Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Hannah Übler, Hannah Übler, , ,
| Summary:
We present observational evidence for three massive, accreting black holes in
the $z=5.0167$ galaxy J0148-4214 from JWST/NIRSpec-IFU spectroscopy. The black
holes are revealed through broad H$alpha$ emission (FWHM = 430-2920 km/s)
without a forbidden-line counterpart in the bright [O III] doublet. Channel
maps of the asymmetric central H$alpha$ profile isolate two spatially distinct
broad line regions (BLRs), separated by $190pm40$ pc, while a third BLR is
found in the galaxy outskirts with a projected separation of 1.7 kpc. Using
single-epoch virial relations, we estimate black hole masses of
$log(M_bullet/M_odot)=7.9pm0.4$ (primary central), $5.8pm0.5$ (secondary
central) and $6.3pm0.5$ (third off-nuclear). We argue that the two central
black holes will likely rapidly merge, with a simple dynamical friction time
estimate of the order of 700 Myr. Assuming that also the off-nuclear black hole
is in the process of sinking towards the centre, it will likely lead to a
second merger, and we investigate the detection probability of such mergers
with LISA. Alternatively, the third black hole may be the result of previous
three-body interaction or a gravitational recoil, where our observations would
provide evidence that such black holes may retain their accretion discs and
BLRs even in the aftermath of such extreme dynamical interactions. The
discovery of a black hole triplet at high redshift, together with other recent
results on distant black hole pairs, indicates that multiple massive black hole
systems were common in the early Universe. Our results highlight the importance
of IFU observations for the detection of massive black hole multiplets in
distant galaxies, the progenitors of massive black hole mergers that may be
detected with next-generation gravitational wave observatories.
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