A MegaCam Survey of Outer Halo Satellites. I. Description of the Survey* ^†

Abstract

We describe a deep, systematic imaging study of satellites in the outer halo of the Milky Way. Our sample consists of 58 stellar overdensities -i.e., substructures classified as either globular clusters, classical dwarf galaxies, or ultra-faint dwarf galaxies -that are located at Galactocentric distances of R GC ≥ 25 kpc (outer halo) and out to ∼ 400 kpc. This includes 44 objects for which we have acquired deep, wide-field, gand rband imaging with the MegaCam mosaic cameras on the 3.6m Canada-France-Hawaii Telescope and the 6.5m Magellan-Clay telescope. These data are supplemented by archival imaging, or published gr photometry, for an additional 14 objects, most of which were discovered recently in the Dark Energy Survey (DES). We describe the scientific motivation for our survey, including sample selection, observing strategy, data reduction pipeline, calibration procedures, and the depth and precision of the photometry. The typical 5σ point-source limiting magnitudes for our MegaCam imaging -which collectively covers an area of ≈ 52 deg 2 -are g lim 25.6 and r lim 25.3 AB mag. These limits are comparable to those from the coadded DES images and are roughly a half-magnitude deeper than will be reached in a single visit with LSST. Our photometric catalog thus provides the deepest and most uniform photometric database of Milky Way satellites available for the foreseeable future. In other papers in this series, we have used these data to explore the blue straggler populations in these objects, their density distributions, star formation histories, scaling relations and possible foreground structures.

Stellar Density Profiles of Dwarf Spheroidal Galaxies

“…The M18 fields which pass this criteria are those for Bootes II, Coma Berenices, Canes Venatici II, Hercules, Leo V, Pisces II, and Willman I. In total, the combination of adopted SDSS, PS1, DES and Muñoz et al (2018) data cover 42 known dSph satellites of the Milky Way. We omit 4 of these galaxies from our sample.…”

A MegaCam Survey of Outer Halo Satellites. VII. A Single Sérsic Index versus Effective Radius Relation for Milky Way Outer Halo Satellites* †

“…Observations of 44 of these objects were carried out using the MegaCam imager on the Canada-France-Hawaii Telescope (CFHT) in the northern hemisphere and the Megacam imager on the Magellan II-Clay Telescope at Las Campanas Observatory in the southern hemisphere. The data for the remaining 14 objects were obtained from different sources, most of them from public data from the DES Year Release 1 (see Muñoz et al 2018a for details). Muñoz et al (2018a) described the data reduction, astrometry, point source photometry, and photometric calibration performed on the whole sample in order to obtain a homogeneous data set.…”

“…The data for the remaining 14 objects were obtained from different sources, most of them from public data from the DES Year Release 1 (see Muñoz et al 2018a for details). Muñoz et al (2018a) described the data reduction, astrometry, point source photometry, and photometric calibration performed on the whole sample in order to obtain a homogeneous data set. To measure the structural parameters and density profiles, a maximum likelihood approach was applied to the observations of every object, assuming a Sérsic density profile (Sérsic 1968) plus a background density (Muñoz et al 2018b).…”

“…It is important to mention that, although our observations come from different instruments and full photometric homogeneity is not possible, as described in Muñoz et al (2018a), care was taken to make the data set as homogeneous as possible: the Megacam imagers used to create the primary catalog are similar in structure and performance, the same bands were used for all 58 objects, the same reduction pipeline and techniques were used for all objects, and the spatial coverage for every object in our data set is comparable (at least five effective radii), with only a few exceptions.…”

“…This paper is part of a series of articles based on a catalog of structural parameters constructed from deep, wide, and homogeneous observations of 58 satellite objects located in the outer halo of the MW (Muñoz et al 2018a(Muñoz et al , 2018b. These parameters include the half-light radius, surface brightness, luminosity, ellipticity, and Sérsic index.…”