CLEAR. I. Ages and Metallicities of Quiescent Galaxies at 1.0 < z < 1.8 Derived from Deep Hubble SpaceTelescope Grism Data
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AbstractWe use deep Hubble Space Telescope spectroscopy to constrain the metallicities and (light-weighted) ages of massive () galaxies selected to have quiescent stellar populations at 1.0<z<1.8. The data include twelve-orbit depth coverage with the WFC3/G102 grism covering 8000<<11,500 at a spectral resolution of R210 taken as part of the CANDELS Ly Emission at Reionization (CLEAR) survey. At 1.0<z<1.8, the spectra cover important stellar population features in the rest-frame optical. We simulate a suite of stellar population models at the grism resolution, fit these to the data for each galaxy, and derive posterior likelihood distributions for metallicity and age. We stack the posteriors for subgroups of galaxies in different redshift ranges that include different combinations of stellar absorption features. Our results give light-weighted ages of tz1.1=3.20.7 Gyr, tz1.2=2.20.6 Gyr, tz1.3=3.10.6 Gyr, and tz1.6=2.00.6 Gyr for galaxies at z1.1, 1.2, 1.3, and 1.6, respectively. This implies that most of the massive quiescent galaxies at 1<z<1.8 had formed >68% of their stellar mass by z>2. The posteriors give metallicities of Zz1.1=1.160.29 Z, Zz1.2=1.050.34 Z, Zz1.3=1.000.31 Z, and Zz1.6=0.950.39 Z. This is evidence that massive galaxies had enriched rapidly to approximately solar metallicities as early as z3.
