# Galaxy Merger Fractions in Two Clusters at $z\sim2$ Using the Hubble Space Telescope

## TL;DR

This study measures galaxy merger fractions in two clusters at redshift around 2 using Hubble Space Telescope data, finding an enhancement compared to the field, which suggests environment influences galaxy interactions at this epoch.

## Contribution

First measurement of galaxy merger fractions in clusters at z~2 using HST imaging and grism data, highlighting environmental effects on galaxy evolution.

## Key findings

- Merger fractions are 11% and 18% in the two clusters.
- Field galaxy merger fraction at z~2 is about 5%.
- Cluster merger fraction appears higher than field, indicating environmental influence.

## Abstract

We measure the fraction of galaxy-galaxy mergers in two clusters at $z\sim2$ using imaging and grism observations from the {\it Hubble Space Telescope}. The two galaxy cluster candidates were originally identified as overdensities of objects using deep mid-infrared imaging and observations from the {\it Spitzer Space Telescope}, and were subsequently followed up with HST/WFC3 imaging and grism observations. We identify galaxy-galaxy merger candidates using high resolution imaging with the WFC3 in the F105W, F125W, and F160W bands. Coarse redshifts for the same objects are obtained with grism observations in G102 for the $z\sim1.6$ cluster (IRC0222A) and G141 for the $z\sim2$ cluster (IRC0222B). Using visual classifications as well as a variety of selection techniques, we measure merger fractions of $11_{-3.2}^{+8.2}$ in IRC0222A and $18_{-4.5}^{+7.8}$ in IRC0222B. In comparison, we measure a merger fraction of $5.0_{-0.8}^{+1.1}\%$ for field galaxies at $z\sim2$. Our study indicates that the galaxy-galaxy merger fraction in clusters at $z\sim2$ is enhanced compared the field population, but note that more cluster measurements at this epoch are needed to confirm our findings.