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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

305 Citations (Scopus)


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
Pages (from-to)177-197
Number of pages21
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 1 Jan 2008
Externally publishedYes


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


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