# Modeling Galaxies in Redshift Space at the Field Level

**Authors:** Marcel Schmittfull, Marko Simonović, Mikhail M. Ivanov, Oliver H. E. Philcox, Matias Zaldarriaga  
**arXiv:** [2012.03334](https://arxiv.org/abs/2012.03334)  
**Date:** 2020-12-06  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2012.03334v1/

## Key points

- Authors: Marcel Schmittfull, Marko Simonović, Mikhail M. Ivanov, Oliver H. E. Philcox, Matias Zaldarriaga
- Analytical forward model based on perturbation theory to predict redshift-space galaxy overdensity at field level using initial conditions
- Residual noise between model and simulated galaxy density exhibits white power spectrum on large scales
- $k^2\mu^2$ correction to noise power spectrum in mildly nonlinear regime indicates increased noise along line of sight and on smaller scales
- Correction aligns with theoretical predictions and confirmed through simulations
- Model galaxy velocity at field-level and compare with simulated velocities; 10% of galaxies contribute to half of root mean square velocity residual
- Enhances understanding of redshift-space galaxy overdensity modeling and relationship between theoretical predictions and observational data in cosmological studies

## Summary

In their paper titled "Modeling Galaxies in Redshift Space at the Field Level," authors Marcel Schmittfull, Marko Simonović, Mikhail M. Ivanov, Oliver H. E. Philcox, and Matias Zaldarriaga present an analytical forward model based on perturbation theory to predict the redshift-space galaxy overdensity at the field level using initial conditions. Their study reveals that the residual noise between the model and simulated galaxy density exhibits a power spectrum that is white on large scales, comparable in size to shot noise. In the mildly nonlinear regime, they observe a $k^2\mu^2$ correction to the noise power spectrum, indicating increased noise along the line of sight and on smaller scales. This correction aligns with theoretical predictions and serves as significant confirmation of its presence through simulations. Additionally, the researchers model the galaxy velocity at the field-level and compare it with simulated galaxy velocities. Intriguingly, they find that approximately 10% of galaxies contribute to half of the root mean square velocity residual in their simulated galaxy sample. Overall, this study not only enhances our understanding of redshift-space galaxy overdensity modeling but also sheds light on the intricate relationship between theoretical predictions and observational data in cosmological studies. The findings presented by Schmittfull et al. pave the way for further advancements in accurately predicting and interpreting galaxy distributions in redshift space at a field level.