HI obs. with FAST for 113 red spirals galaxies

In this work, we observe H I content of the rest 113 massive red spiral galaxies using the Five- hundred-meter Aperture Spherical radio Telescope (FAST). 75 of the 113 galaxies have H I detection with a signal-to-noise ratio (S/N) greater than 4.7. Compared with the red spirals in the same sample that have been observed by the ALFALFA survey, galaxies observed by FAST have on average a higher S/N, and reach to a lower H I mass.

To investigate why many red spirals contain a significant amount of H I mass, we check colour profiles of the massive red spirals using images observed by the DESI Legacy Imaging Surveys. We find that galaxies with H I detection have bluer outer discs than the galaxies without H I detection, for both ALFALFA and FAST samples. For galaxies with H I detection, there exists a clear correlation between galaxy H I mass and g-r colour at outer radius: galaxies with higher H I masses have bluer outer discs.