[en] We report the first identification of a compact dense galaxy overdensity at $z\sim <!--\; ???\; -->8$ called A2744z8OD. A2744z8OD consists of eight Y-dropout galaxies behind Abell 2744 that were originally pinpointed by Hubble Frontier Fields studies. However, so far, no studies have derived the basic physical quantities of structure formation or made comparisons with theoretical models. We obtain a homogeneous sample of dropout galaxies at $z\sim <!--\; ???\; -->8$ from eight field data of Hubble legacy images that are as deep as the A2744z8OD data. Using the sample, we find that a galaxy surface overdensity value of A2744z8OD is very high $\mathrm{\delta <!--\; ??\; -->}\simeq <!--\; ???\; -->130$, where δ is defined by an overdensity in a small circle of 6″ ($\simeq <!--\; ???\; -->30$ physical kiloparsecs) radius. Because there is no such large δ value reported for high-z overdensities to date, A2744z8OD is a system that is clearly different from those found in previous high-z overdensity studies. In the galaxy+structure formation models of Henriques et al., there exists a very similar overdensity, Modelz8OD, that is made of eight model dropout galaxies at $z\sim <!--\; ???\; -->8$ in a 6″ radius circle. Modelz8OD is a progenitor of a today’s ${10}^{14}{M}_{\odot <!--\; ???\; -->}$ cluster, and more than half of the seven Modelz8OD galaxies are merged into the brightest cluster galaxy of the cluster. If Modelz8OD is a counterpart to A2744z8OD, the models suggest that A2744z8OD would be part of a cluster core forming from a ${10}^{14}{M}_{\odot <!--\; ???\; -->}$ cluster that began star formation at $z><!--\; >\; -->12$.

[en] We present the redshift evolution of the galaxy effective radius r_e obtained from the Hubble Space Telescope (HST) samples of ∼190,000 galaxies at z = 0–10. Our HST samples consist of 176,152 photo-z galaxies at z = 0–6 from the 3D-HST+CANDELS catalog and 10,454 Lyman break galaxies (LBGs) at z = 4–10 identified in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), HUDF 09/12, and HFF parallel fields, providing the largest data set to date for galaxy size evolution studies. We derive r_e with the same technique over the wide redshift range of z = 0–10, evaluating the optical-to-UV morphological K correction and the selection bias of photo-z galaxies+LBGs as well as the cosmological surface-brightness dimming effect. We find that r_e values at a given luminosity significantly decrease toward high z, regardless of statistics choices (e.g., $r_{\mathrm{e}}\propto <!--\; ???\; -->{(1+z)}^{-<!--\; ???\; -->1.10\pm <!--\; ??\; -->0.06}$ for median). For star-forming galaxies, there is no evolution of the power-law slope of the size–luminosity relation and the median Sérsic index ($n\sim <!--\; ???\; -->1.5$). Moreover, the r_e distribution is well represented by log-normal functions whose standard deviation ${\mathrm{\sigma <!--\; ??\; -->}}_{\mathrm{l}\mathrm{n}{r}_{\mathrm{e}}}$ does not show significant evolution within the range of ${\mathrm{\sigma <!--\; ??\; -->}}_{\mathrm{l}\mathrm{n}{r}_{\mathrm{e}}}\sim <!--\; ???\; -->0.45-<!--\; ???\; -->0.75$. We calculate the stellar-to-halo size ratio from our r_e measurements and the dark-matter halo masses estimated from the abundance-matching study, and we obtain a nearly constant value of $r_{\mathrm{e}}/r_{\mathrm{v}\mathrm{i}\mathrm{r}}=1.0\mathrm{\%<!--\; \%\; -->}-<!--\; ???\; -->3.5\mathrm{\%<!--\; \%\; -->}$ at z = 0–8. The combination of the r_e-distribution shape+standard deviation, the constant $r_{\mathrm{e}}/r_{\mathrm{v}\mathrm{i}\mathrm{r}}$, and $n\sim <!--\; ???\; -->1.5$ suggests a picture in which typical high-z star-forming galaxies have disk-like stellar components in a sense of dynamics and morphology over cosmic time of $z\sim <!--\; ???\; -->0-<!--\; ???\; -->6$. If high-z star-forming galaxies are truly dominated by disks, the $r_{\mathrm{e}}/r_{\mathrm{v}\mathrm{i}\mathrm{r}}$ value and the disk-formation model indicate that the specific angular momentum of the disk normalized by the host halo is $j_{\mathrm{d}}/m_{\mathrm{d}}\simeq <!--\; ???\; -->0.5-<!--\; ???\; -->1$. These are statistical results for major stellar components of galaxies, and the detailed study of clumpy subcomponents is presented in the paper II.

