AI Insight
This study investigates the phenomenon of galactic conformity, where galaxies tend to have similar quenching properties to their neighbors, using simulations from IllustrisTNG300-1. The researchers demonstrate that the statistical pattern of quenched neighbors follows the linear matter correlation function over scales of 2-40 Mpc/h, and that galaxy assembly bias at fixed halo mass dominates this signal rather than simple halo mass differences. They show that the amplitude of two-halo conformity is primarily driven by galaxy assembly bias, while the measurement technique effectively isolates the linear clustering component by suppressing nonlinear effects.
Why it matters
Understanding galactic conformity and assembly bias is crucial for accurate cosmological analyses and galaxy formation models. This work provides a framework to use galactic conformity as a probe of large-scale structure rather than treating it as a systematic uncertainty, potentially improving constraints on dark matter and galaxy evolution.
Understand the Science
arXiv:2607.04022v2 Announce Type: replace
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 $xi_{rm mm}^{rm lin}(r)$, 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 $r$, $Delta f_{Q}(r)$, and related quantities in real space, compute the required correlations, perform shuffling tests at fixed halo mass, compare several $Delta f$ observables, and explore the transformed family $G_n$. We show explicitly that $Delta f_{Q}(r)$ can be written directly in terms of correlation functions and that, over $sim 2$–$40,h^{-1},mathrm{Mpc}$, it is well described by $A_{rm fit},xi_{rm mm}^{rm lin}(r)$. 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.