Prof. Zaritsky, in collaboration with UA graduate student Jennifer Kadowaki and researcher Richard Donnerstein, is undertaking a large program to survey nearly a third of the sky for ultra diffuse galaxies (UDGs). The largest of these galaxies appear to be analogs to the Milky Way galaxy that have only formed 1% as many stars. As such, they are dark matter dominated at all radii and provide the first known examples of dark matter halos that have total masses of 10^12 solar masses and which have been relatively undisturbed by baryonic processes. The program involves using the DESI preimaging data to identify candidates and then various techniques to estimate or measure redshifts. So far, they have used the Large Binocular Telescope to produce the largest spectroscopically confirmed sample of UDGs. Zaritsky is proposing to dedicate a 2-m telescope with an integral field spectrograph for a large spectroscopic survey of UDGs. Ultimately, binary UDGs will be used to test the structure of dark matter halos.

Prof. Zaritsky, in collaboration with UA postdoctoral fellow Huanian Zhang, is utilizing the millions of spectra provided by the Sloan Digital Sky Survey in a novel approach to produce the first measurements ever of diffuse Halpha emission from intermediate temperature gas in the halos of nearby galaxies. The same spectra can be used to probe absorption by similar gas in our own Galaxy. The latter can be used to study the 3D distribution of the gas and its kinematics in the Milky Way. The detection of Halpha emission in other halos enables directed surveys of nearby galaxies (because the gas is in emission bright background sources against which to measure absorption are no longer needed). This work opens up a new avenue for the exploration of this important, perhaps dominant, baryonic component of galaxies.

Prof. Zaritsky, in collaboration with UA graduate student Melissa Halford, is investigating evidence for stellar initial mass function variations in Local Group stellar clusters. By obtaining the most precise velocity dispersion measurements available of these clusters, they have sufficient precision in the mass-to-light ratio measurements to detect differences among the clusters. These can be interpreted as variations in the bottom end of the stellar mass function. They are investigating alternative interpretations as well. These objects are particularly valuable for the study of the mass function because with the larger telescopes coming on-line it will be possible to directly confirm or refute variations by counting stars.