Masaru Ajiki

The First Release COSMOS Optical and Near-IR Data and Catalog*

We present imaging data and photometry for the COSMOS survey in 15 photometric bands between 0.3 and 2.4 μm. These include data taken on the Subaru 8.3 m telescope, the KPNO and CTIO 4 m telescopes, and the CFHT 3.6 m telescope. Special techniques are used to ensure that the relative photometric calibration is better than 1% across the field of view. The absolute photometric accuracy from standard-star measurements is found to be 6%. The absolute calibration is corrected using galaxy spectra, providing colors accurate to 2% or better. Stellar and galaxy colors and counts agree well with the expected values. Finally, as the first step in the scientific analysis of these data we construct panchromatic number counts which confirm that both the geometry of the universe and the galaxy population are evolving.

COSMOS Morphological Classification with the Zurich Estimator of Structural Types (ZEST) and the Evolution Since z = 1 of the Luminosity Function of Early, Disk, and Irregular Galaxies

Motivated by the desire to reliably and automatically classify structure of thousands of COSMOS galaxies, we present ZEST, the Zurich Estimator of Structural Types. To classify galaxy structure, ZEST uses (1) five nonparametric diagnostics: asymmetry, concentration, Gini coefficient, second-order moment of the brightest 20% of galaxy pixels, and ellipticity; and (2) the exponent n of single-Sersic fits to the two-dimensional surface brightness distributions. To fully exploit the wealth of information while reducing the redundancy present in these diagnostics, ZEST performs a principal component (PC) analysis. We use a sample of ~56,000 I_(AB) ≤ 24 COSMOS galaxies to show that the first three PCs fully describe the key aspects of the galaxy structure, i.e., to calibrate a three-dimensional classification grid of axes PC_1, PC_2, and PC_3. We demonstrate the robustness of the ZEST grid on the z = 0 sample of Frei et al. The ZEST classification breaks most of the degeneracy between different galaxy populations that affects morphological classifications based on only some of the diagnostics included in ZEST. As a first application, we present the evolution since z ~ 1 of the luminosity functions (LFs) of COSMOS galaxies of early, disk, and irregular galaxies and, for disk galaxies, of different bulge-to-disk ratios. Overall, we find that the LF up to a redshift z = 1 is consistent with a pure luminosity evolution (of about 0.95 mag at z ~ 0.7). We highlight, however, two trends that are in general agreement with a downsizing scenario for galaxy formation, i.e., (1) a deficit of a factor of about 2 at z ~ 0.7 of M_B > -20.5 structurally classified early-type galaxies and (2) an excess of a factor of about 3, at a similar redshift, of irregular galaxies.

Errata : The SUBARU Deep Field Project: Lyman α Emitters at a Redshift of 6.6

We present new results of a deep optical imaging survey using a narrow band filter (NB921) centered at λ = 9196 u A together with B, V, R, i � ,a ndzbroadband 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 α 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 Ly α emitters at z ∼ 6.5-6.6, including the two emitters reported by Kodaira et al. (2003, PASJ, 55, L17). Since our Ly α-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 ρSFR � 5.7 ×10 −4 h0.7 Myr −1 Mpc −3 at z ≈ 6.6, being

The HI content of star-forming galaxies at z= 0.24

We use observations from the Giant Metrewave Radio Telescope (GMRT) to measure the atomic hydrogen gas content of star-forming galaxies at z = 0.24 (i.e. a look-back time of ∼3 Gyr). The sample of galaxies studied were selected from Hα-emitting field galaxies detected in a narrow-band imaging survey with the Subaru Telescope. The Anglo-Australian Telescope was used to obtain precise optical redshifts for these galaxies. We then co-added the H I 21-cm emission signal for all the galaxies within the GMRT spectral line data cube. From the co-added signal of 121 galaxies, we measure an average atomic hydrogen gas mass of (2.26 ± 0.90) × 10 9 M� . We translate this H I signal into a cosmic density of neutral gas at z = 0.24 ‐ ‐

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 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.

