Extremely Red Objects in a hierarchical universe

TL;DR

This study evaluates hierarchical galaxy formation models against observations of Extremely Red Objects, finding that models with AGN feedback accurately reproduce their abundance and distribution, emphasizing the importance of AGN feedback in galaxy evolution.

Contribution

It demonstrates that including AGN feedback in hierarchical models is essential to match observed properties of massive red galaxies at high redshift.

Findings

Radio-mode AGN feedback model matches observed ERO counts

Superwind model underestimates ERO abundance by an order of magnitude

AGN feedback is crucial for understanding massive galaxy formation at z >= 1

Abstract

We analyse whether hierarchical formation models based on Lambda cold dark matter cosmology can produce enough massive red galaxies to match observations. For this purpose, we compare with observations the predictions from two published models for the abundance and redshift distribution of Extremely Red Objects (EROs), which are red, massive galaxies observed at z >= 1. One of the models invokes a "superwind" to regulate star formation in massive haloes and the other suppresses cooling through "radio-mode" AGN feedback. The first one underestimates the number counts of EROs by an order of magnitude, whereas the radio-mode AGN feedback model gives excellent agreement with the number counts of EROs and redshift distribution of K-selected galaxies. This study highlights the need to consider AGN feedback in order to understand the formation and evolution of massive galaxies at z >= 1.