Collective Properties of Quasar Narrow Associated Absorption Lines

Abstract

This paper statistically investigates the properties of C IV and Mg II narrow absorption lines (NALs) to look for velocity cuts that can well constrain quasar-associated NALs. The coverage fraction ( f c ) is defined as the ratio between the number of quasars exhibiting at least one detected absorber and the total number of quasars that can be used to detect absorptions with given criteria. We find that, for both C IV and Mg II absorbers, both the number density of absorbers in given velocity intervals (dn/dβ) and the f c show very significant excess at the low-velocity offset from the quasars, relative to the random occurrence that is expected for cosmologically intervening absorbers. These relative excess extensions for Mg II absorptions are not only evidently related to absorption strength but also to quasar luminosity, while they are mainly constrained within 2000 km s . Turning to C IV absorptions, the relative excess extensions of both dn/dβ and f c are mainly limited within v abs < 4000 km s, and depend neither on absorption strength nor on quasar luminosity. And also, the absorbers with v abs < 4000 km sshow obviously different redshift number density evolution from those with v abs > 4000 km s −1. We suggest velocity cuts of 4000 km s to define quasar C IV and Mg II associated NALs, respectively.

The Associated Absorption Features in Quasar Spectra of the Sloan Digital Sky Survey. I. Mg ii Absorption Doublets

“…Therefore, one often expects that the quasar absorption systems would exhibit a clustering distribution around the quasar emission redshift relative to the cosmologically absorption systems. This phenomenon has been confirmed by previous works (e.g., Nestor et al 2008;Wild et al 2008;Perrotta et al 2016;Chen & Pan 2017). In this section, we will statistically analyze the distributions of the absorber number density (dn/dυ) around quasars, where the dn/dυ is defined as the number of absorbers per unit of velocity interval, and investigate the dependence of the dn/dυ on quasar luminosity.…”

“…Firstly, the dn/dz evolution profiles are similar for the ab- sorbers with υ r > 2000 km s −1 , but differ from those that also account for the absorbers with lower velocity offsets. Chen & Pan (2017) has claimed that most of the Mg II associated absorbers are constrained within υ r < 2000 km s −1 , which is also supported by Figure 3. In other words, the population of absorbers with υ r > 2000 km s −1 is dominated by intervening absorbers, though there are some outflow absorbers with υ r > 2000 km s −1 .…”

“…Therefore, we firstly limit the quasar samples with 4000/2800 < (1 + z em ) < 8800/2800 for the DR7Q catalog and 3800/2800 < (1 + z em ) < 10000/2800 for the DR12Q catalog, where we do not consider the two end data since they are usually noisy. Chen & Pan (2017) shows that most of the associated Mg II NALs are constrained within a relative velocity 4 υ r < 2000 km s −1 . The quasar radiation has a potential to drive associated absorption clouds up to a high velocity.…”

“…The natures of absorbers This paper searched for associated Mg II absorption systems in quasar spectra data with υ r ≤ 10 000 km s −1 . Chen & Pan (2017) has claimed that most of the associated Mg II absorbers are constrained within υ r < 2000 km s −1 , though some outflow absorbers with high velocity (e.g. ; Chen & Qin 2013;Hacker et al 2013) would be beyond this limit.…”

The first detection of radio recombination lines at cosmological distances

“…Morganti et al 2005). Via Sloan Digital Sky Survey (SDSS) optical spectra of ∼17 000 quasars, the majority of associated absorbers are found out to 2000 km s −1 -4000 km s −1 , with tails to 10 000 km s −1 , albeit for warmer gas (Chen & Pan 2017). Additionally, warm gas with narrow line widths and velocities of -14 050 km s −1 has been observed in radiation-driven outflows (Hamann et al 2011), and with veloc-ities up to -3000 km s −1 in low-ionisation species, 900 pc away from the quasar (Xu et al 2018).…”