Weighing Supermassive Black Holes

Understanding the formation and evolution of galaxies is central to much of contemporary astrophysics. The relations between black hole mass and various galaxy properties imply a tight connection between the growth of central supermassive black holes (SMBHs) and that of galaxies, and these relations now underlie a staggering number of observations and simulations.

However, the number of reliable SMBH mass measurements is small, and the number of independent measuring methods even smaller. A team led by Prof Bureau has recently shown that the dense molecular gas of galaxies is the best tracer of their circular velocities, and thus of their masses. Most importantly, following the first SMBH mass measurement published in Nature, the team has now shown that these measurements are both much more accurate and much easier to carry out than with other methods. It is thus time to scale up those efforts and renew our knowledge of SMBHs.

As part of the WISDOM team (mm-Wave Interferometric Survey of Dark Object Masses), the student will use current mm/sub-mm telescopes to pursue a programme of SMBH mass measurements in a large sample of local galaxies spanning a range of morphological types, masses, and nuclear activities. This will primarily use ALMA, the largest ground-based telescope project in existence, on which WISDOM has received large allocations of observing time.

There are thus much data in hand already, with more to come, and the tools necessary to model the velocity fields and estimate uncertainties have already been developed. The student will thus exploit a well-oiled machinery to make multiple measurements, and thus explore how SMBH masses and galaxy properties correlate, in addition to probing the nuclear-scale gas dynamics that allows SMBHs to be fed.

The project will thus significantly increase the number of reliable SMBH masses available, and it will revolutionise our understanding of the co-evolution of SMBHs and galaxies.