MIGHTEE-HI: HI galaxy properties in the large scale structure environment at z 0.37 from a stacking experiment

We present the first measurement of HI mass of star-forming galaxies in different large scale structure environments from a blind survey at z∼ 0.37. In particular, we carry out a spectral line stacking analysis considering 2875 spectra of colour-selected star-forming galaxies undetected in HI at 0.23 < z < 0.49 in the COSMOS field, extracted from the MIGHTEE-HI Early Science datacubes, acquired with the MeerKAT radio telescope. We stack galaxies belonging to different subsamples depending on three different definitions of large scale structure environment: local galaxy overdensity, position inside the host dark matter halo (central, satellite, or isolated), and cosmic web type (field, filament, or knot). We first stack the full star-forming galaxy sample and find a robust HI detection yielding an average galaxy HI mass of M_ HI=(8.12± 0.75)× 10^9 M_⊙ at ∼ 11.8σ. Next, we investigate the different subsamples finding a negligible difference in M_ HI as a function of the galaxy overdensity. We report an HI excess compared to the full sample in satellite galaxies (M_ HI=(11.31±1.22)× 10^9, at ∼ 10.2 σ) and in filaments (M_ HI=(11.62± 0.90)× 10^9. Conversely, we report non-detections for the central and knot galaxies subsamples, which appear to be HI-deficient. We find the same qualitative results also when stacking in units of HI fraction (f_ HI). We conclude that the HI amount in star-forming galaxies at the studied redshifts correlates with the large scale structure environment.