The Ly α, C IV, and He II nebulae around J1000+0234: a galaxy pair at the centre of a galaxy overdensity at z = 4.5

Ly α λ1216 (Ly α) emission extending over ≳ 10 kilo parsec (kpc) around dusty, massive starbursts at z ≳ 3 might represent a short-lived phase in the evolution of present-day, massive quiescent galaxies. To obtain empirical constraints on this emerging scenario, we present Ly α, C IVλ1550 (C IV), and He II λ1640 (He II) observations taken with the Multi-Unit Spectroscopic Explorer towards J1000+0234: a galaxy pair at z = 4.5 composed of a low-mass starburst (J1000+0234-South) neighbouring a massive Submillimeter Galaxy (SMG; J1000+0234-North) that harbours a rotationally supported gas disc. Based on the spatial distribution and relative strength of Ly α, C IV, and He II, we find that star formation in J1000+0234-South and an active galactic nucleus in J1000+0234-North are dominant factors in driving the observed 40 kiloparsec-scale Ly α blob (LAB). We use the non-resonant He II line to infer kinematic information of the LAB. We find marginal evidence for two spatially and spectrally separated He II regions, which suggests that the two-peaked Ly α profile is mainly a result of two overlapping and likely interacting H I clouds. We also report the serendipitous identification of three Ly α emitters spanning over a redshift bin ∆z ≤ 0.007 (i.e. ≲ 380 km s-1) located at ≲ 140 kpc from J1000+0234. A galaxy overdensity analysis confirms that J1000+0234 lies near the centre of a Megaparsec-scale galaxy overdensity at z = 4.5 that might evolve into a galaxy cluster at z = 0. The properties of J1000+0234 and its large-scale environment strengthen the link between SMGs within LABs, tracing overdense regions, as the progenitors of local massive ellipticals in galaxy clusters.