2004/10/31 by S. Lee, Sungho Lee, Soojong Pak +8 · 1 citation
Physics and Astronomy · #Astrophysics and Star Formation Studies #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2005.09259.x
published as Mon.Not.Roy.Astron.Soc. 361 (2005) 1273-1280 · 9 pages, 3 figures, MNRAS in press, Replacement: much condensation in the length but small change in the conclusions
arxiv created 2005/06/07 · openalex publication_date 2005/08/03 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We have observed Hubble V, the brightest H ii region complex in the dwarf irregular galaxy NGC 6822, at near-infrared (near-IR; 1.8–2.4 μm) wavelengths. The line emission maps of Hubble V show the typical structure of a photodissociation region (PDR) where an ionized core, traced by compact He i emission (2.0587 μm) and Brγ emission (2.1661 μm), is surrounded by an outer layer traced by molecular hydrogen (H2) emission. The measured line ratios of H2 2–1 S(1) (2.2477 μm)/1-0 S(1) (2.1218 μm) from 0.2 to 0.6 and the unshifted and unresolved line profiles suggest that the H2 emission originates purely from a PDR. We find no evidence for shock activity. By comparing the H2 results with a PDR model, we conclude that Hubble V includes dense (104.5 cm−3) and warm PDRs. In this environment, most of the H2 molecules are excited by far-ultraviolet photons (with a field strength of 102–4 times that of the average interstellar field), although collisional processes de-excite H2 and contribute significantly to the excitation of the first vibrational level. We expect that Hubble V is in the early stage of molecular cloud dissolution.