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Australian Human Resources Institute Diversity Awards 2013 Finalist

Michelle Cluver, IPAC/Caltech ()

"Powerful H2 Line-Cooling in Stephan's Quintet and the "Death by Debris" Phenomenon in Hickson Compact Groups"

Abstract. tephan's Quintet (SQ) is a strongly interacting compact group experiencing a group-wide shock (~ 30 kpc) due to the high velocity (~ 1000 km/s) collision of an intruder galaxy with the intragroup medium. We find in SQ the phenomenal projected coexistence of hot X-ray plasma and abundant, widespread warm H2. I will discuss the concordance with a model of excited H2 emission driven by turbulent energy transfer. The prevalence of this pathway over other sources of cooling (such as X-rays) in fast galaxy-scale shocks, may have important implications for the cooling of gas in the assembly of the first massive galaxies, as well as shock physics in systems ranging from AGN to ULIRGs to supernovae remnants.Recent studies show that compact groups appear to follow an evolutionary sequence, linked to gas depletion, caused by interactions in the dense environment. Hickson Compact Groups (HCGs) also show a distinctive gap in mid-infrared colour-colour space, suggesting rapid evolution from dusty to dust-free systems. This appears to correlate with HI-depletion, but not the presence of hot X-ray gas. Our current Spitzer spectroscopy study of a sample of 23 HCGs finds enhanced H2 emission in galaxies lying in the colour-colour "gap". We propose a new hypothesis where group galaxies collide with previously stripped material. The result is stochastic heating and/or stripping which effectively shuts down star formation, causing galaxies to move rapidly from actively star forming to passively evolving systems (i.e. dominated by an old stellar population).

Held in the AAO Conference room at 03:30 PM on Thursday, 10 February 2011