The extraordinary mid-infrared spectral properties of FeLoBAL Quasars

TL;DR

This study presents mid-infrared spectra of six FeLoBAL quasars, revealing diverse dust and starburst features, including the most prominent PAHs observed in any quasar, suggesting a phase of merging starburst and AGN evolution.

Contribution

First mid-infrared spectral analysis of FeLoBAL quasars showing diverse dust and starburst properties, highlighting their evolutionary stage.

Findings

Presence of strong PAH emission indicating intense star formation

Diverse spectral shapes from AGN-dominated to starburst-dominated

Evidence supporting a merger-driven evolutionary phase for FeLoBAL QSOs

Abstract

We present mid-infrared spectra of six FeLoBAL QSOs at 1<z<1.8, taken with the Spitzer space telescope. The spectra span a range of shapes, from hot dust dominated AGN with silicate emission at 9.7 microns, to moderately obscured starbursts with strong Polycyclic Aromatic Hydrocarbon (PAH) emission. The spectrum of one object, SDSS 1214-0001, shows the most prominent PAHs yet seen in any QSO at any redshift, implying that the starburst dominates the mid-IR emission with an associated star formation rate of order 2700 solar masses per year. With the caveats that our sample is small and not robustly selected, we combine our mid-IR spectral diagnostics with previous observations to propose that FeLoBAL QSOs are at least largely comprised of systems in which (a) a merger driven starburst is ending, (b) a luminous AGN is in the last stages of burning through its surrounding dust, and (c) which we may be viewing over a restricted line of sight range.