| Title | Radio observations of H II regions in external galaxies. I. H II regions in M33. |
| Authors | Israel, F. P.; van der Kruit, P. C. |
| Bibcode | 1974A&A....32..363I Search ADS ↗ |
| Abstract | Summary. Observations at 1415 MHz with the Westerbork Synthesis Radio Telescope of 67 H ii regions or groups of H ii regions in M 33 are presented. The analysis shows: I Apparently all H ii regions brighter than 2.5 x have been detected. 2. The observed radio luminosity distribution indicates that an appreciable percentage of the total radio flux- density of M 33 at 21 cm may be thermal. 3. Excluding NGC 595 and NGC 604 the excitation parameter distribution has a well-defined maximum at 210 pc cm 2 This indicates that the larger H ii regions are ionisation bounded. 4. Both NGC 595 and NGC 604 consist of a dense core and an extended halo. Comparison with 30 Dor in the Large Magellanic Cloud shows that all three are qualitatively similar and have ionized gas masses of the order of 106 solar masses. 5. The radio flux-density per unit area drops sharply at 2 kpc from the center; within this radius there is a marked maximum of high mass (M> 5 x 104M0) H ii regions. 6. The H ii/H i ratio also shows a sharp decrease around 2 kpc; most H ii regions occur in regions with relatively high surface densities of H i gas (hydrogen spiral arms). 7. When combined with Searle's (1971) Hoc and Hfl flux -densities, the radio results imply internal absorption up to 1 !'3. 8. No point source was observed at the optical nucleus of M 33. The upper limit implies an intrinsic flux about 70 times weaker than that of Sgr. A. Key words: H ii regions - radio continuum - structure ofM33 |
| Objects | 80 Objects Search NED ↙ |
