WISDOM Project -- XXV. Improving the CO-dynamical supermassive black hole mass measurement in the galaxy NGC 1574 using high spatial resolution ALMA observations

TL;DR

This study measures the supermassive black hole mass in galaxy NGC 1574 using high-resolution ALMA observations that spatially resolve the black hole's sphere of influence, demonstrating the importance of such resolution for accurate measurements.

Contribution

First spatially resolved measurement of SMBH mass in NGC 1574 using ALMA, highlighting the significance of high spatial resolution in gas dynamical modeling.

Findings

SMBH mass of (6.2±1.2)×10^7 M_sun derived from ALMA data.

Resolved a central PA warp larger than previous data suggested.

Demonstrated the importance of resolving the SMBH's sphere of influence for accurate mass measurement.

Abstract

We present a molecular gas dynamical supermassive black hole (SMBH) mass measurement in the nearby barred lenticular galaxy NGC 1574, using Atacama Large Millimeter/sub-millimeter Array observations of the $^{12}$CO(2-1) emission line with synthesised beam full-widths at half-maximum of $0.''078\times0.''070$ ($\approx7.5\times6.7$ pc$^2$). The observations are the first to spatially resolve the SMBH's sphere of influence (SoI), resulting in an unambiguous detection of the Keplerian velocity increase due to the SMBH towards the centre of the gas disc. We also detect a previously known large-scale kinematic twist of the CO velocity map, due to a position angle (PA) warp and possible mild non-circular motions, and we resolve a PA warp within the central $0.''2\times0.''2$ of the galaxy, larger than that inferred from previous intermediate-resolution data. By forward modelling the data cube, we infer a SMBH mass of $(6.2\pm1.2)\times10^7$ M$_\odot$ ($1\sigma$ confidence interval), slightly smaller than but statistically consistent with the SMBH mass derived from the previous intermediate-resolution data that did not resolve the SoI, and slightly outside the $1\sigma$ scatter of the SMBH mass -- stellar velocity dispersion relation. Our measurement thus emphasises the importance of observations that spatially resolve the SMBH SoI for accurate SMBH mass measurements and gas dynamical modelling.