A unifying evolutionary framework for infrared-selected obscured and
  unobscured quasar host haloes
  Recent measurements of the dark matter halo masses of infrared-selected
obscured quasars are in tension --- some indicate that obscured quasars have
higher halo mass compared to their unobscured counterparts, while others find
no difference. The former result is inconsistent with the simplest models of
quasar unification that rely solely on viewing angle, while the latter may
support such models. Here, using empirical relationships between dark matter
halo and supermassive black hole masses, we provide a simple evolutionary
picture that naturally explains these findings and is motivated by more
sophisticated merger-driven quasar fueling models. The model tracks the growth
rate of haloes, with the black hole growing in spurts of quasar activity in
order to "catch-up" with the $M_{\textrm{BH}}$ - $M_{\textrm{star}}$ -
$M_{\textrm{halo}}$ relationship. The first part of the quasar phase is
obscured and is followed by an unobscured phase. Depending on the luminosity
limit of the sample, driven by observational selection effects, a difference in
halo masses may or may not be significant. For high luminosity samples, the
difference can be large (a few to 10 times higher masses in obscured quasars),
while for lower luminosity samples the halo mass difference is very small, much
smaller than current observational constraints. Such a simple model provides a
qualitative explanation for the higher mass haloes of obscured quasars, as well
as rough quantitative agreement with seemingly disparate results.
