RESOLVE Survey Photometry and Volume-limited Calibration of the Photometric Gas Fractions Technique

TL;DR

This paper improves photometry methods for the RESOLVE survey, calibrates the photometric gas fractions technique using volume-limited data, and develops a probabilistic model for galaxy gas content predictions.

Contribution

It introduces enhanced photometry processing, a new calibration of the PGF technique, and a probabilistic modeling approach for galaxy gas fractions.

Findings

Improved photometry yields brighter magnitudes and larger radii.

Calibration using volume-limited data enhances gas fraction predictions.

Probabilistic modeling accurately predicts galaxy gas content, including upper limits.

Abstract

We present custom-processed UV, optical, and near-IR photometry for the RESOLVE survey, a volume-limited census of stellar, gas, and dynamical mass within two subvolumes of the nearby universe (RESOLVE-A and -B), complete down to baryonic mass ~10^9.1-9.3 Msun. In contrast to standard pipeline photometry (e.g., SDSS), our photometry uses optimal background subtraction, avoids suppressing color gradients, and includes 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 masses from our photometry with the RESOLVE-A HI mass census, we create 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 vs. 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, with two-component structure for red colors. We use the RESOLVE-B 21cm census to test several PGF calibrations, finding that most systematically under- or overestimate gas masses, but the full probability density method performs well.