Kavli Affiliate: John D. Silverman
| First 5 Authors: Yongming Liang, Masami Ouchi, Dongsheng Sun, Nobunari Kashikawa, Zheng Cai
| Summary:
We report the identification of a quasar overdensity in the BOSSJ0210 field,
dubbed Cosmic Himalayas, consisting of 11 quasars at $z=2.16-2.20$, the densest
overdensity of quasars ($17sigma$) in the $sim$10,000 deg$^2$ of the Sloan
Digital Sky Survey. We present the spatial distributions of galaxies and
quasars and an HI absorption map of the intergalactic medium (IGM). On the map
of 465 galaxies selected from the MAMMOTH-Subaru survey, we find two galaxy
density peaks that do not fall on the quasar overdensity but instead exist at
the northwest and southeast sides, approximately 25 $h^{-1}$ comoving-Mpc apart
from the quasar overdensity. With a spatial resolution of 15 $h^{-1}$ comoving
Mpc in projection, we produce a three-dimensional HI tomography map by the IGM
Ly$alpha$ forest in the spectra of 23 SDSS/eBOSS quasars behind the quasar
overdensity. Surprisingly, the quasar overdensity coincides with neither an
absorption peak nor a transmission peak of IGM HI but lies near the border
separating opaque and transparent volumes, with the more luminous quasars
located in an environment with lesser IGM HI. Hence remarkably, the overdensity
region traced by the 11 quasars, albeit all in coherently active states, has no
clear coincidence with peaks of galaxies or HI absorption densities. Current
physical scenarios with mixtures of HI overdensities and quasar photoionization
cannot fully interpret the emergence of Cosmic Himalayas, suggesting this
peculiar structure is an excellent laboratory to unveil the interplay between
galaxies, quasars, and the IGM.
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