Euclid: Early Release Observations -- The intracluster light and intracluster globular clusters of the Perseus cluster

Abstract: We study the intracluster light (ICL) and intracluster globular clusters (ICGCs) in the nearby Perseus galaxy cluster using Euclid's EROs. By modelling the isophotal and iso-density contours, we mapped the distributions and properties of the ICL and ICGCs out to radii of 200-600 kpc (up to ~1/3 of the virial radius) from the brightest cluster galaxy (BCG). We find that the central 500 kpc hosts 70000$\pm$2800 GCs and $1.7\times10^{12}$ L$\odot$ of diffuse light from the BCG+ICL in the near-infrared H$_E$. This accounts for 38$\pm$6% of the cluster's total stellar luminosity within this radius. The ICL and ICGCs share a coherent spatial distribution, suggesting a common origin or that a common potential governs their distribution. Their contours on the largest scales (>200 kpc) are offset from the BCG's core westwards by 60 kpc towards several luminous cluster galaxies. This offset is opposite to the displacement observed in the gaseous intracluster medium. The radial surface brightness profile of the BCG+ICL is best described by a double S\'ersic model, with 68$\pm$4% of the H$_E$ light in the extended, outer component. The transition between these components occurs at ~60 kpc, beyond which the isophotes become increasingly elliptical and off-centred. The radial ICGC number density profile closely follows the BCG+ICL profile only beyond this 60 kpc radius, where we find an average of 60-80 GCs per $10^9$ M$\odot$ of diffuse stellar mass. The BCG+ICL colour becomes increasingly blue with radius, consistent with the stellar populations in the ICL having subsolar metallicities [Fe/H] ~ -0.6 to -1.0. The colour of the ICL, and the specific frequency and luminosity function of the ICGCs suggest that the ICL+ICGCs were tidally stripped from the outskirts of massive satellites with masses of a few $\times10^{10}$ M$_\odot$, with an increasing contribution from dwarf galaxies at large radii.

• The paper quantifies ~70,000 globular clusters and 38% of diffuse near-IR light in the Perseus cluster, highlighting the role of ICL in cluster evolution.
• It employs a double Sersic model to analyze radial brightness profiles, identifying a transition between the brightest cluster galaxy and the extended ICL region.
• The study shows that the spatial offset between the ICL/ICGCs and the BCG implies a complex merger history and provides a tracer for the underlying dark matter distribution.

Overview of Euclid's Early Release Observations on Intracluster Light and Globular Clusters in the Perseus Cluster

The document titled "Euclid: Early Release Observations – The intracluster light and intracluster globular clusters of the Perseus cluster" provides a detailed analysis of the intracluster light (ICL) and intracluster globular clusters (ICGCs) within the Perseus cluster utilizing data from the Euclid space telescope. This paper outlines the processes and findings from the Early Release Observations (ERO), highlighting the contributions of these stellar components to our understanding of galaxy clusters' history and structure.

Key Findings and Methodological Approach

1. Distribution and Measurement of Intracluster Components:
   • The study reveals the existence of approximately 70,000 globular clusters within the central 500 kpc of the Perseus cluster. It identifies about $1.7 \times 10^{12}$ L$_{\odot}$ of diffuse light from the brightest cluster galaxy (BCG) plus ICL in the near-infrared \HE. This diffuse light constitutes about 38% of the cluster's total stellar luminosity within this radius.
   • The spatial distribution of both the ICL and ICGCs suggests a shared origin or governed distribution due to a common gravitational potential. Notably, the contours of these components at scales exceeding 200 kpc were found to be offset westwards by approximately 60 kpc from the BCG's core.
2. Radial Profiles and Structural Analysis:
   • The radial surface brightness profile of the BCG plus the ICL follows a double Sersic model. This profile demonstrates 68% of the \HE light is contained in an extensive outer component. A break in both the surface brightness and GC density profiles indicates a transition beyond which stellar components belong predominantly to the ICL.
3. Globular Cluster Properties and Luminosity Functions:
   • The paper presents the luminosity function of ICGCs, which is essential for understanding the mass-to-light ratios of these clusters and their role in galaxy cluster dynamics. The study outlines that ICGCs' distribution closely aligns with the ICL beyond a certain radius, confirming their use as tracers for the cluster's mass and potential distribution.
4. Implications for Cluster Dynamics and Dark Matter Studies:
   • While the ICL and ICGCs provide critical insights into the evolutionary processes of clusters, their spatial offset from the BCG core suggests potential complex dynamics. The findings imply a significant merger history and suggest a role for these components in mapping the dark matter distribution across the cluster.

Practical and Theoretical Implications

The findings provide both practical and theoretical implications, augmenting our understanding of galaxy cluster formation and evolution. Practically, the data from Euclid's ERO establishes a benchmark for future observations of intracluster stellar components, potentially informing the identification of dark matter distributions in these regions given the alignment between ICL/ICGC profiles and dark matter halos. Theoretically, these observations support models of hierarchical galaxy formation, emphasizing the contribution of massive satellite disruption over time.

Future Prospects

Looking forward, the research outcomes could pave the way for further explorations using Euclid's full capabilities across broader swathes of the sky. Such endeavors could lead to an expanded database of galaxy clusters, enabling more comprehensive mapping of dark matter within cosmic structures and validation of cosmological models on a grand scale.

In summary, the document highlights significant contributions to our understanding of galaxy cluster dynamics through the study of ICL and ICGCs in the Perseus cluster. The Euclid telescope has provided unprecedented data, reinforcing the importance of these stellar components as tracers for the structures and evolutionary histories of galaxies within clusters.