The Discovery of a Very Narrow-Line Star Forming Obat a Redshift of 5.66ject

We report on the discovery of a very narrow-line star forming object beyond redshift of 5. Using the prime-focus camera, Suprime-Cam, on the 8.2 m Subaru telescope together with a narrow-passband filter centered at $\lambda_{\rm c}$ = 8150 \AA with passband of $\Delta\lambda$ = 120 \AA, we have obtained a very deep image of the field surrounding the quasar SDSSp J104433.04$-$012502.2 at a redshift of 5.74. Comparing this image with optical broad-band images, we have found an object with a very strong emission line. Our follow-up optical spectroscopy has revealed that this source is at a redshift of $z=5.655\pm0.002$, forming stars at a rate $\sim 13 ~ h_{0.7}^{-2} ~ M_\odot$ yr$^{-1}$. Remarkably, the velocity dispersion of Ly$\alpha$-emitting gas is only 22 km s$^{-1}$. Since a blue half of the Ly$\alpha$ emission could be absorbed by neutral hydrogen gas, perhaps in the system, a modest estimate of the velocity dispersion may be $\gtrsim$ 44 km s$^{-1}$. Together with a linear size of 7.7 $h_{0.7}^{-1}$ kpc, we estimate a lower limit of the dynamical mass of this object to be $\sim 2 \times 10^9 M_\odot$. It is thus suggested that LAE J1044$-$0123 is a star-forming dwarf galaxy (i.e., a subgalactic object or a building block) beyond redshift 5 although we cannot exclude a possibility that most Ly$\alpha$ emission is absorbed by the red damping wing of neutral intergalactic matter.Comment: 6 pages, 2 figures. ApJ Letters, in pres

A Subaru Search for Lymanα\alpha Emitters at Redshift 5.7

We present the results of a survey for Ly$\alpha$ emitters at $z\approx 5.7$ based on optical narrow-band ($\lambda_{\rm c} = 8150$ \AA ~ and $\Delta\lambda = 120$ \AA), and broad-band ($B$, $R_{\rm C}$, $I_{\rm C}$, and $z^\prime$) observations of the field surrounding the high redshift quasar, SDSSp J104433.04$-$012522.2, on the 8.2 m Subaru Telescope with the Subaru Prime Focus Camera, Suprime-Cam. This survey covers a sky area of $\approx 720$ arcmin$^2$ and a co-moving volume of $\simeq 2 \times 10^5 ~ h_{0.7}^{-3}$ Mpc$^3$. We have found 20 candidates of Ly$\alpha$ emitters at $z \approx$ 5.7 with $\Delta z \approx 0.1$. Two of them have been confirmed star-forming galaxies at $z=5.655$ and $z=5.687$ from our follow-up optical spectroscopy. We discuss star-formation properties of the 20 objects from a statistical point of view. Our survey leads to a new estimate of the star formation rate density at $z \approx 5.7$, $\sim 1.2 \times 10^{-3} h_{0.7} M_\odot$ yr$^{-1}$ Mpc$^{-3}$.Comment: 18 pages, 19 figures, accepted for A

Subaru Studies of the Cosmic Dawn

An overview on the current status of the census of the early universe population is given. Observational surveys of high redshift objects provide direct opportunities to study the early epoch of the Universe. The target population included are Lyman Alpha Emitters (LAE), Lyman Break Galaxies (LBG), gravitationally lensed galaxies, quasars and gamma-ray bursts (GRB). The basic properties of these objects and the methods used to study them are reviewed. The present paper highlights the fact that the Subaru Telescope group made significant contributions in this field of science to elucidate the epoch of the cosmic dawn and to improve the understanding of how and when infant galaxies evolve into mature ones.Comment: 14 pages, 11 figures, accepted for publication in the Proceedings of the Japan Academy, Series