CHILES. VIII. Probing the Evolution of Average H I Content in Star-forming Galaxies over the Past 5 Gyr

Utilizing the COSMOS H I Large Extragalactic Survey (CHILES) data set, we investigate the evolution of the average atomic neutral hydrogen (H I) properties of galaxies over the continuous redshift range 0.09 < z < 0.47. First, we introduce a simple multistep, multiscale imaging and continuum subtraction process that we apply to each observing session. These sessions are then averaged onto a common uv-grid and run through a Fourier filtering artifact mitigation technique. We then demonstrate how this process results in science quality data products by comparing to the expected noise and image-cube kurtosis. This work offers the first-look description and scientific analysis after the processing of the entire CHILES database. These data are used to measure the average H I mass in four redshift bins, out to a redshift 0.47, by separately stacking blue cloud (near-UV, NUV-r = −1 to 3) and red sequence (NUV-r = 3-6) galaxies. We find little-to-no change in gas fraction for the total ensemble of blue galaxies and make no detection for red galaxies. Additionally, we split up our sample of blue galaxies into an intermediate stellar mass bin (M_* = 10⁹⁻¹⁰M_⊙) and a high stellar mass bin (M_* = 10^10−12.5M_⊙). We find that in the high-mass bin galaxies are becoming increasingly H I poor with decreasing redshift, while the intermediate-mass galaxies maintain a constant H I gas mass. We place these results in the context of the star-forming main sequence of galaxies and hypothesize about the different mechanisms responsible for their different evolutionary tracks.