MAGIICAT III. Interpreting Self-Similarity of the Circumgalactic Medium
  with Virial Mass using MgII Absorption
  In Churchill et al., we used halo abundance matching applied to 182 galaxies
in the MgII Absorber-Galaxy Catalog (MAGIICAT, Nielsen et al.) and showed that
the mean MgII 2796 equivalent width follows a tight inverse-square power law,
W_r(2796) ~ (D/R_vir)^-2, with projected location relative to the galaxy virial
radius and that the MgII absorption covering fraction is invariant with galaxy
virial mass, M_h, over the range 10.7 < M_h/M_solar < 13.9. In this work, we
explore multivariate relationships between W_r(2796), virial mass, impact
parameter, virial radius, and the theoretical cooling radius that further
elucidate self-similarity in the cool/warm (T=10^{4-4.5} K) circumgalactic
medium (CGM) with virial mass. We show that virial mass determines the extent
and strength of the MgII absorbing gas such that the mean W_r(2796) increases
with virial mass at fixed distance while decreasing with galactocentric
distance for fixed virial mass. The majority of the absorbing gas resides
within D ~ 0.3 R_vir, independent of both virial mass and minimum absorption
threshold; inside this region, and perhaps also in the region 0.3 < D/R_vir =
1, the mean W_r(2796) is independent of virial mass. Contrary to
absorber-galaxy cross-correlation studies, we show there is no anti-correlation
between W_r(2796) and virial mass. We discuss how simulations and theory
constrained by observations fully support self-similarity of the cool/warm CGM
via the physics governing star formation, gas-phase metal enrichment, recycling
efficiency of galactic scale winds, filament and merger accretion, and
overdensity of local environment as a function of virial mass.
