Shape evolution of massive early-type galaxies: confirmation of increased disk prevalence at z gt 1

Y.-Y. Chang, A. van der Wel, H.-W. Rix, S. Wuyts, S. Zibetti, B. Ramkumar, B. Holden

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We use high-resolution K-band VLT/HAWK-I imaging over 0.25 deg2 to study the structural evolution of massive early-type galaxies since z ~ 2. Mass-selected samples, complete down to log(M/M ☉) ~ 10.7 such that "typical" (L*) galaxies are included at all redshifts, are drawn from pre-existing photometric redshift surveys. We then separate the samples into different redshift slices and classify them as late- or early-type galaxies on the basis of their specific star formation rate. Axis-ratio measurements for the ~400 early-type galaxies in the redshift range 0.6 < z < 1.8 are accurate to 0.1 or better. The projected axis-ratio distributions are then compared with lower redshift samples. We find strong evidence for evolution of the population properties: early-type galaxies at z > 1 are, on average, flatter than at z < 1 and the median projected axis ratio at a fixed mass decreases with redshift. However, we also find that at all epochs z lesssim 2, the most massive early-type galaxies (log(M/M ☉) > 11.3) are the roundest, with a pronounced lack of galaxies that are flat in projection. Merging is a plausible mechanism that can explain both results: at all epochs, merging is required for early-type galaxies to grow beyond log(M/M ☉) ~ 11.3, and all early types over time gradually and partially lose their disk-like characteristics.
Original languageEnglish
Pages (from-to)83
Number of pages1
JournalAstrophysical Journal
Issue number2
Early online date18 Dec 2012
Publication statusPublished - 1 Jan 2013


  • cosmology: observations, galaxies: elliptical and lenticular, cD, galaxies: evolution, galaxies: formation, galaxies: structure


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