Metal Deficiency in Two Massive Dead Galaxies at $z\sim2$
  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.