The Hα Luminosity Function and Star Formation Rate at z ≈ 0.24 Based on Subaru Deep Imaging Data*

We have carried out a deep imaging survey for Hα-emitting galaxies at z ≈ 0.24 using a narrowband filter tuned with the redshifted line. The total sky area covered is 706 arcmin2 within a redshift range from 0.234 to 0.252 (δz = 0.018). This corresponds to a volume of 3.9 × 103 Mpc3 when Ωmatter = 0.3, ΩΛ = 0.7, and H0 = 70 km s-1 Mpc-1 are adopted. We obtain a sample of 348 Hα-emitting galaxies whose observed emission-line equivalent widths are greater than 12 A. We find an extinction-corrected Hα luminosity density of 10 ergs s-1 Mpc-3. Using the Kennicutt relation between the Hα luminosity and the star formation rate, the star formation rate density in the covered volume is estimated to be 0.036 M☉ yr-1 Mpc-3. This value is higher by a factor of 3 than the local star formation rate density.

The Hα luminosity function and star formation rate at z ≈ 0.24 in the COSMOS 2 square degree field

To derive a new Hα luminosity function and to understand the clustering properties of star-forming galaxies at z≈ 0.24, we have made a narrowband imaging survey for Hα-emitting galaxies in the Hubble Space Telescope (HST) COSMOS 2 square degree field. We used the narrowband filter NB816 (λ_c = 8150 A, Δ λ = 120 A) and sampled Hα emitters with EW_(obs)(H α + [N II]) > 12A in a redshift range between z = 0.233 and 0.251 corresponding to a depth of 70 Mpc. We obtained 980 Hα-emitting galaxies in a sky area of 5540 arcmin^2, corresponding to a survey volume of 3.1 × 10^4 Mpc^3. We derive a Hα luminosity function with a best-fit Schechter function parameter set of α = − 1.35_(−0.13)^(+0.11), log ф_* = − 2.65_(−0.38)^(+0.27), and log L_*(ergs s^(−1)) = 41.94_(−0.23)^(+0.38). The Hα luminosity density is 2.7_(−0.6)^(+0.7) × 10^(39) ergs s^(−1) Mpc^(−3). After subtracting the AGN contribution (15%) to the Hα luminosity density, the star formation rate density is evaluated as 1.8_(−0.4)^(+0.7) × 10^(−2) M_סּ yr^(−1) Mpc^(−3). The angular two-point correlation function of Hα-emitting galaxies of log L(H α) > 39.8 is well fit by a power-law form of w(θ) = 0.013−_(0.001)^(+0.002)θ^(−0.88 ± 0.03), corresponding to the correlation function of ξ (r) = (r/1.9 Mpc)^(−1.88). We also find that the Hα emitters with higher Hα luminosity are more strongly clustered than those with lower luminosity.

The Discovery of Two Lyman α Emitters beyond Redshift 6 in the Subaru Deep Field

We performed a deep optical imaging survey using a narrow-band filter (NB921) centered at λ=9196 u A together

A New High-Redshift Lyα Emitter: Possible Superwind Galaxy at z = 5.69*

During the course of our deep optical imaging survey for Ly alpha emitters at z approximately 5.7 in the field around the z=5.74 quasar SDSSp J104433.04-012502.2, we have found a candidate strong emission-line source. Follow-up optical spectroscopy shows that the emission line profile of this object is asymmetric, showing excess red-wing emission. These properties are consistent with an identification of Ly alpha emission at a redshift of z=5.687 +/- 0.002. The observed broad line width, Delta V_{FWHM} ~= 340 km s^{-1} and excess red-wing emission also suggest that this object hosts a galactic superwind.

A Search for Lyα Emitters at Redshift 3.7

We present the results of a survey for emission-line objects based on optical intermediate-band (