Galaxy And Mass Assembly (GAMA): Refining the Local Galaxy Merger Rate
  using Morphological Information
  We use the Galaxy And Mass Assembly (GAMA) survey to measure the local
Universe mass dependent merger fraction and merger rate using galaxy pairs and
the CAS structural method, which identifies highly asymmetric merger candidate
galaxies. Our goals are to determine which types of mergers produce highly
asymmetrical galaxies, and to provide a new measurement of the local galaxy
major merger rate. We examine galaxy pairs at stellar mass limits down to
$M_{*} = 10^{8}M_{\odot}$ with mass ratios of $<$100:1 and line of sight
velocity differences of $\Delta V<500$ km s$^{-1}$. We find a significant
increase in mean asymmetries for projected separations less than the sum of the
individual galaxy's Petrosian 90 radii. For systems in major merger pairs with
mass ratios of $<$4:1 both galaxies in the pair show a strong increase in
asymmetry, while in minor merger systems (with mass ratios of $>$4:1) the lower
mass companion becomes highly asymmetric, while the larger galaxy is much less
affected. The fraction of highly asymmetric paired galaxies which have a major
merger companion is highest for the most massive galaxies and drops
progressively with decreasing mass. We calculate that the mass dependent major
merger fraction is fairly constant at $\sim1.3-2\%$ between
$10^{9.5}<M_{*}<10^{11.5} M_{\odot}$, and increases to $\sim4\%$ at lower
masses. When the observability time scales are taken into consideration, the
major merger rate is found to approximately triple over the mass range we
consider. The total co-moving volume major merger rate over the range
$10^{8.0}<M_{*}<10^{11.5} M_{\odot}$ is $(1.2 \pm 0.5) \times 10^{-3}$
$h^{3}_{70}$ Mpc$^{-3}$ Gyr$^{-1}$.
