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Cosmic Galaxy-IGM HI Relation at ${it{z}}sim 2-3$ Probed in the COSMOS/UltraVISTA $1.6$ deg$^2$ Field | Shiro Mukae
; Masami Ouchi
; Koki Kakiichi
; Nao Suzuki
; Yoshiaki Ono
; Zheng Cai
; Akio K.Inoue
; Yi-Kuan Chiang
; Takatoshi Shibuya
; Yuichi Matsuda
; | Date: |
2 May 2016 | Abstract: | We present spatial correlations of galaxies and IGM neutral hydrogen HI in
the COSMOS/UltraVISTA 1.62 deg$^2$ field. Our data consist of 13415 photo-$z$
galaxies at $zsim2-3$ with $K_s<23.4$ and the Ly$alpha$ forest absorptions in
the background quasar spectra selected from SDSS data with no signature of
damped Ly$alpha$ system contamination. We estimate a galaxy overdensity
$delta_{gal}$ in an impact parameter of 2.5 pMpc, and calculate the Ly$alpha$
forest fluctuations $delta_{langle F
angle}$ whose negative values
correspond to the strong Ly$alpha$ forest absorptions. We identify a weak
anti-correlation between $delta_{gal}$ and $delta_{langle F
angle}$ with a
Spearman’s rank correlation coefficient of $-0.39$ suggesting that the galaxy
overdensities and the Ly$alpha$ forest absorptions positively correlate in
space at the $sim90\%$ confidence level. This positive correlation indicates
that high-$z$ galaxies exist around an excess of HI gas in the Ly$alpha$
forest. We find four cosmic volumes, dubbed $A_{obs}$-$D_{obs}$, that have
extremely large (small) values of $delta_{gal} simeq0.8$ ($-1$) and
$delta_{langle F
angle}$ $simeq0.1$ ($-0.4$), three out of which,
$B_{obs}$-$D_{obs}$, significantly depart from the correlation, and weaken the
correlation signal. We perform cosmological hydrodynamical simulations, and
compare with our observational results. Our simulations reproduce the
correlation, agreeing with the observational results. Moreover, our simulations
have model counterparts of $A_{obs}$-$D_{obs}$, and suggest that the
observations pinpoint, by chance, a galaxy overdensity like a proto-cluster,
gas filaments lying on the sightline, a large void, and orthogonal low-density
filaments. Our simulations indicate that the significant departures of
$B_{obs}$-$D_{obs}$ are produced by the filamentary large-scale structures and
the observation sightline effects. | Source: | arXiv, 1605.0379 | Services: | Forum | Review | PDF | Favorites |
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