Neutral Hydrogen Mass in Galaxies Estimated via Optical Spectroscopy

Abstract: We propose to employ emission line luminosities obtained via optical spectroscopy to estimate the content of neutral hydrogen (HI) in galaxies. We use the optical spectroscopy data from the Mapping of Nearby Galaxies at APO (MaNGA) survey released in the frames of public DR17 of the Sloan Digital Sky Survey (SDSS). We compare the HI mass estimated by us for a large sample of SDSS/MaNGA galaxies with direct HI measurements from the ALFALFA survey and find a tight correlation between the masses with the correlation coefficient (CC) of 0.91 and the r.m.s scatter of 0.15 dex for the logarithmic mass. The obtained relationship is verified via another sample of MaNGA galaxies with HI masses measured with the Green Bank Telescope. Despite the coarser angular resolution of the radio data, the relation between the estimated and measured directly HI mass is tight as well - in this case CC=0.74 and the r.nm.s. is 0.29 dex. The established relations allow us to estimate the total mass of neutral hydrogen as well as the spatial distribution of HI surface density in galaxies from optical spectroscopic observations only in a simple and efficient way.