演講資訊

摘要：

Local massive early-type galaxies are believed to have completed most of their star formation ∼10Gyr 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 (logM∗/Msun ∼11), z∼2.2 dead galaxies, that appear markedly metal deficient given this scenario. Using 17-band HST+Ks+Spitzer photometry and deep HST grism spectra from the GLASS and SN Refsdal followup campaigns covering features near λrest ∼4000 ˚A, we find these systems to be dominated by A-type stars with logZ∗/Zsun =−0.40±0.02 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 logZ∗/Zsun =−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.

作者：

Morishita, T.; Abramson, L. E.; Treu, T.; Wang, X.

期刊：

arXiv