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 ⋆) 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 dyn) estimator as an SED-independent check on stellar mass. We first construct a statistical model of the high-dimensional space of galaxy properties; including size (R e ), velocity dispersion (σ e ), surface brightness (I e ), mass-to-light ratio (M ⋆/L), rest-frame color, Sérsic index (n), and dynamical mass (M dyn), and accounting for selection effects and covariant errors. We disentangle the correlations among galaxy properties and find that the variation in M ⋆/M dyn is driven by σ e , Sérsic index and color. We use these parameters to calibrate an SED-independent M ⋆ estimator, M ˆ ⋆ . We find the random scatter of the relation M ⋆ − M ˆ ⋆ to be 0.108 dex and 0.147 dex for quiescent and star-forming galaxies, respectively. Finally, we inspect the residuals as a function of SPS parameters (dust, age, metallicity, and star formation rate) and spectral indices (Hα, Hδ, and D n 4000). For quiescent galaxies, ∼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 ∼13% of the scatter. These results leave us with remaining unmodelled scatters of 0.055 dex and 0.122 dex for quiescent and star-forming galaxies, respectively. This can be interpreted as a conservative limit on the precision in M ⋆ that can be achieved via simple SPS modeling.