ISRAEL F.P., BAAS F., RUDY R.J., SKILLMAN E.D. and WOODWARD C.E.
Abstract (from CDS):
We present maps of the first-ranked HII region complex Hubble V in the metal-poor Local Group dwarf galaxy NGC 6822 in the first four transitions of 12CO, the 158µm transition of C+, the 21-cm line of HI, the Paβ line of HII, and the continuum at 21cm and 2.2µm wavelengths. We have also determined various integrated intensities, notably of HCO+ and near-IR h50–12 emission. Although the second-ranked HII region Hubble X is located in a region of relatively strong HI emission, our mapping failed to reveal any significant CO emission from it. The relatively small CO cloud complex associated with Hubble V is comparable in size to the ionized HII region. The CO clouds are hot (Tkin=150K) and have high molecular gas densities (n(h50–12)≃104cm–3). Molecular hydrogen probably extends well beyond the CO boundaries. C+ column densities are more than an order of magnitude higher than those of CO. The total mass of the complex is about 106M☉ and molecular gas accounts for more than half of this. The complex is excited by luminous stars reddened or obscured at visual, but apparent at near-infrared wavelengths. The total embedded stellar mass may account for about 10% of the total mass, and the mass of ionized gas for half of that. Hubble V illustrates that modest star formation efficiencies may be associated with high CO destruction efficiencies in low-metallicity objects. The analysis of the Hubble V photon-dominated region (PDR) confirms in an independent manner the high value of the CO-to-h50–12 conversion factor X found earlier, characteristic of starforming low-metallicity regions.
galaxies: individual: NGC 6822 - galaxies: ISM - galaxies: irregular - galaxies: Local Group - radio lines: ISM - ISM: molecules