Abstract
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 158 μm transition of C+, the 21-cm line of HI, the Paβ line of HII, and the continuum at 21 cm and 2.2 μm wavelengths. We have also determined various integrated intensities, notably of HCO+ and near-IR H2 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 = 150 K) and have high molecular gas densities (n(H2) ≈ 104 cm-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 106 M⊙ 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-H2 conversion factor X found earlier, characteristic of starforming low-metallicity regions.
Original language | English (US) |
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Pages (from-to) | 87-97 |
Number of pages | 11 |
Journal | Astronomy and Astrophysics |
Volume | 397 |
Issue number | 1 |
DOIs | |
State | Published - Jan 2003 |
Keywords
- Galaxies: ISM
- Galaxies: individual: NGC 6822
- Galaxies: irregular
- Galaxies: local group
- ISM: molecules
- Radio lines: ISM