Abstract
In a multi-wavelength survey of $13$ quasars at $5.8złesssim6.5$,
we find five objects with extremely small proximity zone sizes that may imply
UV-luminous lifetimes of $100,000$ years. Proximity zones are regions
of enhanced transmitted flux in the vicinity of the quasars that are sensitive
to the quasars' lifetimes because the intergalactic gas has a finite response
time to their radiation. We combine sub-mm observations from the Atacama Large
Millimetre Array (ALMA) and the NOrthern Extended Millimeter Array (NOEMA), as
well as deep optical and near-infrared spectra from medium-resolution
spectrographs on the Very Large Telescope (VLT) and on the Keck telescopes, in
order to identify and characterize these new young quasars, which provide
valuable clues about the accretion behavior of supermassive black holes (SMBHs)
in the early universe, and pose challenges on current black hole formation
models to explain the rapid formation of billion solar mass black holes. We
measure the quasars' systemic redshifts, black hole masses, Eddington ratios,
emission line luminosities, and star formation rates of their host galaxies.
Combined with previous results we estimate the fraction of young objects within
the high-redshift quasar population at large to be $5\%f_\rm
young9\%$. One of these objects, PSOJ158-14, shows one of the
brightest $C\,II$ emission lines ($F_line=7.180.33\,mJy$)
observed to date in high-redshift quasars, and thus indicates a highly
star-bursting host galaxy with a star formation rate of approximately
$1200\,M_ødot\,yr^-1$.
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