Observing the circumgalactic medium of simulated galaxies through
  synthetic absorption spectra
  We explore the multiphase structure of the circumgalactic medium (CGM) probed
by synthetic spectra through a cosmological zoom-in galaxy formation
simulation. We employ a Bayesian method for modelling a combination of
absorption lines to derive physical properties of absorbers with a formal
treatment of detections, including saturated systems, and non-detections in a
uniform manner. We find that in the lines of sight passing through localized
density structures, absorption lines of low, intermediate and high ions are
present in the spectrum and overlap in velocity space. Low, intermediate and
high ions can be combined to derive the mass-weighted properties of a
density-varying peak, although the ions are not co-spatial within the
structure. By contrast, lines of sight that go through the hot halo only
exhibit detectable HI and high ions. In such lines of sight, the absorption
lines are typically broad due to the complex velocity fields across the entire
halo. We show that the derived gas density, temperature, and metallicity match
closely the corresponding HI mass-weighted averages along the LOS. We also show
that when the data quality allows, our Bayesian technique allows one to recover
the underlying physical properties of LOS by incorporating both detections and
non-detections. It is especially useful to include non-detections, of species
such as NV or NeVIII, when the number of detections of strong absorbers, such
as HI and OVI, is smaller than the number of model parameters (density,
temperature, and metallicity).
