The Subaru Deep Field Project: Lymanα\alpha Emitters at Redshift of 6.6

We present new results of a deep optical imaging survey using a narrowband filter ($NB921$) centered at $\lambda =$ 9196 \AA ~ together with $B$, $V$, $R$, $i^\prime$, and $z^\prime$ broadband filters in the sky area of the Subaru Deep Field which has been promoted as one of legacy programs of the 8.2m Subaru Telescope. We obtained a photometric sample of 58 Ly$\alpha$ emitter candidates at $z \approx$ 6.5 -- 6.6 among $\sim 180$ strong $NB921$-excess ($z^\prime - NB921 > 1.0$) objects together with a color criterion of $i^\prime - z^\prime > 1.3$. We then obtained optical spectra of 20 objects in our $NB921$-excess sample and identified at least nine Ly$\alpha$ emitters at $z \sim 6.5$ -- 6.6 including the two emitters reported by Kodaira et al. (2003). Since our Ly$\alpha$ emitter candidates are free from strong amplification of gravitational lensing, we are able to discuss their observational properties from a statistical point of view. Based on these new results, we obtain a lower limit of the star formation rate density of $\rho_{\rm SFR} \simeq 5.5 \times 10^{-4}$ $h_{0.7}$ $M_\odot$ yr$^{-1}$ Mpc$^{-3}$ at $z \approx 6.6$, being consistent with our previous estimate. We discuss the nature of star-formation activity in galaxies beyond $z=6$.Comment: 49 pages, 16 figures, PASJ, Vol. 57, No. 1, in pres

Clustering of Lyman Break Galaxies at z=4 and 5 in The Subaru Deep Field: Luminosity Dependence of The Correlation Function Slope

We explored the clustering properties of Lyman Break Galaxies (LBGs) at z=4 and 5 with an angular two-point correlation function on the basis of the very deep and wide Subaru Deep Field data. We found an apparent dependence of the correlation function slope on UV luminosity for LBGs at both z=4 and 5. More luminous LBGs have a steeper correlation function. To compare these observational results, we constructed numerical mock LBG catalogs based on a semianalytic model of hierarchical clustering combined with high-resolution N-body simulation, carefully mimicking the observational selection effects. The luminosity functions for LBGs predicted by this mock catalog were found to be almost consistent with the observation. Moreover, the overall correlation functions of LBGs were reproduced reasonably well. The observed dependence of the clustering on UV luminosity was not reproduced by the model, unless subsamples of distinct halo mass were considered. That is, LBGs belonging to more massive dark haloes had steeper and larger-amplitude correlation functions. With this model, we found that LBG multiplicity in massive dark halos amplifies the clustering strength at small scales, which steepens the slope of the correlation function. The hierarchical clustering model could therefore be reconciled with the observed luminosity-dependence of the angular correlation function, if there is a tight correlation between UV luminosity and halo mass. Our finding that the slope of the correlation function depends on luminosity could be an indication that massive dark halos hosted multiple bright LBGs (abridged).Comment: 16 pages, 17 figures, Accepted for publication in ApJ, Full resolution version is available at http://zone.mtk.nao.ac.jp/~kashik/sdf/acf/sdf_lbgacf.pd

A Strong Lyman-alpha Emitter at z=6.33 in the Subaru Deep Field Selected as an i' Dropout

We report on the discovery of a star-forming galaxy at z=6.33 in the Subaru Deep Field. This object is selected as a candidate of an i'-dropout, high-redshift galaxy around z=6 because of its red i'-z' color in our deep optical imaging survey in the Subaru Deep Field. Our follow up optical spectroscopy reveals that this object is a strong Ly-alpha emitter with only very faint ultraviolet continuum. The rest-frame equivalent width of the detected Ly-alpha emission is as much as 130 A. Thus the light detected in our z' image is largely attributed to the Ly-alpha emission, i.e., ~40% of the z'-band flux is the strong Ly-alpha emission, giving a very red i'-z' color. This is consistent with the photometric property of this object because the narrow-band data obtained with the NB921 filter shows a significant depression, z'-NB921 = -0.54 mag. By using the photometric data, we show that some other objects among the 48 i'-dropout high-redshift galaxy candidates found in the Subaru Deep Field also show a significant NB921 depression. We briefly discuss the nature of these NB921-depressed objects