Kavli Affiliate: Jinyi Shangguan
| First 5 Authors: Yan-Rong Li, Jinyi Shangguan, Jian-Min Wang, Ric Davies, Daryl J. Santos
| Summary:
The geometric distances of active galactic nuclei (AGNs) are challenging to
measure because of their exceptionally compact structure yet vast cosmic
distances. A combination of spectroastrometry and reverberation mapping (SARM)
of broad-line regions (BLRs) constitutes a novel means to probe the geometric
distance of AGNs, which has recently become practically feasible owing to
successful interferometric observations with VLTI/GRAVITY. Here, we perform
SARM analysis of four nearby quasars: Mrk 509, PDS 456, 3C 273, and NGC 3783.
Results for the former two are reported for the first time and the latter two
are revisited using our improved BLR dynamical modeling that includes the
radial-dependent responsivity of BLRs. This allows us to self-consistently
account for the emissivity weighting of the BLR in spectroastrometry and
responsivity weighting in reverberation mapping. We obtain angular-diameter
distances of the four quasars, from which we derive a Hubble constant of
$H_0=69_{-10}^{+12},rm km,s^{-1},Mpc^{-1}$. Although this consititutes a
large uncertainty for a measurement of $H_0$, it is anticipated that the
precision will improve to a competitive level once a greater number of AGNs are
accessible following the upgrade of GRAVITY in the near future. From SARM
analysis, the black hole masses of the four quasars are also measured with the
statistical uncertainty ranging from 0.06 to 0.23 dex, consistent with the
correlations between black hole masses and properties of the host bulges.
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