Our group has been working on a project to measure the masses of supermassive black holes in nearby elliptical galaxies using observations from the Atacama Large Millimeter/submillimeter Array. Our strategy is to search the Hubble Space Telescope archives to find ellipticals that have very nice, round, flat dust disks around their nuclei, and then use ALMA to measure the rotation of these disks using the CO(2-1) emission line. We initially start with observations at about 0.3 arcsec resolution to check for the presence of high-velocity rotation within the black hole’s sphere of influence (the small region in the galaxy’s center where the black hole’s gravitational pull is the dominant force), and then, in cases where we see rapid rotation at small scales, we then propose for higher resolution observations to measure the black hole mass accurately. Our first paper from this project was recently accepted for publication in ApJ. It describes our overall strategy, the initial observations of NGC 1332, and our dynamical modeling method. We do see clear evidence of rapid rotation, but because these initial observations don’t fully resolve the black hole’s sphere of influence, we don’t yet get an accurate measurement of the black hole mass from this observation. Higher-resolution ALMA observations can do the job. A key takeaway point from the paper is that there are a lot of potential systematic errors that cause trouble if your observations don’t resolve the black hole’s sphere of influence, and we argue that in order to get precise and accurate measurements of black hole masses, resolving this sphere of influence region is really crucial.
You can find a prepreint here: