I will present a measurement of the supermassive black hole (SMBH) mass in NGC 383, a nearby lenticular galaxy hosting a low-power radio jet, based on ALMA observations of the CO(2-1) emission line with an angular resolution of 0.′′050 × 0.′′024 (≈ 16 pc × 8 pc). These observations spatially resolve the nuclear molecular gas disc down to ≈ 41300 Schwarzschild radii and the SMBH sphere of influence by a factor of ≈ 24 radially, better than any other SMBH mass measurement using molecular gas to date and probing the same physical scale as observations of nuclear megamaser discs with VLBI. We detect a clear Keplerian increase (towards the centre) of the (deprojected) circular velocities up to 1040 km/s and evidence for a mild position angle warp and/or non-circular motions within the central ≈ 0.′′3. If confirmed, the position angle warp would imply that the ratio jet in the galaxy is more aligned with the circumnuclear molecular gas disc than the large-scale molecular gas disc, a feature previously only seen in megamaser discs. By forward modelling the mass distribution and ALMA data cube, we infer a SMBH mass of (3.59 ± 0.18) × 10^9 M⊙ (1휎 confidence interval), more precise (5%) but consistent with (only ≈ 1.4휎 smaller than) the previous measurement using lower-resolution molecular gas data. Our measurement emphasises the importance of high spatial resolution observations to obtaining precise SMBH masses and probing CO gas closer to the accretion disc that powers the central AGN.
BIO
Hengyue Zhang (张恒悦) is a third-year PhD student in Astrophysics at Oxford University. He is working with Prof. Martin Bureau in the WISDOM collaboration on measuring the masses of supermassive black holes using high-resolution molecular gas observations with ALMA to constrain black hole-galaxy scaling relations. He obtained a Bachelor's degree in Physics at the University of California, Santa Barbara, where he searched for nearby exoplanets and compact objects with direct imaging.
Host: Cheng Li
