2026/03/31 by Kun Xu, Carlos S. Frenk, Y. P. Jing +37 · 1 voice
Physics and Astronomy · #astro-ph.CO #astro-ph.GA
39 pages, 38+12 figures. Main results in Figure 34, 36 and 38. Accepted for publication in MNRAS
arxiv created 2026/08/03 · arxiv updated 2026/08/04
Understanding dwarf galaxy formation is crucial for testing dark matter models and reionization physics. However, constructing stellar-mass complete spectroscopic samples at low masses is increasingly difficult, and the potential existence of a local void complicates studies in an average environment. The Photometric object Around Cosmic webs (PAC) method, which combines deep photometric and spectroscopic data to measure the excess surface density n2w_\rmp(r_\rmp) of photometric objects around spectroscopic tracers, offers a promising path forward. We model 349 n2w_\rmp(r_\rmp) measurements from DESI Y1 BGS and DECaLS, reaching M_*=106.4 \rm M\odot, using a stellar mass-halo mass relation (SHMR)-based subhalo abundance matching framework applied to two high-resolution N-body simulations from the Jiutian suite. The resulting SHMR is constrained down to M\rm h≃108.0 h-1\rm M\odot, revealing a clear upturn at ∼1010.0 h-1\rm M\odot toward lower masses, indicating rising star-formation efficiency (SFE) in small haloes. This feature persists under extensions of the model that allow mass-dependent scatter, reionization-induced suppression of the halo occupation fraction, galaxy assembly bias, and alternative cosmologies. Combining with the results from Paper I, we find that central red galaxies dominate the low-mass regime. Our results motivate a hypothesis in which SFE is significantly higher than previously thought prior to reionization, enabling relatively massive galaxies to form in small haloes. These systems are subsequently quenched by the UV background, producing the central red dwarf galaxies observed. Finally, we obtain 3σ and 5σ upper mass bounds of 108.80 h-1\rm M\odot and 1010.24 h-1\rm M\odot on the smallest haloes required to exist.