| Description |
We propose to obtain deep PACS + SPIRE far-IR photometry and 2D PACS C II 158 um spectroscopy of 7 cooling-flow clusters with extended Halpha filaments to constrain the properties of the dust and cooling gas in these systems. Our targets are part of a large sample of clusters that were imaged at Halpha using the Maryland Magellan Tunable Filter (MMTF) as part of a comprehensive multiwavelength survey. The superb sensitivity and resolution of the MMTF data have uncovered, often for the very first time, spectacular filaments of warm ionized gas extending as far as 50 kpc from the cluster core. The origin and heating source of these filaments remains a mystery. Our MMTF images have served as a guide to extract on-filament X-ray and optical spectra for a large sample of clusters, leading to the discovery that the X-ray ICM is cooling at a highly accelerated rate in the vicinity of these filaments. This direct link between the warm and hot phases may be the first direct evidence for the purported cooling flow. Given the high FIR fluxes detected in cluster cores, it is possible that dust grain cooling plays an important role in the cooling flow process. However, it remains unclear whether the observed dust is associated with the warm filaments or limited to the center of the brightest cluster galaxy (BCG). Current key programs cannot address this question given their lack of information on the Halpha filaments. Our proposed Herschel observations of the 7 cooling-flows clusters from our sample with the most extended Halpha filaments will directly address this question and help us determine: a) the role of dust cooling in the cooling-flow process, b) whether the observed dust is associated with the BCG or the warm filaments, and c) whether gas is cooling below 10^4 K, the temperature probed by Halpha. Providing answers to these questions will improve our understanding of the cooling processes in galaxy clusters and constrain the role of heating processes, such as AGN feedback, in preventing such cooling. |
