Research

Often weak, but critical, atomic and molecular lines provide access to the state of the interstellar medium (ISM).  My research focuses on understanding galaxies as ecosystems, utilizing the more transparent radio frequencies (<80 GHz) to understand the interplay between  star-formation and black hole growth, and the physical and chemical state of the ISM.  My current favorite molecules include water (H₂O), methanol (CH₃OH),  ammonia (NH₃), and methanimine (CH₂NH). I mostly use telescopes like the Karl G. Jansky Very Large Array (VLA)  and  enhanced Multi-Element Radio Linked Interferometer Network ( eMERLIN),  to observe nearby galaxies. 

 A significant fraction (~20%) of Luminous and Ultraluminous Infrared Galaxies (U/LIRGS) host extremely opaque nuclei. With column densities  akin to trying to stare through 10 cm of steel, virtually no light escapes the nucleus.  Consequently, it is not known what powers the extreme infrared luminosities of these galaxies.  The power source may be an early stage of supermassive black hole growth or an unusual mode of star formation. Using radio telescopes, which observe a longer more transparent wavelengths,  I am to understand physical and chemical properties of the most opaque galaxy nuclei to understand what powers the universes most luminous galaxies.

While recent multi-wavelength deep field surveys in conjunction with cosmological models are revolutionizing our understanding of galaxy formation and evolution, it is becoming clear that accurate, physically motivated prescriptions of the underlying connection between the ISM and star formation — how are molecular clouds formed, how they turn molecular gas into stars, what is the effect of mechanical and radiative feed-back processes — are the main source of uncertainty limiting future progress.  Nearby galaxies permit access to weak, but diagnostically important tracers to be applied to a much wider range of galactic star formation rates and environments. The goal of this project is to characterize the structure of the molecular ISM simultaneously across the inner disks of nearby star forming galaxies at and below GMC scales. The image to the left shows the ammonia content plotted over an infrared map of galaxy NGC 253.