[en] We investigate the evolution of clumpy galaxies with Hubble Space Telescope (HST) samples of ∼17,000 photo-z and Lyman break galaxies at z ≃ 0–8. We detect clumpy galaxies with off-center clumps in a self-consistent algorithm that is well tested with previous study results, and we measure the number fraction of clumpy galaxies at the rest-frame UV, $f_{\mathrm{c}\mathrm{l}\mathrm{u}\mathrm{m}\mathrm{p}\mathrm{y}}^{\mathrm{U}\mathrm{V}}$. We identify an evolutionary trend of $f_{\mathrm{c}\mathrm{l}\mathrm{u}\mathrm{m}\mathrm{p}\mathrm{y}}^{\mathrm{U}\mathrm{V}}$ over z ≃ 0–8 for the first time: $f_{\mathrm{c}\mathrm{l}\mathrm{u}\mathrm{m}\mathrm{p}\mathrm{y}}^{\mathrm{U}\mathrm{V}}$ increases from z ≃ 8 to z ≃ 1–3 and subsequently decreases from z ≃ 1 to z ≃ 0, which follows the trend of the Madau–Lilly plot. A low average Sérsic index of n ≃ 1 is found in the underlining components of our clumpy galaxies at z ≃ 0–2, indicating that typical clumpy galaxies have disk-like surface brightness profiles. Our $f_{\mathrm{c}\mathrm{l}\mathrm{u}\mathrm{m}\mathrm{p}\mathrm{y}}^{\mathrm{U}\mathrm{V}}$ values correlate with physical quantities related to star formation activities for star-forming galaxies at z ≃ 0–7. We find that clump colors tend to be red at a small galactocentric distance for massive galaxies with $\mathrm{l}\mathrm{o}\mathrm{g}{M}_{\ast <!--\; ???\; -->}/M_{\odot <!--\; ???\; -->}\gtrsim <!--\; ???\; -->11$. All of these results are consistent with the picture that a majority of clumps form in the violent disk instability and migrate into the galactic centers.

[en] We present the statistics of faint submillimeter/millimeter galaxies (SMGs) and serendipitous detections of a submillimeter/millimeter line emitter (SLE) with no multi-wavelength continuum counterpart revealed by the deep ALMA observations. We identify faint SMGs with flux densities of 0.1-1.0 mJy in the deep Band-6 and Band-7 maps of 10 independent fields that reduce cosmic variance effects. The differential number counts at 1.2 mm are found to increase with decreasing flux density down to 0.1 mJy. Our number counts indicate that the faint (0.1-1.0 mJy, or SFR_IR ∼ 30-300 M _☉ yr^–1) SMGs contribute nearly a half of the extragalactic background light (EBL), while the remaining half of the EBL is mostly contributed by very faint sources with flux densities of <0.1 mJy (SFR_IR ≲ 30 M _☉ yr^–1). We conduct counts-in-cells analysis with multifield ALMA data for the faint SMGs, and obtain a coarse estimate of galaxy bias, b _g < 4. The galaxy bias suggests that the dark halo masses of the faint SMGs are ≲ 7 × 10¹² M _☉, which is smaller than those of bright (>1 mJy) SMGs, but consistent with abundant high-z star-forming populations, such as sBzKs, LBGs, and LAEs. Finally, we report the serendipitous detection of SLE-1, which has no continuum counterparts in our 1.2 mm-band or multi-wavelength images, including ultra deep HST/WFC3 and Spitzer data. The SLE has a significant line at 249.9 GHz with a signal-to-noise ratio of 7.1. If the SLE is not a spurious source made by the unknown systematic noise of ALMA, the strong upper limits of our multi-wavelength data suggest that the SLE would be a faint galaxy at z ≳ 6.

