New criteria for the selection of galaxy close pairs from cosmological
  simulations: evolution of the major and minor merger fraction in MUSE deep
  fields
  It is still a challenge to assess the merger fraction of galaxies at
different cosmic epochs in order to probe the evolution of their mass assembly.
Using the Illustris cosmological simulations, we investigate the relation
between the separation of galaxies in a pair, both in velocity and projected
spatial separation space, and the probability that these interacting galaxies
will merge in the future. From this analysis, we propose a new set of criteria
to select close pairs of galaxies along with a new corrective term to be
applied to the computation of the galaxy merger fraction. We then probe the
evolution of the major and minor merger fraction using the latest MUSE deep
observations over the HUDF, HDFS, COSMOS-Gr30 and Abell 2744 regions. From a
parent sample of 2483 galaxies with spectroscopic redshifts, we identify 366
close pairs spread over a large range of redshifts ($0.2<z<6$) and stellar
masses ($10^7-10^{11}M_{\odot}$). Using the stellar mass ratio between the
secondary and primary galaxy as a proxy to split the sample into major, minor
and very minor mergers, we found a total of 183 major, 142 minor and 47 very
minor close pairs corresponding to a mass ratio range of 1:1-1:6, 1:6-1:100 and
lower than 1:100, respectively. Due to completeness issues, we do not consider
the very minor pairs in the analysis. Overall, the major merger fraction
increases up to $z\approx 2-3$ reaching 25% for pairs with the most massive
galaxy 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 the
minor merger fraction is roughly constant with cosmic time, with a fraction of
20% at $z<3$ and a slow decrease between $3\leq z \leq6$ to 8-13%.
