Utilizing deep Hubble Space Telescope imaging from the two largest field galaxy surveys , the Extended Groth Strip ( EGS ) and the COSMOS survey , we examine the structural properties , and derive the merger history for 21 , 902 galaxies with M _ { * } > 10 ^ { 10 } M _ { \odot } at z < 1.2 .
We examine the structural CAS parameters of these galaxies , deriving merger fractions , at 0.2 < z < 1.2 , based on the asymmetry and clumpiness values of these systems .
We find that the merger fraction between z = 0.2 and z = 1.2 increases from roughly f _ { m } = 0.04 \pm 0.01 to f _ { m } = 0.13 \pm 0.01 .
We furthermore detect , at a high significance , an abrupt drop in the merger fraction at z < 0.7 , which appears relatively constant from z = 0.7 to z = 1.2 .
We explore several fitting formalisms for parameterising the merger fraction , and compare our results to other structural studies and pair methods within the DEEP2 , VVDS , and COSMOS fields .
We also examine the basic features of these galaxies , including our selection for mergers , and the inherent error budget and systematics associated with finding mergers through structure .
We find that for galaxies selected by M _ { * } > 10 ^ { 10 } M _ { \odot } , the merger fraction can be parameterised by f _ { m } = f _ { 0 } \times ( 1 + z ) ^ { m } with the power-law slope m = 2.3 \pm 0.4 .
By using the best available z = 0 prior the slope increases to m = 3.8 \pm 0.2 , showing how critical the measurement of local merger properties are for deriving the evolution of the merger fraction .
We furthermore show that the merger fraction derived through structure is roughly a factor of 3-6 higher than pair fractions .
Based on the latest cosmological simulations of mergers we show that this ratio is predicted , and that both methods are likely tracing the merger fraction and rate properly .
We calculate , utilising merger time scales from simulations , and previously published merger fractions within the Hubble Deep and Ultra Deep Fields , that the merger rate of galaxies with M _ { * } > 10 ^ { 10 } M _ { \odot } increases linearly between z = 0.7 and z = 3 .
Finally , we show that a typical galaxy with a stellar mass of M _ { * } > 10 ^ { 10 } M _ { \odot } undergoes between 1-2 major mergers at z < 1.2 .