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تسجيل مستخدم جديدSpectroscopic Confirmation of two Extremely Massive Protoclusters BOSS1244 and BOSS1542 at $z=2.24$
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Dongdong Shi
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We present spectroscopic confirmation of two new massive galaxy protoclusters at $z=2.24pm0.02$, BOSS1244 and BOSS1542, traced by groups of Coherently Strong Ly$alpha$ Absorption (CoSLA) systems imprinted in the absorption spectra of a number of quasars from the SDSS III and identified as overdensities of narrowband-selected H$alpha$ emitters (HAEs). Using MMT/MMIRS and LBT/LUCI near-infrared (NIR) spectroscopy, we confirm 46 and 36 HAEs in the BOSS1244 and BOSS1542 fields, respectively. BOSS1244 displays a South-West (SW) component at $z=2.230pm0.002$ and another North-East (NE) component at $z=2.246pm0.001$ with the line-of-sight velocity dispersions of $405pm202$ km s$^{-1}$ and $377pm99$ km s$^{-1}$, respectively. Interestingly, we find that the SW region of BOSS1244 contains two substructures in redshift space, likely merging to form a larger system. In contrast, BOSS1542 exhibits an extended filamentary structure with a low velocity dispersion of $247pm32$ km s$^{-1}$ at $z=2.241pm0.001$, providing a direct confirmation of a large-scale cosmic web in the early Universe. The galaxy overdensities $delta_{rm g}$ on the scale of 15 cMpc are $22.9pm4.9$, $10.9pm2.5$, and $20.5pm3.9$ for the BOSS1244 SW, BOSS1244 NE, and BOSS1542 filament, respectively. They are the most overdense galaxy protoclusters ($delta_{rm g}>20$) discovered to date at $z>2$. These systems are expected to become virialized at $zsim0$ with a total mass of $M_{rm SW}=(1.59pm0.20)times10^{15}$ $M_{odot}$, $M_{rm NE} =(0.83pm0.11)times10^{15}$ $M_{odot}$ and $M_{rm filament}=(1.42pm0.18)times10^{15}$ $M_{odot}$, respectively. Together with BOSS1441 described in Cai et al. (2017a), these extremely massive overdensities at $z=2-3$ exhibit different morphologies, indicating that they are in different assembly stages in the formation of early galaxy clusters.
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