http://arxiv.org/abs/1803.01852
Local massive early-type galaxies are believed to have completed most of their star formation $\sim10$Gyr ago and evolved without having substantial star formation since. If so, their progenitors should have roughly solar stellar metallicities ($Z_$), comparable to their values today. We report the discovery of two lensed massive ($\log M_/M_\odot\sim11$), $z\sim2.2$ dead galaxies, that appear markedly metal deficient given this scenario. Using 17-band $HST$+$K_{s}$+$Spitzer$ photometry and deep $HST$ grism spectra from the GLASS and SN Refsdal follow-up campaigns covering features near $\lambda_{\rm rest}\sim4000$\AA, we find these systems to be dominated by A-type stars with $\log Z_/Z_\odot=-0.40\pm0.02$ and $-0.49\pm0.03$ ($30$-$40\%$ 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 $\log Z_/Z_\odot=-0.6$ 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.
T. Morishita, L. Abramson, T. Treu, et. al.
Wed, 7 Mar 18
58/65
Comments: Accepted for publication in Astrophysical Journal Letters; 6 pages, 3 figures, 1 table
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