Flexible Models for Galaxy Star Formation Histories Both Shift and Scramble the Optical Color-M/L Relationship

Abstract

The remarkably tight relationship between galaxy optical color and stellar mass-to-light ratio ($M_{\ast }/L$) is widely used for efficient stellar mass estimates. However, it remains unclear whether this low scatter comes from a natural order in the galaxy population, or whether it is driven by simple relationships in the models used to describe them. In this work we investigate the origins of the relationship by contrasting the derived relationship from a simple 4-parameter SED model with a more sophisticated 14-dimensional Prospector-$\alpha$ model including nonparametric star formation histories (SFHs). We apply these models to 63,430 galaxies at $0.5<z<3$ and fit a hierarchical Bayesian model (HBM) to the population distribution in the $(g-r)$--$\log (M/L_g)$ plane. We find that Prospector-$\alpha$ infers systematically higher $M_{\ast }/L$ by 0.12 dex, a result of nonparametric SFHs producing older ages, and also systematically redder rest-frame $(g-r)$ by 0.06 mag owing to the contribution from nebular emission. Surprisingly, the combined effects of the $M_{\ast }/L$ and $(g-r)$ offsets produce a similar average relationship for the two models, though Prospector-$\alpha$ produces a higher scatter of 0.28 dex compared to the simple model of 0.12 dex. Also, unlike the simple model, the Prospector-$\alpha$ relationship shows substantial redshift evolution due to stellar aging. These expected and testable effects produce overall older and redder galaxies, though the color--$M_{\ast }/L$ relationship is measured only at $0.5<z<3$. Finally, we demonstrate that the HBM produces substantial shrinkage in the individual posteriors of faint galaxies, an important first step toward using the observed galaxy population directly to inform the SED fitting priors.

References in corpus (17)

• Array Programming with NumPy
• The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
• EAZY: A Fast, Public Photometric Redshift Code
• K-corrections and filter transformations in the ultraviolet, optical, and near infrared
• The EAGLE simulations of galaxy formation: calibration of subgrid physics and model variations
• Improving the full spectrum fitting method: accurate convolution with Gauss-Hermite functions
• Some Aspects of Measurement Error in Linear Regression of Astronomical Data
• A simple model to interpret the ultraviolet, optical and infrared emission from galaxies
• An ultra-deep near-infrared spectrum of a compact quiescent galaxy at z=2.2
• 3D-HST WFC3-selected Photometric Catalogs in the Five CANDELS/3D-HST Fields: Photometry, Photometric Redshifts and Stellar Masses
• Constraining the Low-Mass Slope of the Star Formation Sequence at 0.5<z<2.5
• Color--Mass-to-Light Ratio Relations for Disk Galaxies
• The Diversity and Variability of Star Formation Histories in Models of Galaxy Evolution
• A Bayesian Population Model for the Observed Dust Attenuation in Galaxies
• Recovering stellar population parameters via different population models and stellar libraries
• SDSS-IV MaNGA: Stellar M/L gradients and the M/L-colour relation in galaxies
• The Relation between Dynamical Mass-to-Light Ratio and Color for Massive Quiescent Galaxies out to z~2 and Comparison with Stellar Population Synthesis Models

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• RUBIES: Evolved Stellar Populations with Extended Formation Histories at $z\sim 7-8$ in Candidate Massive Galaxies Identified with JWST/NIRSpec
• Inferring More from Less: Prospector as a Photometric Redshift Engine in the Era of JWST
• Quantifying the Effects of Known Unknowns on Inferred High-redshift Galaxy Properties: Burstiness, the IMF, and Nebular Physics