Constraints on the Intracluster Dust Emission in the Coma Cluster of Galaxies

TL;DR

This study used deep infrared imaging to search for intracluster dust emission in the Coma cluster, finding no significant detection and setting upper limits that suggest a substantial deficiency of dust near the cluster center.

Contribution

The paper provides the deepest mid and far-infrared observations of a galaxy cluster to date, setting new upper limits on intracluster dust emission and challenging previous detections.

Findings

No significant infrared excess detected in the Coma cluster.

Upper limits on dust emission are consistent with dust deficiency.

Infrared source confusion likely explains marginal excess signals.

Abstract

We have undertaken a search for the infrared emission from the intracluster dust in the Coma cluster of galaxies by the Multiband Imaging Photometer for Spitzer. Our observations yield the deepest mid and far-infrared images of a galaxy cluster ever achieved. In each of the three bands, we have not detected a signature of the central excess component in contrast to the previous report on the detection by Infrared Space Observatory (ISO). We still find that the brightness ratio between 70 and 160 microns shows a marginal sign of the central excess, in qualitative agreement with the ISO result. Our analysis suggests that the excess ratio is more likely due to faint infrared sources lying on fluctuating cirrus foreground. Our observations yield the 2 sigma upper limits on the excess emission within 100 kpc of the cluster center as 5 x 10^-3 MJy/sr, 6 x 10^-2 MJy/sr, and 7 x 10^-2 MJy/sr, at 24, 70, and 160 microns, respectively. These values are in agreement with those found in other galaxy clusters and suggest that dust is deficient near the cluster center by more than 3 orders of magnitude compared to the interstellar medium.