Measurement of redshift dependent cross correlation of HSC clusters and Fermi $\gamma$ rays

TL;DR

This study analyzes the redshift-dependent cross-correlation between Fermi gamma-ray data and Subaru HSC galaxy clusters, revealing signals consistent with models of gamma-ray emitters, and extends previous work by including high-redshift clusters.

Contribution

It provides the first cross-correlation analysis with a high-redshift galaxy cluster catalogue up to z=1.1, improving understanding of the gamma-ray background's origins.

Findings

Detected cross-correlation signals at 2.0-2.3σ significance for all and low-redshift clusters.

Weaker signals (1.6-1.9σ) observed for high-redshift clusters.

Results are consistent with theoretical models involving blazars, star-forming, and radio galaxies.

Abstract

The cross-correlation study of the unresolved $\gamma$-ray background (UGRB) with galaxy clusters has a potential to reveal the nature of the UGRB. In this paper, we perform a cross-correlation analysis between $\gamma$-ray data by the Fermi Large Area Telescope (Fermi-LAT) and a galaxy cluster catalogue from the Subaru Hyper Suprime-Cam (HSC) survey. The Subaru HSC cluster catalogue provides a wide and homogeneous large-scale structure distribution out to the high redshift at $z=1.1$, which has not been accessible in previous cross-correlation studies. We conduct the cross-correlation analysis not only for clusters in the all redshift range ($0.1 < z < 1.1$) of the survey, but also for subsamples of clusters divided into redshift bins, the low redshift bin ($0.1 < z < 0.6$) and the high redshift bin ($0.6 < z < 1.1$), to utilize the wide redshift coverage of the cluster catalogue. We find the evidence of the cross-correlation signals with the significance of 2.0-2.3$\sigma$ for all redshift and low-redshift cluster samples. On the other hand, for high-redshift clusters, we find the signal with weaker significance level (1.6-1.9$\sigma$). We also compare the observed cross-correlation functions with predictions of a theoretical model in which the UGRB originates from $\gamma$-ray emitters such as blazars, star-forming galaxies and radio galaxies. We find that the detected signal is consistent with the model prediction.