Stellar Population Inference with Prospector

Abstract

Inference of the physical properties of stellar populations from observed photometry and spectroscopy is a key goal in the study of galaxy evolution. In recent years the quality and quantity of the available data has increased, and there have been corresponding efforts to increase the realism of the stellar population models used to interpret these observations. Describing the observed galaxy spectral energy distributions in detail now requires physical models with a large number of highly correlated parameters. These models do not fit easily on grids and necessitate a full exploration of the available parameter space. We present Prospector, a flexible code for inferring stellar population parameters from photometry and spectroscopy spanning UV through IR wavelengths. This code is based on forward modeling the data and Monte Carlo sampling the posterior parameter distribution, enabling complex models and exploration of moderate dimensional parameter spaces. We describe the key ingredients of the code and discuss the general philosophy driving the design of these ingredients. We demonstrate some capabilities of the code on several datasets, including mock and real data.

Deriving ages and horizontal branch properties of integrated stellar populations

“…The bias towards younger ages found in old (> 9 Gyr) clusters when using this type of models is clear, and is consistent with what has been found in other recent works (e.g. Conroy et al 2018;Gonçalves et al 2020;Johnson et al 2020).…”

“…Finally, we note there is the potential to improve these results by folding in the information about the SED when modelling the stellar integrated stellar populations like it is done with other algorithms e.g. Johnson et al (2020); Werle et al (2020), as well as implementing a more sophisticated modelling of the extended HB. This will be explored in a future work.…”

“…However, despite all this, the presence of extended HB stars in old stellar populations remains a severe limitation in the age determination of unresolved stellar populations, even when using state-of-the-art tools e.g. Perina et al (2011); Conroy et al (2018); Gonçalves et al (2020); Johnson et al (2020).…”

SQuIGGLE: Studying Quenching in Intermediate-z Galaxies -- Gas, AnguLar Momentum, and Evolution

“…In this section, we use the Prospector stellar population synthesis fitting code Leja et al 2017;Johnson et al 2020) to investigate the stellar masses, dust properties, metallicities, SFRs, and star formation histories (SFHs) of galaxies in the SQuIGG LE sample.…”

“…We fit the SEDs of all SQuIGG LE galaxies using the Prospector stellar population synthesis fitting software Leja et al 2017;Johnson et al 2020). We use the dynesty dynamic nested sampling package (Speagle 2020), the FSPS stellar population synthesis models (Conroy et al 2009;Conroy & Gunn 2010), the MILES spectral library (Sánchez-Blázquez et al 2006;Falcón-Barroso et al 2011), and the MIST isochrones (Choi et al 2016;Dotter 2016;based on MESA, Paxton et al 2011.…”