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Abstract Interpretation of data from faint dwarf galaxies is made challenging by observations limited to only the brightest stars. We present a major improvement to tackle this challenge by undertaking zoomed cosmological simulations that resolve the evolution of all individual stars more massive than 0.5M_⊙, thereby explicitly tracking all observable stars for the Hubble time. For the first time, we predict observable color–magnitude diagrams and the spatial distribution of ≈100,000 stars within four faint (M_⋆ ≈ 10⁵M_⊙) dwarf galaxies directly from their cosmological initial conditions. In all cases, simulations predict complex light profiles with multiple components, implying that typical observational measures of structural parameters can make the totalV-band magnitudes appear up to 0.5 mag dimmer compared to estimates from simulations. Furthermore, when only small (⪅100) numbers of stars are observable, shot noise from realizations of the color–magnitude diagram introduces uncertainties comparable to the population scatter in, e.g., the total magnitude, half-light radius, and mean iron abundance measurements. Estimating these uncertainties with fully self-consistent mass growth, star formation, and chemical enrichment histories paves the way for more robust interpretation of dwarf galaxy data. 

Abstract Using the N -body+Smoothed particle hydrodynamics code, ChaNGa, we identify two merger-driven processes—disk disruption and supermassive black hole (SMBH) feedback—which work together to quench L * galaxies for over 7 Gyr. Specifically, we examine the cessation of star formation in a simulated Milky Way (MW) analog, driven by an interaction with two minor satellites. Both interactions occur within ∼100 Myr of each other, and the satellites both have masses 5–20 times smaller than that of their MW-like host galaxy. Using the genetic modification process of Roth et al., we generate a set of four zoom-in, MW-mass galaxies all of which exhibit unique star formation histories due to small changes to their assembly histories. In two of these four cases, the galaxy is quenched by z = 1. Because these are controlled modifications, we are able to isolate the effects of two closely spaced minor merger events, the relative timing of which determines whether the MW-mass main galaxy quenches. This one–two punch works to: (1) fuel the SMBH at its peak accretion rate and (2) disrupt the cold, gaseous disk of the host galaxy. The end result is that feedback from the SMBH thoroughly and abruptly ends the star formation of the galaxy by z ≈ 1. We search for and find a similar quenching event in R omulus 25, a hydrodynamical (25 Mpc) 3 volume simulation, demonstrating that the mechanism is common enough to occur even in a small sample of MW-mass quenched galaxies at z = 0.