Kirsten R. Hall
Ph.D. Candidate
Johns Hopkins University
Department of Physics & Astronomy
Former Space Fellow (2016-2019), Space@Hopkins



Research Interests: I study the formation and evolution of galaxies and the large-scale structure of the Universe. I am interested in the link between dark matter and normal matter, and the roles that active supermassive black holes and high rates of star formation play in the evolution of galaxies across all of cosmic time.
Click HERE for a quick link to my ADS publications page.

Research Highlights:

Figure 1: The most effective halo mass at
hosting dusty star-forming galaxies as a function
of redshift (z; a proxy for "look-back time").
Downsizing of Star Formation: Weighing Dark Matter Halos Hosting Dusty Star-Forming Galaxies
Figure 1 to the left is a key result from my publication, Hall et al. 2018.
Summary: 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 most of cosmic time. I found that when the Universe was most actively forming stars ~10 billion years ago, 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".

Figure 2: Our model tSZ effect (red line) in
quasar
environments near the peak of activity
in the Universe plotted over the residual data
points.
Probing Quasar Feedback via the thermal Sunyaev-Zel'dovich (tSZ) Effect:
Figure 2 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. 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. Figure 2 shows our measured tSZ spectrum (red line) plotted over the corresponding residual data points. 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.