STAR CLUSTER PROPERTIES IN TWO LEGUS GALAXIES COMPUTED WITH STOCHASTIC STELLAR POPULATION SYNTHESIS MODELS
- Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)
- Department of Astronomy, Oskar Klein Centre, Stockholm University, SE-10691 Stockholm (Sweden)
- Institute for Computational Cosmology and Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom)
- Institut d’Astrophysique de Paris, 98bis Boulevard Arago, F-75014 Paris (France)
- Department of Astronomy, University of Massachusetts–Amherst, Amherst, MA (United States)
- Space Telescope Science Institute, Baltimore, MD (United States)
- Centre for Astronomy, Institute for Theoretical Astrophysics, University of Heidelberg, Heidelberg (Germany)
- Korea Astronomy and Space Science Institute, Daejeon (Korea, Republic of)
- Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL (United States)
- Department of Astronomy, University of Wisconsin–Madison, Madison, WI (United States)
- European Space Agency/Space Telescope Science Institute, Baltimore, MD (United States)
- Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD (United States)
- Department of Physics and Astronomy, Uppsala University, Uppsala (Sweden)
We investigate a novel Bayesian analysis method, based on the Stochastically Lighting Up Galaxies (slug) code, to derive the masses, ages, and extinctions of star clusters from integrated light photometry. Unlike many analysis methods, slug correctly accounts for incomplete initial mass function (IMF) sampling, and returns full posterior probability distributions rather than simply probability maxima. We apply our technique to 621 visually confirmed clusters in two nearby galaxies, NGC 628 and NGC 7793, that are part of the Legacy Extragalactic UV Survey (LEGUS). LEGUS provides Hubble Space Telescope photometry in the NUV, U, B, V, and I bands. We analyze the sensitivity of the derived cluster properties to choices of prior probability distribution, evolutionary tracks, IMF, metallicity, treatment of nebular emission, and extinction curve. We find that slug's results for individual clusters are insensitive to most of these choices, but that the posterior probability distributions we derive are often quite broad, and sometimes multi-peaked and quite sensitive to the choice of priors. In contrast, the properties of the cluster population as a whole are relatively robust against all of these choices. We also compare our results from slug to those derived with a conventional non-stochastic fitting code, Yggdrasil. We show that slug's stochastic models are generally a better fit to the observations than the deterministic ones used by Yggdrasil. However, the overall properties of the cluster populations recovered by both codes are qualitatively similar.
- OSTI ID:
- 22518754
- Journal Information:
- Astrophysical Journal, Vol. 812, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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