Predictions for the FAST telescope’s CRAFTS extragalactic H i survey

ABSTRACT The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has started the Commensal Radio Astronomy FasT Survey (CRAFTS). In this paper, we use the technical parameters of FAST derived from commissioning observations to simulate the completeness function for extragalactic H i survey of CRAFTS, H i galaxies from two kinds of mock catalogues are selected. One is generated by Monte Carlo simulation based on the interpolated mass–velocity width function of the ALFALFA $100{{\ \rm per\ cent}}$ (a.k.a. α.100) catalogue. The other is constructed by semi-analytical N-body simulation based on the ΛCDM model. Our results suggest that a two-pass CRAFTS extragalactic H i survey will be able to detect nearly 4.8 × 105 galaxies, from which the ‘faint end’ slope of the H i mass function (HIMF) can be recovered to $\mathrm{10^{7}\, M_{\odot }}$ and the ‘knee mass’ of the HIMF can be measured to a redshift of 0.1. Considering the radio frequency interference status and sensitivity limitation, CRAFTS will be efficient in detecting H i galaxies at redshifts below 0.1, which implies a tremendous potential in exploring the galaxy interactions in different environments and the spatial distribution of H i galaxies in the local universe.

The H i mass function of group galaxies in the ALFALFA survey

ABSTRACT We estimate the H i mass function (HIMF) of galaxies in groups based on thousands of ALFALFA (Arecibo Legacy Fast ALFA survey) H i detections within the galaxy groups of four widely used SDSS (Sloan Digital Sky Survey) group catalogues. Although differences between the catalogues mean that there is no one definitive group galaxy HIMF, in general we find that the low-mass slope is flat, in agreement with studies based on small samples of individual groups, and that the ‘knee’ mass is slightly higher than that of the global HIMF of the full ALFALFA sample. We find that the observed fraction of ALFALFA galaxies in groups is approximately 22 per cent. These group galaxies were removed from the full ALFALFA source catalogue to calculate the field HIMF using the remaining galaxies. Comparison between the field and group HIMFs reveals that group galaxies make only a small contribution to the global HIMF as most ALFALFA galaxies are in the field, but beyond the HIMF ‘knee’ group galaxies dominate. Finally, we attempt to separate the group galaxy HIMF into bins of group halo mass, but find that too few low-mass galaxies are detected in the most massive groups to tightly constrain the slope, owing to the rarity of such groups in the nearby Universe where low-mass galaxies are detectable with existing H i surveys.