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Brightest Cluster Galaxies (BCGs) are typically massive ellipticals at thecenters of clusters. They are believed to experience strong environmentalprocessing, and their mass assembly and star formation history are stilldebated. We have selected three star forming BCGs in the equatorial field ofthe Kilo-Degree Survey (KiDS) at intermediate redshifts. We have observed themwith the IRAM-30m telescope in the first three CO transitions. We remarkablydetected all BCGs at high signal-to-noise ratio ${\rm S/N}\simeq(3.8-10.2)$,for a total of 7 detected lines out of 8, corresponding to a success rate of$88\%$. This allows us to double the number of distant BCGs with cleardetections in at least two CO lines. We have then combined our observationswith available stellar, star formation, and dust properties of the BCGs, and wehave compared them with a sample of $\sim100$ distant cluster galaxies withobservations in CO. Our analysis yields large molecular gas reservoirs$M_{H_2}\simeq(0.5-1.4)\times10^{11}~M_\odot$, excitation ratios $r_{31}=L^{\prime}_{\rm CO(3\rightarrow2)}/L^{\prime}_{\rmCO(1\rightarrow0)}\simeq(0.1-0.3)$, long depletion times $\tau_{\rmdep}\simeq(2-4)$~Gyr, and high $M_{H_2}/M_{\rm dust}\simeq(170-300)$. Theexcitation ratio $r_{31}$ of intermediate-$z$ BCGs appears to be wellcorrelated with the star formation rate and efficiency, which suggests thatexcited gas is found only in highly star forming and cool-core BCGs. Byperforming color-magnitude plots and a red sequence modeling we find thatrecent bursts of star formation are needed to explain the fact that the BCGsare measurably bluer than photometrically selected cluster members. We suggestthat a substantial amount of the molecular gas has been accreted by the KiDSBCGs, but still not efficiently converted into stars.

Star forming and gas rich brightest cluster galaxies at $z\sim0.4$ in the Kilo-Degree Survey