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We search for galaxies with a strong Balmer break (Balmer break galaxies; BBGs) at z ∼ 6 over a 0.41 deg2 effective area in the COSMOS field. Based on rich imaging data, including data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA), three candidates are identified by their extremely red K–[3.6] colors, as well as by nondetection in the X-ray, optical, far-infrared, and radio bands. The nondetection in the deep ALMA observations suggests that they are not dusty galaxies but BBGs at z ∼ 6, although contamination from active galactic nuclei at z ∼ 0 cannot be completely ruled out for the moment. Our spectral energy distribution analyses reveal that the BBG candidates at z ∼ 6 have stellar masses of ≈5 × 1010M⊙ dominated by old stellar populations with ages of ≳ 700 Myr. Assuming that all three candidates are real BBGs at z ∼ 6, we estimate the stellar mass density to be Mpc−3. This is consistent with an extrapolation from the lower-redshift measurements. The onset of star formation in the three BBG candidates is expected to be several hundred million yr before the observed epoch of z ∼ 6. We estimate the star formation rate density (SFRD) contributed by progenitors of the BBGs to be 2.4–12 × 10−5M⊙ yr−1 Mpc−3 at z > 14 (99.7% confidence range). Our result suggests a smooth evolution of the SFRD beyond z = 8. [ABSTRACT FROM AUTHOR]

We present the Atacama Large Millimeter/submillimeter Array detection of the [O iii] 88 μm line and rest-frame 90 μm dust continuum emission in a Y-dropout Lyman break galaxy (LBG), MACS0416_Y1 lying behind the Frontier Field cluster MACS J0416.1−2403. This [O iii] detection confirms the LBG with a spectroscopic redshift of z = 8.3118 ± 0.0003, making this object one of the farthest galaxies ever identified spectroscopically. The observed 850 μm flux density of 137 ± 26 μJy corresponds to a de-lensed total infrared (IR) luminosity of if assuming a dust temperature of Tdust = 50 K and an emissivity index of β = 1.5, yielding a large dust mass of . The ultraviolet-to-far-IR spectral energy distribution modeling where the [O iii] emissivity model is incorporated suggests the presence of a young (τage ≈ 4 Myr), star-forming ( yr−1), moderately metal-polluted (Z ≈ 0.2Z⊙) stellar component with a mass of Mstar = 3 × 108M⊙. An analytic dust mass evolution model with a single episode of star formation does not reproduce the metallicity and dust mass in τage ≈ 4 Myr, suggesting a pre-existing evolved stellar component with Mstar ∼ 3 × 109M☉ and τage ∼ 0.3 Gyr as the origin of the dust mass. [ABSTRACT FROM AUTHOR]

The physical properties and elemental abundances of the interstellar medium in galaxies during cosmic reionization are important for understanding the role of galaxies in this process. We report the Atacama Large Millimeter/submillimeter Array detection of an oxygen emission line at a wavelength of 88 micrometers from a galaxy at an epoch about 700 million years after the Big Bang. The oxygen abundance of this galaxy is estimated at about one-tenth that of the Sun. The nondetection of far-infrared continuum emission indicates a deficiency of interstellar dust in the galaxy. A carbon emission line at a wavelength of 158 micrometers is also not detected, implying an unusually small amount of neutral gas. These properties might allow ionizing photons to escape into the intergalactic medium. [ABSTRACT FROM AUTHOR]

We present very faint dropout galaxies at z ∼ 6−9 with a stellar mass M⋆ down to that are found in deep optical/near-infrared (NIR) images of the full data sets of the Hubble Frontier Fields (HFF) program in conjunction with deep ground-based and Spitzer images and gravitational-lensing magnification effects. We investigate stellar populations of the HFF dropout galaxies with the optical/NIR photometry and BEAGLE models made of self-consistent stellar population synthesis and photoionization models, carefully including strong nebular emission impacting on the photometry. We identify 453 galaxies with . Our best-estimate function is comparable to a model of star formation duration time of 100 Myr that is assumed in Bouwens et al. We derive the galaxy stellar mass functions (GSMFs) at z ∼ 6–9 that agree with those obtained by previous studies at , and that extend to . Estimating the stellar mass densities with the GSMFs, we find a very slow evolution from z ∼ 9 to z ∼ 6–7, which is consistent with the one estimated from star formation rate density measurements. In conjunction with the estimates of the galaxy effective radii Re on the source plane, we have pinpointed four objects with low stellar masses () and very compact morphologies ( pc) that are comparable with those of globular clusters (GCs) in the Milky Way today. These objects are candidates of star clusters, some of which may be related to GCs today. [ABSTRACT FROM AUTHOR]

We report the Subaru Hyper Suprime-Cam (HSC) discovery of two Lyα blobs (LABs), dubbed z70-1 and z49-1 at z = 6.965 and z = 4.888, respectively, that are Lyα emitters with a bright () and spatially extended Lyα emission, and present the photometric and spectroscopic properties of a total of seven LABs: the two new LABs and five previously known LABs at z = 5.7–6.6. The z70-1 LAB shows extended Lyα emission with a scale length of 1.4 ± 0.2 kpc, about three times larger than the UV continuum emission, making z70-1 the most distant LAB identified to date. All of the seven LABs, except z49-1, exhibit no active galactic nucleus (AGN) signatures such as X-ray emission, N v λ1240 emission, or Lyα line broadening, while z49-1 has a strong C iv λ1548 emission line indicating an AGN on the basis of the UV-line ratio diagnostics. We carefully model the point-spread functions of the HSC images and conduct two-component exponential profile fitting to the extended Lyα emission of the LABs. The Lyα scale lengths of the core (star-forming region) and halo components are rc = 0.6–1.2 kpc and rh = 2.0–13.8 kpc, respectively. The relations between the scale lengths and galaxy properties (Lyα luminosity LLyα, Lyα rest-frame equivalent width EW0, and UV continuum magnitude MUV) of our LABs are similar to those of Lyα halos (LAHs) identified around star-forming galaxies found previously by the Very Large Telescope/MUSE at similar redshifts, suggesting that our LABs are likely the bright version of high-z LAHs. [ABSTRACT FROM AUTHOR]

We present the Lyα luminosity function (LF) derived from 34 Lyα emitters (LAEs) at z = 7.0 on an area of sky of 3.1 deg2, the largest sample of those in the literature to date obtained at a redshift z ≳ 7. The LAE sample is compiled from deep large-area narrowband observations with Subaru conducted by the Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) project. The z = 7.0 Lyα LF of our project is consistent with those of the previous Dark Energy Camera and Subaru studies at the bright and faint ends, respectively, while having uncertainties that are significantly smaller than those of the previous study results. Exploiting the small errors of our measurements, we investigate the shape of the Lyα LF from the faint end to the bright end. We find that the shape of the z = 7.0 Lyα LF can be explained by the steep slope of α ≃ −2.5 suggested at z = 6.6, and that there is no clear signature of a bright-end excess at z ≃ 7 claimed by the previous work, which was thought to be created by the ionized bubbles around bright LAEs, whose Lyα photons could easily escape from the partly neutral intergalactic medium (IGM) at z ≃ 7. We estimate the Lyα luminosity densities (LDs) with Lyα LFs at z ≃ 6–8 given by our studies and the previous ones, and compare the evolution of the UV-continuum LD estimated with dropouts. The Lyα LD monotonically decreases from z ∼ 6 to 8, and evolves more strongly than the UV-continuum LD, which is indicative of the Lyα damping wing absorption of the IGM toward the heart of the reionization epoch. [ABSTRACT FROM AUTHOR]