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Investigating the Gunn-Peterson trough of high redshift quasars (QSOs) is a powerful way to reveal the cosmic reionization. As one of such attempts, we perform a series of analyses to examine the absorption lines observed with one of the highest redshift QSOs, PSO J006.1240+39.2219, which we previously discovered at z = 6.62. Using the Subaru telescope, we obtained medium-resolution spectrum with a total exposure time of 7.5 hours. We calculate the Ly$\alpha$ transmission in different redshift bins to determine the near zone radius and the optical depth at 5.6$$5.8). All three analyses based on this QSO show increasingly neutral hydrogen towards higher redshifts, adding precious measurements up to z$\sim$6.5., Comment: 11 pages, 10 figures, 5 tables, Accepted for Publication in ApJ

Nature of dark energy remains unknown. Especially, to constrain the time variability of the dark-energy, a new, standardisable candle that can reach more distant Universe has been awaited. Here we propose a new distance measure using fast radio bursts (FRBs), which are a new emerging population of $\sim$ ms time scale radio bursts that can reach high-$z$ in quantity. We show an empirical positive correlation between the time-integrated luminosity (L$_{\nu}$) and rest-frame intrinsic duration ($w_{\rm int,rest}$) of FRBs. The L$_{\nu}-w_{\rm int,rest}$ correlation is with a weak strength but statistically very significant, i.e., Pearson coefficient is $\sim$ 0.5 with p-value of $\sim$0.038, despite the smallness of the current sample. This correlation can be used to measure intrinsic luminosity of FRBs from the observed $w_{\rm int,rest}$. By comparing the luminosity with observed flux, we measure luminosity distances to FRBs, and thereby construct the Hubble diagram. This FRB cosmology with the L$_{\nu}-w_{\rm int,rest}$ relation has several advantages over SNe Ia, Gamma-Ray Burst (GRB), and well-known FRB dispersion measure (DM)-$z$ cosmology; (i) access to higher redshift Universe beyond the SNe Ia, (ii) high event rate that is $\sim$ 3 order of magnitude more frequent than GRBs, and (iii) it is free from the uncertainty from intergalactic electron density models, i.e., we can remove the largest uncertainty in the well-debated DM-$z$ cosmology of FRB. Our simulation suggests that the L$_{\nu}-w_{\rm int,rest}$ relation provides us with useful constraints on the time variability of the dark energy when the next generation radio telescopes start to find FRBs in quantity., Comment: Accepted in MNRAS. Summary of the paper can be found at https://youtu.be/1gBBujgiNuQ

A linear correlation has been proposed between the CO luminosity ($\rm{L}^{\prime}_{\rm{CO}}$) and full-width at half maximum (FWHM) for high-redshift (z > 1) submillimeter galaxies. However, the controversy concerning the $\rm{L}^{\prime}_{\rm{CO}}$-FWHM correlation seems to have been caused by the use of heterogeneous samples (e.g., different transition lines) and/or data with large measurement uncertainties. In order to avoid the uncertainty caused by using different rotational transitions, in this work we make an extensive effort to select only CO($J = 1-0$) data from the literature. We separate these wide-ranging redshift data into two samples : the low-redshift (z < 1) and high-redshift (z > 1) samples. The samples are corrected for lensing magnification factors if gravitational-lensing effects appeared in the observations. The correlation analysis shows that there exists significant $\rm{L}^{\prime}_{\rm{CO}}$-FWHM correlations for both the low-redshift and high-redshift samples. A comparison of the low- and high-redshift $\rm{L}^{\prime}_{\rm{CO}}$-FWHM correlations does not show strong evolution with redshift. Assuming that there is no evolution, we can use this relation to determine the model independent distances of high-redshift galaxies. We then constrain cosmological models with the calibrated high-redshift CO data and the sample of Type Ia supernovae in the Union 2.1 compilation. In the constraint for wCDM with our samples, the derived values are w_{0} = -1.02 {\pm} 0.17, ��_{m0} = 0.30{\pm}0.02, and H_{0} = 70.00 {\pm}0.60 km\,s^{-1}\,Mpc^{-1}., 11 pages, 7 figures, accepted for publication in MNRAS. Please see the summary talk of this paper : https://www.youtube.com/watch?v=VEDoCUw6g1c

We report a promising candidate for a distant supercluster at z $\sim 1.1$ in the Dark Energy Survey Science Verification data. We examine smoothed semi-3D galaxy density maps in various photo-z slices. Among several overdense regions, in this work we report the most significant one as having a $3\sigma$ overdensity at a redshift of $\sim1.1$, over a $\sim160$ Mpc scale, much larger than the regular cluster scale (several Mpc). The shape of the supercluster is not circular in the sky projection. Therefore, we regard the point of maximum overdensity as the center for quantitative measurements. Two different estimates suggest the mass of the supercluster to be $1.37\substack{+1.31 \\ -0.79} \times 10^{17} M_{\odot}$, more than one order more massive than regular galaxy clusters. Except for protosuperclusters found with emission-line galaxies, this could be the most distant supercluster to date defined by regular galaxies. A spectroscopic confirmation would make this a very interesting object for cosmology. We discuss the possible implications of such a massive structure for $\Lambda$CDM cosmology.