The Ly$\hat{I}\pm$, CIV, and HeII nebulae around J1000+0234: a galaxy pair at the center of a galaxy overdensity at $z=4.5$

Abstract

Ly$\hat{I}\pm$ $\hat{I}»$1216 (Ly$\hat{I}\pm$) emission extending over $\gtrsim 10\mathrm{kiloparsec}(\mathrm{kpc})$ around dusty, massive starbursts at $z\gtrsim 3$ 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$\hat{I}\pm$, CIV $\hat{I}»$1550 (CIV), and HeII $\hat{I}»$1640 (HeII) observations taken with the Multi Unit Spectroscopic Explorer towards J1000$+$0234: a galaxy pair at $z=4.5$ composed of a low-mass starburst (J1000$+$0234$-$South) neighboring a massive Submillimeter Galaxy (SMG; J1000$+$0234$-$North) that harbors a rotationally supported gas disk. Based on the spatial distribution and relative strength of Ly$\hat{I}\pm$, CIV, and HeII, we find that star formation in J1000+0234$-$South and an active galactic nucleus in J1000+0234$-$North are dominant factors in driving the observed 40 kiloparsec-scale Ly$\hat{I}\pm$ blob (LAB). We use the non-resonant HeII line to infer kinematic information of the LAB. We find marginal evidence for two spatially and spectrally separated HeII regions, which suggests that the two-peaked Ly$\hat{I}\pm$ profile is mainly a result of two overlapping and likely interacting HI clouds. We also report the serendipitous identification of three Ly$\hat{I}\pm$ emitters spanning over a redshift bin $\hat{I}”z\le 0.007$ (i.e., $\lesssim 380\mathrm{km}{\mathrm{s}}^{-1}$) located at $\lesssim 140\mathrm{kpc}$ 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.

Accepted for publication in MNRAS