Clumpy Galaxies in GOODS and GEMS: Massive Analogs of Local Dwarf Irregulars

TL;DR

This study investigates the evolution of clumpy galaxies in deep fields, revealing a progression from clump clusters to spiral galaxies, and finds they resemble local dwarf irregulars, supporting a model of gravitational instabilities in turbulent gas.

Contribution

It provides a detailed analysis of the morphological evolution of high-redshift clumpy galaxies and links them to local dwarf irregulars, highlighting the role of gravitational instabilities.

Findings

Clumpy galaxies evolve into spiral types over time.

Clump clusters resemble local dwarf irregulars.

Morphological changes suggest gradual disk and bulge formation.

Abstract

Clumpy galaxies in the GEMS and GOODS fields are examined for clues to their evolution into modern spirals. The magnitudes of the clumps and the surface brightnesses of the interclump regions are measured and fitted to models of stellar age and mass. There is an evolutionary trend from clump clusters with no evident interclump emission to clump clusters with faint red disks, to spiral galaxies of the flocculent or grand design types. Along this sequence, the interclump surface density increases and the mass surface density contrast between the clumps and the interclump regions decreases, suggesting a gradual dispersal of clumps to form disks. Also along this sequence, the bulge-to-clump mass ratios and age ratios increase, suggesting a gradual formation of bulges. All of these morphological types occur in the same redshift range, indicating that the clump cluster morphology is not the result of bandshifting. Comparisons to local galaxies with the same rest wavelength and spatial resolution show that clump clusters resemble local dwarf Irregulars. This resemblance is consistent with a model in which the clumpy morphology comes from gravitational instabilities in gas with a high turbulent speed compared to the rotation speed and a high mass fraction compared to the stars.