The nucleus of M87 displays a LINER spectrum at optical wavelengths , with a nuclear disk of nebulosity that is resolved by the Hubble Space Telescope .
We present new results from optical and ultraviolet spectra of the central \sim 40 pc as measured by HST .
In contrast with previous results for the extended disk , the emission-line spectrum of the central region is best reproduced by a multi-component photoionization scenario , rather than shock heating .
The nebular properties as well as energetic considerations suggest a transition on scales of several tens of parsecs , from predominantly photoionization by a central accretion source , to shock ionization within the disk .
If this source is at all representative , it suggests that many LINERs may be composite in terms of the energetic processes that give rise to the emission spectrum .
We also report measurements of resonance-line absorption for the nucleus .
The absorption spectrum , like the emission lines , is characterized by low ionization .
The absorption line measurements coupled with independent constraints suggest a total hydrogen column density of 10 ^ { 19 } -10 ^ { 20 } cm ^ { -2 } , outflowing from the galaxy center with a velocity of \sim 126 km s ^ { -1 } .
The kinematic signature of an outflow , along with evidence that the absorber covers the power-law continuum source but not the emission-line clouds , suggests that the absorbing matter is related to accretion phenomena in the nucleus .
The presence of such an outflow resembles similar behavior in luminous AGNs , although the low ionization that characterizes LINERs is probably indicative of a different mode of accretion in these sources .