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The dividing line between galaxies that are quenched by reionization (“relics”) and galaxies that survive reionization (i.e., continue forming stars) is commonly discussed in terms of a halo mass threshold. We probe this threshold in a physically more complete and accurate way than has been possible to date, using five extremely high resolution (M_target= 4M_⊙) cosmological zoom-in simulations of dwarf galaxies within the halo mass range (1–4) × 10⁹M_⊙. The employed LYRA simulation model features resolved interstellar medium physics and individual, resolved supernova explosions. Interestingly, two out of five of the simulated dwarf galaxies lie close to the threshold mass but are neither full reionization relics nor full reionization survivors. These galaxies initially quench at the time of reionization but merely remain quiescent for ∼500 Myr. Atz∼ 5 they recommence star formation in a synchronous way and remain star-forming until the present day. The parallel timing indicates consistent sound-crossing and cooling times between the halos. While the star formation histories we find are diverse, we show that they are directly related to the ability of a given halo to retain and cool gas. Whereas the latter is most strongly dependent on the mass (or virial temperature) of the host halo at the time of reionization, it also depends on its growth history, the UV background (and its decrease at late times), and the amount of metals retained within the halo.

We present measurements of black hole masses and Eddington ratios (λ_Edd) for a sample of 38 bright (M₁₄₅₀< −24.4 mag) quasars at 5.8 ≲z≲ 7.5, derived from Very Large Telescope/X–shooter near–IR spectroscopy of their broad Civand Mgiiemission lines. The black hole masses (on average,M_BH∼ 4.6 × 10⁹M_⊙) and accretion rates (0.1 ≲λ_Edd≲ 1.0) are broadly consistent with that of similarly luminous 0.3 ≲z≲ 2.3 quasars, but there is evidence for a mild increase in the Eddington ratio abovez≳ 6. Combined with deep Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [CII] 158μm line from the host galaxies and VLT/MUSE investigations of the extended Lyαhalos, this study provides fundamental clues to models of the formation and growth of the first massive galaxies and black holes. Compared to local scaling relations,z≳ 5.7 black holes appear to be over-massive relative to their hosts, with accretion properties that do not change with host galaxy morphologies. Assuming that the kinematics of theT∼ 10⁴K gas, traced by the extended Lyαhalos, are dominated by the gravitational potential of the dark matter halo, we observe a similar relation between black hole mass and circular velocity as reported forz∼ 0 galaxies. These results paint a picture where the first supermassive black holes reside in massive halos atz≳ 6 and lead the first stages of galaxy formation by rapidly growing in mass with a duty cycle of order unity. The duty cycle needs to drastically drop toward lower redshifts, while the host galaxies continue forming stars at a rate of hundreds of solar masses per year, sustained by the large reservoirs of cool gas surrounding them.