Several UV and near-infrared color selection methods have identified galaxies at z = 1-3. Since each method suffers from selection biases, we have simultaneously applied three leading techniques (Lyman break, BX/BM, and BzK selection) in the Subaru Deep Field. This field has reliable (Δz/(1 + z) = 0.02-0.09) photometric redshifts for 53,000 galaxies from 20 bands (1500 -2.2 μm). The BzK, LBG, and BX/BM samples suffer contamination from z < 1 interlopers of 6%, 8%, and 20%, respectively. Around the redshifts where it is most sensitive (z 1.9 for star-forming BzK, z 1.8 for z 2 LBGs, z 1.6 for BM, and z 2.3 for BX), each technique finds 60%-80% of the census of the three methods. In addition, each of the color techniques shares 75%-96% of its galaxies with another method, which is consistent with previous studies that adopt identical criteria on magnitudes and colors. Combining the three samples gives a comprehensive census that includes 90% of z phot = 1-3 galaxies, using standard magnitude limits similar to previous studies. In fact, we find that among z = 1-2.5 galaxies in the color selection census, 81%-90% of them can be selected by just combining the BzK selection with one of the UV techniques (z 2 LBG or BX and BM). The average galaxy stellar mass, reddening, and star formation rates (SFRs) all decrease systematically from the sBzK population to the LBGs, and to the BX/BMs. The combined color selections yield a total cosmic SFR density of 0.18 0.03 M yr-1 Mpc-3 for K AB ≲ 24. We find that 65% of the star formation is in galaxies with E(B - V) > 0.25mag, even though they are only one-fourth of the census by number. © 2011. The American Astronomical Society. All rights reserved..

We combined deep U-band and optical/near-infrared imaging, in order to select Lyman Break Galaxies (LBGs) at using U-V and colors in the Subaru Deep Field. The resulting sample of 5161 LBGs gives a UV luminosity function (LF) down to , with a steep faint-end slope of . We analyze UV-To-NIR energy distributions (SEDs) from optical photometry and photometry on IR median-stacked images. In the stacks, we find a systematic background depression centered on the LBGs. This results from the difficulty of finding faint galaxies in regions with higher-Than-Average surface densities of foreground galaxies, so we corrected for this deficit. Best-fit stellar population models for the LBG SEDs indicate stellar masses and star formation rates of and M o yr-1 at , down to and yr-1 at . The faint LBGs show a ∼1 mag excess over the stellar continuum in K-band. We interpret this excess flux as redshifted [O iii] lines. The observed excesses imply equivalent widths that increase with decreasing mass, reaching A (rest-frame). Such strong [O iii] emission is seen only in a miniscule fraction of local emission-line galaxies, but is probably universal in the faint galaxies that reionized the universe. Our halo occupation distribution analysis of the angular correlation function gives a halo mass of for the full sample of LBGs, and for the brightest half of the sample.

We present results from Subaru Fiber Multi Object Spectrograph near-infrared spectroscopy of 118 star-forming galaxies at z∼1.5 in the Subaru Deep Field. These galaxies are selected as [O ii]λ3727 emitters at z ≈ 1.47 and 1.62 from narrow-band imaging. We detect the Hα emission line in 115 galaxies, the [O iii]λ5007 emission line in 45 galaxies, and Hβ, [N ii]λ6584, and [S ii]λλ6716, 6731 in 13, 16, and 6 galaxies, respectively. Including the [O ii] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate the physical conditions of the interstellar medium in star-forming galaxies at z∼1.5. We find a tight correlation between Hα and [O ii], which suggests that [O ii] can be a good star formation rate indicator for galaxies at z∼1.5. The line ratios of Hα/[O ii] are consistent with those of local galaxies. We also find that [O ii] emitters have strong [O iii] emission lines. The [O iii]/[O ii] ratios are larger than normal star-forming galaxies in the local universe, suggesting a higher ionization parameter. Less massive galaxies have larger [O iii]/[O ii] ratios. With evidence that the electron density is consistent with local galaxies, the high ionization of galaxies at high redshifts may be attributed to a harder radiation field by a young stellar population and/or an increase in the number of ionizing photons from each massive star.

