# A semi-analytical perspective on massive galaxies at $z\sim0.55$

## TL;DR

This study uses a semi-analytical model to simulate massive galaxies at redshift ~0.55, comparing the mock data with observations to understand galaxy formation, clustering, and the galaxy-halo connection.

## Contribution

It introduces a semi-analytical mock galaxy catalog that replicates observed properties and explores galaxy clustering and environmental effects at intermediate redshift.

## Key findings

- Good agreement in galaxy-halo connection between model and observations
- Overestimation of clustering amplitude due to model limitations
- A down-sampled mock reproduces observed clustering within 1σ

## Abstract

The most massive and luminous galaxies in the Universe serve as powerful probes to study the formation of structure, the assembly of mass, and cosmology. However, their detailed formation and evolution is still barely understood. Here we extract a sample of massive mock galaxies from the semi-analytical model of galaxy formation (SAM) GALACTICUS from the MultiDark-Galaxies, by replicating the CMASS photometric selection from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). The comparison of the GALACTICUS CMASS-mock with BOSS-CMASS data allows us to explore different aspects of the massive galaxy population at $0.5<z<0.6$, including the galaxy-halo connection and the galaxy clustering. We find good agreement between our modelled galaxies and observations regarding the galaxy-halo connection, but our CMASS-mock over-estimates the clustering amplitude of the 2-point correlation function, due to a smaller number density compared to BOSS, a lack of blue objects, and a small intrinsic scatter in stellar mass at fixed halo mass of $<0.1$ dex. To alleviate this problem, we construct an alternative mock catalogue mimicking the CMASS colour-magnitude distribution by randomly down-sampling the SAM catalogue. This CMASS-mock reproduces the clustering of CMASS galaxies within 1$\sigma$ and shows some environmental dependency of star formation properties that could be connected to the quenching of star formation and the assembly bias.