PhD Candidate, Princeton University,
Department of Astrophysical Sciences,
NSF Graduate Research Fellow
I am a 5th (and final!) year PhD student in the Department of Astrophysical Sciences at Princeton University. My research is focused on modeling stellar streams in the Milky Way and external galaxies to constrain the nature of dark matter, from the scale of the stellar halo down to subhalos. I will be on the academic job market in the Fall (2025).
The banner image displays the looping stellar stream around NGC 5907, courtesy of R Jay GaBany. Full image here. From the stream's morphology, the dark matter halo of NGC 5907 was found to be oblate and disk-aligned in Nibauer et al. 2023.
We present the first fully data-driven measurement of the Galactic acceleration field from stellar streams. Using 6D phase-space measurements of the GD-1 stream, we infer that the inner dark matter halo of the Milky Way is tilted by around 20 deg in the direction of the Sun. The configuration is consistent with the Geometry of the stellar halo, and the warp of the Milky Way.
arXiv / ApJL
Stellar streams are sensitive to low-mass dark matter subhalos. We present a flexible model using Hamiltonian perturbation theory to capture time-dependent forces—such as the LMC and Galactic bar—and ~100 expected subhalo impacts in streams like GD-1 and Pal 5. We show that stream velocity dispersion links directly to dark matter physics and provide a framework for efficiently modeling stream populations based on dark matter properties.
arXiv / ApJ
What can be learned about the gravitational from an image of its tidal features? Here we develop a direct observable connection between the curvature of extragalactic tidal streams and the underlying geometry of dark matter halos. The method is successfully demonstrated on N-body simulations, and provides a means to measure halo shapes from the thousands of extragalactic tidal features expected from the Rubin Observatory, the Roman Space Telescope, and Euclid.
arXiv / ApJ
Torques imparted from major mergers are expected to excite tilting modes in galactic disks, which can persist for several billion years. We explore and model how stellar streams respond to disk tilting, finding that the disk's angular momentum evolution can leave distinctive signatures on the morphology of the streams. We find that the width and asymmetry of the Pal 5 stream is extremely well captured by a simple tilting disk model.
arXiv / ApJ
From a noisy Galactic foreground, how do we extract a low signal-to-noise stream from a high dimensional dataset? We develop a statistical framework based on interpretable machine learning to model the phase-space density of stellar streams. We develop a simultaneous model for the stream's astrometric and photometric track, and derive a data-driven distance modulus along stream track. The method generates membership catalogs for Milky Way streams, and provides a rigorous means to characterize streams.
arXiv / ApJ
Traditional methods for modeling Galactic potential rely on restrictive assumptions about the functional form of the of the Galaxy's mass distribution. Here we develop a method to infer the 3D acceleration field in the neighborhood of a stream, by exploiting the ordered structure of tidal tails due to their dynamically cold nature.
arXiv / ApJ
By modeling the velocity dispersion of the GD-1 stream, we constrain the parameter space of velocity dependent self-interacting dark matter.
Lookout for the arXiv preprint in Fall 2025!I co-taught the undergraduate course PHYS130, Introduction to Astronomy, at South Woods State Prison in New Jersey through the Prison Teaching Initiative (PTI). PTI offers high quality, college accredited courses to incarcerated students in New Jersey. At the same facility, I also worked as a tutor for MATH015 (introduction to algebra).
Assistant Instructor. Undergraduate courses at Princeton. Led recitations, review sessions, office hours.
Teaching Assistant. Undergraduate course at UPenn. Led three recitation sessions per week including weekly review sessions for five semesters. A collection of my recitation problems and handwritten lecture notes for Penn’s Math 114 are hosted at Professor Robert Ghrist’s site, here. Additional problems/solutions here.
Helped lead public observing nights at Princeton, open to the surrounding community.
Worked as the Physics Curriculum Chair and Head TA to bring interactive physics labs to West Philadelphia schools. Crafted and taught hands on lesson plans for middle and high school students, and managed a team of volunteers carrying out weekly lessons in Philadelphia.
Public program discussing the scientific contributions and legacy of Dr. Charlotte Moore Sitterly to stellar astronomy, and the connections of Dr. Sitterly to Chester County.
ApJ, A&A
Working group member: higlighted actions to be taken in improving the overall working environment for department members at Princeton.
Email: jnibauer@princeton.edu