RGB stars in NGC 6822, Ca II triplet

Our assignment of individual reddening values makes our analysis more sensitive to spatial variations in metallicity than previous studies. We divide our sample into metal-rich and metal-poor stars; the former were found to cluster towards small radii with the metal-poor stars more evenly distributed across the galaxy. The velocity dispersion of the metal-poor stars was found to be higher than that of the metal-rich stars {sigma}_vMP_=27.4km/s; {sigma}_vMR_=21.1km/s); combined with the age-metallicity relation this indicates that the older populations have either been dynamically heated during their lifetimes or were born in a less disc-like distribution than the younger stars..

The low ratio v_rot_/{sigma}_v_ suggests that within the inner 10-arcmin, NGC 6822's stars are dynamically decoupled from the HI gas, and possibly distributed in a thick disc or spheroid structure.