[en] We present statistics of 133 faint 1.2 mm continuum sources detected in about 120 deep Atacama Large Millimeter/submillimeter Array (ALMA) pointing data that include all the archival deep data available by 2015 June. We derive number counts of 1.2 mm continuum sources down to 0.02 mJy partly with the assistance of gravitational lensing, and find that the total integrated 1.2 mm flux of the securely identified sources is ${22.9}_{-<!--\; ???\; -->5.6}^{+6.7}$ Jy deg⁻² which corresponds to ${104}_{-<!--\; ???\; -->25}^{+31}\mathrm{\%<!--\; \%\; -->}$ of the extragalactic background light (EBL) measured by Cosmic Background Explorer observations. These results suggest that the major 1.2 mm EBL contributors are sources with 0.02 mJy, and that very faint 1.2 mm sources with ≲0.02 mJy contribute negligibly to the EBL with the possible flattening and/or truncation of number counts in this very faint flux regime. To understand the physical origin of our faint ALMA sources, we measure the galaxy bias b_g by the counts-in-cells technique, and place a stringent upper limit of b_g < 3.5 that is not similar to b_g values of massive distant red galaxies and submillimeter galaxies but comparable to those of UV-bright, star-forming BzK galaxies (sBzKs) and Lyman break galaxies (LBGs). Moreover, in the optical and near-infrared (NIR) deep fields, we identify optical-NIR counterparts for 59% of our faint ALMA sources, the majority of which have luminosities, colors, and the IRX-β relation the same as sBzKs and LBGs. We thus conclude that about a half of our faint ALMA sources are dust-poor, high-z galaxies as known as sBzKs and LBGs in optical studies, and that these faint ALMA sources are not miniature (U)LIRGs simply scaled down with the infrared brightness.

[en] As Lyα photons are scattered by neutral hydrogen, a change with redshift in the Lyα equivalent width (EW) distribution of distant galaxies offers a promising probe of the degree of ionization in the intergalactic medium and hence when cosmic reionization ended. This simple test is complicated by the fact that Lyα emission can also be affected by variations in the kinematics and dust content of the host galaxies. In the first paper in this series, we demonstrated both a luminosity- and redshift-dependent trend in the fraction of Lyα emitters seen within color-selected 'Lyman break' galaxies (LBGs) over the range 3 < z < 6; lower luminosity galaxies and those at higher redshift show an increased likelihood of strong emission. Here, we present the results from 12.5 hr exposures with the Keck DEIMOS spectrograph focused primarily on LBGs at z ≅ 6 which enable us to confirm the redshift dependence of line emission more robustly and to higher redshift than was hitherto possible. We find that 54% ± 11% of faint z ≅ 6 LBGs show strong (W_Lyα,0>25 A) emission, an increase of 55% from a sample of similarly luminous z ≅ 4 galaxies. With a total sample of 74 z ≅ 6 LBGs, we determine the luminosity-dependent Lyα EW distribution. Assuming continuity in these trends to the new population of z ≅ 7 sources located with the Hubble WFC3/IR camera, we predict that unless the neutral fraction rises in the intervening 200 Myr, the success rate for spectroscopic confirmation using Lyα emission should be high.

