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I study the formation and evolution of galaxies and the large-scale structure of the Universe. I am interested in the roles that active supermassive black holes and high rates of star formation play in the evolution of galaxies across all of cosmic time, as well as the link between dark matter and normal matter.
As a Schmidt Science Fellow, I made a 2 year pivot into climate and atmospheric science. I have focused on atmospheric rivers, and their connection to larger-scale climate dynamics.
Click HERE for a quick link to my ADS publications page.
Below are a couple of technical publication highlights.
Stratosphere-Troposphere Transport of Ozone Associated with Atmospheric Rivers:
The figure above is from my publication, Hall et al. 2024. Long filaments of rapidly moving water vapor in the atmosphere, known as atmospheric rivers (ARs), play a vital role in the Earth's water cycle. Because of this, research continues to expand into ARs' relationship with large-scale climate patterns. In this paper, we use data from the Modern Era Retrospective analysis for Research Applications to examine several extreme ARs that made landfall on the U.S. West Coast and their relationship to the transport of ozone from the stratosphere to the troposphere. In the figure above, the pink contours identify an intense AR that hit California in December 2010. The teal shading shows the excess ozone concentration in the lower atmosphere. Of note is the long stream of ozone that follows the AR contours. Ozone in the lower atmosphere is a harmful pollutant and a potent greenhouse gas. We also combine eleven years of December AR and ozone data in order to study the average trend of ozone transport in connection with ARs. We quantify the AR-related ozone transport for the first time, and we find ARs with more intense water vapor transport result in the transport of higher concentrations of ozone. Quantifying ozone transport into the troposphere in connection with ARs is important as ARs may become more intense and/or more frequent with climate change, and ozone in the troposphere has consequences for human/plant health and the greenhouse effect.
Probing Quasar Feedback via the thermal Sunyaev-Zel'dovich (tSZ) Effect:
The figure to the left is from my publication, Hall et al. 2019. Quasar is a term to describe one of the most energetic phenomena in the Universe -- actively growing supermassive black holes at the centers of galaxies. The stream of material falling into the supermassive black hole produces vast amounts of energy (radiation), and launches high velocity winds out into the galaxy. What is left behind is a bubble of very hot, post-shock gas that is diffuse and difficult to detect via observational emission signatures (such as Xrays). In this paper, we use data from the Atacama Cosmology Telescope to measure the total thermal energy in the environments of quasars across cosmic time through the distortion of their spectral energy distributions due to the thermal Sunyaev-Zel'dovich (tSZ) effect. The tSZ effect is the up-scattering of low energy Cosmic Microwave Background photons off of free electron in the hot gas. The amplitude of the tSZ effect is directly proportional to the total thermal energy of the gas. This figure shows our measured tSZ spectrum (red line) plotted over the corresponding residual data points after subtracting away emission from the host galaxies. We find that the amount of thermal energy in quasar environments is great enough to have a significant impact on their host galaxies and their surrounding dark matter halos. In the paper, we further explore the extent to which this may occur.
Downsizing of Star Formation: Weighing Dark Matter Halos Hosting Dusty Star-Forming Galaxies
The figure to the left is a key result from my publication, Hall et al. 2018. Galaxies evolve inside of large, collapsed structures of dark matter that we refer to as "dark matter halos". Linking different types of galaxies (e.g., very mass or highly star forming) is an active area of research. In this paper, I devised a unique method to measure the most effective dark matter halo masses that host dusty star forming galaxies as a function of bulk of cosmic time. I found that when the Universe was most actively forming stars around10 billion years ago and before (z>2 in the plot on the left), the most intensely star-forming galaxies were hosted in dark matter halos that were significantly more massive than in the present-day universe. This is direct observational evidence for a phenomenon known as "downsizing".
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