We present two independent projects studying galaxy and structure formation in the Lambda-Cold Dark Matter Universe.

A recent study conducted by van Dokkum et al. (2022a) examined the ultra-diffuse galaxies (UDGs) in the NGC1052 group, which includes two galaxies deficient in dark matter, NGC1052-DF2 (DF2) and NGC1052-DF4 (DF4). The study identified a distinctive alignment of the UDGs and suggested that DF2 and DF4 share a common formation site and time, which was approximately 8 Gyr ago. This result supports the formation scenario that proposes the possibility of generating multiple dark matter-deficient galaxies (DMDGs) through a single high-velocity satellite-satellite galaxy ''Mini-bullet" collision, an analogy of the Bullet Cluster. In this study, we present a suite of galaxy collision simulations starting from initial conditions tailored to match the observed physical properties, kinematics, and alignment of the UDGs in the NGC1052 group. Our simulations, supplemented with orbit integration of the galaxies, demonstrate that appropriate initial orbital and structural parameters of the colliding satellite progenitor galaxies can lead to the formation of a series of multiple DMDGs, including two massive DMDGs with Mstar > 10^8 Msun that replicate the observed motions of DF2 and DF4. We further report on a few findings that could be examined in future observation programs, including stellar properties of the produced DMDGs.

When galaxies and stars began to form, they released ionizing radiation into the intergalactic medium which resulted in its reionization over the course of the first billion years. This ionizing radiation was dominated by massive stars. Reionization was inhomogeneous in space and time, reflecting the clustering of galaxies, and the inhomogeneous density field into which their radiation caused ionization fronts to propagate, resulting in different arrival times of those ionization fronts at different locations. The same massive stars that released this ionizing radiation also formed and released heavy elements when they exploded as supernovae, enriching the metal-free primordial gas both inside galaxies and outside them, by driving winds into the surrounding IGM. Just as reionization was inhomogeneous, so must the rise of metallicity during the EoR have been. The theory of this inhomogeneous rise of metallicity is, therefore, inseparable from the theory of reionization, and predicting its observable consequences requires us to model both processes, together, self-consistently. Towards this end, we have analyzed the results of the latest state-of-the-art radiation-hydro simulation of fully-coupled galaxy formation and reionization by The Cosmic Dawn (CoDa) Project, CoDa III, including its self-consistent tracking of the inhomogeneous rise of metallicity thru the end of the EoR and beyond, down to z = 4.6. We present these CoDa III results for the inhomogeneous evolution of metallicity in the universe and its observable consequences.