nIFTy Cosmology: Comparison of Galaxy Formation Models

TL;DR

This study compares 14 galaxy formation models using the same simulation data, revealing significant variability in predictions due to lack of recalibration, and aims to establish a common calibration framework to improve model consistency.

Contribution

It provides a unified description of diverse galaxy formation models and presents an initial uncalibrated comparison as a baseline for future calibration efforts.

Findings

Wide scatter in model predictions without recalibration

Models show significant differences in stellar mass functions and star formation rates

Establishes a baseline for future calibration to reduce prediction variability

Abstract

We present a comparison of 14 galaxy formation models: 12 different semi-analytical models and 2 halo-occupation distribution models for galaxy formation based upon the same cosmological simulation and merger tree information derived from it. The participating codes have proven to be very successful in their own right but they have all been calibrated independently using various observational data sets, stellar models, and merger trees. In this paper we apply them without recalibration and this leads to a wide variety of predictions for the stellar mass function, specific star formation rates, stellar-to- halo mass ratios, and the abundance of orphan galaxies. The scatter is much larger than seen in previous comparison studies primarily because the codes have been used outside of their native environment within which they are well tested and calibrated. The purpose of the `nIFTy comparison of galaxy formation models' is to bring together as many different galaxy formation modellers as possible and to investigate a common approach to model calibration. This paper provides a unified description for all participating models and presents the initial, uncalibrated comparison as a baseline for our future studies where we will develop a common calibration framework and address the extent to which that reduces the scatter in the model predictions seen here.