Using the Cosmic Origins Spectrograph ( COS ) on the Hubble Space Telescope ( HST ) the COS Science Team has conducted a high signal-to-noise survey of 14 bright QSOs .
In a previous paper ( Savage et al .
2014 ) these far-UV spectra were used to discover 14 “ warm ” ( T \geq 10 ^ { 5 } K ) absorbers using a combination of broad Ly \alpha and broad O VI absorptions .
A reanalysis of a few of this new class of absorbers using slightly relaxed fitting criteria finds as many as 20 warm absorbers could be present in this sample .
A shallow , wide spectroscopic galaxy redshift survey has been conducted around these sightlines to investigate the warm absorber environment , which is found to be spiral-rich groups or cluster outskirts with radial velocity dispersions \sigma = 250-750 km s ^ { -1 } .
While 2 \sigma evidence is presented favoring the hypothesis that these absorptions are associated with the galaxy groups and not with the individual , nearest galaxies , this evidence has considerable systematic uncertainties and is based on a small sample size so it is not entirely conclusive .
If the associations are with galaxy groups , the observed frequency of warm absorbers ( d \mathcal { N } / dz = 3.5–5 per unit redshift ) requires them to be very extended as an ensemble on the sky ( \sim 1 Mpc in radius at high covering factor ) .
Most likely these warm absorbers are interface gas clouds whose presence implies the existence of a hotter ( T \sim 10 ^ { 6.5 } K ) , diffuse and probably very massive ( > 10 ^ { 11 } M _ { \odot } ) intra-group medium which has yet to be detected directly .