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Register a new userSILVERRUSH. VI. A simulation of Ly$alpha$ emitters in the reionization epoch and a comparison with Subaru Hyper Suprime-Cam survey early data
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Akio K. Inoue
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The survey of Lyman $alpha$ emitters (LAEs) with Subaru Hyper Suprime-Cam, called SILVERRUSH (Ouchi et al.), is producing massive data of LAEs at $zgtrsim6$. Here we present LAE simulations to compare the SILVERRUSH data. In 162$^3$ comoving Mpc$^3$ boxes, where numerical radiative transfer calculations of reionization were performed, LAEs have been modeled with physically motivated analytic recipes as a function of halo mass. We have examined $2^3$ models depending on the presence or absence of dispersion of halo Ly$alpha$ emissivity, dispersion of the halo Ly$alpha$ optical depth, $tau_alpha$, and halo mass dependence of $tau_alpha$. The unique free parameter in our model, a pivot value of $tau_alpha$, is calibrated so as to reproduce the $z=5.7$ Ly$alpha$ luminosity function (LF). We compare our model predictions with Ly$alpha$ LFs at $z=6.6$ and $7.3$, LAE angular auto-correlation functions (ACFs) at $z=5.7$ and $6.6$, and LAE fractions in Lyman break galaxies at $5<z<7$. The Ly$alpha$ LFs and ACFs are reproduced by multiple models, but the LAE fraction turns out to be the most critical test. The dispersion of $tau_alpha$ and the halo mass dependence of $tau_alpha$ are essential to explain all observations reasonably. Therefore, a simple model of one-to-one correspondence between halo mass and Ly$alpha$ luminosity with a constant Ly$alpha$ escape fraction has been ruled out. Based on our best model, we present a formula to estimate the intergalactic neutral hydrogen fraction, $x_{rm HI}$, from the observed Ly$alpha$ luminosity density at $zgtrsim6$. We finally obtain $x_{rm HI}=0.5_{-0.3}^{+0.1}$ as a volume-average at $z=7.3$.
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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 $zsim2.2$ 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 $z=2.177pm0.023$ down to the Ly$alpha$ luminosity of $L_{text{Ly}alpha}approx 2 times 10^{42} {rm erg~s}^{-1}$ 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 $delta_{rm LAE}$ and the effective optical depth $tau_{rm LoS}$ 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 $4pm1$ pMpc, LAEs tend to cluster in the regions rich in HI gas, indicated by the high $tau_{rm LoS}$, and avoid the low $tau_{rm LoS}$ region where the HI gas is deficient. By averaging the $tau_{rm LoS}$ as a function of the projected distance ($d$) to LAEs, we find a $30%$ excess signal at $2sigma$ 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 $zsim2.2$.
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Narrow-line regions excited by active galactic nuclei (AGN) are important for studying AGN photoionization and feedback. Their strong [O III] lines can be detected with broadband images, allowing morphological studies of these systems with large-area imaging surveys. We develop a new technique to reconstruct the [O III] images using the Subaru Hyper Suprime-Cam (HSC) Survey aided with spectra from the Sloan Digital Sky Survey (SDSS). The technique involves a careful subtraction of the galactic continuum to isolate emission from the [O III]$lambda$5007 and [O III]$lambda$4959 lines. Compared to traditional targeted observations, this technique is more efficient at covering larger samples with less dedicated observational resources. We apply this technique to an SDSS spectroscopically selected sample of 300 obscured AGN at redshifts 0.1 - 0.7, uncovering extended emission-line region candidates with sizes up to tens of kpc. With the largest sample of uniformly derived narrow-line region sizes, we revisit the narrow-line region size-luminosity relation. The area and radii of the [O III] emission-line regions are strongly correlated with the AGN luminosity inferred from the mid-infrared (15 $mu$m rest-frame) with a power-law slope of $0.62^{+0.05}_{-0.06} pm 0.10$ (statistical and systemic errors), consistent with previous spectroscopic findings. We discuss the implications for the physics of AGN emission-line region and future applications of this technique, which should be useful for current and next-generation imaging surveys to study AGN photoionization and feedback with large statistical samples.
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