WISEly deconstructing the Great Andromeda Galaxy
A global photometric investigation of the M 31 system is presented using the Wide-field Infrared Survey Explorer (WISE), a survey which mapped the entire sky at mid-infrared wavelengths 3.4 μm (W1), 4.6 μm (W2), 12 μm (W3) and 22 μm (W4), as well as previous studies across the electromagnetic spectrum. While numerous surveys of the galaxy exist, very few cover its extended disk and greater halo that incorporates its globular clusters and rich satellite system. WISE observed the entire region of M 31, and with multi-wavelength data and measurements having recently become available for M 31, viz., GALEX in the ultraviolet, Spitzer in the mid and far-infrared and Herschel in the far-infrared, WISE plays a complementary role towards the comprehension of the fundamental processes of formation and evolution in galaxies. A statistical classification scheme is developed to identify (and thereafter remove) the foreground Milky Way population from the WISE images, using WISE and 2MASS fluxes and colors, to obtain a clean measurement of the M 31 system. The scheme is tested using M 33, a smaller yet challenging galaxy, and is found to be an efficient method to trace the Galactic population (the results for this galaxy are, therefore, included). 104762 sources were identified as Milky Way, 70% of the total number of sources in a ~11 deg² elliptical area around the M31 region.
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