UV Absorption Line Ratios in Circumgalactic Medium at Low Redshift in
  Realistic Cosmological Hydrodynamic Simulations
  Utilizing high-resolution cosmological hydrodynamic simulations we
investigate various ultra-violet absorption lines in the circumgalactic medium
of star forming galaxies at low redshift, in hopes of checking and alleviating
the claimed observational conundrum of the ratio of NV to OVI absorbers, among
others. We find a satisfactory agreement between simulations and extant
observational data with respect to the ratios of the following four line pairs
examined, NV/OVI, SiIV/OVI, NIII/OVI and NII/OVI. For the pairs involving
nitrogen lines, we examine two cases of nitrogen abundance, one with constant
N/O ratio and the other with varying N/O ratio, with the latter motivated by
theoretical considerations of two different synthetic sources of nitrogen that
is empirically verified independently. Along a separate vector, for all line
pairs, we examine two cases of radiation field, one with the Haardt-Madau
background radiation field and the other with an additional local radiation
field sourced by hot gas in the host galaxy. In all cases, two-sample
Kolmogorov-Smirnov tests indicate excellent agreements. We find that the
apparent agreements between simulations and observations will be strongly
tested, if the bulk of current upper limits of various line ratios are turned
into actual detections. We show that an increase in observational sensitivity
by 0.2 dex will already start to significantly constrain the models.
