Statistical correlation between the distribution of Ly$\alpha$ emitters and IGM HI at $z\sim 2.2$ mapped by Subaru/Hyper Suprime-Cam

Abstract

The correlation between neutral Hydrogen (HI) in the intergalactic medium (IGM) and galaxies now attracts great interests. We select four fields which include several coherently strong Ly$\alpha$ absorption systems at $z\sim 2.2$ detected by using background quasars from the whole SDSS/(e)BOSS database. Deep narrow-band and $g$-band imaging are performed using the Hyper Suprime-Cam on the Subaru Telescope. We select out 2,642 Ly$\alpha$ emitter (LAE) candidates at $z=2.177\pm 0.023$ down to the Ly$\alpha$ luminosity of $L_{\text{Ly}\alpha }\approx 2\times 10^{42}{\mathrm{erg}\mathrm{s}}^{-1}$ to construct the galaxy overdensity maps, covering an effective area of 5.39 deg${}^2$. Combining the sample with the Ly$\alpha$ absorption estimated from 64 (e)BOSS quasar spectra, we find a moderate to strong correlation between the LAE overdensity ${\delta }_{\mathrm{LAE}}$ and the effective optical depth ${\tau }_{\mathrm{LoS}}$ in line-of-sights, with $P$-value$=0.09\%$ ($<0.01\%$) when the field that contains a significant quasar overdensity is in(ex)cluded. The cross-correlation analysis also clearly suggests that up to $4\pm 1$ pMpc, LAEs tend to cluster in the regions rich in HI gas, indicated by the high ${\tau }_{\mathrm{LoS}}$, and avoid the low ${\tau }_{\mathrm{LoS}}$ region where the HI gas is deficient. By averaging the ${\tau }_{\mathrm{LoS}}$ as a function of the projected distance ($d$) to LAEs, we find a $30\%$ excess signal at $2\sigma$ level at $d<200$ pkpc, indicating the dense HI in circumgalactic medium, and a tentative excess at $400<d<600$ pkpc in IGM regime, corroborating the cross-correlation signal detected at about $0.5$ pMpc. These statistical analyses indicate that galaxy$-$IGM HI correlations exist on scales ranging from several hundred pkpc to several pMpc at $z\sim 2.2$.

27 pages, 15 figures; Resubmitted to ApJ after the first referee's report. Comments are welcome

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