2025/10/20 by Kundu, Aritra, Sanderson, Robyn, Lidz, Adam +6
#Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2510.17968
The `near-far' approach to studying reionization leverages the star formation histories of the Milky Way (MW) or Local Group (LG) galaxies, derived from resolved photometry, to infer the low-mass/faint-end of the stellar mass functions (SMFs) or the ultraviolet luminosity functions (UVLFs) of high-redshift galaxies (z \gtrsim 6), beyond the current JWST detection limits (MUV \gtrsim -15). Previous works considered only intact low-mass galaxies in the MW and LG, neglecting disrupted galaxies such as stellar streams and phase-mixed objects. Using the FIRE-2 simulations, we show that these disrupted galaxies contribute up to ∼50% of the total stellar mass budget of the proto-MW/LG at z =6-9. Including all the progenitors of these disrupted galaxies improves the normalization of the recovered SMFs/UVLFs by factors of ∼2-3 and reduces the halo-to-halo variation in the slope by ∼20-40%. This enables robust constraints down to at least the resolution limit of the simulations, near M_⋆ ∼ 105 M_\odot or MUV ∼ -10 at z \gtrsim 6. We also show that `fossil record' reconstructions - which assume each present-day system descends from a single reionization-era progenitor - are sensitive to the stellar mass/UV magnitude thresholds, which introduces bias in the inferred low-mass/faint-end slopes. Additionally, we demonstrate that neglecting disrupted systems underestimates the contribution of galaxies with MUV \lesssim -15 to the reionization-era UV luminosity density. Finally, we estimate that a significant fraction (∼50%) of streams with M_⋆ \gtrsim 106 M_\odot at z=0 should be detectable from upcoming Rubin Observatory and Roman Space Telescope observations.