Molecular gas in cool-core Brightest Cluster Galaxies at z~0.4

Brightest cluster galaxies (BCG) are today passive and very massive galaxies at the center of their clusters, still accreting mass through swallowing companions, and flows of cold gas, regulated by radio-mode AGN feedback. However, their formation history is still a matter of debate. I will present new results based on NOEMA millimeter interferometric observations (24 hr in total), mapping the cold molecular gas (CO) that feeds the star formation of distant BCGs. We selected three among the strongest cool-core BCGs at intermediate redshifts (z=~0.4), all associated with powerful radio-loud AGN, namely RX 1532, MACS 1447, and CHIPS 1911. Previous unresolved millimeter observations and multi-wavelength analysis showed that they are among the most star forming (SFR~100 Msun/yr) and gas rich (MH2~1e+11 Msun) BCGs at intermediate redshifts. The selected BCGs are thus caught in a phase of rapid mass assembly, which makes them ideal targets for high-resolution observations of their molecular gas. We find that all three BCGs show point-like and steep-spectrum (alpha=0.8) continuum emission at mm wavelengths, interpreted as optically-thin synchrotron emission from the AGN. By combining our NOEMA intensity and velocity maps with archival deep optical / IR images from HST, we unambiguously detect in-situ star formation, filaments of accreting cold gas likely regulated by AGN feedback, disturbed morphology associated with tidal tails of molecular gas, as well as gas compression and tails originated from ram pressure stripping. Altogether, despite the underlying homogeneous selection, the BCGs exhibit a broad variety of environment-driven mechanisms responsible for the processing of their cold gas: cooling flows, galactic tides, and ram pressure stripping. This study thus sheds new insights on the physical mechanisms responsible for the mass assembly of galaxies hosting AGN at the center of clusters.