The sloan digital sky survey reverberation mapping project: velocity shifts of quasar emission lines
- Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States)
- Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)
- Department of Physics, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104 (United States)
- Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
- Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)
- Institut d’Astrophysique de Paris, Université Paris 6 et CNRS, 98bis Boulevard Arago, F-75014 Paris (France)
- Aix Marseille Université, CNRS/IN2P3, CPPM UMR 7346, F-13288 Marseille (France)
Quasar emission lines are often shifted from the systemic velocity due to various dynamical and radiative processes in the line-emitting region. The level of these velocity shifts depends both on the line species and on quasar properties. We study velocity shifts for the line peaks (not the centroids) of various narrow and broad quasar emission lines relative to systemic using a sample of 849 quasars from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project. The coadded (from 32 epochs) spectra of individual quasars have sufficient signal-to-noise ratio (S/N) to measure stellar absorption lines to provide reliable systemic velocity estimates, as well as weak narrow emission lines. The large dynamic range in quasar luminosity (∼2 dex) of the sample allowed us to explore potential luminosity dependence of the velocity shifts. We derive average line peak velocity shifts as a function of quasar luminosity for different lines, and quantify their intrinsic scatter. We further quantify how well the peak velocity can be measured as a function of continuum S/N, and demonstrate that there is no systematic bias in the velocity measurements when S/N is degraded to as low as ∼3 per SDSS pixel (∼69 km s{sup −1}). Based on the observed line shifts, we provide empirical guidelines on redshift estimation from [O ii] λ3727, [O iii] λ5007, [Ne v] λ3426, Mg ii, C iii], He ii λ1640, broad Hβ, C iv, and Si iv, which are calibrated to provide unbiased systemic redshifts in the mean, but with increasing intrinsic uncertainties of 46, 56, 119, 205, 233, 242, 400, 415, and 477 km s{sup −1}, in addition to the measurement uncertainties. These results demonstrate the infeasibility of measuring quasar redshifts to better than ∼200 km s{sup −1} with only broad lines.
- OSTI ID:
- 22868553
- Journal Information:
- Astrophysical Journal, Vol. 831, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Near-infrared spectra and intrinsic luminosities of candidate type II quasars at 2 < z < 3.4
Rest-frame optical properties of luminous 1.5 < Z < 3.5 quasars: The Hβ-[O iii] region