ON THE ORIGIN OF THE EXTENDED Hα FILAMENTS IN COOLING FLOW CLUSTERS

Abstract

We present a high spatial resolution Halpha survey of 23 cooling flow\nclusters using the Maryland Magellan Tunable Filter (MMTF), covering 1-2 orders\nof magnitude in cooling rate, dM/dt, temperature and entropy. We find 8/23\n(35%) of our clusters have complex, filamentary morphologies at Halpha, while\nan additional 7/23 (30%) have marginally extended or nuclear Halpha emission,\nin general agreement with previous studies of line emission in cooling flow\ncluster BCGs. A weak correlation between the integrated near-UV luminosity and\nthe Halpha luminosity is also found for our complete sample, with a large\namount of scatter about the expected relation for photoionization by young\nstars. We detect Halpha emission out to the X-ray cooling radius, but no\nfurther, in several clusters and find a strong correlation between the Halpha\nluminosity contained in filaments and the X-ray cooling flow rate of the\ncluster, suggesting that the warm ionized gas is linked to the cooling flow.\nFurthermore, we detect a strong enhancement in the cooling properties of the\nICM coincident with the Halpha emission, compared to the surrounding ICM at the\nsame radius. While the filaments in a few clusters may be entrained by buoyant\nradio bubbles, in general, the radially-infalling cooling flow model provides a\nbetter explanation for the observed trends. The correlation of the Halpha and\nX-ray properties suggests that conduction may be important in keeping the\nfilaments ionized. The thinness of the filaments suggests that magnetic fields\nare an important part of channeling the gas and shielding it from the\nsurrounding hot ICM.\n