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Connecting Low- and High-redshift Weak Emission-line Quasars via Hubble Space Telescope Spectroscopy of Lyα Emission

Journal Article · · The Astrophysical Journal
 [1];  [1];  [2];  [3];  [4];  [5];  [6];  [7];  [8];  [9];  [4];  [10];  [11]
  1. Univ. of Nevada, Reno, NV (United States)
  2. Univ. of North Texas, Denton, TX (United States)
  3. Univ. of Washington, Seattle, WA (United States)
  4. Pennsylvania State Univ., University Park, PA (United States)
  5. Univ. of Arizona, Tucson, AZ (United States)
  6. Univ. of Michigan, Ann Arbor, MI (United States)
  7. Nanjing Univ. (China)
  8. Pennsylvania State Univ., University Park, PA (United States); Univ. of Edinburgh, Scotland (United Kingdom)
  9. Drexel Univ., Philadelphia, PA (United States)
  10. Xiamen Univ. (China)
  11. Pennsylvania State Univ., University Park, PA (United States); Yunnan Observatories (China); Chinese Academy of Agricultural Sciences (China)
+ Show Author Affiliations
We present ultraviolet spectroscopy covering the Lyα + N v complex of six candidate low-redshift (0.9 < z < 1.5) weak emission-line quasars (WLQs) based on observations with the Hubble Space Telescope. The original systematic searches for these puzzling Type 1 quasars with intrinsically weak broad emission lines revealed an N ≈ 100 WLQ population from optical spectroscopy of high-redshift (z > 3) quasars, defined by a Lyα + N v rest-frame equivalent width (EW) threshold <15.4 Å. Identification of lower-redshift (z < 3) WLQ candidates, however, has relied primarily on optical spectroscopy of weak broad emission lines at longer rest-frame wavelengths. With these new observations expanding existing optical coverage into the ultraviolet, we explore unifying the low- and high-z WLQ populations via EW[Lyα+N v]. Two objects in the sample unify with high-z WLQs, three others appear consistent with the intermediate portion of the population connecting WLQs and normal quasars, and the final object is consistent with typical quasars. The expanded wavelength coverage improves the number of available line diagnostics for our individual targets, allowing a better understanding of the shapes of their ionizing continua. The ratio of EW[Lyα+N v] to EW[Mg ii] in our sample is generally small but varied, favoring a soft ionizing continuum scenario for WLQs, and we find a lack of correlation between EW[Lyα+N v] and the X-ray properties of our targets, consistent with a "slim-disk" shielding gas model. We also find indications that weak absorption may be a more significant contaminant in low-z WLQ populations than previously thought.
Research Organization:
US Department of Energy (USDOE), Washington, DC (United States). Office of Science, Sloan Digital Sky Survey (SDSS)
Sponsoring Organization:
Alfred P. Sloan Foundation; National Aeronautics and Space Administration (NASA); National Science Foundation (NSF); USDOE Office of Science (SC)
OSTI ID:
1983247
Journal Information:
The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 1 Vol. 929; ISSN 0004-637X
Publisher:
IOP PublishingCopyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
active galactic nuclei
high energy astrophysics
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supermassive black holes