Presentation #113.03 in the session “Galaxy Morphology and Star Formation”.
In this talk, we aim to present our first insights from the application of quantitative measures of morphology in star cluster classification and evolution. We perform the analysis that led us to these insights on samples of clusters drawn from the PHANGS-HST survey, a 122 orbit HST Treasury Program designed to investigate fundamental aspects of star formation in 38 nearby galaxies. The first set of clusters we analyze are ones specially selected for the derivation of aperture corrections, to which effect they are in relative isolation to prevent contamination due to light from nearby sources, and they are relatively bright. During the selection process, these clusters are separated into three classes; centrally concentrated with a symmetric light profile (class 1), centrally concentrated and with an asymmetric light profile (class 2), and multi-peaked compact associations (class 3). We began our search with an investigation featuring the M20 parameter, or the normalized second-order moment of the brightest 20% of the flux from a light source, which has widely been used to quantify galaxy morphologies. Measuring M20 on our isolated set of clusters we find that this parameter is remarkably effective in separating the class 1 and 2 clusters from class 3’s, successfully capturing the multi-peaked light profile of compact associations. Importantly, further testing reveals this result to hold true for the full cluster catalogs of the PHANGS-HST science products, albeit with slightly less significance. This affirms that the distinguishing power of M20 does not disappear even when measured on clusters not in relative isolation. The UBVI colors of our clusters reveal another important trend: class 2 and 3 objects tend to reside on the bluer part of this space where younger objects reside, whereas the class 1 clusters dominantly populate the redder part where older objects reside. This shows that M20 coupled with the UBVI colors form a parameter space where all three classes of objects occupy distinct loci. We will conclude this talk by commenting on the implications of our results on the star cluster evolution paradigm, and by providing an overview of our future prospects involving similar multivariate investigations.