The Extent of NGC 6822 Revealed by Its C Star Population

Using the CFH12K camera, we apply the four-band photometric technique to identify 904 carbon stars in an area 28′ × 42′ centered on NGC 6822. A few C stars outside of this area were also discovered with the Las Campanas Swope Telescope. The NGC 6822 C star population has ⟨I⟩ = 19.26 leading to an ⟨MI⟩ = -4.70, a value essentially identical to the mean magnitude obtained for the C stars in IC 1613. Contrary to stars highlighting the optical image of NGC 6822, C stars are seen at large radial distances and trace a huge, slightly elliptical halo, which does not coincide with the huge H I cloud surrounding NGC 6822. The previously unknown stellar component of NGC 6822 has a exponential scale length of 3.′0±0.′1 and can be traced to 5 scale lengths. The C/M ratio of NGC 6822 is evaluated to be 1.0 ± 0.2.