Galaxy And Mass Assembly (GAMA): Stellar-to-Dynamical Mass Relation I. Constraining the Precision of Stellar Mass Estimates

Abstract

In this empirical work, we aim to quantify the systematic uncertainties in stellar mass $(M_{\star })$ estimates made from spectral energy distribution (SED) fitting through stellar population synthesis (SPS), for galaxies in the local Universe, by using the dynamical mass $(M_{\text{dyn}})$ estimator as an SED-independent check on stellar mass. We first construct a statistical model of the high dimensional space of galaxy properties; size $(R_e)$, velocity dispersion $(\ddot{I}{ƒ}_e)$, surface brightness $(I_e)$, mass-to-light ratio $(M_{\star }/L)$, rest-frame colour, Sérsic index $(n)$ and dynamical mass $(M_{\text{dyn}})$; accounting for selection effects and covariant errors. We disentangle the correlations among galaxy properties and find that the variation in $M_{\star }/M_{\text{dyn}}$ is driven by $\ddot{I}{ƒ}_e$, Sérsic index and colour. We use these parameters to calibrate an SED-independent $M_{\star }$ estimator, ${\hat{M}}_{\star }$. We find the random scatter of the relation $M_{\star }-{\hat{M}}_{\star }$ to be $0.108\text{dex}$ and $0.147\text{dex}$ for quiescent and star-forming galaxies respectively. Finally, we inspect the residuals as a function of SPS parameters (dust, age, metallicity, star formation rate) and spectral indices (H$\hat{I}\pm$, H$\hat{I}´$, $D_{n}4000)$. For quiescent galaxies, $\sim 65\%$ of the scatter can be explained by the uncertainty in SPS parameters, with dust and age being the largest sources of uncertainty. For star-forming galaxies, while age and metallicity are the leading factors, SPS parameters account for only $\sim 13\%$ of the scatter. These results leave us with remaining unmodelled scatters of $0.055\text{dex}$ and $0.122\text{dex}$ for quiescent and star-forming galaxies respectively. This can be interpreted as a conservative limit on the precision in $M_{\star }$ that can be achieved via simple SPS-modelling.

Accepted for publication in the Astrophysical Journal on 14 June 2023