# The intragroup light in KiDS+GAMA groups: A stacking analysis

## TL;DR

This study measures the diffuse intragroup light in galaxy groups using stacking techniques on KiDS and GAMA data, providing new insights into group growth and comparing observations with simulations.

## Contribution

Introduces a specialized pipeline for detecting intragroup light in large galaxy samples and presents the first robust measurements from KiDS+GAMA data.

## Key findings

- IGL fraction ranges from 3% to 21% in the sample.
- Stacked measurements reach surface brightness levels of 31-32 mag/arcsec$^2$.
- Results are consistent with hydrodynamic simulation predictions.

## Abstract

Galaxy groups and clusters assembled through dynamical interactions of smaller systems, resulting in the formation of a diffuse stellar halo known as the intragroup or intracluster light (IGL/ICL). By preserving the records of these interactions, the IGL/ICL provides valuable insight into the growth history of galaxy groups and clusters. Groups are especially interesting because they represent the link between galactic haloes and massive clusters. However, the low surface brightness of this diffuse light makes it extremely challenging to detect individually. Recent deep wide-field imaging surveys allow us to push such measurements to lower brightness limits by stacking data for large ensembles of groups. In this work, we present a special-purpose pipeline to reprocess individual $r-$band Kilo-Degree Survey (KiDS) exposures to optimise the IGL detection. Using an initial sample of 2385 groups with at least five spectroscopically-confirmed member galaxies from the Galaxy and Mass Assembly (GAMA) survey and reprocessed deep images from the KiDS, we present the first robust measurement of IGL from a large group sample (~ 750) down to 31-32 mag/arcsec$^2$ (varying in different stacked bins). We also compare our stacked IGL measurements to predictions from matched mock observations from the Hydrangea cosmological hydrodynamic simulations. Systematics in the imaging data can affect IGL measurements, even with our special-purpose pipeline. However, with a large sample and optimised analysis, we can place well-constrained upper and lower limits on the IGL fraction (3 - 21 per cent) for our group ensemble across $0.09\leq z\leq 0.27$ and $12.5\leq \log_{10}[M_{200}/\mathrm{M}_\odot] \leq 14.0$. This work explores the potential performance of stacked statistical analysis of diffuse light in large samples of systems from next-generation observational programs, such as $Euclid$ and LSST.