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

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 $10\mathrm{kpc}$ from the galaxy center. Methods: We first studied the stellar mass and mass-weighted density slope within $10\mathrm{kpc}$, respectively $M_{\ast ,10}$ and ${\Gamma }_{\ast ,10}$, of a sample of early-type galaxies from the GAMA survey. We measured the ${\Gamma }_{\ast ,10}-M_{\ast ,10}$ relation and its evolution over the redshift range $0.17\le z\le 0.37$. 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 ${\Gamma }_{\ast ,10}-M_{\ast ,10}$ relation is consistent with a dry-merger evolution scenario. Results: From the observations, we do not detect evidence for an evolution of the ${\Gamma }_{\ast ,10}-M_{\ast ,10}$ relation. We put an upper limit on the redshift derivative of the normalization$(\mu )$ and slope$(\beta )$of the ${\Gamma }_{\ast ,10}-M_{\ast ,10}$ relation $|\partial \mu /\partial \log (1+z)|\le 0.13$ and $\left|\partial \beta /\partial \log (1+z)\right|\le 1.10$, respectively. Simulations show that most mergers induce a decrease in ${\Gamma }_{\ast ,10}$ and an increase in $M_{\ast ,10}$, although some show a decrease in $M_{\ast ,10}$, 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 $0.17\le z\le 0.37$. 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 $\Delta t\ge 3.2\mathrm{Gyr}$, should enable us to detect a signal and help us better understand the late growth of ETGs.

15 pages, 12 figures, accepted by Astronomy & Astrophysics. A 2-minute summary video is available at this link: https://youtu.be/QP7v_Wn_AIs

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