SUPER. VI. A giant molecular halo around a z ~ 2 quasar

Vol. 654
1. Letters

SUPER. VI. A giant molecular halo around a z ~ 2 quasar

High-redshift galaxies are much richer in gas than local ones, and their gas fraction can reach 90 percent of their baryonic mass, while it is only 5-10 percent in nearby spiral galaxies. It is however surprising to find CO emission much more extended than the stellar disk because of negative radial metallicity gradients. In the halo of CID346, a z=2.2 quasar, Cicone et al. have discovered large amounts of molecular gas, with the Atacama Compact Array (ACA). The CO(3-2) emission corresponds to 14 times more flux than that measured within an 8 kpc radius, and it extends out to 200 kpc in projected size. This is the most extended molecular reservoir that has ever been mapped. It shows complex kinematics, with an overall broad line profile of 1000km/s. CID346 has no apparent companion, but hosts AGN-driven ionized outflows. The latter may have played a crucial rule in seeding metal-enriched dense gas on halo scales.