The Ionised- and Cool-Gas Content of The BR1202-0725 System as seen by MUSE and ALMA
Abstract
We present 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 utilise these data in conjunction with existing ALMA observations to compare and contrast the spatially resolved ionised- and cool-gas content of this system which hosts a quasar (QSO), a sub-millimeter galaxy (SMG), the two known optical companions ("LAE1", "LAE2"), and an additional companion discovered in this work "LAE3" just 5 arcsec 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≥1E-17 erg/s/cm2/arcsec2. 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) but the gas motion is to some extent kinematically coupled with the previously observed [CII] bridge between the QSO and the SMG. We note that the object known in the literature as LAE2 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 LAE3 are typical of high-redshift LAEs; we measure FLyα(LAE3) = 0.240.03E-16 erg/s/cm2, corresponding to SFRLyα≈\ 5.00.5 M/yr. The velocity width is v(LAE3) ≈ 400 km/s, and equivalent width EW0(Lyα\,5σ\,lim)≥ 34.05 \, consistent with star formation being the primary driver of Lyα emission. We also note a coherent absorption feature at -400km/s in spectra from at least three objects; the QSO, LAE1 and "LAE2" which could imply the presence of an expanding neutral gas shell with an extent of at least 24 pkpc.