pop-cosmos: A comprehensive picture of the galaxy population from COSMOS data

TL;DR

pop-cosmos is a detailed model of galaxy populations from COSMOS data that jointly fits galaxy characteristics, evolution, and observational effects, enabling robust predictions of galaxy properties across redshifts.

Contribution

It introduces a novel, comprehensive forward modeling approach using a score-based diffusion model and optimal transport to calibrate galaxy population models with multi-band photometry.

Findings

Accurately predicts galaxy mass functions and redshift distributions.

Models key relations like mass-metallicity-redshift and star-forming sequence.

Provides a comprehensive picture of galaxy evolution up to redshift 4.

Abstract

We present pop-cosmos: a comprehensive model characterizing the galaxy population, calibrated to $140,938$ ($r<25$ selected) galaxies from the Cosmic Evolution Survey (COSMOS) with photometry in $26$ bands from the ultra-violet to the infra-red. We construct a detailed forward model for the COSMOS data, comprising: a population model describing the joint distribution of galaxy characteristics and its evolution (parameterized by a flexible score-based diffusion model); a state-of-the-art stellar population synthesis (SPS) model connecting galaxies' instrinsic properties to their photometry; and a data-model for the observation, calibration and selection processes. By minimizing the optimal transport distance between synthetic and real data we are able to jointly fit the population- and data-models, leading to robustly calibrated population-level inferences that account for parameter degeneracies, photometric noise and calibration, and selection. We present a number of key predictions from our model of interest for cosmology and galaxy evolution, including the mass function and redshift distribution; the mass-metallicity-redshift and fundamental metallicity relations; the star-forming sequence; the relation between dust attenuation and stellar mass, star formation rate and attenuation-law index; and the relation between gas-ionization and star formation. Our model encodes a comprehensive picture of galaxy evolution that faithfully predicts galaxy colors across a broad redshift ($z<4$) and wavelength range.