CLUES III: Do User Choices Impact The Results of SED Fitting? Tests of 'Off-The-Shelf' Stellar Population and Dust Extinction Models in the CLUES Sample

TL;DR

This study evaluates how user choices in stellar population models and dust extinction curves affect the accuracy of spectral energy distribution fitting for young stellar clusters, highlighting significant variability at the individual level but robustness in population statistics.

Contribution

It systematically tests four SPS codes and extinction curves, quantifying their impact on SED fitting results and providing guidance on the reliability of population-level analyses.

Findings

Choice of models and extinction curves causes significant scatter in individual cluster parameters.

Population-level properties are relatively unaffected by model choices, ensuring robustness in large sample analyses.

Model and extinction curve selection can lead to up to 10-fold differences in derived cluster masses.

Abstract

The simple stellar population models produced by stellar population and spectral synthesis (SPS) codes are used as spectral templates in a variety of astrophysical contexts. In this paper, we test the predictions of four commonly used stellar population synthesis codes (YGGDRASIL, BPASS, FSPS, and a modified form of GALAXEV which we call GALAXEVneb) by using them as spectral templates for photometric SED fitting with a sample of 18 young stellar clusters. All clusters have existing HST COS FUV spectroscopy that provide constraints on their ages as well as broadband photometry from HST ACS and WFC3. We use model spectra that account for both nebular and stellar emission, and additionally test four extinction curves at different values of $R_V$. We find that for individual clusters, choice of extinction curve and SPS model can introduce significant scatter into the results of SED fitting. Model choice can introduce scatter of 34.8 Myr in age, a factor of 9.5 in mass, and 0.40mag in extinction. Extinction curve choice can introduce scatter of up to a factor of 32.3 Myr in age, a factor of 10.4 in mass, and 0.41mag in extinction. We caution that because of this scatter, one-to-one comparisons between the properties of individual objects derived using different SED fitting setups may not be meaningful. However, our results also suggest that SPS model and extinction curve choice do not introduce major systematic differences into SED fitting results when the entire cluster population is considered. The distribution of cluster properties for a large enough sample is relatively robust to user choice of SPS code and extinction curve.