S319p.37 — Towards a complete history of galaxy assembly: Major merger fractions at 2 ≤ z ≤ 6 in the CANDELS fields

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Aug 10th at 6:00 PM until 6:00 PM

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Author(s): Kenneth James Duncan2, Chris Conselice2, Carl Joseph Mundy2, CANDELS Collaboration1

Institution(s): 1. Space Telescope Science Institute, 2. University of Nottingham

In recent years, remarkable progress has been made in studying the growth of the first galaxies through studies of the luminosity functions, star-formation rates and stellar masses. However, there are still very few observational constraints on the merger rates of galaxies during this formative period. Such measurements are vital in understanding the importance of mergers in the early lives of today’s most massive galaxies and what role they played (if any) in the creation of the first quiescent galaxies already seen at z ∼ 4. We present new results on the major merger rates (mass ratios from 1:1 to 1:4) of galaxies at 2 ≤ z ≤ 6 in the CANDELS HST survey. By using PDF analysis of photometric close pairs we are able to compute accurate merger fractions for both mass and number density selected samples over the first few billion years of galaxy formation. We present the evolution of the merger fraction as well as the estimated merger rates, exploring their evolution with respect to semi-analytic models and hydrodynamical simulations. In conjunction with similar analysis being applied to wide-area surveys at z ≤ 3 (Mundy et al. in prep), this work represents the first consistent study of major mergers over the bulk of cosmic history. In addition to the evolution of the merger rate itself, we explore the effect of mergers on star-formation rates at high redshift through comparison of the properties of galaxies in merging systems to similar galaxies in isolated environments.