Direct Measurement of Galaxy Assembly Bias using DESI DR1 Data

2025/10/23 by Shao, Zhiwei, Zu, Ying, Salcedo, Andrés N. +54
#Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences

paper · doi:10.48550/arxiv.2510.20896

Abstract

We report the first direct measurement of galaxy assembly bias, a critical systematic in cosmology, from the Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey. We introduce a novel, cosmology-independent method to measure the halo occupation distribution (HOD) by combining a state-of-the-art group catalog with weak gravitational lensing. For groups binned by total luminosity, we determine the galaxy occupation number N_{\rm gal} from group-galaxy cross-correlations, while weak lensing constrains the average halo mass M_h. Applying this to a volume-limited sample at z∈[0.05,0.2], we measure the dependence of HOD, N_{\rm gal}(M_h), on large-scale overdensity δ_g. Focusing on the satellite galaxies, we find an assembly bias parameter of Q_{\rm sat}=0.05±0.14, a result consistent with zero and in tension with many empirical galaxy formation models. Our method provides a robust approach for characterizing galaxy assembly bias to achieve precision cosmology with DESI and future Stage-V surveys.

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