Infall of galaxies in groups facilitate mergers within clusters

With grad student Jose Benavides (IATE, Argentina) we looked into mergers happening in and around clusters using the Illustris simulations. These events might be connected to the formation of lenticular galaxies and compact dwarfs.

Accretion of galaxy groups into galaxy clusters

Within galaxy clusters, the relative velocity of galaxies is too large to allow for mergers to happen. However, observationally, we see signatures of recent and ongoing mergers. How can this be explained within LCDM?

In collaboration with grad student in Argentina, Jose Benavides and his PhD supervisor Mario Abadi, we looked into the assembly of galaxy clusters like Virgo in the Illustris simulations. What we found is interesting: about 40% of all galaxies today in clusters came as part of a smaller group or association and not directly as a central from the field.

A consequence of this is… yes, mergers! The smaller potential wells of groups (compared to that in clusters) allow for slower relative velocities between galaxy group members. And these smaller velocities results, in some cases in galaxy mergers happening after the group has been accreted and is within the galaxy cluster. Interestingly, we find that most mergers in the dwarf regime are gas-rich which could lead to the formation of compact dwarfs, observed typically associated to clusters. On the other hand, mergers of more massive galaxies can be gas rich or gas poor and we hypothesize that some lenticular galaxies may form in this way.

You can download the ArXiv version here

Check also some of the media articles on our results:

OAC Press-release (English)

OAC Press-release (Spanish)

(Special thanks to Facundo Rodriguez for writing this super nice press-release!)