KiDS 1433 CO spectra

We thus increase the still limited sample of distant BCGs with detections in multiple CO transitions. The double-horn emission for the KiDS 1433 BCG implies a low gas concentration, while a modeling of the spectra yields an extended molecular gas reservoir, with a characteristic radius of (5-7) kpc, which is reminiscent of the mature extended-disk phase that is observed in some local BCGs. For the remaining two BCGs, we are able to set robust upper limits of M_H2_/M*<0.07 and <0.23, which are among the lowest for distant BCGs.We then combined our observations with available stellar, star formation, and dust properties of the targeted BCGs, and compared them with a sample of ~100 distant cluster galaxies, including additional intermediate-z BCGs, with observations in CO from the literature.

Altogether, our analysis shows that the molecular gas properties of star-forming BCGs are heterogeneous. On the one hand, gas-rich BCGs show extended gas reservoirs that sustain the significant star formation activity, but the efficiency is low, which is reminiscent of recent gas infall. On the other hand, the existence of similarly star forming but gas-poor BCGs suggests that gas depletion precedes star formation quenching.