Near-IR spectroscopy of luminous LoBAL quasars at 1<z<2.5
  We present near-IR spectroscopy of 22 luminous low-ionization broad
absorption line quasars (LoBAL QSOs) at redshift 1.3<z<2.5, with 12 objects at
z~1.5 and 10 at z~2.3. The spectra cover the rest-frame H$\alpha$ and H$\beta$
line regions, allowing us to obtain robust black hole mass estimates based on
the broad H$\alpha$ line. We use these data, augmented by a lower-redshift
sample from the Sloan Digital Sky Survey, to test the proposed youth scenario
for LoBALs, which suggests that LoBALs constitute an early short-lived
evolutionary stage of quasar activity, by probing for any difference in their
masses, Eddington ratios, or rest-frame optical spectroscopic properties
compared to normal quasars. In addition, we construct the UV to mid-IR spectral
energy distributions (SEDs) for the LoBAL sample and a matched non-BAL quasar
sample. We do not find any statistically significant difference between LoBAL
QSOs and non-BAL QSOs in their black hole mass or Eddington ratio
distributions. The mean UV to mid-IR SED of the LoBAL QSOs is consistent with
non-BAL QSOs, apart from their stronger reddening. At z>1 there is no clear
difference in their optical emission line properties. We do not see
particularly weak [OIII] or strong FeII emission. The LoBAL QSOs do not show a
stronger prevalence of ionized gas outflows as traced by the [OIII] line,
compared to normal QSOs of similar luminosity. We conclude that the optical-MIR
properties of LoBAL QSOs are consistent with the general quasar population and
do not support them to constitute a special phase of active galactic nucleus
evolution.
