A candels WFC3 grism study of emission-line galaxies at z ∼ 2: A mix of nuclear activity and low-metallicity star formation

Jonathan R. Trump, Benjamin J. Weiner, Claudia Scarlata, Dale D. Kocevski, Eric F. Bell, Elizabeth J. McGrath, David C. Koo, S. M. Faber, Elise S. Laird, Mark Mozena, Cyprian Rangel, Renbin Yan, Hassen Yesuf, Hakim Atek, Mark Dickinson, Jennifer L. Donley, James S. Dunlop, Henry C. Ferguson, Steven L. Finkelstein, Norman A. GroginNimish P. Hathi, Stéphanie Juneau, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Kirpal Nandra, Jeffrey A. Newman, Steven A. Rodney, Amber N. Straughn, Harry I. Teplitz

Research output: Contribution to journalArticlepeer-review

43 Scopus citations

Abstract

We present Hubble Space Telescope Wide Field Camera 3 (WFC3) slitless grism spectroscopy of 28 emission-line galaxies at z 2, in the GOODS-S region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey. The high sensitivity of these grism observations, with >1σ detections of emission lines to f > 2.5 × 10-18ergs-1cm -2, means that the galaxies in the sample are typically 7 times less massive (median M * = 109.5 M than previously studied z 2 emission-line galaxies. Despite their lower mass, the galaxies have [O III]/Hβ ratios which are very similar to previously studied z 2 galaxies and much higher than the typical emission-line ratios of local galaxies. The WFC3 grism allows for unique studies of spatial gradients in emission lines, and we stack the two-dimensional spectra of the galaxies for this purpose. In the stacked data the [O III] emission line is more spatially concentrated than the Hβ emission line with 98.1% confidence. We additionally stack the X-ray data (all sources are individually undetected), and find that the average L [O III]/L 0.5-10 keV ratio is intermediate between typical z 0 obscured active galaxies and star-forming galaxies. Together the compactness of the stacked [O III] spatial profile and the stacked X-ray data suggest that at least some of these low-mass, low-metallicity galaxies harbor weak active galactic nuclei.

Original languageEnglish (US)
Article number144
JournalAstrophysical Journal
Volume743
Issue number2
DOIs
StatePublished - Dec 20 2011

Keywords

  • galaxies: abundances
  • galaxies: active
  • galaxies: evolution
  • quasars: emission lines

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