Resolve survey Photometry and volume-limited calibration of the Photometric gas fractions technique

Abstract

We present custom-processed ultraviolet, optical, and near-infrared photometry for the REsolved Spectroscopy of a
Local VolumE (RESOLVE) survey, a volume-limited census of stellar, gas, and dynamical mass within two
subvolumes of the nearby universe (RESOLVE-A and RESOLVE-B). RESOLVE is complete down to baryonic
mass 10 ~ 9.1 9.3 - M, probing the upper end of the dwarf galaxy regime. In contrast to standard pipeline photometry
(e.g., SDSS), our photometry uses optimal background subtraction, avoids suppressing color gradients, and
employs multiple flux extrapolation routines to estimate systematic errors. With these improvements, we measure
brighter magnitudes, larger radii, bluer colors, and a real increase in scatter around the red sequence. Combining
stellar mass estimates based on our optimized photometry with the nearly complete H I mass census for
RESOLVE-A, we create new z = 0 volume-limited calibrations of the photometric gas fractions (PGF) technique,
which predicts gas-to-stellar mass ratios (G/S) from galaxy colors and optional additional parameters. We analyze
G/S-color residuals versus potential third parameters, finding that axial ratio is the best independent and physically
meaningful third parameter. We define a “modified color” from planar fits to G/S as a function of both color and
axial ratio. In the complete galaxy population, upper limits on G/S bias linear and planar fits. We therefore model
the entire PGF probability density field, enabling iterative statistical modeling of upper limits and prediction of full
G/S probability distributions for individual galaxies. These distributions have two-component structure in the red
color regime. Finally, we use the RESOLVE-B 21 cm census to test several PGF calibrations, finding that most
systematically under- or overestimate gas masses, but the full probability density method performs well.