# Young Stars in the Outer HI Disc of NGC 6822

January 30, 2003
Filed under , ,

Astrophysics, abstract
astro-ph/0301494

```From: Erwin de Blok <[email protected]>
Date: Fri, 24 Jan 2003 12:17:15 GMT   (325kb)
```

Young Stars in the Outer HI Disc of NGC 6822

Authors:
W.J.G. de Blok (Cardiff University),
F. Walter (NRAO)

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 HI cloud, indicating that star formation was triggered in the
companion in the last 10^8 yr. In general, blue stars are present where the HI
surface densities reach values > 5 x 10^20 cm^(-2). However, over one-third of
the blue stars detected are found at lower surface densities. The young stars
trace the distribution of the neutral hydrogen surprisingly well, but seem to
be avoiding the supergiant HI 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 HI 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

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