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What do we see when we look at a nearby, well-resolved galaxy? Thousands ofindividual sources are detected in multiband imaging observations of even afraction of a nearby galaxy, and characterizing those sources is a complexprocess. This work analyses a ten-band photometric catalogue of nearly 70 000point sources in a 7.3 square arcmin region of the nearby spiral galaxy Messier83, made as part of the Early Release Science programme with the Hubble SpaceTelescope's Wide Field Camera 3. Colour distributions were measured for bothbroad-band and broad-and-narrow-band colours; colours made from broad-bandswith large wavelength differences generally had broader distributions althoughB - V was an exception. Two- and three-dimensional colour spaces were generatedusing various combinations of four bands and clustered with the K-Means andMean Shift algorithms. Neither algorithm was able to consistently segment thecolour distributions: while some distinct features in colour space wereapparent in visual examinations, these features were not compact or isolatedenough to be recognized as clusters in colour space. K-Means clustering of theUBVI colour space was able to identify a group of objects more likely to bestar clusters. Mean Shift was successful in identifying outlying groups at theedges of colour distributions. For identifying objects whose emission isdominated by spectral lines, there was no clear benefit from combiningnarrow-band photometry in multiple bands compared to a simple continuumsubtraction. The clustering analysis results are used to inform recommendationsfor future surveys of nearby galaxies.

Deconstructing a galaxy: colour distributions of point sources in Messier 83