CRA seminar (Prof. Massimo Ricotti)

November 7, 2016 @ 3:00 pm - 4:00 pm

Title: The formation of the first star clusters: impact on reionization, JWST observations and near-field cosmology

Abstract: In this talk I will focus on understanding what determines the

morphology of the stellar component in the first low mass galaxies,

using parsec- scale cosmological simulations performed with an

adaptive mesh hydrodynamics code. Although the dense gas in which

stars are formed has a disk structure, stars are found in spheroids

with little rotation. Nearly independent of stellar mass, we observe

a large range of half-light radii for the stars, from a few parsecs to

a few hundred parsecs and surface brightnesses and mass-to-light

ratios ranging from those typical of globular clusters to ultra-faint

dwarf spheroidals (UFDs). This can be understood because although all

stars form in dense stellar clusters, a fraction of these clusters

remain bound after the gas is removed by feedback, but the rest is

destroyed and their stars, which typically have velocity dispersions

of 20 to 40 km/s, expand until they become bound by the dark matter

halo, creating a low-surface brightness dwarf spheroidal galaxy. This model

can explain the origin of the UFD satellites of the Milky Way and

Andromeda, and their old Globular Clusters population. I will discuss

why this result is in agreement with studies of GC formation in a

cosmological context and the implications of clusters formation on

reionization and future observations of the first galaxies by JWST.