We obtained mid-infrared 3.6 and 4.5μm imaging of a z = 6.96 Lyα emitter (LAE), IOK-1, discovered in the Subaru Deep Field, using Spitzer Space Telescope Infrared Array Camera observations. After removal of a nearby bright source, we found that IOK-1 is not significantly detected in any of these infrared bands to m3:6μm ∼ 24.00 and m4:5μm ∼ 23.54 at 3φ. Fitting population synthesis models to the spectral energy distribution consisting of the upper limit fluxes of the optical-to-infrared non-detection images and fluxes in detection images, we constrained the stellar mass, M*, of IOK-1. This LAE could have either a mass as low as M* . ≤2-9 × 108 M for young age (≤10 Myr) and low dust reddening (AV ∼ 0) or a mass as large as M* . 1-4 × 1010 M for either old age (>100 Myr) or high dust reddening (AV ∼ 1.5). This would be within the range of masses of z ∼ 3-6.6 LAEs studied to date, ∼106-10 10M. Hence, IOK-1 is not a particularly unique galaxy with extremely high mass or low mass, but is similar to one of the LAEs seen at later epochs. © 2010. Astronomical Society of Japan.

SDF line-emitting galaxies in four narrowband filters at low and intermediate redshifts are presented. Broadband colors, follow-up optical spectroscopy, and multiple NB filters are used to distinguish Hα, [O II], and [O III] emitters at z = 0.07-1.47 to construct their LFs. These LFs are derived down to faint magnitudes, allowing for an accurate determination of the faint-end slope. With a large (N ∼ 200-900) sample for each redshift interval, a Schechter profile is fitted to each LF. Prior to dust extinction corrections, the [O III] and [O II] LFs agree reasonably well with those of Hippelein et al. The z = 0.08 Ha LF, which reaches 2 orders of magnitude fainter than Gallego et al., is steeper by 25%. This indicates that there are more low-luminosity star-forming galaxies for z < 0.1. The faint-end slope α and Φ*, show a strong redshift evolution, while L * shows little evolution. The evolution in α indicates that low-luminosity galaxies have a stronger evolution compared to brighter ones. Integrated SFR densities are derived via Hα, [O III], and [O III] for 0.07 < z < 1.47. A steep increase in the SFR density, as a function of redshift, is seen for 0.4 < z < 0.9. For z > 1, the SFR densities are similar. The latter is consistent with previous UVand [O II] measurements. Below z < 0.4, the SFR densities are consistent with several Ha, [O II], and UV measurements, but others are a factor of 2 higher. For example, the z = 0.066-0.092 LF agrees with Jones & Bland-Hawthorn, but at z = 0.24 and 0.40, their number densities are twice as high. This discrepancy can be explained by cosmic variance. © 2007. The American Astronomical Society. All rights reserved.

We present spectroscopy of 15 star-forming BzK galaxies (sBzKs) with K(AB)<23 in the Subaru Deep Field, for which Halpha and some other emission lines are detected in 0.9 to 2.3 micron spectra with a resolution of R=500. Using Halpha luminosities, we obtain star formation rates (SFRs), and then specific SFRs (SSFRs) dividing SFRs by stellar masses, which are derived from SED fitting to BVRi'z'K photometry. It is found that sBzKs with higher stellar masses have larger SFRs. A negative correlation is seen between stellar mass and SSFR, which is consistent with the previous results for z~2 galaxies. This implies that a larger growth of stellar mass occurs in less massive galaxies. In addition, gas-phase oxygen abundances, 12+log(O/H), are derived from the ratio of NII(lambda 6584) to Halpha using the N2 index method. We have found a correlation between stellar mass and oxygen abundance in the sense that more massive sBzKs tend to be more metal rich, which is qualitatively consistent with the relation for UV-selected z~2 galaxies. However, the metallicity of the sBzKs is ~0.2 dex higher than that of UV-selected galaxies with similar stellar masses, which is significant considering the small uncertainties. The sBzKs in our sample have redder R-K colors than the UV-selected galaxies. This galaxy color-dependence in the oxygen abundance may be caused by older or dustier galaxies having higher metallicities at z~2.

