Speaker: Dr. Lim Jeremy
Affiliation: Department of Physics, University of Hong Kong
Title: The Enigmatic Nebula at the Center of the Perseus Cluster
Time: 2 pm, (Friday) Aug 19, 2011
Location: Middle Conference Room, 3rd floor

Abstract:
The optically-luminous nebula associated with the central giant elliptical galaxy of the Perseus cluster, NGC 1275, has been an enigma ever since its discovery more than 50 years ago. Today, we know that such luminous nebulae are commonly associated with the central galaxies of cool-core groups/clusters but not otherwise, providing circumstantial evidence for a link with (residual) X-rays cooling flows. I review current understanding of the composition, excitation, origin, and possible fate of the nebula associated with NGC 1275, emphasizing observational tests of models for the nature of this nebula. The nebula is multiphase, comprising molecular, atomic, and ionized gas with temperatures ranging from ~100 K to ~106 K. The bulk of the nebula is not photoionized; instead, the nebula is most likely collisionally excited by energetic particles. Our observations, however, argue against the only population of energetic particles so far observed in NGC 1275 as the source of the excitation. The inner region of the nebula may be deposited by a residual X-ray cooling flow, whereas the outer region may have been structured by nebular material dragged outwards by rising bubbles. I show for the first time the velocity field of the entire optical nebula in NGC 1275, and compare the measured velocity field against models for the flow pattern behind rising bubble. Finally, I discuss the role of the nebula in forming stars and fueling the AGN in NGC 1275.