Radial scalelengths of the galactic thin and thick disc with 2MASS data

Abstract

This paper presents a global analysis of the 2MASS (Two Micron All Sky Survey) data as observed in seven fields at different galactic latitudes in our Galaxy. The data allow the preliminary determination of the scale parameters, which lead to strong constraints on the radial and vertical structure of the galactic thin and thick disc. The interpretation of star counts and colour distributions of stars in the near-infrared with the synthetic stellar population model gives strong evidence that the galactic thin disc density scalelength (h R ) is rather short (2.8 ± 0.3 kpc). The galactic thick disc population is revisited in the light of new data. We find the thick disc to have a local density of 3.5 ± 2.0 per cent of the thin disc, exponential scaleheight (h z ) of 860±200 pc and exponential scalelength (h R ) of 3.7 ± 0.8 0.5 kpc.