TAP Lectureship: Some New Ways to Probe the Nature of Dark Matter with Tidal Streams

Abstract: Lambda CDM predicts that dark matter halos are moderately triaxial and are not static but tumble slowly and coherently out to 60% of the virial radius. The tumbling rate (pattern speed) inferred from cosmological simulations is so small (15-40 degrees/Gyr) that it has been assumed to have negligible effects on baryons. We recently showed that the torque from even a slowly tumbling halo can significantly perturb tidal streams in the Milky Way. We also showed, from the first analysis of figure rotation in cosmological simulations with baryons, that the prevalence and magnitude of figure rotation is one of the only predictions of Lambda CDM on scales of galaxies that is relatively unaffected by the presence of baryons. The standard method of measuring figure rotation in simulations uses a quantity called the shape tensor which is extremely sensitive to the presence of sub-halos and satellites. Although the Milky Way is one of the best places to attempt to measure figure rotation, the fact that it is currently being  perturbed by a massive companion like the Large Magellanic Cloud (LMC) has led us to develop a new method based on Basis Function Expansions (BFEs). This method can not only  measure the pattern speeds and rotation axes of halos but can help to determine why halos have figure rotation. I will also describe a new probe of the cusp/core issue in dwarf galaxies that uses the structure of tidal streams from accreted globular clusters. Finally, I will briefly describe some recent results on the GD-1 tidal stream obtained with the Dark Energy Spectroscopic Instrument.

Bio:

Monica Valluri is a Research Professor in the Department of Astronomy at the University of Michigan, in Ann Arbor. Her work relies on theoretical framework of Galactic Dynamics to explore two profoundly mysterious unseen components of galaxies: central supermassive black holes and dark matter halos. She interprets and models the properties of galaxies using the motions of stars observed with state-of-the-art telescopes using simulations as well as powerful numerical analysis methods. She got a BS/MS in Physics, at the Birla Institute of Technology and Science in Pilani India and a PhD in Astrophysics at the Indian Institute of Science, Bangalore, India. She did postdoctoral work at Columbia University and Rutgers University. She was a Senior Research Associate and Assistant Director of the Kavli Institute for Cosmological Physics at the University of Chicago before moving to Michigan in 2007.

Location: Steward Observatory, Room N305 

Reception: Refreshments at 10:00 AM

Live stream: Zoom Meeting ID: 417 674 3144    Passcode:  1985Astro

Watch later:  TAP YouTube Channel