Dark and bright sides of the Broad Line Region clouds as seen in the FeII emission of SDSS RM 102

TL;DR

This paper analyzes the FeII emission in quasar RM 102 using advanced CLOUDY models, revealing highly metallic gas and inflow geometry, while highlighting limitations in current atomic data for FeII.

Contribution

It introduces a constant pressure model for FeII emission in quasars, considering geometrical effects and mechanical heating, and identifies the presence of highly metallic gas in RM 102's broad line region.

Findings

RM 102 has highly metallic gas in its broad line region.

FeII emission suggests inflow geometry favoring dark cloud sides.

CLOUDY lacks some atomic data, limiting FeII feature reproduction.

Abstract

Contamination from singly ionized iron emission is one of the greatest obstacles to determining the intensity of emission lines in the UV and optical wavelength ranges. This study presents a comprehensive analysis of the FeII emission in the bright quasar RM 102, based on the most recent version of the CLOUDY software, with the goal of simultaneously reproducing UV and optical FeII emission. We employ a constant pressure model for the emitting clouds, instead of the customary constant density assumption. The allowed parameter range is broad, with metallicity up to 50 times the solar value and turbulent velocity up to 100 km s$^{-1}$ for a subset of models. We also consider geometrical effects that could enhance the visibility of the non-illuminated faces of the clouds, as well as additional mechanical heating. Our investigation reveals that the broad line region of RM 102 is characterized by highly metallic gas. The observed FeII features provide strong evidence for an inflow pattern geometry that favours the dark sides of clouds over isotropic emission. This study confirms the presence of chemically enriched gas in the broad line region of bright quasars, represented by RM 102, which is necessary to explain the strong FeII emission and its characteristic features. Additionally, we report that CLOUDY currently still lacks certain transitions in its atomic databases which prevents it from fully reproducing some observed FeII features in quasar spectra.