Spectroscopic study of the HST/ACS pears emission-line galaxies

Lifang Xia, Sangeeta Malhotra, James Rhoads, Norbert Pirzkal, Zhenya Zheng, Gerhardt Meurer, Amber Straughn, Norman Grogin, David Floyd

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


We present spectroscopy of 76 emission-line galaxies (ELGs) in Chandra Deep Field South taken with the LDSS3 spectrograph on the Magellan Telescope. These galaxies are selected because they have emission lines with the Advanced Camera for Surveys (ACS) grism data in the Hubble Space Telescope Probing Evolution and Reionization Spectroscopically (PEARS) grism Survey. The ACS grism spectra cover the wavelength range 6000-9700 Å and most PEARS grism redshifts are based on a single emission line + photometric redshifts from broadband colors; the Magellan spectra cover a wavelength range from 4000 Å to 9000 Å and provide a check on redshifts derived from PEARS data.We find an accuracy of αz = 0.006 for the ACS grism redshifts with only one catastrophic outlier.We probe for active galactic nuclei (AGNs) in our sample via several different methods. In total, we find 7 AGNs and AGN candidates out of 76 galaxies. Two AGNs are identified from the X-ray full-band luminosity, LX-ray,FB > 1043 erg s-1, the line widths, and the power-law continuum spectra. Two unobscured faint AGN candidates are identified from the X-ray full-band luminosity LX-ray,FB ∼ 1041 erg s-1, the hardness ratio and the column density, and the emission-line and X-ray derived SFRs. Two candidates are classified based on the line ratio of [N ii]λ6584/Hα versus [Oiii]λ5007/Hβ(BPT diagram), which are between the empirical and theoretical demarcation curves, i.e., the transition region from star-forming galaxies to AGNs. One AGN candidate is identified from the high-ionization emission line He iiÅ4686.

Original languageEnglish (US)
JournalAstronomical Journal
Issue number2
StatePublished - Feb 2011


  • Galaxies: Star formation
  • Quasars: Emission lines
  • Techniques: Spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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