VERY EXTENDED X-RAY AND H#alpha# EMISSION IN M82: IMPLICATIONS FOR THE SUPERWIND PHENOMENON

摘要

We discuss the properties and implications of the recently discovered 3.'5 x 0.'9 (3.7 x 0.9 kpc) region of spatially coincident X-ray and H#alpha# emission about ll' (11.6 kpc) to the north of the prototypical starburst/superwind galaxy M82. The total H#alpha# flux from this ridge of emission is l.5 x 10~(-13) ergs s~(-1) cm~(-2), or about 0.3 of the total M82 H#alpha# flux. The implied H#alpha# luminosity of this region is 2.4 x 10~38 ergs s~(-1). Diffuse soft X-ray emission is seen over the same region by the ROSAT PSPC and HRI. The PSPC X-ray spectrum is fitted by thermal plasma absorbed by only the Galactic foreground column density (N_H = 3.7 x 10~20 cm~(-2)) and having a temperature of kT = 0.80 +- 0.17 keV. The total unab- sorbed flux from the ridge is 1.4 x 10~(-13) ergs cm-2 s~(-1) (approx2.2 x 10~38 ergs s~(-1)), comprising about 0.7 of the total X-ray emission from M82. We evaluate the relationship of the X-ray/H#alpha# ridge to the M82 superwind. The H#alpha# emission could be excited by ionizing radiation from the starburst that propagates into the galactic halo along the cavity carved by the superwind. However, the main properties of the X-ray emission can all be explained as being due to shock heating driven as the superwind encounters a massive ionized cloud in the halo of M82 (possibly related to the tidal debris seen in H I in the inter- acting M81/M82/NGC 3077 system). This encounter drives a slow shock into the cloud, which contrib- utes to the excitation of the observed H#alpha# emission. At tlie same time, a fast bow shock develops in the superwind