UCLA

The puzzling origins of globular clusters have been greatly debated over the years. We present a new formation channel for globular clusters, linking them to objects that formed without dark matter (DM) in the early Universe in the presence of a supersonic relative velocity between baryons and DM. This stream velocity arises due to the drop in radiation pressure of baryons from matter-radiation decoupling and induces a physical separation between baryonic and DM overdensity peaks. This effect gives rise to gas dominant objects with little to no DM. These gas-rich structures, called Supersonically Induced Gas Objects (SIGOs), form naturally outside of DM halos as a consequence of the stream velocity. In this thesis, we present a detailed investigation of the physical properties of SIGOs, which leads to a promising connection to globular clusters.

One of the physical parameters often invoked to understand galaxy formation is the spin parameter of halos, which characterizes galaxies' rotational structure. We, thus, first investigate the spins of DM halos and SIGOs with stream velocity. We find that the spin parameter of DM halos follows a lognormal distribution, and the median increases and the misalignment angle between the angular momenta of baryons and DM has a nearly isotropic distribution. We generalize the spin parameter to SIGOs and find that they also have a lognormal distribution. Furthering existing hydrodynamic AREPO simulations by including radiative cooling, we find that this cooling channel has negligible effects on SIGO properties compared to only adiabatic cooling. We find that SIGOs density is high enough to allow stars to form using a simple density threshold criterion based on the balance of gravity and thermal/turbulent energy. Then, we model the star formation process and estimate the luminosity of the first star clusters within a SIGO. We find that SIGOs occupy a different part of the luminosity-mass parameter space than classical DM halos with gas. We further adopt a simple model to evolve the SIGOs to present-day and show that their masses, radii, and luminosities are consistent with present-day (local) globular clusters. Since the stream velocity is coherent over scales of a few Mpc, we predict that if this is the dominant mechanism for globular clusters, the abundances of galaxies hosting global clusters vary significantly over these scales. The upcoming James Webb Space Telescope will elucidate the mysteries of the first galaxies and will further shed light on the link between SIGOs as progenitors to globular clusters.