Assembly bias from nuisance to probe I: the relation between galactic conformity and the linear matter clustering
Abstract
Two-halo galactic conformity is commonly interpreted as a manifestation of galaxy assembly bias, but its statistical structure and physical origin remain unclear. We aim to write the quenched-neighbour statistic in correlation-function form, test whether its scale dependence follows the linear matter correlation function ξmmlin(r), and separate the contributions of halo-mass bias and assembly bias to its amplitude. Using galaxies in IllustrisTNG300-1 at z=0, we measure the two-halo galactic conformity statistic of quenched neighbours at distance r, ΔfQ(r), and related quantities in real space, compute the required correlations, perform shuffling tests at fixed halo mass, compare several Δf observables, and explore the transformed family Gn. We show explicitly that ΔfQ(r) can be written directly in terms of correlation functions and that, over ∼ 2--40 h−1 Mpc, it is well described by Afit ξmmlin(r). Thus nonlinear and baryonic terms do not dominate the residual scale dependence isolated by this statistic. Halo-mass bias alone predicts lower amplitudes than measured, while fixed-mass shuffling strongly suppresses the signal; in TNG300 the amplitude is therefore dominated by galaxy assembly bias at fixed halo mass. Quenching, colour, and concentration share a common rescaled shape, whereas stellar-mass and halo-mass splits do not. These results suggest that galaxy assembly bias sets the amplitude of two-halo conformity, while the double-difference structure of the statistic suppresses nonlinear residuals when the compared populations have similar halo-mass and transition-scale structure.
Versions
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BibTeX
@misc{padilla2026assembly,
title = {{Assembly bias from nuisance to probe I: the relation between galactic conformity and the linear matter clustering}},
author = {Nelson Padilla and Ivan Lacerna and Dante Paz},
howpublished = {arXiv},
year = {2026},
month = jul,
doi = {10.48550/arxiv.2607.04022},
eprint = {2607.04022},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.04022},
}
RIS
TY - UNPB
TI - Assembly bias from nuisance to probe I: the relation between galactic conformity and the linear matter clustering
AU - Nelson Padilla
AU - Ivan Lacerna
AU - Dante Paz
PY - 2026
DA - 2026/07/21
PB - arXiv
DO - 10.48550/arxiv.2607.04022
UR - https://arxiv.org/abs/2607.04022
AB - Two-halo galactic conformity is commonly interpreted as a manifestation of galaxy assembly bias, but its statistical structure and physical origin remain unclear. We aim to write the quenched-neighbour statistic in correlation-function form, test whether its scale dependence follows the linear matter correlation function ξ_mm^lin(r), and separate the contributions of halo-mass bias and assembly bias to its amplitude. Using galaxies in IllustrisTNG300-1 at z=0, we measure the two-halo galactic conformity statistic of quenched neighbours at distance r, Δf_Q(r), and related quantities in real space, compute the required correlations, perform shuffling tests at fixed halo mass, compare several Δf observables, and explore the transformed family G_n. We show explicitly that Δf_Q(r) can be written directly in terms of correlation functions and that, over ∼ 2--40 h^−1 Mpc, it is well described by A_fit ξ_mm^lin(r). Thus nonlinear and baryonic terms do not dominate the residual scale dependence isolated by this statistic. Halo-mass bias alone predicts lower amplitudes than measured, while fixed-mass shuffling strongly suppresses the signal; in TNG300 the amplitude is therefore dominated by galaxy assembly bias at fixed halo mass. Quenching, colour, and concentration share a common rescaled shape, whereas stellar-mass and halo-mass splits do not. These results suggest that galaxy assembly bias sets the amplitude of two-halo conformity, while the double-difference structure of the statistic suppresses nonlinear residuals when the compared populations have similar halo-mass and transition-scale structure.
ER -