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Research Projects


The focus of my research is the conditions in the molecular gas in the central hundred parsecs of our galaxy. What processes heat these clouds to temperatures far in excess of those in the disk? How dense do the giant molecular clouds in this region become, and why do the majority of them not show signs of star formation?

Answering these questions in our own galaxy can help us to understand the processes which operate on the molecular gas in the unresolved centers of other galaxies, both active and quiescent.

Recent Publications:

Mills, E.A.C., et al. Abundant CH3OH Masers but no New Evidence for Star Formation in GCM0.253+0.016. 2015, ApJ, 805:72-96

Mills, E.A.C., et al. The Excitation of HCN and HCO+ in the Galactic Center Circumnuclear Disk. 2013, ApJ, 779:47-67

Mills, E.A.C. & Morris, M.R. Detection of Widespread Hot Ammonia in the Galactic Center. 2013, ApJ, 772:105-124


An ATCA survey of the Central 500 Parsecs


SWAG My newest project is a 450 hour survey of H2O and NH3 with the Australia Telescope Compact Array; I am a Co-I with Juergen Ott and David Meier. Our goal is to resolve the physical conditions in Galactic center molecular gas, and the mechanisms responsible. Observations will begin in 2014.


A VLA study of Galactic Center Molecular Cloud Properties


Brick I am the PI for a RSRO (Resident Shared Risk Observing) project using the updated capabilities of the Karl G. Jansky Very Large Array to investigate the nature of the molecular gas heating in the central 200 parsecs of the Galactic center. In January 2012 we observed 20 fields toward the Galactic center, and we are imaging the continuum and numerous molecular lines in these fields to study the temperature and density structure of the molecular clouds, and their interaction with their environment. An overview of the survey is published here . We also have a poster on this work which was presented at Protostars and Planets VI, with an accompanying video.



Properties of Extremely Hot Gas in the Galactic Center


Ammonia 9-9 One of my primary interests in the gas in the central kiloparsec of our Galaxy is just how extreme the conditions can become: how hot and dense is the molecular gas here? Using Green Bank Telescope observations of the ammonia molecule, we measured a very hot (~400 K) gas component in the clouds in this region. This study is published, and we are now working to determine just how much of the gas is this hot, and to investigate whether the properties of this hot gas vary with environment, from the center of our Galaxy to the centers of more extreme starburst galaxies (and whether it is even hot at all!).




Gas near the Supermassive Black Hole: Dense Enough to Form Stars?


Ammonia 9-9 One region I am particularly interested in is the Circumnuclear disk at the center of the Galaxy. This is a rotating ring of gas and dust about 5 light years away from the central supermassive black hole. This structure is intriguing because it is the closest dense gas to the black hole, and the conditions in this gas (how hot it is, and whether it can hold together or will be torn apart by the tidal pull of the black hole) likely depend on its proximity to this central source. I have been involved in investigations of the future fate of this disk which are trying to determine whether it will form stars, or if the structure we see is unstable. The current results indicate that almost all of the gas is not dense enough to form stars, and we need to probe further to determine what it will do instead!



The Extinction toward the Sgr A East HII regions


Hubble As part of a Hubble study of the central hundred parsecs of the Galaxy in the Paschen Alpha emission line of hydrogen, I investigated a group of HII regions around young stars located 10 parsecs from the central supermassive black hole. These HII regions are curious because they appear to lie just at the edge of a supernova remnant, however the ages of the HII regions appear to be inconsistent with the supernova triggering their formation. I compared the Paschen alpha emission from these stars to archival radio data in order to determine the extinction toward these regions and better understand their placement with respect to the supernova remnant and a nearby molecular cloud. You can read more about this work in Mills et al. 2011