Jeremy D. Bradford


I am interested in the dark matter content, the evolution and the kinematics of galaxies.  More specifically, I am interested in testing Lambda-CDM cosmology using isolated galaxies. Galaxies in low density environments can be used to minimize the complex physics involved in galaxy-galaxy interactions and therefore put tighter constraints on observables.

This site is constantly updated. Data links are for data files that contain everything from the table listed or everything you need to recreate the figure listed. If a link is not active and you would like access to data or code for the projects below, feel free to send me a quick email to let me know.

The Effect of AGNs on the Global HI Content of Isolated Low-Mass Galaxies

Summary and Key Results: Large samples of Active Galactic Nuclei (AGNs) have only recently been discovered in low-mass galaxies with stellar masses less than  109.5 M (Reines, 2013). In this work, we obtain neutral hydrogen (HI) observations of a sample of isolated low-mass galaxies with evidence of AGN activity from the [O iii]/Hβ and [N ii]/Hα Baldwin Phillips Terlevich (BPT) diagram. We identify a set of isolated low-mass galaxies with large distances from the BPT star-forming sequence that are gas-depleted relative to the rest of our low-mass sample. This is unexpected because all isolated low-mass galaxies are found to be gas-rich (Bradford, 2015) and star-forming (Geha, 2012). These galaxies are red and do not show signs of current star formation, suggesting that the emission lines indicate black hole feedback or shocks from extremely bursty star formation.

A Slippery Slope: Systematic Uncertainties in the Baryonic Tully-Fisher Relation

Summary and Key Results: The baryonic Tully-Fisher relation is a commonly used litmus test of galaxy formation. We explore the uncertainty in the slope and scatter using a homogeneously measured dataset of isolated galaxies. We obtain slopes ranging from 2.64 to 3.46 and scatter measurements ranging from 0.16 to 0.41 dex. Literature calibrations have similar ranges of fits. Fitting a power-law model to the BTFR is an oversimplification, therefore we recommend direct statistical comparisons between datasets with commensurable properties.

A Study in Blue: The Baryon Content of Isolated Low Mass Galaxies

Summary and Key Results: We present the results of a lengthy single-dish HI observing program of isolated low mass galaxies. We study the baryon content of galaxies in isolated environments and compare these isolated galaxies to galaxies in denser environments. We find that isolated low mass galaxies tend to be gas dominated and we do not observe any isolated low mass galaxy below an atomic gas fraction of 0.3. Galaxy scaling relations appear to be unaffected by environment. We calculate several estimates of baryon fractions and find that baryons are only depleted at low masses when an abundance matching relation between stellar mass and halo mass is used.

Structure and Dynamics of the Globular Cluster Palomar 13

Summary and Key Results: The mass-to-light ratio of the Galactic globular cluster Palomar 13 is too large to explain with its baryon content alone. We perform multi-epoch radial velocity measurements using Keck/DEIMOS spectroscopy and careful membership selection. We identify variable stars that may inflate the velocity dispersion of Palomar 13. We conclusively rule out a significant dark matter component, supporting the claim that globular clusters are dominated by baryons.