Broad HI Absorbers as Metallicity-Independent Tracers of the Warm-Hot
  Intergalactic Medium
  Thermally broadened Ly alpha absorbers (BLAs) offer an alternative method to
highly-ionized metal lines for tracing the WHIM. We compile a catalog of
reliable BLA candidates along seven AGN sight lines from a larger set of Lya
absorbers observed by HST/STIS. We compare our measurements based on
independent reduction and analysis of the data to those published by other
research groups. Purported BLAs are grouped into probable (15), possible (48)
and non-BLA (56) categories. We infer a line frequency (dN/dz)_BLA=18+-11,
comparable to observed OVI absorbers. There is significant overlap between BLA
and OVI absorbers (20-40%) and we find that OVI detections in BLAs are found
closer to galaxies than OVI non-detections. Based on 164 measured COG HI line
measurements, we statistically correct the observed line widths via a Monte-
Carlo simulation. Gas temperature and neutral fraction f(HI) are inferred from
these statistically-corrected line widths and lead to a distribution of total
hydrogen columns. We find Omega_BLA=(6.3+1.1-0.8)x10^-3. There are a number of
critical systematic assumptions implicit in this calculation, and we discuss
how each affects our results and those of previously published work. Taking our
value, current OVI and BLA surveys can account for ~20% of the baryons in the
local universe. Finally, we present new, high-S/N observations of several of
the BLA candidate lines from Early Release Observations made by the Cosmic
Origins Spectrograph on HST.