[en] We present comprehensive analyses of faint dropout galaxies up to z ∼ 10 with the first full-depth data set of the A2744 lensing cluster and parallel fields observed by the Hubble Frontier Fields (HFF) program. We identify 54 dropouts at z ∼ 5-10 in the HFF fields and enlarge the size of the z ∼ 9 galaxy sample obtained to date. Although the number of highly magnified (μ ∼ 10) galaxies is small because of the tiny survey volume of strong lensing, our study reaches the galaxies' intrinsic luminosities comparable to the deepest-field HUDF studies. We derive UV luminosity functions with these faint dropouts, carefully evaluating by intensive simulations the combination of observational incompleteness and lensing effects in the image plane, including magnification, distortion, and multiplication of images, with the evaluation of mass model dependencies. Our results confirm that the faint-end slope, α, is as steep as –2 at z ∼ 6-8 and strengthen the evidence for the rapid decrease of UV luminosity densities, ρ_UV, at z > 8 from the large z ∼ 9 sample. We examine whether the rapid ρ_UV decrease trend can be reconciled with the large Thomson scattering optical depth, τ_e, measured by cosmic microwave background experiments, allowing a large space of free parameters, such as an average ionizing photon escape fraction and a stellar-population-dependent conversion factor. No parameter set can reproduce both the rapid ρ_UV decrease and the large τ _e. It is possible that the ρ_UV decrease moderates at z ≳ 11, that the free parameters significantly evolve toward high z, or that there exist additional sources of reionization such as X-ray binaries and faint active galactic nuclei

[en] We report our Keck/MOSFIRE and Magellan/Low-Dispersion Survey Spectrograph spectroscopy for an [O II] Blob, O II B 10, that is a high-z galaxy with spatially extended [O II] λλ3726, 3729 emission over 30 kpc recently identified by a Subaru large-area narrowband survey. The systemic redshift of O II B 10 is z = 1.18 securely determined with [O III] λλ4959, 5007 and Hβ emission lines. We identify Fe II λ2587 and Mg II λλ2796, 2804 absorption lines blueshifted from the systemic redshift by 80 ± 50 and 260 ± 40 km s^–1, respectively, which indicates gas outflow from O II B 10 with the velocity of ∼80-260 km s^–1. This outflow velocity is comparable with the escape velocity, 250 ± 140 km s^–1, estimated under the assumption of a singular isothermal halo potential profile. Some fraction of the outflowing gas could escape from the halo of O II B 10, suppressing O II B 10's star-formation (SF) activity. We estimate a mass loading factor, η, that is a ratio of mass outflow rate to SF rate, and obtain η > 0.8 ± 0.1, which is relatively high compared with low-z starbursts including U/LIRGs and active galactic nuclei (AGNs). The major energy source of the outflow is unclear with the available data. Although no signature of AGNs is found in the X-ray data, O II B 10 falls in the AGN/star-forming composite region in the line diagnostic diagrams. It is possible that the outflow is powered by SF and a type-2 AGN with narrow FWHM emission line widths of 70-130 km s^–1. This is the first detailed spectroscopic study of oxygen-line blobs that includes analyses of the escape velocity, the mass loading factor, and the presence of an AGN, and is a significant step to understanding the nature of oxygen-line blobs and the relation between gas outflow and SF quenching at high redshift.

[en] We conduct a systematic search for galaxies at $z=0.1\text{--}1.5$ with [O ii]$\mathrm{\lambda <!--\; ??\; -->}3727$, [O iii]$\mathrm{\lambda <!--\; ??\; -->}5007$, or Hα $\mathrm{\lambda <!--\; ??\; -->}6563$ emission lines extended over at least 30 kpc by using deep narrowband and broadband imaging in the Subaru-XMM Deep Survey field. These extended emission-line galaxies are dubbed [O ii], [O iii], or Hα blobs. Based on a new selection method that securely selects extended emission-line galaxies, we find 77 blobs at $z=0.40\text{--}1.46$ with the isophotal area of emission lines down to $1.2\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->18}$ erg s⁻¹ cm⁻² kpc⁻². Four of them are spectroscopically confirmed to be [O iii] blobs at z = 0.83. We identify AGN activities in eight blobs with X-ray and radio data, and find that the fraction of AGN contribution increases with increasing isophotal area of the extended emission. With the Kolmogorov–Smirnov (KS) and Anderson–Darling tests, we confirm that the stellar-mass distributions of Hα and [O ii] blobs are not drawn from those of the emitters at the $><!--\; >\; -->90$% confidence level in that Hα and [O ii] blobs are located at the massive end of the distributions, but cannot reject a null hypothesis of being the same distributions in terms of the specific star formation rates. It is suggested that galactic-scale outflows tend to be more prominent in more massive star-forming galaxies. Exploiting our sample homogeneously selected over the large area, we derive the number densities of blobs at each epoch. The number densities of blobs decrease drastically with redshifts at a rate that is larger than that of the decrease of cosmic star formation densities.

