Metallicity gradients in the Sagittarius dwarf spheroidal galaxy

¹ Institut d'Astrophysique de Paris, 98bis boulevard Arago, 75014 Paris, France
² Observatoire de Paris, 77 avenue Denfert Rochereau, 75014 Paris, France

Received: 11 April 2001
Accepted: 14 June 2001

Abstract

Metallicity gradients in the Sagittarius dwarf Galaxy (Sgr) are investigated by using infrared photometric data from the 2MASS survey. To search for metallicity effects, the giant branch in a field situated near the Center of the Sgr is compared to the giant branch in a field situated near its southern edge. The contamination of the Sgr giant branch by foreground Galactic stars is canceled by statistical subtraction of diagrams symmetrical in Galactic latitude. After subtraction it is possible to reconstruct the Sgr giant branch with excellent accuracy. The giant branch in the two fields have similar slopes but are shifted in color. Even after correction for the differential reddening between the fields, the shift in color between the branch remains, and is very significant. This variation in the color of the giant branch corresponds to a metallicity variation of about -0.25 dex. The existence of a metallicity gradient in Sgr may indicate that there are two different stellar population in Sgr. One has low metallicity, and another one of higher metallicity has a smaller spatial extension.