Letter to the Editor

Photometric versus dynamical stellar masses and their impact on scaling relations in nearby disc galaxies

¹ INAF – Padova Astronomical Observatory, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy
² Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
³ Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, Via G. Sansone 1, I-50019 Sesto Fiorentino, Firenze, Italy
⁴ Leiden Observatory, Leiden University, P.O. Box 9513 2300 RA Leiden, The Netherlands

^⋆ Corresponding author; antonino.marasco@inaf.it

Received: 27 January 2025
Accepted: 24 February 2025

Abstract

The study of scaling relations of disc galaxies and their evolution across cosmic time requires accurate estimates of galaxy stellar masses, M_⋆, over broad redshift ranges. While photometric M_⋆ estimates (M_phot) based on spectral energy distribution (SED) modelling methods are employed routinely at high-z, it is unclear to what extent these are compatible with dynamical M_⋆ estimates (M_dyn), available for nearby galaxies. Here, we compare newly determined, SED-model-based M_phot with previously obtained M_dyn inferred via rotation curve decomposition techniques in a sample of ∼100 nearby galaxies from the SPARC database. We find that the two mass estimates show a systematic agreement at the ∼12% (0.05 dex) level and a ∼55% (0.22 dex) scatter across almost 5 dex in M_⋆. Our M_phot estimates correspond to mass-to-light ratios in the 3.6 μm band that increase gradually with 3.6 μm luminosity, as a consequence of the earlier (later) assembly history of high-mass (low-mass) disc galaxies. The choice of using either M_dyn or M_phot has only a marginal impact on the slope and zero-point of the Tully-Fisher and Fall relations: the observed orthogonal scatter in both relations is virtually the same for the two methods, and indistinguishable from that derived using a constant mass-to-light ratio in the 3.6 μm band. M_⋆ estimates based on the assumption that discs are marginally stable lead to the largest scatter in the scaling relations.