Galaxy Evolution in All Five CANDELS Fields and IllustrisTNG: Morphological, Structural, and the Major Merger Evolution to z ∼ 3

The Astrophysical Journal, vol. 919, pp. 139

Abstract

Abstract A fundamental feature of galaxies is their structure, yet we are just now understanding the evolution of structural properties in quantitative ways. As such, we explore the quantitative nonparametric structural evolution of 16,778 galaxies up to z ∼ 3 in all five CANDELS fields, the largest collection of high-resolution images of distant galaxies to date. Our goal is to investigate how the structure, as opposed to size, surface brightness, or mass, changes with time. In particular, we investigate how the concentration and asymmetry of light evolve in the rest-frame optical. To interpret our galaxy structure measurements, we also run and analyze 250 simulation realizations from IllustrisTNG to determine the timescale of mergers for the CAS system. We measure that from z = 0–3, the median asymmetry merger timescale is 0.50 − 0.18 + 0.33 Gyr, and find that it does not vary with redshift. Using these data, we find that galaxies become progressively asymmetric at a given mass at higher redshifts, and we derive merger rates that scale as ∼ 1 + z 1.87 ± 0.04 Gyr−1, which agrees well with recent machine-learning and galaxy-pair approaches, removing previous inconsistencies. We also show that far-infrared selected galaxies that are invisible to the Hubble Space Telescope have a negligible effect on our measurements. We also find that galaxies are more concentrated at higher redshifts. We interpret this as a sign that their formation occurs from a smaller initial galaxy that later grows into a larger one through mergers, consistent with the size growth of galaxies from the inside out, suggesting that the centers are the oldest parts of most galaxies.

Authors 4

1. A. Whitney corresponding

   University of Nottingham

   Affiliation as printed

   University of Nottingham, School of Physics & Astronomy, Nottingham, NG7 2RD, UK; amy.whitney@nottingham.ac.uk

   University of Nottingham, School of Physics & Astronomy, Nottingham, NG7 2RD, UK

2. Leonardo Ferreira

   University of Nottingham

   Affiliation as printed

   University of Nottingham, School of Physics & Astronomy, Nottingham, NG7 2RD, UK; amy.whitney@nottingham.ac.uk

   University of Nottingham, School of Physics & Astronomy, Nottingham, NG7 2RD, UK

3. Christopher J. Conselice

   University of Nottingham · University of Manchester

   Affiliation as printed

   Jodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road, Manchester UK

   University of Nottingham, School of Physics & Astronomy, Nottingham, NG7 2RD, UK; amy.whitney@nottingham.ac.uk

   University of Nottingham, School of Physics & Astronomy, Nottingham, NG7 2RD, UK

4. K. J. Duncan Aachen Leiden Observatory

   Leiden University · Royal Observatory · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, The Netherlands

   SUPA, Institute for Astronomy, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK