Tom Rose is a postdoctoral researcher at the University of Waterloo focusing on radio observations of massive galaxies and galaxy clusters. His principal work looks at the shadows of molecular gas clouds cast against the bright active galactic nuclei at the centres of these galaxies. This can tell us about the properties of the gas and how it relates to supermassive black hole accretion.
Talk Title and Abstract
Molecular absorption line surveys toward the AGN of brightest cluster galaxies
Observations and simulations suggest that active galactic nuclei are, to a large extent, powered by the accretion of cold molecular gas. Unfortunately, observing this gas on small spatial scales is difficult because it can normally only be seen en masse through weak emission lines. I will present observations which allow us to observe molecular gas in brightest cluster galaxies on scales of just a few tens to hundreds of solar masses. This is achieved by high angular resolution observations of the galaxies’ bright and extremely compact continuum sources — against which we see the shadows of gas clouds in the form of molecular absorption lines. Our ALMA surveys of several galaxies have detected dozens of gas clouds with multiple molecular tracers, including CO, CN, HCO+, and HCN. Characteristics of the absorption lines, such as their strength and width, can then be used to infer the clouds’ mass, temperature, and chemistry. Through this, we have shown that the gas in these most massive of galaxies has remarkably similar properties to gas present in the Milky Way. Perhaps most interestingly, the velocity of the gas we detect is revealed by the absorption line’s redshift. In many cases, we observe clouds which are moving towards their supermassive black hole at several hundred km/s. We also see that on average, the cold gas we detect has a bias for motion towards the core of the host galaxy, where the AGN lies.
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