Molecular gas and nuclear activity in early-type galaxies: any link with radio loudness?

Aims: We want to study the amount of molecular gas in a sample of nearby early-type galaxies (ETGs) that host low-luminosity active galactic nuclei (AGN). We look for possible differences between the radio-loud (RL) and radio-quiet (RQ) AGN. Methods: We observed the CO(1-0) and CO(2-1) spectral lines with the IRAM 30 m and NRO 45 m telescopes for eight galaxies. They belong to a large sample of 37 local ETGs that host both RQ and RL AGN. We gather data from the literature for the entire sample. Results: We report the new detection of CO(1-0) emission in four galaxies (UGC 0968, UGC 5617, UGC 6946, and UGC 8355) and CO(2-1) emission in two of them (UGC 0968 and UGC 5617). The CO(2-1)/CO(1-0) ratio in these sources is ~ 0.7 ± 0.2. Considering both the new observations and the literature, the detection rate of CO in our sample is 55± 9%, with no statistically significant difference between the hosts of RL and RQ AGNs. For all the detected galaxies we converted the CO luminosities into the molecular masses, MH2, which range from 106.5 to 108.5 M⊙, without any statistically significant differences between RL and RQ galaxies. This suggests that the amount of molecular gas does not likely set the radio loudness of the AGN. Furthermore, despite the low statistical significance, the presence of a weak trend between the H2 mass with various tracers of nuclear activity (mainly [O III] emission line nuclear power) cannot be excluded.