We report on early results from very deep and wide-field narrow-band imaging on a 543 arcmin 2 area of the Subaru Deep Field. We find 87 Lyman α emitters (LAEs) at z = 4.86 ± 0.03 which are photometrically selected by a combination of two broad bands (R and i ′ ) and one narrow band (N B711; λ c = 7126Å, ∆λ = 73Å). We derive the luminosity functions (LFs) of the LAEs at Lyα luminosity and at UV-continuum (rest-frame 1700Å) luminosity. The LFs show little evolution between z=3.4 and z=4.86 either in Lyα or UV-continuum emission. The amplitude of the LAE LF tends to decline at the bright magnitudes more rapidly than that of the LBG LF at similar redshifts. We calculate the angular correlation function of our LAEs up to ∼ 15 arcmin separations. The angular correlation ω(θ) is found to increase with decreasing angular separations, showing a clear signal of clustering. It is also found that the distribution of LAEs shows a large density gradient with a scale of 15 arcmin, which would indicate the existence of a large-scale structure of LAEs on 20h −1 Mpc scales. We fit the observed correlation function by A ω θ −0.8 to find A ω = 29 arcsec 0.8 . The estimated correlation length is r 0 = 3.5 +0.3 −0.3 h −1 Mpc in comoving units (Ω m = 0.3 and Ω Λ = 0.7), which is slightly larger than the value for z ∼ 4 LBGs with i ′ < 26. We calculate the angular correlation function for two sub-samples of the 87 LAEs divided by Lyα luminosity, UV-continuum luminosity, and Lyα equivalent width (EW ). The Lyα-bright sub-sample shows a larger correlation amplitude than the Lyα-faint sub-sample, while no significant difference is found for the sub-samples divided by UV-continuum luminosity or EW . This may indicate that galaxies with bright Lyα emission are possibly biased against the underlying dark matter halos more strongly than those with bright UV continuum.

We report the discovery of a large-scale structure of Lya emitters (LAEs) at based on wide-field z p 4.86 imaging with the prime-focus camera (Suprime-Cam) overdensity ( ), which may be the progenitor of a cluster of galaxies. Assuming this circular region to be d p 2 S a sphere with a spatial overdensity of 2, we compare our observation with predictions by cold dark matter models. We find that an flat model with predicts the number of such spheres consistent with the Q p 0.3 j p 0. 9 0 8 observed number (one sphere in our survey volume) if the bias parameter of LAEs is . This value suggests b Ӎ 6 that the typical mass of dark halos hosting LAEs at is of the order of 10 12 M , . Such a large mass poses z Ӎ 5 an interesting question about the nature of LAEs.

The Subaru Deep Field (SDF) project is a program of Subaru Observatory to carry out a deep galaxy survey over a blank field as large as 34 ′ ×27 ′ . The program consists of very deep multi-band optical imaging, near infrared imaging for smaller portions of the field and follow-up optical spectroscopy. Major scientific goals of the project are to construct large samples of Lyman-break galaxies at z ≃ 4 − 5 and Lyman alpha emitters at z ≃ 5.7 and 6.6, and to make detailed studies these very high-redshift galaxy populations.In this paper, we describe the optical imaging observations and data reduction, presenting mosaicked images and object catalogs in seven bandpasses. The optical imaging was made through five broad-band filters, B, V , R, i ′ , z ′ , and two narrow-band filters, NB816 (λ c = 8150Å) and NB921 (λ c = 9196Å) with almost 10 hours long integrations for each band. The limiting magnitudes measured at 3σ on a 2 ′′ aperture are B = 28.45, V = 27.74, R = 27.80, i ′ = 27.43, z ′ = 26.62, NB816 = 26.63, and NB921 = 26.54 in the AB system. The object catalog constructed for each of the seven bands contains more than 10 5 objects. The galaxy number counts corrected for detection incompleteness and star count contribution are found to be consistent with previous results in the literature. The mosaicked images and catalogs of all the bands have been made open to the public on Oct. 1, 2004 on the SDF project website at http://soaps.naoj.org/sdf/.

We present new results of a deep optical imaging survey using a narrow band filter (NB921) centered at λ = 9196Å together with B, V , R, i ′ , and z ′ broadband 1 filters in the sky area of the Subaru Deep Field, which has been promoted as one of legacy programs of the 8.2 m Subaru Telescope. We obtained a photometric sample of 58 Lyα emitter candidates at z ≈ 6.5 -6.6 among ∼ 180 strong NB921-excess (z ′ − NB921 > 1.0) objects together with a color criterion of i ′ − z ′ > 1.3. We then obtained optical spectra of 20 objects in our NB921-excess sample, and identified at least nine Lyα emitters at z ∼ 6.5 -6.6, including the two emitters reported by Kodaira et al. (2003, PASJ, 55, L17). Since our Lyα-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 obtained a lower limit of the star-formation rate density of ρ SFR ≃ 5.7 × 10 −4 h 0.7 M ⊙ yr −1 Mpc −3 at z ≈ 6.6, being consistent with our previous estimate. We discuss the nature of star-formation activity in galaxies beyond z = 6.

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 confirmed the previous result that the clustering strength of LBGs depends on the UV luminosity in the sense that brighter LBGs are more strongly clustered. In addition, 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. The bias parameter was found to be a scale-dependent function for bright LBGs, whereas it appears to be almost scale-independent for faint LBGs. Luminous LBGs have a higher bias at smaller angular scales, which decreases as the scale increases. 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 and the overall correlation functions for LBGs at z = 4 and 5 predicted by this mock catalog were found to be almost consistent with the observation. 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 halos 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 correlation function. The hierarchical clustering model could therefore be reconciled with the observed luminosity dependence of the 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.