Astro Tuesday: Alex Ji and Sam McDermott

12:00–1:00 pm ERC 401

Alex Ji "Dwarf Galaxy Archaeology in the Gaia Era"

The Milky Way's satellite dwarf galaxies are powerful probes of many important astrophysical processes. Their kinematics provide insights into galactic dynamics and the nature of dark matter, while their chemical compositions preserve a history of early galaxy formation and nucleosynthesis. Recently, all-sky astrometry from the Gaia satellite has enabled the discovery and characterization of dwarf galaxies at different stages of tidal disruption. These new galaxies lie at the extremes of dwarf galaxy parameter space, whether in their structural properties or their star formation histories. In this talk, I will show how spectroscopic observations of the kinematics and chemistry of these newly discovered dwarf galaxies can provide crucial insights into galactic dynamics and nucleosynthesis. I will present a recent kinematic study of the extremely diffuse dwarf galaxy Antlia II that shows it is in the early stages of tidal disruption. The kinematics of Antlia II also clearly show that the Milky Way reference frame has been perturbed by the Large Magellanic Cloud. I will also highlight how two completely disrupted dwarf galaxies contribute to increasingly clear evidence that the rapid neutron-capture process requires both prompt and delayed sources to explain the diverse chemical evolution histories of dwarf galaxies.

Sam McDermott "Degenerate Fermions… In Space!"

Dark matter (DM) with a mass below a few keV must have a phase space distribution that differs substantially from that of the Standard Model: otherwise, it will be too “hot” to form cosmic structures. If DM in this mass range is a fermion, it will have a non-negligible momentum in the early Universe (even in the absence of a temperature) because the fermions were denser at higher redshifts, and thus experienced Pauli degeneracy pressure. As they fill up the lowest-momentum states, a typical DM particle gains a momentum ~ O(p_F) that can exceed its mass m_psi. In this talk, I will derive a simple relation between m_psi, the current fraction f_psi of the cold DM energy density in light fermions, and the redshift at which they were relativistic, and I will derive bounds and unique signatures in the f_psi-m_psi plane.

Event Type

Seminars

May 10