An ALMA survey of CO in submillimetre galaxies:companions, triggering, and the environment in blended sources
We present ALMA observations of the mid J 12CO emission from six single dish selected 870 mm sources in the Extended Chandra Deep Field South and UKIDSS Ultra Deep Survey fields. These six single dish submillimetre sources were selected based on previous ALMA continuum observations, which showed that each comprised a blend of emission from two or more individual submillimetre galaxies (SMGs) separated on 5 10 arcsec scales. The six single dish submillimetre sources targeted correspond to a total of 14 individual SMGs, of which seven have previously measured robust optical/near infrared spectroscopic redshifts, which were used to tune our ALMA observations. We detect CO(3 2) or CO(4 3) at z 2.3 3.7 in 7 of the 14 SMGs, and in addition serendipitously detect line emission from three gas rich companion galaxies, as well as identify four new 3.3 mm selected continuum sources in the six fields. Joint analysis of our CO spectroscopy and existing data suggests that 64( 18) per cent} of the SMGs in blended submillimetre sources are unlikely to be physically associated. However, three of the SMG fields (50 per cent) contain new, serendipitously detected CO emitting (but submillimetre faint) sources at similar redshifts to the 870 mm selected SMGs we targeted. These data suggest that the SMGs inhabit overdense regions, but that these are not sufficiently overdense on ~100 kpc scales to influence the source blending given the short lifetimes of SMGs. We find that 21+ 12{ per cent} of SMGs have spatially distinct and kinematically close companion galaxies ~8 150 kpc and 300 km s 1) which may have enhanced their star formation via gravitational interactions.