Diffuse X-Ray Emission from HII Complexes - Scent of SNRs
Session 27 -- Hat Creek
Oral presentation, Tuesday, 8:30-12:30, Dwinelle 155 Room

## [27.06] Diffuse X-Ray Emission from HII Complexes - Scent of SNRs

Y.-H. Chu (U. Illinois)

The Einstein IPC has detected diffuse X-ray emission from many large HII complexes: the Carina Nebula in our Galaxy, 30 Dor, N44 and N51D in the Large Magellanic Cloud (LMC), and NGC 604 in M33. Their X-ray luminosities range from a few $\times$10$^{35}$ to 10$^{37}$ erg s$^{-1}$.

The observed X-ray luminosities of the ring-shaped HII complexes, N44 and N51D, are at least an order of magnitude higher than those expected from superbubble models. Off-center SNRs hitting the superbubble walls are suggested to explain the observed X-ray emission (Chu \& Mac Low 1990, ApJ, 365, 510). For 30 Dor, the X-ray emission correlates well with the large expanding shell structures; the superposed high-velocity ($\Delta$ V $\gg$ 100 km s$^{-1}$) features provide direct evidence of additional acceleration which is most likely caused by SNRs (Chu \& Kennicutt 1993, in preparation). The X-ray emission from 30 Dor, too, may be explained by off-center SNRs hitting supershell walls. NGC 604 is not adequately resolved for such detailed analysis, but its similarity to 30 Dor in X-ray luminosity and kinematic structure implies that its X-ray emission may also require SNRs.

The Carina Nebula is the only HII complex that has been suggested to be powered solely by stellar winds (Seward \& Chlebowski 1982, ApJ, 256, 530; Walborn \& Hesser 1982, ApJ, 252, 156). However, our ROSAT PSPC pointed observations of LMC HII complexes similar to Carina in stellar content do not show comparable amounts of X-ray emission. Furthermore, Carina's high-velocity interstellar absorption components (Walborn \& Hesser 1982) and anomalous N(Mn)/N(Fe) ratio in the -89 km s$^{-1}$ component (Laurent et al. 1982, ApJ, 260, 163) are both indicative of SN activities. We suggest that the diffuse X-ray emission from the Carina Nebula is caused by off-center SNRs, as in N51D or N44.

Conclusion: SNRs play a dominant role in producing diffuse X-ray emission from large HII complexes.