Quasar Outflows: New Evidence for Acceleration of BALs Driven by Central Source Radiation

In summary, while previous studies suggest that velocity shifts in BALs are rare in quasar outflows, recent research has discovered a number of cases where such shifts have occurred. These cases demonstrate a correlation between the velocity shifts and the radiation from the central source, suggesting that the shifts are the result of acceleration driven by this radiation. This research provides new insights into the dynamics of quasar outflows and may help to further our understanding of these phenomena.

Previous studies seem to tell us that the velocity shift of BALs is rarely seen in quasar outflows. However, in recent years, in a series of work on BALs that can be broken down into narrow absorption lines (NALs), we have discovered and reported several cases of BALs with velocity shifts (Lu & Lin 2019; Yao et al. 2020; Lu & Lin 2020a,b; Lin & Lu 2020). For example, in 2019, we found an accelerated CIV BAL in the quasar SDSS J120819.29+035559.4, which experienced a velocity shift of 1166 km s-1, within a time scale (rest frame) about 3 years. For another example, in 2020, we reported the coordinated acceleration of MgII and AlIII BALs in another quasar, SDSS J134444.33+315007.6, which experienced velocity shifts of 1101 and 1170 km s-1, respectively, within an interval of about 3.21 years (rest frame). We tried to explore the reasons for the observed velocity shifts of the BALs in these two sources and found that in addition to the velocity shifts, these BALs also exhibited some other similar characteristics: (1) the enhancement of the equivalent widths (EW); (2) obvious weakening of the continuum; (3) the coordinate enhancement of the emission lines. These characteristics all indicate that the outflows of these two sources are affected by the radiation from the central source, so we guess that the velocity shifts of their BALs are possibly an actual acceleration driven by the central source radiation.