The Evolution of Galaxy Mergers and Morphology at z < 1.2 in the Extended Groth Strip
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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 M 20 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 m sources with L(IR) > 10 11 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. 2008. The American Astronomical Society. All rights reserved.
