Superdense and normal early-type galaxies at 1<z<2

TL;DR

This study analyzes early-type galaxies at redshifts 1<z<2, revealing a significant population of both normal-sized and superdense galaxies, indicating diverse formation histories during this epoch.

Contribution

It provides a detailed morphological and physical analysis of 62 early-type galaxies at 0.9<z<2, identifying two distinct populations with different sizes and densities, suggesting varied evolutionary paths.

Findings

Approximately 50% of ETGs follow local size-mass relations.

Half of the ETGs are superdense with sizes 2.5-3 times smaller than local counterparts.

Normal ETGs are not smaller than local galaxies with similar mass.

Abstract

We combined proprietary and archival HST observations to collect a sample of 62 early-type galaxies (ETGs) at 0.9<z<2 with spectroscopic confirmation of their redshift and spectral type. The whole sample is covered by ACS or NICMOS observations and partially by Spitzer and AKARI observations. We derived morphological parameters by fitting their HST light profiles and physical parameters by fitting their spectral energy distributions. The study of the size-mass and the size-luminosity relations of these early-types shows that a large fraction of them (~50) follows the local relations. These 'normal' ETGs are not smaller than local counterparts with comparable mass. The remaining half of the sample is composed of compact ETGs with sizes (densities) 2.5-3 (15-30) times smaller (higher) than local counterparts and, most importantly, than the other normal ETGs at the same redshift and with the same stellar mass. This suggests that normal and superdense ETGs at z~2 come from different histories of mass assembly.