The Ly α, C iv, and He iinebulae around J1000+0234: a galaxy pair at the centre of a galaxy overdensity atz = 4.5

Abstract

Lyα λ1216 (Lyα) emission extending over $\gtrsim \, \rm 10\, kiloparsec\, (kpc)$ 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 Lyα, 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) neighboring a massive Submillimeter Galaxy (SMG; J1000+0234 −North) that harbors a rotationally supported gas disk. Based on the spatial distribution and relative strength of Lyα, 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 Lyα 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 Lyα profile is mainly a result of two overlapping and likely interacting H i clouds. We also report the serendipitous identification of three Lyα emitters spanning over a redshift bin Δz ≤ 0.007 (i.e., $\lesssim 380\, \rm km\, s^{-1}$) located at $\lesssim 140\, \rm kpc$ from J1000+0234. A galaxy overdensity analysis confirms that J1000+0234 lies near the center 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.