Redshifts of emission-line objects in the hubble ultra deep field

Chun Xu, Norbert Pirzkal, Sangeeta Malhotra, James E. Rhoads, Bahram Mobasher, Emanuele Daddi, Caryl Gronwall, Nimish P. Hathi, Nino Panagia, Henry C. Ferguson, Anton M. Koekemoer, Martin Kümmel, Leonidas A. Moustakas, Anna Pasquali, Sperello Di Serego Alighieri, Joel Vernet, Jeremy R. Walsh, Rogier Windhorst, Haojing Yan

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


We present redshifts for 115 emission-line objects in the Hubble Ultra Deep Field identified through the Grism ACS Program for Extragalactic Science (GRAPES) project using the slitless grism spectroscopy mode of the Advanced Camera for Surveys on the Hubble Space Telescope (HST). The sample was selected by an emission-line search on all extracted one-dimensional GRAPES spectra. We identify the emission lines using line wavelength ratios where multiple lines are detected in the grism wavelength range (5800 Å ≤ λ≤ 9600 Å), and using photometric redshift information where multiple lines are unavailable. We then derive redshifts using the identified lines. Our redshifts are accurate to δz ≈ 0.009, based on both statistical uncertainty estimates and comparison with published ground-based spectra. Over 40% of our sample is fainter than typical magnitude limits for ground-based spectroscopy (with Z'AB > 25 mag). Such emission lines would likely remain undiscovered without our deep survey. The emission-line objects fall into three categories: (1) most are low- to moderate-redshift galaxies (0 ≤ z ≤ 2), including many actively star-forming galaxies with strong H II regions; (2) nine are high-redshift (4 ≤ z < 7) Lyα emitters; and (3) at least three are candidate active galactic nuclei.

Original languageEnglish (US)
Pages (from-to)169-178
Number of pages10
JournalAstronomical Journal
Issue number1
StatePublished - Jul 2007

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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