Kavli Affiliate: John D. Silverman
| First 5 Authors: Masafusa Onoue, Xuheng Ding, John D. Silverman, Yoshiki Matsuoka, Takuma Izumi
| Summary:
Understanding the rapid formation of supermassive black holes (SMBHs) in the
early universe requires an understanding of how stellar mass grows in the host
galaxies. Here, we perform an analysis of rest-frame optical spectra and
imaging from JWST of two quasar host galaxies at z>6 which exhibit Balmer
absorption lines. These features in the stellar continuum indicate a lack of
young stars, similar to low-redshift post-starburst galaxies whose star
formation was recently quenched. We find that the stellar mass (log(M_* /
M_sun) > 10.6) of each quasar host grew in a starburst episode at redshift 7 or
8. One of the targets exhibits little ongoing star formation, as evidenced by
the photometric signature of the Balmer break and a lack of spatially resolved
H-alpha emission, placing it well below the star formation main sequence at z =
6. The other galaxy is transitioning to a quiescent phase; together, the two
galaxies represent the most distant massive post-starburst galaxies known. The
maturity of these two galaxies is further supported by the stellar velocity
dispersions of their host galaxies, placing them slightly above the upper end
of the local M_BH – sigma_* relation. The properties of our two post-starburst
galaxies, each hosting an active SMBH with log(M_BH / M_sun) > 9, suggests that
black holes played a major role in shaping the formation of the first massive
galaxies in the Universe.
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