we get a conservative overdensity of at least a factor of 2 along the line of sight. The galaxies found in this redshift peak are also localized in the plane of the sky in a nonrandom manner, occupying about half of the ACS chip. Thus the volume overdensity is a factor of 4. The star formation rate derived from detected sources in this overdense region is sufficient to reionize the local IGM.

• 出版日期2005-6-20
• 单位中国科学技术大学