We present a re-analysis of the ROSAT PSPC data within the central 100 kpc of M87 to search for intrinsic oxygen absorption similar to that recently measured in several galaxies and groups .
Since M87 is the brightest nearby galaxy or cluster possessing an average temperature ( \sim 2 keV ) within the PSPC bandpass , it is the ideal target for this study .
Using a spatial-spectral deprojection analysis we find the strongest evidence to date for intrinsic oxygen absorption in the hot gas of a galaxy , group , or cluster .
Single-phase plasma models modified by intervening Galactic absorption can not fit the 0.2-2.2 keV PSPC data as they under-predict the 0.2-0.4 keV region and over-predict the 0.5-0.8 keV region where the emission and absorption residuals are obvious upon visual inspection of the spectral fits .
These absorption and emission features are significant out to the largest radii investigated .
Since the excess emission between 0.2-0.4 keV rules out intrinsic absorption from cold gas or dust , the most reasonable model for the excess emission and absorption features is warm , collisionally ionized gas with a temperature of \sim 10 ^ { 6 } K. Simple multiphase models ( cooling flow , two phases ) modified by both intervening Galactic absorption and by a single oxygen edge provide good fits and yield temperatures and Fe abundances of the hot gas that agree with previous determinations by ASCA and SAX .

The multiphase models of M87 inferred from the PSPC can account for the excess EUV emission observed with EUVE and the excess X-ray absorption inferred from Einstein and ASCA data above 0.5 keV .
This evidence for a multiphase warm+hot ISM in M87 essentially confirms the original detection by Canizares et al .
within the central \sim 2 \arcmin using the Einstein FPCS .
Although the total mass of the warm gas implied by the oxygen absorption is consistent with the matter deposited by a cooling flow , the suppression of the mass deposition rate and the distortion of the X-ray isophotes in the region where the radio emission is most pronounced suggest some feedback effect from the AGN on the cooling gas .