PHANGS–HST: Star Cluster Spectral Energy Distribution Fitting with CIGALE
The sensitivity and angular resolution of photometric surveys executed by theHubble Space Telescope(HST) enablestudies of individual star clusters in galaxies out to a few tens of megaparsecs. The fitting of spectral energy distri-butions (SEDs) of star clusters is essential for measuring their physical properties and studying their evolution. Wereport on the use of the publicly available Code Investigating GALaxy Emission (cigale) SED fitting package toderive ages, stellar masses, and reddenings for star clusters identified in the Physics at High Angular resolution inNearby GalaxieS–HST (PHANGS–HST) survey. Using samples of star clusters in the galaxy NGC 3351, we presentresults of benchmark analyses performed to validate the code and a comparison to SED fitting results from the LegacyExtraGalactic Ultravolet Survey (LEGUS). We consider procedures for the PHANGS–HST SED fitting pipeline, e.g.,the choice of single stellar population models, the treatment of nebular emission and dust, and the use of fluxes versusmagnitudes for the SED fitting. We report on the properties of clusters in NGC 3351 and find, on average, the clustersresiding in the inner star-forming ring of NGC 3351 are young (<10 Myr) and massive (105M) while clusters inthe stellar bulge are significantly older. Cluster mass function fits yieldβvalues around−2, consistent with priorresults with a tendency to be shallower at the youngest ages. Finally, we explore a Bayesian analysis with additionalphysically-motivated priors for the distribution of ages and masses and analyze the resulting cluster distributions.
Paper submitted to MNRAS. Submitted version found here