Open AccessYoung stars in the outer H i disc of NGC 6822
Author(s) -
De Blok W. J. G.,
Walter F.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06669.x
Subject(s) - physics , astrophysics , dwarf galaxy , stars , galaxy , irregular galaxy , astronomy , local group , star formation , supergiant , star count , k type main sequence star , t tauri star , interacting galaxy
We present wide‐field optical imaging covering the entire neutral hydrogen disc of the Local Group dwarf galaxy NGC 6822. These observations reveal the presence of numerous blue, young stars at large galactocentric radii well beyond R 25 . Blue stars are also found that are associated with NGC 6822's companion H i cloud, indicating that star formation was triggered in the companion in the last 10 8 yr . In general, blue stars are present where the H i surface densities reach values ≳ 5 × 10 20 cm −2 . However, over one‐third of the blue stars detected within the H i disc are found at lower surface densities. The young stars trace the distribution of the neutral hydrogen in the inner disc, but seem to be avoiding the supergiant H i shell in NGC 6822, setting a lower limit for its age of 10 8 yr . The extended distribution of young stars implies that stars can form at large galactocentric radii in dwarf galaxies; the H i is therefore not necessarily much more extended than the stellar population. This finding has important consequences for the chemical enrichment of the interstellar medium throughout (dwarf) galaxies.