The $10~\rm{kpc}$ collar of early-type galaxies -- probing evolution by focusing on the inner stellar density profile

TL;DR

This study investigates the evolution of early-type galaxies within 10 kpc by analyzing their stellar density profiles, combining observational data from GAMA with toy models of galaxy mergers to constrain growth scenarios.

Contribution

It provides the first observational constraints on the evolution of the inner stellar density profile of ETGs and tests the dry-merger scenario against these observations.

Findings

No significant evolution detected in the $\Gamma_{*,10}$-$M_{*,10}$ relation.

Upper limits placed on the redshift evolution of the relation's parameters.

Merger models suggest limited mass growth consistent with observational constraints.

Abstract

Aims: In this work we aim to investigate the late evolution of ETGs, both observationally and theoretically, by focusing on the stellar mass density profile inside a fixed aperture, within $10 ~\rm{kpc}$ from the galaxy center. Methods: We first studied the stellar mass and mass-weighted density slope within $10 ~\rm{kpc}$, respectively $M_{*,10}$ and $\mathit{\Gamma_{*,10}}$, of a sample of early-type galaxies from the GAMA survey. We measured the $\mathit{\Gamma_{*,10}} - M_{*,10}$ relation and its evolution over the redshift range $0.17\leq z \leq 0.37$. We then built a toy model for the merger evolution of galaxies, based on N-body simulations, to explore to what extent the observed growth in $\mathit{\Gamma_{*,10}} - M_{*,10}$ relation is consistent with a dry-merger evolution scenario. Results: From the observations, we do not detect evidence for an evolution of the $\mathit{\Gamma_{*,10}} - M_{*,10}$ relation. We put an upper limit on the redshift derivative of the normalization$~(\mu)$ and slope$~(\beta)$of the $\mathit{\Gamma_{*,10}} - M_{*,10}$ relation $|\partial \mu/\partial \log (1+z)| \leq 0.13$ and $\left|\partial \beta/\partial \log (1+z)\right| \leq 1.10$, respectively. Simulations show that most mergers induce a decrease in $\mathit{\Gamma_{*,10}}$ and an increase in $M_{*,10}$, although some show a decrease in $M_{*,10}$, particularly for the most extended galaxies and smaller merger mass ratios. By combining the observations with our merger toy model, we placed an upper limit on $f_M = 11.2 \%$ in the redshift range $0.17 \leq z \leq 0.37$. Conclusions: While our measurement is limited by systematics, the application of our approach to samples with a larger redshift baseline, particularly with a time interval $\Delta t \geq 3.2~\mathrm{Gyr}$, should enable us to detect a signal and help us better understand the late growth of ETGs.