Joint State-and-Dynamics Inference for Galaxy Population Evolution on an Effective Manifold

Abstract

Galaxy surveys provide noisy, incomplete, selection-affected population snapshots rather than complete evolutionary histories. We formulate galaxy evolution as joint inference of effective physical states, their population intensity, and cross-epoch dynamics. An effective state is a coarse-grained description defined by predictive adequacy and distinguished from measured variables and learned representations. The intrinsic population is a finite non-negative measure evolving through one-galaxy transport, source and removal terms, and nonlocal two-to-one merger jumps. A sub-probability observational kernel maps this population to survey catalogs and supplies the likelihood for state inference. Projected luminosity and stellar-mass functions generally do not obey closed dynamics and cannot identify the underlying channels alone. In a restricted IllustrisTNG proof of concept, a finite-time non-merger kernel and reduced merger operator are calibrated on training root merger trees and evaluated on held-out lineages. Dynamical propagation improves the normalized later mass--sSFR distribution relative to a static baseline, while the merger channel captures number loss from disappearing secondary progenitors. Under noisy and censored mock observations, the propagated prior improves posterior-stacked reconstruction of the latent population relative to a frozen-static prior. The framework provides an observation-directed, simulation-assisted route to galaxy state-and-dynamics inference.

33 pages, 3 figures, revised after a referee report