Testing the presence of multiple photometric components in nearby early-type galaxies using SDSS

TL;DR

This study analyzes nearby early-type galaxies using SDSS imaging to identify multiple photometric components, revealing insights into their formation, structure, and evolution, especially regarding size growth and accretion history.

Contribution

It demonstrates that many nearby ETGs have multi-component structures, linking these features to their formation history and environmental influences, which advances understanding of galaxy evolution.

Findings

Double-component ETGs are younger and more metal-rich.

Outer components tend to be more elliptical.

Fraction of double-component ETGs increases with velocity dispersion.

Abstract

We investigate two-dimensional image decomposition of nearby, morphologically selected early-type galaxies (ETGs). We are motivated by recent observational evidence of significant size growth of quiescent galaxies and theoretical development advocating a two-phase formation scenario for ETGs. We find that a significant fraction of nearby ETGs show changes in isophotal shape that require multi-component models. The characteristic sizes of the inner and outer component are $\sim 3$ and $\sim 15$ kpc. The inner component lies on the mass-size relation of ETGs at $z \sim 0.25-0.75$, while the outer component tends to be more elliptical and hints at a stochastic buildup process. We find real physical differences between the single- and double-component ETGs, with the double-component galaxies being younger and more metal-rich. The fraction of double component ETGs increases with increasing $\sigma$ and decreases in denser environments. We hypothesize that double-component systems were able to accrete gas and small galaxies until later times, boosting their central densities, building up their outer parts, and lowering their typical central ages. In contrast, the oldest galaxies, perhaps due to residing in richer environments, have no remaining hints of their last accretion episode.