Imaging and spectroscopy of damped Lyα quasi-stellar object absorption-line clouds

James D. Lowenthal, Craig J. Hogan, Richard F. Green, Bruce Woodgate, Adeline Caulet, Larry Brown, Jill Bechtold

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Abstract

We present the results of a multifaceted search for line emission from the vicinities of high-redshift quasi-stellar object (QSO) absorption-line clouds, most of them damped Lyα systems at z ≳ 2. Seven fields containing QSOs with known intervening damped Lyα absorbers were imaged with the GSFC Fabry-Perot Imager to search for diffuse redshifted Lyα. Apart from the one Lyα companion galaxy reported previously, no confirmed extended Lyα emission was detected down to 3 σ flux levels of around 3 x 10-17 ergs s-1 cm-2, corresponding to star formation rates ≲1 M yr-1, assuming case B recombination, a reasonable initial mass function, and negligible extinction by dust. One of the damped Lyα systems studied here, toward Q0836+113, has been reported to show faint, extended Lyα emission. While our Lyα images of that field are not sensitive enough to confirm the reported flux levels, we did detect and spectroscopically confirm redshifted [O II] λ3727 and continuum emission from a closer intervening system, a Mg II system at z = 0.788, at the same spatial position as the reported Lyα emission from the more distant object, and we suggest the possibility that all the observations of this field can be explained by the closer system alone. Six damped Lyα systems, including two that were imaged with the Fabry-Perot, were also imaged with two-dimensional long-slit CCD spectroscopy at ∼2 Å resolution in the core of the Lyα absorption line. No convincing Lyα emission was found from any of the systems, including Q0836+113, for which our sensitivity was again insufficient to confirm the previously reported extended Lyα emission. However, there is yet another independent claim of Lyα emission from that cloud, but spatially unresolved, in conflict with the report of extended emission; our observations do not reproduce the report of compact Lyα emission, which should have appeared at about the 7 σ level. Although observationally allowable quantities of dust in the damped Lyα clouds can in some cases quench Lyα flux by up to several orders of magnitude, several of the damped clouds studied here are arguably metal and dust poor, leading us to believe that our limits on Lyα emission generally constrain the star formation rates to be ≲10 M yr-1, comparable to normal Sc galaxies today. Whatever their exact nature, the damped Lyα clouds therefore appear not to be spectacular primeval galaxies seen in the act of forming a galaxy's worth of stars.

Original languageEnglish (US)
Pages (from-to)484-497
Number of pages14
JournalAstrophysical Journal
Volume451
Issue number2
StatePublished - Oct 1 1995

Keywords

  • Quasars: absorption lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Lowenthal, J. D., Hogan, C. J., Green, R. F., Woodgate, B., Caulet, A., Brown, L., & Bechtold, J. (1995). Imaging and spectroscopy of damped Lyα quasi-stellar object absorption-line clouds. Astrophysical Journal, 451(2), 484-497.