Synthetic photometry of star clusters that accounts for the stochastic sampling of the IMF and the ionized gas: analysis of GALAXEV-C models and HST observations

Prof. Aida Wofford (UNAM)
Tuesday, September 28, 2021 - 11:00am

Low-mass (<1E4) star clusters contain a significant fraction of the stars in star-forming galaxies. In particular, star clusters with initial masses between 1E1 and 1E3 Msun contain the same total mass in stars as those with initial masses between 1E3 and 1E5 Msun. At fixed initial cluster mass and age, the observed NUV-to-NIR photometry of OB-star clusters is expected to show variations due to the stochastic sampling of the stellar initial mass function (IMF), particularly for low-mass star clusters. Thus, when deriving  the V-band extinction (Av), mass, and age of low-mass OB-star clusters via SED-fitting, one should account for this stochastic variation and its effect on the emission properties of the associated H II regions. In this talk, I will present a pilot GALAXEV-C library of synthetic NUV-to-NIR photometry that accounts for ionized gas and stochasticity. I will also describe how models from this library compare with i) deterministic models and ii) clusters observed from the NUV to the NIR as part of the HST Legacy ExtraGalactic UV survey (LEGUS). Finally, I will compare the Av value, mass, and age of the observed star clusters that are obtained using Bayesian inference with independent codes. In particular, I will compare to results obtained with SLUG. A main difference between the GALAXEV-C and SLUG models is that the SLUG models do not include the effect of the stochastic variation in the shape of the ionizing continuum, on the nebular emission.

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