The 2175 \AA~ Bump Features in FeLoBAL Quasars: One Indicator of MW-like Dust in the Nuclear Region of Quasar

TL;DR

This study identifies Milky Way-like 2175 Å bump dust features in FeLoBAL quasars, suggesting the presence of small, resilient dust grains in quasar nuclear regions facilitated by outflow shielding.

Contribution

It provides the first evidence of MW-like dust extinction features in FeLoBAL quasars, highlighting the role of outflows in dust survival near active galactic nuclei.

Findings

Detection of 2175 Å bump features similar to MW dust in FeLoBAL quasars.

Outflows may shield dust grains, allowing their survival in harsh quasar environments.

The dust properties are comparable to those in the Milky Way and LMC.

Abstract

To investigate the properties of dust in the nuclear region of quasars, we explored the extinction curves of the iron low-ionization broad absorption line (FeLoBAL) quasar SDSS J163004.29+311957.6 and its two analogues. The parameterized extinction curves indicated the Milky Way-like 2175 \AA~ bump features in underlying extinction, which are similar to those seen in the Local Group and a subset of high-redshift star-forming galaxies. Compared to the bump features in the Large Magellanic Clouds (LMC), the detections in this work are much closer to those in the Milky Way (MW). These bump features, as well as those in the high- and low-ionization broad absorption line (BAL) quasars of Zhang et al., are probably the counterpart of the 2175 \AA~ bump features in the quasar environment. This type of dust grain is generally small, easily disrupted by high-energy photons and has difficulty surviving in the radiation field of the active galactic nucleus (AGN). However, due to the presence of absorption-line outflows, the 2175 \AA~ bump feature in quasars, which should be rare, is seen many times in BAL quasars. The shielding effect of outflow clouds allows the MW-like dust grains to be assembled or extends the survival period in the quasar nuclear region. The process, and physical and chemical conditions deserve further observational study and investigation.