The 10 kpc collar of early-type galaxies: Probing evolution by focusing on the inner stellar density profile

Context. The post-quenching evolution process of early-type galaxies (ETGs), which is typically driven by mergers, is still not fully understood. The amount of growth in stellar mass and size incurred after quenching is still under debate. Aims. In this work, we investigated the late evolution of ETGs, both observationally and theoretically, by focusing on the stellar mass density profile inside a fixed aperture, within 10 kpc from the galaxy center. Methods. We first studied the stellar mass and the mass-weighted density slope within 10 kpc, respectively M *, 10 and Γ*, 10, of a sample of ETGs from the GAMA survey. We measured the Γ*, 10 − M *, 10 relation and its evolution over the redshift range 0.17 ≤ z ≤ 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 Γ*, 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 Γ*, 10 − M *, 10 relation relation. We put an upper limit on the redshift derivative of the normalization (μ) and slope (β) of the Γ*, 10 − M *, 10 relation: |∂μ/∂log(1 + z)| ≤ 0.13 and |∂β/∂log(1+z)| ≤ 1.10, respectively. Simulations show that most mergers induce a decrease in Γ*, 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 place an upper limit on the fractional stellar mass growth of f M = 11.2% in the redshift range 0.17 ≤ z ≤ 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 Δt ≥ 3.2 Gyr, should enable detection of a signal and improves our understanding of the late growth of ETGs.