hiss, a new tool for H i stacking: application to NIBLES spectra

H i stacking has proven to be a highly effective tool to statistically analyse average H i properties for samples of galaxies which may or may not be directly detected. With the plethora of H i data expected from the various upcoming H i surveys with the SKA Precursor and Pathfinder telescopes, it will be helpful to standardize the way in which stacking analyses are conducted. In this work we present a new python-based package, hiss, designed to stack H i (emission and absorption) spectra in a consistent and reliable manner. As an example, we use hiss to study the H i content in various galaxy sub-samples from the NIBLES survey of SDSS galaxies which were selected to represent their entire range in total stellar mass without a prior colour selection. This allowed us to compare the galaxy colour to average H i content in both detected and non-detected galaxies. Our sample, with a stellar mass range of $10^8 \lt {{ M}}_\star \, (\text{M}_\odot) \lt 10^{12}$, has enabled us to probe the H i-to-stellar mass gas fraction relationship more than half an order of magnitude lower than in previous stacking studies.