DeCAF Seminar Series:

Abstract: In the current cosmological paradigm, galaxies are teeming with dark matter substructures with masses as low as that of Earth (M~10^{-6} Msol). These objects do not form stars, and are only detectable through the perturbations they induce on the motion of visible objects. Being the most dark matter (DM)–dominated galaxies in the Universe, dwarf spheroidal galaxies (dSPhs) provide excellent targets for testing this prediction.

In this talk I will show that the presence of a large population of DM subhaloes generates a fluctuating gravitational field that injects energy into stellar orbits, driving a gradual expansion of dSphs. In addition, individual dark subhaloes can also capture field stars gravitationally, becoming "luminous" during the process. Although these objects are rare, they may be detectable as faint stellar overdensities with unusual kinematics and identical chemical composition as the host galaxy. I will finish the talk by discussing some promising candidates discovered in the Milky Way dSphs.

Speaker Bio: Jorge Peñarrubia is a theoretical astrophysicist at the University of Edinburgh. He obtained his PhD in 2003 from the University of Heidelberg, Germany, and held postdoctoral positions at the Max Planck fuer Astronomie (Germany), the University of Victoria (Canada) and the University of Cambridge (UK). He was a Ramon y Cajal Fellow, and member of the Spanish Astronomical Society. His research is focused on an exciting topic of Cosmology: the nature of Dark Matter including but not limit to dwarf spheroidal galaxies, stellar haloes, and tidal streams.