The evolution of galaxy mergers and morphology at z < 1.2 in the extended groth strip

Jennifer M. Lotz, M. Davis, S. M. Faber, P. Guhathakurta, S. Gwyn, J. Huang, D. C. Koo, E. Le Floc'H, Lihwai Lin, J. Newman, K. Noeske, C. Papovich, C. N.A. Willmer, A. Coil, C. J. Conselice, M. Cooper, A. M. Hopkins, A. Metevier, J. Primack, G. RiekeB. J. Weiner

Research output: Contribution to journalArticlepeer-review

316 Scopus citations


We present the quantitative rest-frame B morphological evolution and galaxy merger fraction at 0.2 < z < 1.2 as observed by the All-Wavelength Extended Groth Strip International Survey (AEGIS). We use the Gini coefficient and M20 to identify major mergers and classify galaxy morphology for a volume-limited sample of 3009 galaxies brighter than 0 4L*B, assuming pure luminosity evolution. We find that the merger fraction remains roughly constant at 10% ± 2% for 0.2 < z < 1.2. The fraction of E/S0/Sa galaxies increases from 21% ± 3% at z ∼ 1.1 to 44% ±9% at z ∼ 0.3, while the fraction of Sb-Ir galaxies decreases from 64% ± 6% at z ∼ 1.1 to 47% ± 9% at z ∼ 0.3. The majority ofz < 1.2 Spitzer MIPS 24 μm sources with L(IR) > 1011 L are disk galaxies, and only ∼15% are classified as major merger candidates. Edge-on and dusty disk galaxies (Sb-Ir) are almost a third of the red sequence at z ∼ 1.1, while E/S0/Samake up over 90% of the red sequence at z ∼ 0.3. Approximately 2% of our full sample are red mergers. We conclude (1) the merger rate does not evolve strongly between 0.2 < z < 1.2; (2) the decrease in the volume-averaged star formation rate density since z ∼ 1 is a result of declining star formation in disk galaxies rather than a disappearing population of major mergers; (3) the build-up of the red sequence at z < 1 can be explained by a doubling in the number of spheroidal galaxies since z ∼ 1.2.

Original languageEnglish (US)
Pages (from-to)177-197
Number of pages21
JournalAstrophysical Journal
Issue number1
StatePublished - Jan 1 2008


  • Galaxies: evolution
  • Galaxies: high-redshift
  • Galaxies: interactions
  • Galaxies: structure

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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