About me

I am an astronomy PhD student at Yale University. I work with Dr. Marla Geha, investigating the mechanisms that have disrupted star formation in the smallest galaxies. My interests include the influence of AGN on the lowest-mass quiescent galaxies in isolation and comparative studies of large volume simulations; you can see the key results from my most recent works below. I received my B.A. in Physics from Pomona College in 2014.

As a member of the Graduate and Professional Student Title IX Advisory Board and the Astronomy Climate and Diversity Committee, I also work closely with the Title IX coordinators and my fellow graduate students to foster a diverse and equitable climate within our academic community.

Beyond my academic work, I enjoy rock climbing, backpacking, and baking. Like many astronomers, I also dabble in photography. You can reach me at claire (dot) dickey (at) yale (dot) edu

Research: AGN all the way down?

AGN-like line ratios are ubiquitous in the lowest-mass quiescent galaxies in isolation.

In this study, I investigated the lowest-mass quiescent galaxies known to exist in isolated environments [M∗ = 10^(9.0−9.5) M⊙ ; 1.5 Mpc from a more massive galaxy]. This population may represent the lowest stellar mass galaxies in which internal feedback quenches galaxy-wide star formation.

In this paper, we presented Keck/ESI long-slit spectroscopy for 27 isolated galaxies in this regime: 20 quiescent galaxies and 7 star-forming galaxies. We measured emission line strengths as a function of radius and place galaxies on the Baldwin Phillips Terlevich (BPT) diagram. Remarkably, 16 of 20 quiescent galaxies in our sample host central AGN-like line ratios. Only 5 of these quiescent galaxies were identified as AGN-like in SDSS due to lower spatial resolution and signal-to-noise.

We found that many of the quiescent galaxies in our sample have spatially-extended emission across the non-SF regions of BPT-space. When considering only the central 1′′, we identify a tight relationship between distance from the BPT star-forming sequence and host galaxy stellar age as traced by Dn4000, such that older stellar ages are associated with larger distances from the star-forming locus (see figure below). Our results suggest that the presence of hard ionizing radiation (AGN-like line ratios) is intrinsically tied to the quenching of what may be the lowest-mass self-quenched galaxies.

Research: apples to apples

Comparing the populations of isolated & quiescent galaxies across simulations and observations

This project began with an observation: isolated galaxies in SDSS cannot self-quench below a sharp mass threshold of M* = 10^9 M⊙; and a question: do simulations predict this distinctive feature of the local universe?
Motivated by this missing bridge between the observations and simulations, I developed Orchard, a methodology for building not just mock observations but full mock surveys to directly compare galaxy quenching in observations and simulations.
As a member of the IQ-Collaboratory, I am using Orchard to recreate observations of the quiescent fraction of isolated galaxies, using observational definitions of isolation and quenching to ensure an “apples to apples” comparison between observations and simulations. We have examined three hydrodynamic simulations with large volumes (L ~ 100 Mpc): EAGLE, Illustris-TNG, and SIMBA, shown below.

Service & Outreach

Warrior Scholar Project