Structure of the Sagittarius dwarf galaxy at low Galactic latitudes

Abstract

We report the detection of $\sim$ 1500 RR Lyrae of Bailey type ab located in the Sagittarius dwarf galaxy (Sgr). These variables have been detected on two ESO Schmidt fields centred on (l,b)=(3.1 deg,-7.1 deg) and (6.6 deg, -10.8 deg), covering an area of $\sim$50 square degree. We present a surface density map of Sgr based on the spatial distribution of these RRab, allowing us to trace its structure in a region that was still almost unexplored between b=-14 deg and b=-4 deg. We present the results of the fit of different models to the density profile of Sgr. The best fit to the core of Sgr is an exponential with a scale length of 4.1 deg along the major axis. When we look at the extension of Sgr we find a break (significant at the $\sim2σ$ level) in the slope of the surface density along the main axis of Sgr. The nearly flat (or at least very slowly decreasing) profile in the outer region of Sgr shows that this dwarf galaxy is probably extending even further out our fields.