Near-IR observations of NGC 6822: AGB stars, distance, metallicity and structure^*

¹ European Southern Observatory, Karl–Schwarzschild–Straße 2, 85748 Garching bei München, Germany e-mail: mcioni@eso.org
² Sterrewacht Leiden, Niels Bohrweg 2, 2333 RA Leiden, The Netherlands

Received: 7 July 2004
Accepted: 3 September 2004

Abstract

Observations in the IJK_s wave bands covering the central of the Local Group galaxy NGC 6822 have been made with the William Herschel Telescope in La Palma. They have allowed us to characterize, for the first time in the near-infrared across the whole galaxy, its late-type stellar population (i.e. red giant and asymptotic giant branch stars) and to derive from the ratio between carbon-rich and oxygen-rich asymptotic giant branch stars an indication about spatial variations in metallicity. These amount to about 1.56 dex, twice of what has been previously found within each Magellanic Cloud using the same technique. We have calibrated our photometry on the DENIS (I-band) and 2MASS (J and K_s bands) data and obtained a distance modulus of from the position of the tip of the RGB. The large scale distribution of late-type stars suggests that either the galaxy is viewed under a high inclination angle or it has a non-negligible thickness.