WISDOM project -- XIV. SMBH mass in the early-type galaxies NGC0612, NGC1574, and NGC4261 from CO dynamical modelling

Abstract

We present a CO dynamical estimate of the mass of the super-massive black hole (SMBH) in three nearby early-type galaxies: NGC0612, NGC1574 and NGC4261. Our analysis is based on Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 3-6 observations of the ${}^{12}$CO(2-1) emission line with spatial resolutions of $14-58$ pc ($0.01"-0.26"$). We detect disc-like CO distributions on scales from $\lesssim 200$ pc (NGC1574 and NGC4261) to $\approx 10$ kpc (NGC0612). In NGC0612 and NGC1574 the bulk of the gas is regularly rotating. The data also provide evidence for the presence of a massive dark object at the centre of NGC1574, allowing us to obtain the first measure of its mass, $M_{\mathrm{BH}}=(1.0\pm 0.2)\times 10^8$ M${}_{\odot }$ (1$\ddot{I}ƒ$ uncertainty). In NGC4261, the CO kinematics is clearly dominated by the SMBH gravitational influence, allowing us to determine an accurate black hole mass of $(1.62\pm 0.04)\times 10^9$ M${}_{\odot }$ ($1\ddot{I}ƒ$ uncertainty). This is fully consistent with a previous CO dynamical estimate obtained using a different modelling technique. Signs of non-circular gas motions (likely outflow) are also identified in the inner regions of NGC4261. In NGC0612, we are only able to obtain a (conservative) upper limit of $M_{\mathrm{BH}}\lesssim 3.2\times 10^9$ M${}_{\odot }$. This has likely to be ascribed to the presence of a central CO hole (with a radius much larger than that of the SMBH sphere of influence), combined with the inability of obtaining a robust prediction for the CO velocity curve. The three SMBH mass estimates are overall in agreement with predictions from the $M_{\mathrm{BH}}-\ddot{I}{ƒ}_{\star }$ relation.

Main text: 20 pages, 14 Figures; Appendix: 7 pages, 6 Figures. Accepted for publication in MNRAS on 2023 March 28