Extended region of the sky surrounding the Magellanic Clouds, as seen in neutral hydrogen emission. The Galactic plane, the location of the LMC and SMC, and both "leading" and "trailing" arms of the Magellanic Stream are clearly visible. The positions of the fields studied in this survey are shown by the overplotted symbols. The main control fields are marked with purple filled circles, and the ancillary control fields whose designations begin with "F4C" are shown as purple asterisks. The fields marked in blue triangles are the ones going away due north from the LMC, roughly parallel to the Galactic plane. The orange triangles show other fields that trace the extended LMC structure, with designations beginning with "F1." Fields tracing the trailing arm of the Magellanic stream are shown as light blue squares: their designations begin with "F3." Red crosses mark fields along the leading arm of the stream, designations begin with "F4." The yellow squares show fields with names beginning in "F5," designed to trace the extended structure of the SMC. The blue crosses cut across the line of motion of the LMC and designations begin with "F6." Image credit: S. Janowiecki and the Galactic All Sky Survey (McClure-Griffiths et al. 2009).
The Outer Limits Survey (OLS) is designed to detect, map, and characterize the extended structure of the Large and Small Magellanic Clouds (LMC and SMC). The survey consists of deep CTIO 4-m Mosaic2 images of 55 0 6 × 0 6 fields distributed at distances up to 20° from the Clouds, with 10 fields at larger distances representing controls for contamination by Galactic foreground stars and background galaxies. The field locations probe the outer structure of both the LMC and SMC, as well as exploring areas defined by the Magellanic Stream, the Leading Arm, and the LMC orbit as recently measured from its proper motion. The images were taken with C, M, R, I, and DDO51 filters on the CTIO Blanco 4 m telescope and Mosaic2 camera, with supporting calibration observations taken at the CTIO 0.9 m telescope. The CRI images reach depths below the oldest main-sequence (MS) turnoffs at the distance of the Clouds, thus yielding numerous probes of structure combined with good ability to measure stellar ages and metallicities. The M and DDO51 images allow for discrimination of LMC and SMC giant stars from foreground dwarfs, allowing one to use giants as additional probes of Cloud structure and populations. From photometry of eight fields located at radii of 7°-19° north of the LMC bar, MS stars associated with the LMC are found out to 16° from the LMC center, while the much rarer giants can be convincingly detected out to 11°.
OLS at a Glance
|Years of Observation||2006-2009|
|Sample:||11 Fields in the outskirts of the LMC and SMC|
|Bands||C, M, R, I, DDO51|
|Median Depth (5σ)||(C, M, R, I, DDO51) = (26.0, 24.9, 25.2, 24.3, 24.7)|
|Median Seeing||(C, M, R, I, DDO51) = (1.0, 1.1, 0.9, 0.9, 1.0) arcsec|
|Number of images||144 (11 fields, each with 2 filters in 2 depths plus 3 filters with 3 depths)|