A team of EPFL scientists have revealed how larger galaxies alter the chemistry and dynamical history of these small galaxies in an upcoming article in Astronomy & Astrophysics.
The Milky Way is surrounded by dozens of satellite dwarf galaxies (so called because of their small size). Being extremely small they are also extremely faint, hence very little has been known about them until quite recently including, how are they affected by the Milky Ways gravity, when did they form their stars, and how did their chemistry evolve in time. Using new simulations based upon previous work both at EPFL and abroad, we have begun to answer some of these questions.
Dwarf galaxies that have passed through their perigalacticon (the closest approach to the Milky Way), cease forming stars as what ever gas they hold is stripped through the combination of tidal forces and supernovae ejection. This halting of star formation, also serves to pause their chemical evolution, potentially making the current elemental abundances a good indication of when a dwarf began orbiting the Milky Way. Such forces also expand the dwarf galaxy, removing much of the metallicity gradient (the change in the elemental composition of stars from the centre to the edge) that would otherwise be present as well as lowering the total brightness of the galaxy through the removal of stars. Although many details still remain to be worked out, the simulations have begun to reproduce many of the observed features and future work will try to make an even better description of the Milky Ways captured satellites.
Author: Matthew Nichols
Source: Laboratoire d'astrophysique