Detection of rest-frame optical lines from x-shooter spectroscopy of weak emission-line quasars

Richard M. Plotkin, Ohad Shemmer, Benny Trakhtenbrot, Scott F. Anderson, W. N. Brandt, Xiaohui Fan, Elena Gallo, Paulina Lira, Bin Luo, Gordon T. Richards, Donald P. Schneider, Michael A. Strauss, Jianfeng Wu

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32 Scopus citations

Abstract

Over the past 15 yr, examples of exotic radio-quiet quasars with intrinsically weak or absent broad emission line regions (BELRs) have emerged from large-scale spectroscopic sky surveys. Here, we present spectroscopy of seven such weak emission line quasars (WLQs) at moderate redshifts (z = 1.4-1.7) using the X-shooter spectrograph, which provides simultaneous optical and near-infrared spectroscopy covering the rest-frame ultraviolet (UV) through optical. These new observations effectively double the number of WLQs with spectroscopy in the optical rest-frame, and they allow us to compare the strengths of (weak) high-ionization emission lines (e.g., C iv) to low-ionization lines (e.g., Mg ii, Hβ, H) in individual objects. We detect broad Hβ and H emission in all objects, and these lines are generally toward the weaker end of the distribution expected for typical quasars (e.g., Hβ has rest-frame equivalent widths ranging from 15-40). However, these low-ionization lines are not exceptionally weak, as is the case for high-ionization lines in WLQs. The X-shooter spectra also display relatively strong optical Fe ii emission, Hβ FWHM ≲ 4000 km s-1, and significant C iv blueshifts (≈1000-5500 km s-1) relative to the systemic redshift; two spectra also show elevated UV Fe ii emission, and an outflowing component to their (weak) Mg ii emission lines. These properties suggest that WLQs are exotic versions of "wind-dominated" quasars. Their BELRs either have unusual high-ionization components, or their BELRs are in an atypical photoionization state because of an unusually soft continuum.

Original languageEnglish (US)
Article number123
JournalAstrophysical Journal
Volume805
Issue number2
DOIs
StatePublished - Jun 1 2015

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • accretion accretion disks
  • galaxies: active
  • quasars: emission lines

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    Plotkin, R. M., Shemmer, O., Trakhtenbrot, B., Anderson, S. F., Brandt, W. N., Fan, X., Gallo, E., Lira, P., Luo, B., Richards, G. T., Schneider, D. P., Strauss, M. A., & Wu, J. (2015). Detection of rest-frame optical lines from x-shooter spectroscopy of weak emission-line quasars. Astrophysical Journal, 805(2), [123]. https://doi.org/10.1088/0004-637X/805/2/123