Exploring Halo Substructure with Giant Stars. VIII. The Extended Structure of the Sculptor Dwarf Spheroidal Galaxy

(Abridged) We explore the spatial distribution of stars in the Sculptor dwarfspheroidal (dSph) galaxy over an area of 7.82 deg^2. We identify red giantbranch (RGB) starts via Washington M, T_2+DDO51 photometry and a bluehorizontal branch (BHB) population to map the spatial structure of the dSph. Aspectroscopically observed subset of Sculptor candidate stars yield a systemicheliocentric velocity for the system of v_{hel}=110.43 km/s, in good agreementwith previous studies, and a global velocity dispersion of sigma_v=8.8 km/s,which may rise slightly past 0.4r_{lim}. To a limit of M~19, we find 94% of thephotometrically-selected Sculptor giant star candidates with spectrocopicmeasurements are kinematically associated with Sculptor, and four of ten starsnot selected photometrically are selected kinematically; our candidate samplesare likely to be very pure. We take considerable care in assessing thecontaminating background level in our photometric sample to ensure accuratedensity profiles. These assessments verify that we detect a considerablestellar density of Sculptor stars to the limits of our survey area in both theRGB and BHB samples. We find the Sculptor density profile is well-fit by a Kingprofile of limiting radius r_{lim} = 79.6 within ~60 arcmin, beyond which a"break" to a power law profile occurs. This break population must be either abound group of "halo stars" around the Sculptor dSph or unbound tidal debris.The latter is supported by 2D distribution analyses and, if true, implies afractional mass-loss rate of ~0.042 Gyr^{-1} for Sculptor. Finally, likely moremetal-poor RGB stars (as selected by color and magnitude) are significantlyless centrally concentrated and, therefore, constitute the primary contributorto the likely tidally-stripped parts of the dSph.Comment: 88 pages, 23 figures, 14 tables; Received 3 Jan 2005; Accepted 29 July 200