The Near-Infrared Imaging of the Andromeda Galaxy

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Sick, Jonathan
astronomy , near-infrared , M31 , extragalactic
The Andromeda Galaxy (M31) is an ideal target for detailed studies of galaxy structure and tests of stellar population models. This thesis presents deep Canada-France-Hawaii Telescope WIRCam near-infrared J- and Ks-band photometric maps of M31. These near-infrared data alleviate the age-metallicity-dust degeneracy that plagues stellar population analysis of optical-only maps. For the sake of calibrating stellar population models, a detailed reconstruction of the M31 near-infrared surface brightness and a study of sky subtraction uncertainties is needed. The analysis of our 2007 and 2009 WIRCam data has revealed unexpected spatial variations in the sky background shapes over the width of the WIRCam fields. In order to solve for the offset caused by such fluctuations, we have used couplings between images. Scalar sky offsets are optimized to produce a mosaic that is seamless within 0.02% of the sky background. These offsets are solved hierarchically, to reduce the dimensionality of optimizations, and an adaptation of the Nelder Mead downhill simplex ensures a globally optimal solution. Variations in sky shape are well-characterised in median sky images built by nodding to a random ring of sky fields every 1.2 minutes. Sky shape appears consistent across the 3˚ ring of sky fields, while levels do change by ~2%, suggesting that the dominant sky structures extend beyond the M31 survey region. Planar sky offset optimization was tested and promises to significantly improve continuity across the outer disk of M31. Our near-infrared data are part of an effort to assemble a multi-wavelength data set for M31 to study a broad suite of topics in stellar and galaxy evolution.
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