A photometric sample of 8000 V < 25.3 candidate Lyman break galaxies (LBGs) has been selected by combining Subaru/Suprime-Cam BV R C i′z′ optical data with deep GALEX/NUV imaging of the Subaru Deep Field. Follow-up spectroscopy confirmed 24 LBGs at 1.5 ≲ z ≲ 2.7. Among the optical spectra, 12 have Lyα emission with rest-frame equivalent widths of 5-60 . The success rate for identifying LBGs as NUV-dropouts at 1.5 < z < 2.7 is 86%. The rest-frame UV (1700 ) luminosity function (LF) is constructed from the photometric sample with corrections for stellar contamination and z < 1.5 interlopers (lower limits). The LF is 1.7 0.1 (1.4 0.1 with a hard upper limit on stellar contamination) times higher than those of z 2 BXs and z 3 LBGs. Three explanations were considered, and it is argued that significantly underestimating low-z contamination or effective comoving volume is unlikely: the former would be inconsistent with the spectroscopic sample at 93% confidence, and the second explanation would not resolve the discrepancy. The third scenario is that different photometric selection of the samples yields nonidentical galaxy populations, such that some BX galaxies are LBGs and vice versa. This argument is supported by a higher surface density of LBGs at all magnitudes while the redshift distribution of the two populations is nearly identical. This study, when combined with other star formation rate (SFR) density UV measurements from LBG surveys, indicates that there is a rise in the SFR density: a factor of 3-6 (3-10) increase from z 5 (z 6) to z 2, followed by a decrease to z 0. This result, along with past sub-mm studies that find a peak at z 2 in their redshift distribution, suggests that z 2 is the epoch of peak star formation. © 2009. The American Astronomical Society.

We present a search for CO (3-2) emission in SDF-26821, a BzK-selected star-forming galaxy (sBzK) at z = 2.044, using the 45-m telescope of the Nobeyama Radio Observatory and the Nobeyama Millimeter Array. We did not detect significant emission, and derived the 2σ limits: CO luminosity of L′co < 3.1 × 1010K kms-1 pc -2, ratio of far-infrared luminosity to CO luminosity of L FIR/L′co > 57 L⊙ (K km s-1 pc2)-1, and molecular gas mass of MH2 < 2.5 × 1010 M⊙, assuming a velocity width of 200 kms -1 and a CO-to-H2 conversion factor of αco = 0.8 M⊙ (K km s-1 pc2) -1. The ratio LFIR/L′CO, a measure of the star-formation efficiency (SFE), is comparable to, or higher than, the two z ∼ 1.5 sBzKs detected in CO (2-1) previously, suggesting that sBzKs can have a wide range of SFEs. Comparisons of far-infrared luminosity, gas mass, and stellar mass among the sBzKs suggest that SDF-26821 is at an earlier stage of forming stars with a similar SFE and/or more efficiently forming stars than the two z ∼ 1.5 sBzKs. The higher SFEs and specific star-formation rates of the sBzKs compared to local spirals are indicative of a difference in the star-formation modes between these systems, suggesting that sBzKs are not just scaled-up versions of local spirals. © 2009. Astronomocal Society of Japan.

We report the discovery of a protocluster at z∼6 containing at least eight cluster member galaxies with spectroscopic confirmations in the wide-field image of the Subaru Deep Field (SDF). The overdensity of the protocluster is significant at the 6σ level, based on the surface number density of i′-dropout galaxies. The overdense region covers 6′ × 6′ (14 Mpc × 14 Mpc in comoving units at z = 6) and includes 30 i′-dropout galaxies. Follow-up spectroscopy revealed that 15 of these are real z 6 galaxies (5.7 < z < 6.3). Of these 15, 8 are clustering in a narrow redshift range (Δz < 0.05 centered at z = 6.01), corresponding to a seven-fold increase in number density over the average in redshift space. We found no significant difference in the observed properties, such as Lyα luminosities and UV continuum magnitudes, between the eight protocluster members and the seven non-members. The velocity dispersion of the eight protocluster members is 647 ± 124 km s-1, which is about three times higher than that predicted by the standard cold dark matter model. This discrepancy could be attributed to the distinguishing three-dimensional distribution of the eight protocluster members. We discuss two possible explanations for this discrepancy: either the protocluster is already mature, with old galaxies at the center, or it is still immature and composed of three subgroups merging to become a larger cluster. In either case, this concentration of z = 6.01 galaxies in the SDF may be one of the first sites of formation of a galaxy cluster in the universe. © © 2012. The American Astronomical Society. All rights reserved.

We present observations of SDF-05M05, an unusual optical transient discovered in the Subaru Deep Field (SDF). The duration of the transient is > 800 days in the observer frame, and the maximum brightness during observation reached approximately 23mag in the i′ and z′ bands. The faint host galaxy is clearly identified in all five optical bands of the deep SDF images. The photometric redshift of the host yields z 0.6 and the corresponding absolute magnitude at maximum is - 20. This implies that this event shone with an absolute magnitude brighter than -19mag for approximately 300days in the rest frame, which is significantly longer than a typical supernova and ultraluminous supernova. The total radiated energy during our observation was 1 × 1051 erg. The light curves and color evolution are marginally consistent with some luminous IIn supernovae. We suggest that the transient may be a unique and peculiar supernova at intermediate redshift. © 2012. The American Astronomical Society. All rights reserved..