[en] By stacking publicly available deep Spitzer/MIPS 24 μm and Herschel/PACS images for 213 $z\simeq <!--\; ???\; -->2.18$ $\mathrm{L}\mathrm{y}\mathrm{\alpha <!--\; ??\; -->}$ Emitters (LAEs) in GOODS-South, we obtain a strong upper limit to the IR luminosity of typical LAEs and discuss their attenuation curve for the first time. The $3\mathrm{\sigma <!--\; ??\; -->}$ upper limit $L_{\mathrm{T}\mathrm{I}\mathrm{R}}^{3\mathrm{\sigma <!--\; ??\; -->}}$ $=1.1\times <!--\; ??\; -->{10}^{10}{L}_{\odot <!--\; ???\; -->}$, determined from the MIPS data providing the lowest limit, gives $\mathrm{I}\mathrm{R}\mathrm{X}\equiv <!--\; ???\; -->L_{\mathrm{T}\mathrm{I}\mathrm{R}}/L_{\mathrm{U}\mathrm{V}}⩽<!--\; ???\; -->2.2$. Here we assume that the local calibration between the 8 μm emission and the dust SED shape and metallicity applies at high redshifts and that our LAEs have low metallicities as suggested by previous studies. The inferred escape fractions of $\mathrm{L}\mathrm{y}\mathrm{\alpha <!--\; ??\; -->}$, 16–37%, and UV continuum, $⩾<!--\; ???\; -->44\mathrm{\%<!--\; \%\; -->}$, are higher than the cosmic averages at the same epoch. The SMC attenuation curve is consistent with the IRX and the UV slope $\mathrm{\beta <!--\; ??\; -->}=-<!--\; ???\; -->{1.4}_{-<!--\; ???\; -->0.2}^{+0.2}$ of our stacked LAE, while the Meurer’s relation (Calzetti curve) predicts a 3.8 times higher IRX; we also discuss the validity of PACS-based $L_{\mathrm{T}\mathrm{I}\mathrm{R}}^{3\mathrm{\sigma <!--\; ??\; -->}}$ allowing the Meurer’s relation. SED fitting using the Calzetti curve also gives a ∼10 times higher SFR than from the $L_{\mathrm{T}\mathrm{I}\mathrm{R}}^{3\mathrm{\sigma <!--\; ??\; -->}}$ and $L_{\mathrm{U}\mathrm{V}}$. With $M_{\star <!--\; ???\; -->}={6.3}_{-<!--\; ???\; -->2.0}^{+0.8}\times <!--\; ??\; -->{10}^8{M}_{\odot <!--\; ???\; -->}$, our LAEs lie on a lower-mass extrapolation of the star formation main sequence at $z\sim <!--\; ???\; -->2$, suggesting that the majority of $z\sim <!--\; ???\; -->2$ LAEs are mildly star forming with relatively old ages of ∼200 Myr. The faint $L_{\mathrm{T}\mathrm{I}\mathrm{R}}^{3\mathrm{\sigma <!--\; ??\; -->}}$ implies that LAEs contribute little to the faint ($\gtrsim <!--\; ???\; -->100\mathrm{\mu <!--\; ??\; -->}\mathrm{J}\mathrm{y}$) submillimeter number counts by ALMA.