The Dramatic Size and Kinematic Evolution of Massive Early-Type Galaxies

TL;DR

This paper presents a comprehensive model of the size and kinematic evolution of massive early-type galaxies, integrating physical processes from high redshift to the present, and aligns well with observational data.

Contribution

It introduces new analytical estimates for galaxy sizes, timescales, and kinematic properties during evolution, based on physical principles and simulations.

Findings

Good agreement with observed galaxy sizes and kinematic ratios.

Quantitative relations for galaxy evolution as a function of mass and redshift.

Consistent results for local and high-redshift galaxy properties.

Abstract

[ABRIDGED] We aim to provide a holistic view on the typical size and kinematic evolution of massive early-type galaxies (ETGs), that encompasses their high-$z$ star-forming progenitors, their high-$z$ quiescent counterparts, and their configurations in the local Universe. Our investigation covers the main processes playing a relevant role in the cosmic evolution of ETGs. Specifically, their early fast evolution comprises: biased collapse of the low angular momentum gaseous baryons located in the inner regions of the host dark matter halo; cooling, fragmentation, and infall of the gas down to the radius set by the centrifugal barrier; further rapid compaction via clump/gas migration toward the galaxy center, where strong heavily dust-enshrouded star-formation takes place and most of the stellar mass is accumulated; ejection of substantial gas amount from the inner regions by feedback processes, which causes a dramatic puffing up of the stellar component. In the late slow evolution, passive aging of stellar populations and mass additions by dry merger events occur. We describe these processes relying on prescriptions inspired by basic physical arguments and by numerical simulations, to derive new analytical estimates of the relevant sizes, timescales, and kinematic properties for individual galaxies along their evolution. Then we obtain quantitative results as a function of galaxy mass and redshift, and compare them to recent observational constraints on half-light size $R_e$, on the ratio $v/\sigma$ between rotation velocity and velocity dispersion (for gas and stars) and on the specific angular momentum $j_\star$ of the stellar component; we find good consistency with the available multi-band data in average values and dispersion, both for local ETGs and for their $z\sim 1-2$ star-forming and quiescent progenitors.