We explore the spatial distribution of stars in the Sculptor dwarf spheroidal ( dSph ) galaxy over an area of 7.82 deg ^ { 2 } , including coverage of the central region but extending mostly south and east of the dSph core .
Two methods are used to identify stars that are most likely associated with the dSph , and these filtered samples of stars are used to map its spatial structure .
First , following the method of previous contributions in this series , we utilize Washington M,T _ { 2 } + DDO 51 photometry to identify red giant branch ( RGB ) star candidates with approximately the same distance and metallicity as the Sculptor dSph .
Second , a prominent blue horizontal branch ( BHB ) population provides a fairly populous and pure sample of Sculptor stars having broadband colors unlike the bulk of the Galactic field star population .
A spectroscopically observed subset of Sculptor candidate stars ( 147 total stars : \sim 5 \% of all Sculptor candidates , \sim 10 \% of Sculptor giant candidates ) yields a systemic heliocentric velocity for the system of v _ { hel } = 110.43 \pm 0.79 { km s ^ { -1 } } , in good agreement with previous studies .
We also find a global velocity dispersion of \sigma _ { v } = 8.8 \pm 0.6 { km s ^ { -1 } } with slight indications of a rise in the velocity dispersion past \sim 0.4 r _ { lim } .
These spectra also provide a check on the reliability of our candidate Sculptor giant sample to M \sim 19 : 94 % of the photometrically-selected Sculptor giant star candidates with follow-up spectroscopy are found to be kinematically associated with Sculptor , while four out of ten stars outside of our Sculptor giant star selection criteria that we tested spectroscopically appear to be velocity members of Sculptor .
These percentages are in agreement with results for an additional 22 Sculptor field stars with radial velocities in the literature .
All available velocities show that our methodology for picking Sculptor giants is both reliable and conservative .
Thus , these giant star samples should provide a reliable means to explore the structure of the Sculptor dSph .
Nevertheless , considerable care has been taken to assess the level of background contamination in our photometric sample to ensure an accurately derived density profile of the Sculptor dSph to large radii .
Multiple background assessments verify that we detect a considerable stellar density of Sculptor stars to the limits of our main survey area for both the RGB and BHB candidate samples .
While we find that a King profile of limiting radius r _ { lim } = 79 \farcm 6 fits the density profile of Sculptor well to \sim 60 \arcmin , beyond this , we identify a “ break ” in the profile and a clearly detected population of Sculptor stars following a \Sigma \propto r ^ { -2 } decline to more than 2 r _ { lim } .
This break population must signify either the presence of an extremely broad distribution of bound “ halo stars ” around the Sculptor dSph , or the presence of unbound tidal debris .
If the latter is true , we determine a fractional mass-loss rate of approximately 0.042 { Gyr ^ { -1 } } for the Sculptor dSph .
Additional support for the notion that there is tidal disruption comes from the two-dimensional distribution of our Sculptor candidate stars : Both the RGB and BHB samples show increasingly elongated isodensity contours with radius that point to an apparent stretching reminiscent of what is seen in models of disrupting satellite galaxies .
Finally , we find that RGB stars that are more likely to be metal-poor ( based on their color and magnitude ) are significantly less centrally concentrated and therefore constitute the primary contributing stellar population to the likely tidally-stripped parts of the dSph .