Detection of Prominent Stellar Disks in the Progenitors of Present-day Massive Elliptical Galaxies

TL;DR

This study investigates the morphological evolution of massive galaxies from high redshift to the present, revealing that early galaxies had prominent disks that diminished over time due to mergers, leading to the formation of local elliptical galaxies.

Contribution

It provides detailed bulge+disk decompositions for a large sample of galaxies across redshifts, highlighting the presence and subsequent disappearance of stellar disks in massive galaxy evolution.

Findings

High-redshift massive galaxies have prominent stellar disks.

Disks diminish and disappear by z ≈ 0.5, transforming into elliptical galaxies.

Major and minor mergers drive size growth and disk destruction.

Abstract

Massive galaxies at higher redshifts ($\emph{z}$ $>$ 2) show different characteristics from their local counterparts: They are compact and most likely have a disk. In this study, we trace the evolution of local massive galaxies by performing a detailed morphological analysis, namely, fitting single S\'{e}rsic profiles and performing bulge+disk decompositions. We analyze $\sim$ 250 massive galaxies selected from all CANDELS fields (COSMOS, UDS, EGS, GOODS-South and GOODS-North). We confirm that both star-forming and quiescent galaxies increase their sizes significantly from $\emph{z}$ $\approx$ 2.5 to the present day. The global S\'{e}rsic index of quiescent galaxies increases over time (from $n$ $\approx$ 2.5 to $n$ $>$ 4), while that of star-forming galaxies remains roughly constant ($n$ $\approx$ 2.5). By decomposing galaxy profiles into bulge+disk components, we find that massive galaxies at high redshift have prominent stellar disks, which are also evident from visual inspection of the images. By $z$ $\approx$ 0.5, the majority of the disks disappear and massive quiescent galaxies begin to resemble the local elliptical galaxies. Star-forming galaxies have lower bulge-to-total ratios ($B/T$) than their quiescent counterparts at each redshift bin. The bulges of star-forming and quiescent galaxies follow different evolutionary histories, while their disks evolve similarly. We conclude that major mergers, along with minor mergers, have played a crucial role in the significant size increase of high-\emph{z} galaxies and the destruction of their massive and large-scale disks.