The Ly alpha, C iv, and He ii nebulae around J1000+0234: a galaxy pair at the centre of a galaxy overdensity at z=4.5

L y alpha A.1216 (L y alpha) 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 alpha, C IV A.1550 (C IV ), and He II A.1640 (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 alpha, 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 alpha 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 tw o-peak ed Ly alpha profile is mainly a result of two o v erlapping and likely interacting H I clouds. We also report the serendipitous identification of three Ly alpha emitters spanning over a redshift bin delta z <= 0.007 (i.e. ? 380 km s (-1)) located at < 140 kpc from J1000 + 0234. A galaxy o v erdensity analysis confirms that J1000 + 0234 lies near the centre of a Megaparsec-scale galaxy o v erdensity 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 o v erdense regions, as the progenitors of local massive ellipticals in galaxy clusters.