Colour gradients of high-redshift Early-Type Galaxies from hydrodynamical monolithic models

TL;DR

This study examines the evolution of colour gradients in high-redshift early-type galaxies using hydrodynamical models, comparing predictions with observations and exploring the effects of different physical parameters and galaxy mergers.

Contribution

It provides a detailed analysis of colour gradient evolution in ETGs from hydrodynamical models and suggests the role of dry mergers in explaining observed discrepancies at certain redshifts.

Findings

Models agree with optical data at z<1 for low star formation efficiency.

Discrepancies at 1<z<2 suggest additional processes like dry mergers are needed.

Future work should consider wet mergers, environment, dust, and IMF variations.

Abstract

We analyze the evolution of colour gradients predicted by the hydrodynamical models of early type galaxies (ETGs) in Pipino et al. (2008), which reproduce fairly well the chemical abundance pattern and the metallicity gradients of local ETGs. We convert the star formation (SF) and metal content into colours by means of stellar population synthetic model and investigate the role of different physical ingredients, as the initial gas distribution and content, and eps_SF, i.e. the normalization of SF rate. From the comparison with high redshift data, a full agreement with optical rest-frame observations at z < 1 is found, for models with low eps_SF, whereas some discrepancies emerge at 1 < z < 2, despite our models reproduce quite well the data scatter at these redshifts. To reconcile the prediction of these high eps_SF systems with the shallower colour gradients observed at lower z we suggest intervention of 1-2 dry mergers. We suggest that future studies should explore the impact of wet galaxy mergings, interactions with environment, dust content and a variation of the Initial Mass Function from the galactic centers to the peripheries.