We present new [OIII] 88-mu m observations of five bright z similar to 7 Lyman-break galaxies spectroscopically confirmed by ALMA through [CII] 158 mu m, unlike recent [OIII] detections where Lyman... Show moreWe present new [OIII] 88-mu m observations of five bright z similar to 7 Lyman-break galaxies spectroscopically confirmed by ALMA through [CII] 158 mu m, unlike recent [OIII] detections where Lyman alpha was used. This nearly doubles the sample of Epoch of Reionization galaxies with robust (5 sigma) [CII] and [OIII] detections. We perform a multiwavelength comparison with new deep HST images of the rest-frame UV, whose compact morphology aligns well with [OIII] tracing ionized gas. In contrast, we find more spatially extended [CII] emission likely produced in neutral gas, as indicated by an [NII] 205-mu m non-detection in one source. We find a correlation between the optical [OIII]+H beta equivalent width and [OIII]/[CII], as seen in local metal-poor dwarf galaxies. cloudy models of a nebula of typical density harbouring a young stellar population with a high-ionization parameter adequately reproduce the observed lines. Surprisingly, however, our models fail to reproduce the strength of [OIII] 88-mu m, unless we assume an alpha/Fe enhancement and near-solar nebular oxygen abundance. On spatially resolved scales, we find [OIII]/[CII] shows a tentative anticorrelation with infrared excess, L-IR/L-UV, also seen on global scales in the local Universe. Finally, we introduce the far-infrared spectral energy distribution fitting code mercurius to show that dust-continuum measurements of one source appear to favour a low dust temperature and correspondingly high dust mass. This implies a high stellar metallicity yield and may point towards the need of dust production or grain-growth mechanisms beyond supernovae. Show less
Bischetti, M.; Feruglio, C.; D'Odorico, V.; Arav, N.; Banados, E.; Becker, G.; ... ; Fiore, F. 2022
Bright quasars, powered by accretion onto billion-solar-mass black holes, already existed at the epoch of reionization, when the Universe was 0.5-1 billion years old(1). How these black holes... Show moreBright quasars, powered by accretion onto billion-solar-mass black holes, already existed at the epoch of reionization, when the Universe was 0.5-1 billion years old(1). How these black holes formed in such a short time isthe subject of debate, particularly asthey lie above the correlation between black-hole mass and galaxy dynamical mass(2,3) in the local Universe. What slowed down black-hole growth, leading towards the symbioticgrowth observed in the local Universe, and when this process started, has hitherto not been known, although black-hole feedback is a likely driver(4). Here we report optical and near-infrared observations of a sample of quasars at redshifts 5.8 less than or similar to z less than or similar to 6.6. About half ofthe quasar spectra reveal broad, blueshifted absorption line troughs, tracing black-hole-driven winds with extreme outflowvelocities, up to 17% of the speed of light. The fraction of quasars with such outflow winds at z greater than or similar to 5.8 approximate to 2.4 is times higher than at z approximate to 2-4. We infer that outflows at z greater than or similar to 5.8 inject large amounts of energy into the interstellar medium and suppress nuclear gas accretion, slowing down black-hole growth. The outflow phase may then mark the beginning of substantial black-hole feedback. The red optical colours of outflow quasars at z greater than or similar to 5.8 indeed suggest that these systems are dusty and may be caught during an initial quenching phase of obscured accretion(5). Show less