CEA News, January 2019

Cosmic hydrodynamics in action with MUSE

A group of galaxies falling into a massive galaxy cluster in the Local Universe (A1367) has been observed with the MUSE integral field spectrograph at the ESO Very Large Telescope. The group, dubbed the Blue Infalling Group (BIG), is filled by a spectacular complex of ionized gas filaments.

Simulation of galaxies and gas in the Universe. Credit: TNG Collaboration.

The image shows the ionized gas in red, superimposed on the stellar light emission from the group galaxies. The superior quality of MUSE data allowed an international team of researchers led by CEA members to derive the past history of the group galaxies.

One galaxy is found to a clear result of a merger of two lower mass systems, while another galaxy is currently being stripped of its atomic gas by hydrodynamic interactions in the group and cluster environments. Atomic gas is removed from the galaxy potentials both by gravitational and hydrodynamic interactions and it is heated-up during these processes allowing observations of a warmer and ionised gas phase.

The researchers concluded that the combined effect of galaxy interactions in the group environment and hydrodynamic interactions with the group system as a whole can reduce the star formation activity of galaxies, leading star forming systems to become quiescent even before they reach the harsher environment of a massive cluster. This phenomenon, called “pre-processing”, is believed to be even more effective in the distant Universe at the epoch of the formation of the first group-like systems.

The paper, “MUSE sneaks a peek at extreme ram-pressure stripping events - IV. Hydrodynamic and gravitational interactions in the Blue Infalling Group”, is to be published by Monthly Notices of the Royal Astronomical Society. A preprint version is available here.