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

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.