This work aims to measure the properties of continuum and emission lines around C iv, Mg ii, Hβ, and Hα for the quasars observed by the extended Baryon Oscillation Spectroscopic Survey (eBOSS) during the first two years. We determine the quasar redshifts based on narrow [O iii] λ5007, broad Mg ii λ2799, and/or C iv λ1548 emission lines. The comparisons between the visual inspection redshifts included in DR14Q and the redshifts determined by us suggest that the visual inspection redshifts would be robust. We also infer the virial black hole mass of quasars based on C iv, Mg ii, Hβ, and/or Hα broad emission lines, using empirical relationships reported by previous studies. Systematic differences are remarkable among different line-based mass estimators reported by previous studies. Using the empirical relationship (Equation (1)), we improve the line-based mass estimators by recalibrating new coefficient (a, b), so that different line-based mass estimators are more consistent. We find that (a, b) = (0.96, 0.5), (0.91, 0.5), (0.82, 0.5), and (0.77, 0.5) are the best choices for the Hα-, Hβ-, Mg ii-, and C iv-based mass estimators, respectively. All these above properties are publicly available. We also find that the line and continuum luminosities are tightly correlated with each other. The Balmer lines show a negative Baldwin effect, while the metal lines display a positive Baldwin effect. In addition, we find that tight correlations are indwelled in different line luminosities.
Using the quasars with z em < 0.9 from the Baryon Oscillation Spectroscopic Survey, we measure the spectral characteristics, including continuum and emission lines, around the Hβ and Hα spectral regions, which are lacking in Quasar Data Release 12 (DR12Q). We estimate the virial black hole mass from broad Hα and/or Hβ, and infer quasar redshifts from [O III] λ5007 emission lines. All the measurements and derived quantities are publicly available. The comparison between [O III] λ5007 based redshifts and the visual inspection redshifts included in DR12Q indicates that the visual inspection redshifts are robust. We find that the FWHMs of the broad Hα are consistent with those of the broad Hβ, while both the equivalent widths and line luminosities of the broad Hα are obviously larger than the corresponding quantities of the broad Hβ. We also find that there is an obviously systematic offset between the Hβ and Hα based mass if they are inferred from the empirical relationships in the literature. Using our large quasar sample, we have improved the Hβ and Hα based mass estimators by minimizing the difference between the Hβ and Hαbased mass. For the black hole mass estimator (Equation (1)), we find that the coefficients (a, b) = (7.00, 0.50) for the Hα and (a, b) = (6.96, 0.50) for the Hβ are the best choices.
Using the SDSS spectra of quasars included in the DR7Q or DR12Q catalogs, we search for Mg II λλ2796,2803 narrow absorption doublets in the spectra data around Mg II λ2798 emission lines. We obtain 17 316 Mg II doublets, within the redshift range of 0.3299 ≤ z abs ≤ 2.5663. We find that a velocity offset of υ r < 6000 km s −1 is a safe boundary to constrain the vast majority of associated Mg II systems, although we find some doublets at υ r > 6000 km s −1 . If associated Mg II absorbers are defined by υ r < 6000 km s −1 , ∼33.3% of the absorbers supposed to be contaminants of intervening systems. Removing the 33.3% contaminants, ∼4.5% of the quasars present at least one associated Mg II system with W λ2796 r ≥ 0.2 Å. The fraction of associated Mg II systems with high velocity outflows correlates with the average luminosities of their central quasars, indicating a relationship between outflows and the quasar feedback power. The υ r distribution of the outflow Mg II absorbers is peaked at 1023 km s −1 , which is smaller than the corresponding value of the outflow C IV absorbers. The redshift number density evolution of absorbers (dn/dz) limited by υ r > −3000 km s −1 differs from that of absorbers constrained by υ r > 2000 km s −1 . While, absorbers limited by υ r > 2000 km s −1 and higher values exhibit similar profile of dn/dz. In addition, the dn/dz is smaller when absorbers are constrained with larger υ r . The distributions of equivalent widths, and the ratio of W λ2796 r /W λ2803 r is the same for associated and intervening systems, and independent on quasar luminosity.
Compared to high ionization C iv absorption lines, variable Mg ii absorption lines are rare. Using spectra from the Sloan Digital Sky Survey, we investigate the variations in Mg ii narrow absorption lines (NALs) for quasars with multi-epoch observations. We have compiled 8958 Mg ii NALs in the spectral regions from the red wings of C iv emission lines to the red wings of Mg ii emission lines. Among these 8958 Mg ii NALs, 22 variable NALs are detected with and with velocity offsets ranging from to 145,513 . We find that: (1) the detected frequency of Mg ii NALs with is significantly larger than the uniformly random value expected for the Mg ii NALs with , (2) the incidence rates of the variable Mg ii NALs with are much larger than those with , (3) the velocity offsets of variable Mg ii NALs with are much smaller than the maximum velocities expected from radiation-driven outflows, and (4) the variations of variable Mg ii NALs with are obviously correlated with the changes in the quasar radiative output. Therefore, the 16 variable Mg ii NALs, whose velocities are smaller than the maximum velocities expected from radiation-driven outflows, are likely related to quasar outflows, while the 6 variable Mg ii NALs, whose velocities are much larger than the maximum velocities expected from radiation-driven outflows, possibly originated in intervening gas. We also find that both the variations and fractional variations in absorption strengths are not related to the velocity offsets of Mg ii NALs and the time intervals between the two epochs of observations. Also, the fractional variations in absorption strengths are inversely correlated with absorption strengths. In addition, both the associated and intervening Mg ii NALs can significantly vary on a timescale of days.
We assemble 207 variable quasars from the Sloan Digital Sky Survey, all with at least 3 observations, to analyze C IV narrow absorption doublets, and obtain 328 C IV narrow absorption line systems. We find that 19 out of 328 C IV narrow absorption line systems were changed by | ∆W λ1548 r
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