The KLEVER Survey: Spatially resolved metallicity maps and gradients in a sample of 1.2 < z < 2.5 lensed galaxies

TL;DR

This study uses near-infrared observations of 42 lensed galaxies at redshifts 1.2 to 2.5 to produce detailed metallicity maps, revealing mostly flat gradients and complex local variations, informing galaxy evolution models.

Contribution

It provides the first comprehensive spatially resolved metallicity maps for a large sample of high-redshift lensed galaxies, highlighting the prevalence of flat gradients and complex structures.

Findings

85% of galaxies have metallicity gradients shallower than 0.05 dex/kpc.

89% are consistent with flat metallicity gradients within 3σ.

Detection of inverted gradients in three galaxies, indicating possible recent gas accretion or radial flows.

Abstract

We present near-infrared observations of 42 gravitationally lensed galaxies obtained in the framework of the KMOS Lensed Emission Lines and VElocity Review (KLEVER) Survey, a program aimed at investigating the spatially resolved properties of the ionised gas in 1.2<z<2.5 galaxies by means of a full coverage of the YJ, H and K near-infrared bands. Detailed metallicity maps and gradients are derived for a sub-sample of 28 galaxies from reconstructed source plane emission line maps, exploiting the variety of different emission line diagnostics provided by the broad wavelength coverage of the survey. About 85% of these galaxies are characterised by metallicity gradients shallower than 0.05 dex/kpc and 89% are consistent with flat slope within 3$\sigma$ (67% within 1$\sigma$), suggesting a mild evolution with cosmic time. In the context of cosmological simulations and chemical evolution models, the presence of efficient feedback mechanisms and/or extended star formation profiles on top of the classical "inside-out" scenario of mass assembly is generally required to reproduce the observed flatness of the metallicity gradients beyond z$\sim$1 . Three galaxies with significantly (> 3$\sigma$) "inverted" gradients are also found, showing an anti-correlation between metallicity and star formation rate density on local scales, possibly suggesting recent episodes of pristine gas accretion or strong radial flows in place. Nevertheless, the individual metallicity maps are characterised by a variety of different morphologies, with flat radial gradients sometimes hiding non-axisymmetric variations on kpc scales which are washed out by azimuthal averages, especially in interacting systems or in those undergoing local episodes of recent star formation.