2015/03/25 by Richard M. Plotkin, Ohad Shemmer, Benny Trakhtenbrot +11 · 67 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Emission spectrum #Galaxies: Formation, Evolution, Phenomena #Galaxy #Gamma-ray bursts and supernovae #Ion #Ionization #Optics #Photoionization #Physics #Quasar #Redshift #Rest frame #Spectral line #Spectroscopy #Ultraviolet #astro-ph.CO #astro-ph.GA
paper · pdf · doi:10.1088/0004-637x/805/2/123
published in The Astrophysical Journal 805(2), 123 (IOP Publishing) · 22 pages, 9 figures, 6 tables. Accepted for publication in ApJ
arxiv created 2015/03/25 · openalex publication_date 2015/05/28 · arxiv updated 2015/06/03 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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 , H β , H α ) in individual objects. We detect broad H β and H α emission in all objects, and these lines are generally toward the weaker end of the distribution expected for typical quasars (e.g., H β has rest-frame equivalent widths ranging from 15–40 Å). 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, H β 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.