Kavli Affiliate: Hu Zhan
| First 5 Authors: Hang Zhou, Xin Wang, Matthew A. Malkan, Tommaso Treu, Yiming Yang
| Summary:
The MAMMOTH-MOSFIRE program is a deep Keck MOSFIRE K-band spectroscopic
follow-up of emission-line galaxies identified in the MAMMOTH-Grism HST
WFC3/G141 slitless spectroscopic survey, targeting the core regions of three
most massive galaxy protoclusters at cosmic noon. To introduce this program, we
present a comprehensive analysis of the emission-line diagnostics for a unique
sample of 43 protocluster member galaxies at $zsim2$, investigating the impact
of the overdense environment on their interstellar medium conditions. We
characterize their ionization and excitation state using the $rm
[N,II]lambda$6584, $rm [S,II]lambdalambda$6717,6731, and $rm
[O,I]lambda$6300 BPT diagrams, from a full suite of rest-frame optical
emission lines jointly covered by Keck MOSFIRE and HST G141 spectroscopy. Our
analysis reveals a median electron density of $n_{rm e}approx290~{rm
cm}^{-3}$ from $rm [S,II]$ doublets, consistent with measurements from field
galaxies at similar redshifts. Like their field counterparts at $zsim2$,
protocluster galaxies exhibit a systematic offset in the N2 BPT diagram
compared to the local star-forming sequence, but no offset in the S2 BPT
diagram. Notably, we find significantly enhanced $rm [O,I]/H{alpha}$ ratios,
which can be well explained by photoionization models incorporating both $rm
H,II$ regions and shock excitation. This work highlights the powerful synergy
between high-resolution Keck MOSFIRE K-band spectroscopy and HST G141 slitless
spectroscopy, enabling comprehensive coverage of the rest-frame optical spectra
of galaxies at $zsim2$.
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