COOL-LAMPS II. Characterizing the Size and Star Formation History of a Bright Strongly Lensed Early-Type Galaxy at Redshift 1.02

TL;DR

This paper reports the discovery and detailed analysis of a strongly lensed early-type galaxy at redshift 1.02, revealing its size, star formation history, and properties through gravitational lensing and multi-wavelength observations.

Contribution

It presents the first detailed characterization of a highly magnified early-type galaxy at z~1, including its size, mass, and star formation history, using gravitational lens modeling and stellar population analysis.

Findings

Median stellar mass of ~10^10.63 M_sun

Effective radius of ~0.5 kpc, smaller than expected

Star formation rate of ~1.55e-3 M_sun/yr

Abstract

We present COOL J1323+0343, an early-type galaxy at $z = 1.0153 \pm 0.0006$, strongly lensed by a cluster of galaxies at z = $z = 0.353 \pm 0.001$. This object was originally imaged by DECaLS and noted as a gravitational lens by COOL-LAMPS, a collaboration initiated to find strong-lensing systems in recent public optical imaging data, and confirmed with follow-up data. With ground-based grzH imaging and optical spectroscopy from the Las Campanas Observatory and the Nordic Optical Telescope, we derive a stellar mass, metallicity, and star-formation history from stellar-population synthesis modeling. The lens modeling implies a total magnification of $\mu \sim $113. The median remnant stellar mass in the source plane is M$_* \sim 10.63$ $M_\odot$ and the median star-formation rate in the source plane is SFR $\sim 1.55 \times 10^{-3}$ M$_\odot$ yr$^{-1}$ (log sSFR = -13.4 yr$^{-1}$) in the youngest two age bins (0-100 Myr), closest to the epoch of observation. Our measurements place COOL J1323+0343 below the characteristic mass of the stellar mass function, making it an especially compelling target that could help clarify how intermediate mass quiescent galaxies evolve. We reconstruct COOL J1323+0343 in the source plane and fit its light profile. This object is below the expected size-evolution of early-type galaxy at this mass with an effective radius r$_e \sim$ 0.5 kpc. This extraordinarily magnified and bright lensed early-type galaxy offers an exciting opportunity to study the morphology and star formation history of an intermediate mass early-type galaxy in detail at $z \sim $1 .