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It is still a challenge to assess the merger fraction of galaxies atdifferent cosmic epochs in order to probe the evolution of their mass assembly.Using the Illustris cosmological simulations, we investigate the relationbetween the separation of galaxies in a pair, both in velocity and projectedspatial separation space, and the probability that these interacting galaxieswill merge in the future. From this analysis, we propose a new set of criteriato select close pairs of galaxies along with a new corrective term to beapplied to the computation of the galaxy merger fraction. We then probe theevolution of the major and minor merger fraction using the latest MUSE deepobservations over the HUDF, HDFS, COSMOS-Gr30 and Abell 2744 regions. From aparent sample of 2483 galaxies with spectroscopic redshifts, we identify 366close pairs spread over a large range of redshifts ($0.2<z<6$) and stellarmasses ($10^7-10^{11}M_{\odot}$). Using the stellar mass ratio between thesecondary and primary galaxy as a proxy to split the sample into major, minorand very minor mergers, we found a total of 183 major, 142 minor and 47 veryminor close pairs corresponding to a mass ratio range of 1:1-1:6, 1:6-1:100 andlower than 1:100, respectively. Due to completeness issues, we do not considerthe very minor pairs in the analysis. Overall, the major merger fractionincreases up to $z\approx 2-3$ reaching 25% for pairs with the most massivegalaxy with a stellar mass $M^*\geq 10^{9.5}M_{\odot}$. Beyond this redshift,the fraction decreases down to $\sim 5$% at $z\approx 6$. The evolution of theminor merger fraction is roughly constant with cosmic time, with a fraction of20% at $z<3$ and a slow decrease between $3\leq z \leq6$ to 8-13%.

astronomy and astrophysics

New criteria for the selection of galaxy close pairs from cosmological  simulations: evolution of the major and minor merger fraction in MUSE deep  fields