Merging gas-rich galaxies that harbor low-luminosity twin quasars at z = 6.05: a promising progenitor of the most luminous quasars

Kavli Affiliate: John D. Silverman

| First 5 Authors: Takuma Izumi, Yoshiki Matsuoka, Masafusa Onoue, Michael A. Strauss, Hideki Umehata

| Summary:

We present ALMA [CII] 158 $mu$m line and underlying far-infrared (FIR)
continuum emission observations ($0”.57 times 0”.46$ resolution) toward a
quasar-quasar pair system recently discovered at $z = 6.05$ (Matsuoka et al.
2024). The quasar nuclei (C1 and C2) are faint ($M_{rm 1450} gtrsim -23$
mag), but we detect very bright [CII] emission bridging the 12 kpc between the
two objects and extending beyond them (total luminosity $L_{rm [CII]} simeq 6
times 10^9~L_odot$). The [CII]-based total star formation rate of the system
is $sim 550~M_odot$ yr$^{-1}$ (IR-based dust-obscured SFR is $sim
100~M_odot$ yr$^{-1}$), with a [CII]-based total gas mass of $sim
10^{11}~M_odot$. The dynamical masses of the two galaxies are large ($sim 9
times 10^{10}~M_odot$ for C1 and $sim 5 times 10^{10}~M_odot$ for C2).
There is a smooth velocity gradient in [CII], indicating that these quasars are
a tidally interacting system. We identified a dynamically distinct, fast [CII] component around C1: detailed inspection of the line spectrum there reveals the
presence of a broad wing component, which we interpret as the indication of
fast outflows with a velocity of $sim 600$ km s$^{-1}$. The expected mass
loading factor of the outflows, after accounting for multiphase gas, is
$gtrsim 2-3$, which is intermediate between AGN-driven and starburst-driven
outflows. Hydrodynamic simulations in the literature predicted that this pair
will evolve to a luminous ($M_{rm 1450} lesssim -26$ mag), starbursting
($gtrsim 1000~M_odot$ yr$^{-1}$) quasar after coalescence, one of the most
extreme populations in the early universe.

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