The structure of the sculptor dwarf elliptical galaxy. I - The radial profile

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Abstract
The radial profile of the Sculptor dwarf elliptical galaxy has been determined from automated star counts of UK Schmidt Telescope Unit (UKSTU) plates. The ellipticity (e = 0.34 +/- 0.04) and position angle (P.A.(1950.0) = 95.4^deg^ +/- 4.3^deg^) are in agreement with those determined by Hodge (1961b). These profiles have been compared with King (1966) models with a range of tidal and core radii. None have been found to give an excellent fit. The best fit achieved has r_t_ = 95' and r_c_ = 8.9', and has a standard deviation of σ = 0.28 and χ^2^ = 0.71 (indicating a 95+ % confidence limit). Accepting these as roughly the correct values for the core and tidal radii, and using other data from the literature, the mass of the Galaxy has been estimated as M_G_~1.5 +/- 1.1 X 10^11^ M_sun_. However, the data deviate from this model significantly at large radii, there is an observed overdensity above that expected for the King model beyond R_maj_ = 50'. This overdensity is roughly a 2σ effect above the determined background level, and accounts for ~13% of the stars counted. This compares well with the results of Innanen and Papp (1979) that ~10% of Sculptor's variable stars are found beyond R_maj_=53' (Hodge's 1961b value for r_t_). Exponential law fits have also been made, following the suggestion (Faber and Lin 1983) that the halo dwarfs are as well fit by exponential laws as are many disk systems. The mean best fit has an exponential scale of γ= -0.053 +/- 0.001 arcmin^-1^, with a standard deviation of σ= 0.51 and χ^2^ = 3.8 (still a 95% + confidence limit). Given the distance modulus of Kunkel and Demers (1977), this implies a physical scale length of r_e_~0.43 kpc. While the data show the same excess with respect to the exponential law fits as found for the King model fits, this excess is not more severe than is seen in many disk systems. The current data, therefore, do not argue against the hypothesis that the halo dwarfs are the results of ram-pressure stripping of dI systems by the Galactic halo.

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