RESOLVING THE DISCREPANCY OF GALAXY MERGER FRACTION MEASUREMENTS AT z ∼ 0-3

We measure the merger fraction of massive galaxies using the UltraVISTA/COSMOS catalog, complemented with the deeper, higher resolution 3DHST+CANDELS catalog, presenting the largest mass-complete photometric merger sample up to z similar to 3. We find that the variation in the mass ratio probe can explain the discrepant redshift evolution of the merger fraction in the literature: selecting mergers using the H-160-band flux ratio leads to an increasing merger fraction with redshift, while selecting mergers using the stellar mass ratio reveals a merger fraction with little redshift dependence at z = 1-3. Defining major and minor mergers as having stellar mass ratios of 1: 1-4: 1 and 4: 1-10: 1, respectively, the results imply similar to 1 major merger and similar to 0.7 minor merger on average for a massive (log (M*M-circle dot). 10.8) galaxy during z = 0.1-2.5. There may be an additional similar to 0.5(0.4) major (minor) merger if we use the H-band flux ratio selection. The observed amount of major merging alone is sufficient to explain the observed number density evolution for the very massive (log (M*M-circle dot) >= 11.1) galaxies. The observed number of major and minor mergers can increase the size of a massive quiescent galaxy by a factor of two at most. This amount of merging is enough to bring the compact quiescent galaxies formed at z > 2 to lie at 1.5s below the mean of the stellar mass-size relation as measured in some works (e.g., Newman et al.), but additional mechanisms are needed to fully explain the evolution, and to be consistent with works suggesting stronger evolution.