Red nuggets grow inside-out: evidence from gravitational lensing
Lindsay Oldham, Matt Auger, Chris Fassnacht, Tommaso Treu, Brendon J., Brewer, L.V.E. Koopmans, David Lagattuta, Philip Marshall, John McKean,, Simona Vegetti

TL;DR
This study uses gravitational lensing to analyze a population of compact, massive galaxies at intermediate redshifts, providing evidence for inside-out growth through minor mergers and characterizing their structural and stellar properties.
Contribution
It presents a new sample of lensed early-type galaxies, revealing their two-component structures and supporting the inside-out growth model of red nuggets.
Findings
Sources are compact, massive, and below the size-mass relation.
They generally require two Sersic components for modeling.
Color gradients indicate ongoing accretion, especially at lower redshifts.
Abstract
We present a new sample of strong gravitational lens systems where both the foreground lenses and background sources are early-type galaxies. Using imaging from HST/ACS and Keck/NIRC2, we model the surface brightness distributions and show that the sources form a distinct population of massive, compact galaxies at redshifts , lying systematically below the size-mass relation of the global elliptical galaxy population at those redshifts. These may therefore represent relics of high-redshift red nuggets or their partly-evolved descendants. We exploit the magnifying effect of lensing to investigate the structural properties, stellar masses and stellar populations of these objects with a view to understanding their evolution. We model these objects parametrically and find that they generally require two S\'ersic components to properly describe their light…
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