Molecular gas on large circumgalactic scales at z=3.47

We report the ALMA observations of the most massive (star-forming) galaxy in the redshift range 3 < z < 4 within the whole Great Observatories Origins Deep Survey South field (GOODS-S) field. We detect a large elongated structure of molecular gas around the massive primeval galaxy, traced by the CO(4−3) emission, and extended over 40 kpc. We infer a mass of the large gaseous structure of Mgas ∼ 2–6 × 10$^{11}$ M⊙. About 60 per cent of this mass is not directly associated with either the central galaxy or its two lower mass satellites. The CO extended structure is also detected in continuum thermal emission. The kinematics of the molecular gas shows the presence of different components, which cannot be ascribed to simple rotation. Furthermore, on even larger scales, we detect nine additional CO systems within a radius of 250 kpc from the massive galaxy and mostly distributed in the same direction as the CO elongated structure found in the central 40 kpc. The stacked images of these CO systems show detections in the thermal continuum and in the X-rays, suggesting that these systems are forming stars at a rate of 30–120 M⊙ yr$^{-1}$. We suggest that the extended gas structure, combined with its kinematic properties, and the gas-rich star-forming systems detected on larger scales, are tracing the inner and densest regions of large-scale accreting streams, feeding the central massive galaxy. These results corroborate models of galaxy formation, in which accreting streams are clumpy and undergo some star formation (hence enriching the streams with metals) even before accreting onto the central galaxy.This paper makes use of the following ALMA data: ADS/JAO.ALMA#2012.1.00423.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan) and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. RM acknowledges support from the ERC Advanced Grant 695671 ‘QUENCH’. RM, SC and FB acknowledge support from the Science and Technology Facilities Council (STFC). The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement no. 306476