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 quasar Mg ii narrow absorption lines (NALs) with velocity offset ( , where c is the speed of light) , this paper investigates the emissions and reddening associated with Mg ii NALs by constructing composite spectra. Dust extinctions of all the inflow ( ), environment (−750 ≤ r < 600 ), outflow ( ), and strong intervening-like (2000 ≤ r < 6000 ) Mg ii NALs can be described by the SMC extinction curve, which suggest that all four types of Mg ii NALs have similar dust properties. The colors of quasars hosting intervening-like Mg ii NALs with Å and intervening Mg ii NALs ( ) are similar to those of control quasars (without Mg ii NALs with ), which suggests that these two types of Mg ii NALs are mainly formed within media unconnected with background quasars. The other three types of Mg ii NALs have much more obvious reddening to background quasars, and the stronger absorptions or the absorptions detected in radio detected quasars produce larger reddening than the weaker absorptions or the absorptions in radio undetected quasars. In addition, the dust-to-gas ratios within inflow Mg ii NALs are possibly lower than those within environment ones. We find that flux ratios / of quasars hosting inflow, outflow, intervening-like, and intervening Mg ii NALs are similar to those of control quasars. For quasars hosting environment Mg ii NALs, (1) the flux ratio / is much higher than that of control quasars, which suggests that there is a high star formation rate within the host galaxies of environment Mg ii NALs; (2) the flux ratio / is positively correlated with absorption strengths; and (3) radio detected quasars have a slightly higher flux ratio / when compared to radio undetected quasars, which suggests that the quasar feedback enhances the star formation rate within host galaxies of environment absorbers. For quasars hosting outflow Mg ii NALs, we find that emission lines display excesses at blue wings with respect to the line profiles of control quasars, and the excesses are positively correlated with absorption strengths.
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.
Making use of quasar spectra from LAMOST, in the spectral data around the Mg ii emission lines, research described in this paper has detected 217 Mg ii narrow absorption lines (NALs) with W r λ 2796 ≥ 3 σ w and W r λ 2803 ≥ 2 σ w in a redshift range of 0.4554 ≤ z abs ≤ 2.1110. For quasars observed by both LAMOST and SDSS, we find that 135 Mg ii NALs were obviously observed in the LAMOST spectra, 347 Mg ii NALs were were apparent in the SDSS spectra, and 132 Mg ii NALs were clearly present in both the SDSS and LAMOST spectra. The missed Mg ii NALs are likely ascribed to low signal-to-noise ratios of corresponding spectra. Among the Mg ii NALs obviously observed in SDSS or LAMOST spectra, eight Mg ii NALs were significantly changed with | Δ W r λ 2796 | ≥ 3 σ w in time intervals of Δ MJD/(1 + z em) = 359 – 2819 d.
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