2020ApJ...902...37D

We present Multi Unit Spectroscopic Explorer (MUSE) observations of the gas-rich major merger BR1202-0725 at z ∼ 4.7, which constitutes one of the most overdense fields known in the early universe. We utilize these data in conjunction with existing Atacama Large Millimeter/submillimeter Array (ALMA) observations to compare and contrast the spatially resolved ionized- and cool-gas content of this system, which hosts a quasar (QSO), a submillimeter galaxy (SMG), the two known optical companion Lyα emitters ("LAE 1" and "LAE 2"), and an additional companion discovered in this work "LAE 3" just 5'' to the north of the QSO. We find that QSO BR1202-0725 exhibits a large Lyα halo, covering ≃55 pkpc on-sky at surface-brightness levels of SB >= 1 x 10^–17 erg s^–1 cm^–2 arcsec^–2. In contrast, the SMG, of similar far-infrared luminosity and star formation rate (SFR), does not exhibit such a Lyα halo. The QSO's halo exhibits high velocity widths (∼1000 km s^–1) but the gas motion is to some extent kinematically coupled with the previously observed [C II] bridge between the QSO and the SMG. We note that the object known in the literature as LAE 2 shows no local peak of Lyα emission, rather, its profile is more consistent with being part of the QSO's extended Lyα halo. The properties of LAE 3 are typical of high-redshift LAEs; we measure F_Lyα(LAE 3) = 0.24 ± 0.03 x 10^–16 erg s^–1 cm^–2, corresponding to SFR_Lyα ≃ 5.0 ± 0.5 M_☉ yr^–1. The velocity width is Δv(LAE 3) ≃ 400 km s^–1, and the equivalent width is EW₀(Lyα_5σ^lim)≥ 34.05 Å, consistent with star formation being the primary driver of Lyα emission. We also note a coherent absorption feature at ∼-400 km s^–1 in spectra from at least three objects; the QSO, LAE 1, and LAE 2, which could imply the presence of an expanding neutral gas shell with an extent of at least 24 pkpc.