Structures of Local Galaxies Compared to High Redshift Star-forming Galaxies

TL;DR

This study compares the UV morphologies of local starburst and interacting galaxies with high-redshift galaxies, using nonparametric methods to classify galaxy structures and infer evolutionary links.

Contribution

It introduces a combined use of M_20 and Sersic index for efficient morphological classification of galaxies across different redshifts.

Findings

20-30% of high-redshift galaxies have bulge-like structures.

Artificial redshifting shows similar morphological features at different epochs.

Approximately 20-30% of Lyman-break galaxies resemble local starburst mergers.

Abstract

The rest-frame far-ultraviolet (FUV) morphologies of 8 nearby interacting and starburst galaxies (Arp 269, M 82, Mrk 8, NGC 520, NGC 1068, NGC 3079, NGC 3310, NGC 7673) are compared with 54 galaxies at z ~ 1.5 and 46 galaxies at z ~ 4 observed in the GOODS-ACS field. The nearby sample is artificially redshifted to z ~ 1.5 and 4. We compare the simulated galaxy morphologies to real z ~ 1.5 and 4 UV-bright galaxy morphologies. We calculate the Gini coefficient (G), the second-order moment of the brightest 20% of the galaxy's flux (M_20), and the Sersic index (n). We explore the use of nonparametric methods with 2D profile fitting and find the combination of M_20 with n an efficient method to classify galaxies as having merger, exponential disk, or bulge-like morphologies. When classified according to G and M_20, 20/30% of real/simulated galaxies at z ~ 1.5 and 37/12% at z ~ 4 have bulge-like morphologies. The rest have merger-like or intermediate distributions. Alternatively, when classified according to the Sersic index, 70% of the z ~ 1.5 and z ~ 4 real galaxies are exponential disks or bulge-like with n > 0.8, and ~30% of the real galaxies are classified as mergers. The artificially redshifted galaxies have n values with ~35% bulge or exponential at z ~ 1.5 and 4. Therefore, ~20-30% of Lyman-break galaxies (LBGs) have structures similar to local starburst mergers, and may be driven by similar processes. We assume merger-like or clumpy star-forming galaxies in the GOODS field have morphological structure with values n < 0.8 and M_20 > -1.7. We conclude that Mrk 8, NGC 3079, and NGC 7673 have structures similar to those of merger-like and clumpy star-forming galaxies observed at z ~ 1.5 and 4.