MeerKAT H i Observations of Low Surface Brightness/Ultradiffuse Galaxy Candidates Projected around Two Southern Loose Groups

A large catalog of low surface brightness galaxies (LSBGs) from the Dark Energy Survey showed significant clustering around nearby galaxy groups and clusters. Using the HIPASS survey, we tried to determine the redshift of a subsample of these LSBGs and determine whether they were members of the groups they were projected near, but this was hampered by HIPASS’s high spectral rms. This Letter reports on MeerKAT H i observations to determine the redshifts of 52 LSBG candidates projected in the vicinity of two groups from our previous HIPASS study. The main goal is to investigate and ascertain whether these LSBGs are genuine group members. H i was detected with MeerKAT and redshifts were determined for only five of the 52 candidates within a velocity range of ±2500 km s⁻¹ of their respective group velocities. All five H i detections were blue LSBGs, and two of them were confirmed to be ultradiffuse galaxies (UDGs). Both these UDGs were group members, while the other three detections were either foreground or background galaxies. In this Letter we explore scenarios that can explain the 90% nondetection. MeerKAT’s excellent sensitivity allows us to conclude that the majority of the nondetected candidates, particularly the blue galaxies, are not group members but lie at higher redshifts. However, this still leaves the open question of why Tanoglidis LSBG candidates, in particular the red ones, appear to be clustered in projection around nearby groups.