REQUIEM-2D Methodology: Spatially Resolved Stellar Populations of Massive Lensed Quiescent Galaxies from Hubble Space Telescope 2D Grism Spectroscopy

Abstract

We present a novel Bayesian methodology to jointly model photometry and deep Hubble Space Telescope (HST ) 2d grism spectroscopy of high-redshift galaxies. Our requiem2d code measures both unresolved and resolved stellar populations, ages, and star-formation histories (SFHs) for the ongoing REQIUEM (REsolving QUIEscent Magnified) Galaxies Survey, which targets strong gravitationally lensed quiescent galaxies at z∼2. We test the accuracy of requiem2d using a simulated sample of massive galaxies at z∼2 from the Illustris cosmological simulation and find we recover the general trends in SFH and median stellar ages. We further present a pilot study for the REQUIEM Galaxies Survey: MRG-S0851, a quintuply-imaged, massive (log M * /M = 11.02±0.04) red galaxy at z = 1.883±0.001. With an estimated gravitational magnification of µ = 5.7 +0.4 −0.2 , we sample the stellar populations on 0.6 kpc physical size bins. The global mass-weighted median age is constrained to be 1.8 +0.3 −0.2 Gyr, and our spatially resolved analysis reveals that MRG-S0851 has a flat age gradient in the inner 3 kpc core after taking into account the subtle effects of dust and metallicity on age measurements, favoring an early formation scenario. The analysis for the full REQUIEM-2D sample will be presented in a forthcoming paper with a beta-release of the requiem2d code.

An exquisitely deep view of quenching galaxies through the gravitational lens: Stellar population, morphology, and ionized gas

“…This sample forms the backbone of the REsolving QUIEscent Magnified Galaxies Survey (REQUIEM-2D). HST grism observations will enable measurements of spatially resolved stellar populations, in order to quantify age and SFR gradients (Akhshik et al 2020(Akhshik et al , 2021. ALMA surveys of the CO and dust continuum will provide molecular gas mass measurements (Whitaker et al submitted, Man et al in preparation).…”

“…much more evolved. Possible alternatives are log-normal SFHs (Gladders et al 2013) or non-parameteric models (Iyer et al 2019;Leja et al 2019;Akhshik et al 2020).…”

“…The increasing rarity of quiescent galaxies towards higher redshift implies that cluster-lensed quiescent galaxies are uncommon, typically less than one per galaxy cluster. Only nine of such galaxies have been discovered to date (Muzzin et al 2012;Geier et al 2013;Newman et al 2015Newman et al , 2018aHill et al 2016;Toft et al 2017;Ebeling et al 2018;Akhshik et al 2020). The most remarkable finding is the confirmation of a rotating stellar disk that has ceased star formation (Toft et al 2017;Newman et al 2018b).…”

Early Science with the Large Millimeter Telescope: Constraining the Gas Fraction of a Compact Quiescent Galaxy at z=1.883

“…Galaxy MRG-S0851 is a red galaxy at z=1.88 quintuply imaged via strong gravitational lensing by the cluster SDSS J0851+3331 identified in the Sloan Giant Arc Survey (Figure 1; see also Sharon et al 2020). As a target in the REsolving QUIEscent Magnified (REQUIEM) galaxy survey, Akhshik et al (2020b) present the analysis of the stellar population gradients of our main target with surprising evidence supporting a rejuvenation phase in the last 100 Myr (Akhshik et al 2020a). MRG-S0851 is otherwise a prototypical z ∼ 2 quiescent galaxy, with an intrinsic stellar mass of log M * /M = 11.02 ± 0.04, a low SFR of 6±1M /yr, sSFR log(SFR/M ) = -10.32 +0.07 −0.05 yr −1 , a Sérsic index of n = 2.35±0.05, and a compact circularized effective radius of 1.7 +0.3 −0.1 kpc.…”

“…MRG-S0851 is otherwise a prototypical z ∼ 2 quiescent galaxy, with an intrinsic stellar mass of log M * /M = 11.02 ± 0.04, a low SFR of 6±1M /yr, sSFR log(SFR/M ) = -10.32 +0.07 −0.05 yr −1 , a Sérsic index of n = 2.35±0.05, and a compact circularized effective radius of 1.7 +0.3 −0.1 kpc. The SFR estimate of MRG-S0851 from Akhshik et al (2020b) was made using joint spectro-photometric fit assuming a non-parametric Figure 1. MRG-S0851 imaged by LMT/AzTEC.…”