Spectacular H-alpha Image Shows Evidence for Galaxy Collision and Gas Heating

Jeffrey Kenney, Tomer Tal

A new deep and wide-field H-alpha image of the elliptical galaxy M86 taken with the Mosaic imager on the Kitt Peak 4-meter telescope, shows a spectacular complex of warm gas filaments. This provides striking evidence for a previously unsuspected high-speed collision between M86 and the disturbed spiral NGC4438. We now recognize this Virgo cluster system to be the nearest recent collision between a large elliptical and large spiral. The study also strongly suggests that collisions can heat the gas in elliptical galaxies. Like most ellipticals, most of the gas in M86 is hot (million degrees) and emits X-rays. A current mystery is why the biggest galaxies in the universe (elliptical galaxies) stop forming stars. Something needs to heat up the gas so it doesn't cool and form stars. A number of recent studies suggest that energy from active galactic nuclei associated with nuclear black holes may do this, but our new study of M86 shows that gravitational interactions may also do it. While not many galaxies have such extreme collisions as M86, most galaxies experience minor mergers and gas accretion events, and these may play a role in heating the galaxy's gas. These more common but modest events are very hard to study, since their observational signatures are weak. But the same physical processes occur in both strong and weak encounters, and by studying the observable effects in extreme cases like M86 we can learn the role of gravity in the heating of galaxy gas.

 NOAO Press Release

Yale University Press Release 

ApJ