Morphologies of ~190,000 Galaxies at z=0-10 Revealed with HST Legacy Data II. Evolution of Clumpy Galaxies

TL;DR

This study analyzes the evolution of clumpy galaxies over a broad redshift range using HST data, revealing how their properties and prevalence change over cosmic time, and linking these features to galaxy formation processes.

Contribution

It provides the first detailed measurement of the evolution of the fraction of clumpy galaxies from z~8 to z~0, and links their properties to galaxy formation mechanisms.

Findings

f_clumpy^UV increases from z~8 to 1-3 and decreases afterward.

Clumpy galaxies generally have disk-like profiles with low Sersic index.

Clump colors are redder near galactic centers in massive galaxies.

Abstract

We investigate evolution of clumpy galaxies with the Hubble Space Telescope (HST) samples of ~17,000 photo-z and Lyman break galaxies at z~0-8. We detect clumpy galaxies with off-center clumps in a self-consistent algorithm that is well tested with previous study results, and measure the number fraction of clumpy galaxies at the rest-frame UV, f_clumpy^UV. We identify an evolutionary trend of f_clumpy^UV over z~0-8 for the first time: f_clumpy^UV increases from z~8 to z~1-3 and subsequently decreases from z~1 to z~0, which follows the trend of Madau-Lilly plot. A low average Sersic index of n~1 is found in the underlining components of our clumpy galaxies at z~0-2, indicating that typical clumpy galaxies have disk-like surface brightness profiles. Our f_clumpy^UV values correlate with physical quantities related to star formation activities for star-forming galaxies at z~0-7. We find that clump colors tend to be red at a small galactocentric distance for massive galaxies with log(M_*/M_sun)>~11. All of these results are consistent with a picture that a majority of clumps form in the violent disk instability and migrate into the galactic centers.