Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Qinyue Fei, John D. Sivlerman, Seiji Fujimoto, Ran Wang, Luis C. Ho
| Summary:
We conduct a study of the gas kinematics of two quasar host galaxies at
$zgtrsim6$ traced by the [CII] emission line using ALMA. By combining deep
observations at both low and high resolution, we recover the diffuse emission,
resolve its structure, and measure the rotation curves from the inner region of
the galaxy to its outskirts using DysmalPy and 3DBarolo. Assuming that both
galaxies exhibit disk rotation driven by the gravitational potential of the
galaxy, we find that the best-fit disk models have a $V_{rm rot}/sigma
approx 2$ and inferred circular velocities out to $sim$6-8 kpc scales, well
beyond the likely stellar distribution. We then determine the mass profiles of
each component (stars, gas, dark matter) with priors on the baryon and dark
matter properties. We find relatively large dark matter fractions within their
effective radii ($f_{rm DM}(R<R_e)$ = $0.61_{-0.08}^{+0.08}$ and
$0.53_{-0.23}^{+0.21}$, respectively), which are significantly larger than
those extrapolated from lower redshift studies and remain robust under
different input parameters verified by Monte-Carlo simulations. The large
$f_{rm DM}(R<R_e)$ corresponds to halo masses of $sim 10^{12.5}-10^{12.8},
M_odot$, thus representative of the most massive halos at these redshifts.
Notably, while the masses of these SMBHs are approximately 1 dex higher than
the low-redshift relationship with stellar mass, the closer alignment of SMBH
and halo masses with a local relationship may indicate that the early formation
of these SMBHs is linked to their dark matter halos, providing insights into
the co-evolution of galaxies and black holes in the early universe.
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