Chemical evolution during gas-rich galaxy interactions

We analyse a set of galaxy interactions performed by using a self-consistent chemo-hydrodynamical model which includes star formation, Supernova feedback and chemical evolution. In agreement with previous works, we find that tidally-induced low-metallicity gas inflows dilute the central oxygen abundance and contribute to the flattening of the metallicity gradients. The tidally-induced inflows trigger starbursts which increase the impact of SN II feedback injecting new chemical elements and driving galactic winds which modulate the metallicity distribution. Although $\alpha$-enhancement in the central regions is detected as a result of the induced starbursts in agreement with previous works, our simulations suggest that this parameter can only provide a timing of the first pericentre mainly for non-retrograde encounters. In order to reproduce wet major mergers at low and high redshifts, we have run simulations with respectively 20 and 50 percent of the disc in form of gas. We find that the more gas-rich encounters behave similarly to the less rich ones, between the first and second pericentre where low-metallicity gas inflows are triggered. However, the higher strength of the inflows triggered in the more gas-rich interactions produces larger metal dilutions factors which are afterward modulated by the new chemical production by Supernova. We find that the more gas-rich interaction develops violent and clumpy star formation triggered by local instabilities all over the disc before the first pericentre, so that if these galaxies were observed at these early stages where no important tidally-induced inflows have been able to develop yet, they would tend to show an excess of oxygen. We find a global mean correlation of both the central abundances and the gradients with the strength of the star formation activity. [abridged]
Comment: 13 pages, 13 figures, accepted for publication in MNRAS