The Reddening and [O ii] Emissions of the Quasar Mg ii Absorption-line Systems

Abstract

Abstract 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.