INSPIRE: INvestigating Stellar Populations In RElics. IX. KiDS J0842+0059: the first fully confirmed relic beyond the local Universe

TL;DR

This paper presents high-resolution adaptive optics imaging of KiDS J0842+0059, confirming it as a relic galaxy beyond the local universe, providing insights into early galaxy formation and evolution.

Contribution

First high-resolution AO Ks-band imaging of a confirmed relic galaxy beyond the local universe, validating its morphology and compactness with detailed modeling.

Findings

KiDS J0842+0059 has a disky morphology and is extremely compact.

Its surface mass density profile resembles local relics and high-redshift red nuggets.

Confirmed as a high-redshift relic that missed merger-driven growth.

Abstract

Relics are massive, compact and quiescent galaxies that assembled the majority of their stars in the early Universe and lived untouched until today, completely missing any subsequent size-growth caused by mergers and interactions. They provide the unique opportunity to put constraints on the first phase of mass assembly in the Universe with the ease of being nearby. While only a few relics have been found in the local Universe, the {\tt INSPIRE} project has confirmed 38 relics at higher redshifts ($z \sim 0.2-0.4$), fully characterising their integrated kinematics and stellar populations. However, given the very small sizes of these objects and the limitations imposed by the atmosphere, structural parameters inferred from ground-based optical imaging are possibly affected by systematic effects that are difficult to quantify. In this paper, we present the first high-resolution image obtained with Adaptive Optics Ks-band observations on SOUL-LUCI@LBT of one of the most extreme {\tt INSPIRE} relics, KiDS~J0842+0059 at $z \sim 0.3$. We confirm the disky morphology of this galaxy (axis ratio of $0.24$) and its compact nature (circularized effective radius of $\sim 1$ kpc) by modelling its 2D surface brightness profile with a PSF-convolved S\'ersic model. We demonstrate that the surface mass density profile of KiDS~J0842+0059 closely resembles that of the most extreme local relic, NGC~1277, as well as of high-redshift red nuggets. We unambiguously conclude that this object is a remnant of a high-redshift compact and massive galaxy, which assembled all of its mass at $z>2$, and completely missed the merger phase of the galaxy evolution.