Local massive early-type galaxies are believed to have completed most of their star formation ∼10 Gyr ago and evolved without having substantial star formation since that time. If so, their progenitors should have roughly solar stellar metallicities (Z∗), comparable to their values today. We report the discovery of two lensed massive (), z ∼ 2.2 dead galaxies that appear markedly metal deficient given this scenario. Using 17-band HST+Ks+Spitzer photometry and deep Hubble Space Telescope (HST) grism spectra from the Grism Lens Amplified Survey from Space (GLASS) and supernova (SN) Refsdal follow-up campaigns covering features near λrest ∼ 4000A, we find these systems to be dominated by A-type stars with and -0.49 ± 0.03 (30%-40% solar) under standard assumptions. The second system's lower metallicity is robust to isochrone changes, though this choice can drive the first system's from to 0.1. If these two galaxies are representative of larger samples, this finding suggests that evolutionary paths other than dry minor merging are required for these massive galaxies. Future analyses with direct metallicity measurements - e.g., by the James Webb Space Telescope - will provide critical insight into the nature of such phenomena.
Bibliographical noteFunding Information:
We thank the anonymous referee for insightful suggestions, and Camilla Pacifici and Mia Bovill for fruitful discussion. Support for GLASS (HST-GO-13459, 14041) was provided by NASA through a grant from the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under contract NAS 5-26555. This work uses gravitational lensing models by PIs Bradač Natarajan & Kneib (CATS v4.1), Merten & Zitrin, Sharon, Williams, Keeton, Bernstein & Diego, and the GLAFIC group. B.V. acknowledges support from an Australian Research Council Discovery Early Career Researcher Award (PD0028506).
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- galaxies: abundances
- galaxies: evolution
- galaxies: structure