The dust, nebular emission and dependence on QSO radio properties of the associated Mg II absorption line systems

TL;DR

This study investigates dust reddening and [O II] emission in Mg II associated absorption systems, revealing their dependence on QSO radio properties, black hole mass, and orientation, with implications for understanding their intrinsic nature.

Contribution

It provides a comprehensive analysis of how Mg II AAS properties vary with QSO radio characteristics and black hole parameters, highlighting their intrinsic origin.

Findings

AAS in radio detected QSOs cause significantly higher dust extinction.

Occurrence of AAS is more likely in radio detected QSOs and those with larger black hole masses.

Excess [O II] emission is observed in AAS, related to black hole mass and Eddington ratio.

Abstract

We studied dust reddening and [O II] emission in 1730 Mg II associated absorption systems (AAS; relative velocity with respect to QSOs, < 3000 km/s; in units of velocity of light, \b{eta}, < 0.01) with 0.4 < z_abs < 2 in the SDSS DR7, focusing on their dependence on the radio and other QSO properties. We used control samples, several with matching radio properties to show (i) AAS in radio detected (RD) QSOs cause 2.6 +/- 0.2 times higher dust extinction than those in radio undetected (RUD) ones which, in turn, cause 2.9 +/- 0.7 times the dust extinction in the intervening systems; (ii) AAS in core-dominated QSOs cause 2.0 +/- 0.1 times higher dust extinction than in lobe-dominated QSOs; (iii) occurrence of AAS is 2.1 +/- 0.2 times more likely in RD QSOs than in RUD QSOs and 1.8 +/- 0.1 time more likely in QSOs having black holes with masses larger than 1.23 x 10^{9} M_sun than in those with lower mass black holes; (iv) there is excess flux in [O II]{\lambda}3727 emission in the composite spectra of the AAS samples compared to those of the control samples, which is at the emission redshift. Presence of AAS enhances the O II emission from the AGN and/or the host galaxy. This excess is similar for both RD and RUD samples, and is 2.5 +/- 0.4 times higher in lobe-dominated compared to core-dominated samples. The excess depends on the black hole mass and Eddington ratio. All these point to the intrinsic nature of the AAS except for the systems with z_abs > z_em which could be infalling galaxies.