Spitzer Mid-Infrared Spectra of Cool-Core Galaxy Clusters

TL;DR

This study uses Spitzer mid-infrared spectra to analyze star formation in nine cool-core galaxy clusters, revealing diverse spectral features and suggesting star formation occurs in dust-deficient environments.

Contribution

First mid-infrared spectral analysis of cool-core galaxy clusters highlighting diverse morphologies and unexpected dust properties in star-forming regions.

Findings

Spectra range from classic starbursts to flat, weak dust features.

Most clusters show active star formation but lack strong mid-infrared dust emission.

Star formation may occur in dust-deficient environments near cooling flows and jets.

Abstract

We have obtained mid-infrared spectra of nine cool-core galaxy clusters with the Infrared Spectrograph aboard the Spitzer Space Telescope. X-ray, ultraviolet and optical observations have demonstrated that each of these clusters hosts a cooling flow which seems to be fueling vigorous star formation in the brightest cluster galaxy. Our goal is to use the advantages of the mid-infrared band to improve estimates of star formation. Our spectra are characterized by diverse morphologies ranging from classic starbursts to flat spectra with surprisingly weak dust features. Although most of our sample are known from optical/UV data to be active star-formers, they lack the expected strong mid-infrared continuum. Star formation may be proceeding in unusually dust-deficient circumgalactic environments such as the interface between the cooling flow and the relativistic jets from the active galactic nucleus.