A Hubble Space Telescope Imaging Study of Four FeLoBAL Quasar Host
  Galaxies
  We study the host galaxies of four Iron Low-Ionization Broad Absorption-line
Quasars (FeLoBALs) using Hubble Space Telescope imaging data, investigating the
possibility that they represent a transition between an obscured AGN and an
ordinary optical quasar. In this scenario, the FeLoBALs represent the early
stage of merger-triggered accretion, in which case their host galaxies are
expected to show signs of an ongoing or recent merger. Using PSF subtraction
techniques, we decompose the images into host galaxy and AGN components at
rest-frame ultraviolet and optical wavelengths. The ultraviolet is sensitive to
young stars, while the optical probes stellar mass. In the ultraviolet we image
at the BAL absorption trough wavelengths so as to decrease the contrast between
the quasar and host galaxy emission. We securely detect an extended source for
two of the four FeLoBALs in the rest-frame optical; a third host galaxy is
marginally detected. In the rest-frame UV we detect no host emission; this
constrains the level of unobscured star formation. Thus, the host galaxies have
observed properties that are consistent with those of non-BAL quasars with the
same nuclear luminosity, i.e., quiescent or moderately starforming elliptical
galaxies. However, we cannot exclude starbursting hosts that have the stellar
UV emission obscured by modest amounts of dust reddening. Thus, our findings
also allow the merger-induced young quasar scenario. For three objects, we
identify possible close companion galaxies that may be gravitationally
interacting with the quasar hosts.
