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NGC 1569: the molecular and ionized gas near the superluminous star clusters A and B

A. Greve, R. Becker, L.E.B. Johansson, C.D. McKeith
Abstract: The starburst in the irregular galaxy NGC 1569 has produced two superluminous star clusters A and B which strongly influence their surroundings through UV radiation, stellar winds, supernova explosions, and an outflow of very hot gas. Close to A and B is located the most prominent HII region of NGC 1569; our CO observations indicate that it contains 2 10 M molecular gas which probably still feeds star formation of its internal stellar cluster.

When comparing the molecular gas mass, calculated for Galactic conditions, and the virial mass we obtain a conversion factor 20 times higher than the Galactic value. However, we believe that the molecular clouds near the stellar clusters are not in kinematic equilibrium so that the virial theorem does not apply; we therefore reject this conversion factor as unrealistic. Our spectroscopic observations seem to indicate an optical counterpart of the HI cavity around A, though being smaller in extent, and a surrounding shell of ionized gas of 50 pc diameter.

The compact galaxy NGC 1705 contains a stellar cluster even brighter than A and B. We did not detect CO in this galaxy.
to be published in A&A

Figure 4: Sample spectra from the central 8 of the 2.5 spatial resolution CO map. Spectral resolution is 10 kms. The 2 spacing of the spectra are indicated in the upper left corner of each box as offsets relative to the nuclear pointing position. The velocity scale is relative to the ``nominal'' systemic LSR velocity of 4925 kms.