HIGH-RESOLUTION X-RAY-IMAGING OF THE STARBURST GALAXY M82

Starburst galaxies are predicted to drive hot flows of gas from their central star-forming regions, and to test this expectation, a deep X-r ay image was obtained of the nearby starburst galaxy M82 with the High -Resolution Imager on the X-ray telescope ROSAT. Aside from three nucl ear point sources, the flux is dominated by diffuse emission that we d ecompose into components along the disk and along the minor axis. The X-ray surface brightness of the disk component decreases exponentially with a scale length of 0.27 kpc, as does the optical line emission fr om warm ionized gas. This is not due to steady outflow of gas along th e plane, but may indicate a rapid decrease in the star formation and e nergy input rate beyond the nuclear region. The X-ray emission along t he minor axis is consistent with the outflow of gas in a jet that is p artially confined within 1.6 kpc of the nucleus and expands freely at larger radii; this emission is detected to a distance of 6 kpc. In the center of M82, the hot gas density is 0.2-0.5 cm(-3) and the central gas pressure is P/k approximate to 0.3-3 x 10(7) K cm(-3), which is si milar to estimates of the pressure in the optical emission-line materi al and molecular gas.