The extraordinary mid-infrared spectral properties of FeLoBAL quasars

We present mid-infrared (mid-IR) spectra of six FeLoBAL quasi-stellar objects (QSOs) at 1 z Spitzer Space Telescope. The spectra span a range of shapes, from hot dust-dominated active galactic nuclei (AGNs) with silicate emission at 9.7 μm 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 on the order of 2700 Myr−1. 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 (1) a merger-driven starburst is ending, (2) a luminous AGN is in the last stages of burning through its surrounding dust, and (3) wemay be viewing over a restricted line-of-sight range