We use a newly assembled sample of 3545 star-forming galaxies with secure spectroscopic, grism, and photometric redshifts at z=1.5-2.5 to constrain the relationship between UV slope (β) and dust attenuation (L IR /L UV ≡IRX). Our sample significantly extends the range of L UV and β probed in previous UV-selected samples, including those as faint as M 1600 =−17.4 ( L 0.05 UV *  ) and −2.6β0.0. IRX is measured using stacks of deep Herschel data, and the results are compared with predictions of the IRX−β relation for different assumptions of the stellar population model and obscuration curve. We find that z=1.5-2.5 galaxies have an IRX −β relation that is consistent with the predictions for an SMC curve if we invoke subsolar-metallicity models currently favored for high-redshift galaxies, while the commonly assumed starburst curve overpredicts the IRX at a given β by a factor of 3. IRX is roughly constant with L UV for L UV 3×109 L e . Thus, the commonly observed trend of fainter galaxies having bluer β may simply reflect bluer intrinsic slopes for such galaxies, rather than lower obscurations. The IRX−β relation for young/low-mass galaxies at z2 implies a dust curve that is steeper than the SMC. The lower attenuations and higher ionizing photon output for low-metallicity stellar populations point to Lyman continuum production efficiencies, ξ ion , that may be elevated by a factor of ≈2 relative to the canonical value for L * galaxies, aiding in their ability to keep the universe ionized at z∼2.

We present the ancillary data and basic physical measurements for the galaxies in the ALMA Large Program to Investigate C + at Early Times (ALPINE) survey − the first large multi-wavelength survey which aims at characterizing the gas and dust properties of 118 main-sequence galaxies at redshifts 2 Faisst et al. 4.4 < z < 5.9 via the measurement of [C II] emission at 158 µm and the surrounding far-infrared (FIR) continuum in conjunction with a wealth of optical and near-infrared data. We outline in detail the spectroscopic data and selection of the galaxies as well as the ground-and space-based imaging products. In addition, we provide several basic measurements including stellar masses, star formation rates (SFR), rest-frame ultra-violet (UV) luminosities, UV continuum slopes (β), and absorption line redshifts, as well as Hα emission derived from Spitzer colors. Overall, we find that the ALPINE sample is representative of the 4 < z < 6 galaxy population and only slightly biased towards bluer colors (∆β ∼ 0.2). Using [C II] as tracer of the systemic redshift (confirmed for one galaxy at z = 4.5 for which we obtained optical [O II]λ3727 µm emission), we confirm red shifted Lyα emission and blue shifted absorption lines similar to findings at lower redshifts. By stacking the rest-frame UV spectra in the [C II] rest-frame we find that the absorption lines in galaxies with high specific SFR are more blue shifted, which could be indicative of stronger winds and outflows.

The [C II] 158 μm line is one of the strongest IR emission lines, which has been shown to trace the star formation rate (SFR) of galaxies in the nearby Universe, and up to z ∼ 2. Whether this is also the case at higher redshift and in the early Universe remains debated. The ALPINE survey, which targeted 118 star-forming galaxies at 4.4 <  z <  5.9, provides a new opportunity to examine this question with the first statistical dataset. Using the ALPINE data and earlier measurements from the literature, we examine the relation between the [C II] luminosity and the SFR over the entire redshift range from z ∼ 4 − 8. ALPINE galaxies, which are both detected in [C II] and in dust continuum, show good agreement with the local L([CII])–SFR relation. Galaxies undetected in the continuum by ALMA are found to be over-luminous in [C II] when the UV SFR is used. After accounting for dust-obscured star formation, by an amount of SFR(IR) ≈ SFR(UV) on average, which results from two different stacking methods and SED fitting, the ALPINE galaxies show an L([CII])–SFR relation comparable to the local one. When [C II] non-detections are taken into account, the slope may be marginally steeper at high-z, although this is still somewhat uncertain. When compared homogeneously, the z >  6 [C II] measurements (detections and upper limits) do not behave very differently to the z ∼ 4 − 6 data. We find a weak dependence of L([CII])/SFR on the Lyα equivalent width. Finally, we find that the ratio L([CII])/LIR ∼ (1 − 3) × 10−3 for the ALPINE sources, comparable to that of “normal” galaxies at lower redshift. Our analysis, which includes the largest sample (∼150 galaxies) of [C II] measurements at z > 4 available so far, suggests no or little evolution of the [C II]–SFR relation over the last 13 Gyr of cosmic time.

By using a set of different SFR indicators, including WISE mid-infrared and Hα emission, we study the slope of the Main Sequence (MS) of local star forming galaxies at stellar masses larger than 10 10 M . The slope of the relation strongly depends on the SFR indicator used. In all cases, the local MS shows a bending at high stellar masses with respect to the slope obtained in the low mass regime. While the distribution of galaxies in the upper envelope of the MS is consistent with a log-normal distribution, the lower envelope shows an excess of galaxies, which increases as a function of the stellar mass but varies as a function of the SFR indicator used. The scatter of the best log-normal distribution increases with stellar mass from ∼ 0.3 dex at 10 10 M to ∼ 0.45 at 10 11 M . The MS high-mass end is dominated by central galaxies of group sized halos with a red bulge and a disk redder than the lower mass counterparts. We argue that the MS bending in this region is due to two processes: i) the formation of a bulge component as a consequence of the increased merger activity in groups, and ii) the cold gas starvation induced by the hot halo environment, which cuts off the gas inflow onto the disk. Similarly, the increase of the MS scatter at high stellar masses would be explained by the larger spread of star formation histories of central group and cluster galaxies with respect to lower mass systems.

Context. In the current model of structure formation, bright quasars (QSOs) at z ∼ 6 are assumed to be hosted by the most massive dark matter halos that collapsed at that time. The large-scale structures in which these halos are embedded may extend up to 10 physical Mpc, and probably can be traced by overdensities of star-forming galaxies. To date, the search for these overdensities has been limited to scales of 1-2 physical Mpc around the QSO and did not produce coherent results. Aims. We aim at studying the environment of z ∼ 6 QSOs and verify whether they are associated with large-scale overdensities of galaxies selected at the same redshift as i-band dropouts. Methods. With the wide-field (∼23 × 25 ) Large Binocular Camera (LBC) at the Large Binocular Telescope (LBT), we obtained deep r-, i-and z-band imaging of the fields around four high-z QSOs, namely SDSS J1030+0524 (z = 6.28), SDSS J1148+5251 (z = 6.41), SDSS J1048+4637 (z = 6.20), and SDSS J1411+1217 (z = 5.95). Our photometric catalogs are based on source detection in the z-band image (5σ) and contain from ∼2.3 × 10 4 to ∼2.9 × 10 4 objects, down to a 50% completeness limit of z = 25.0-25.2 AB mag. We adopted color-color selections within the i − z vs. r − z plane to identify samples of i-band dropouts at the QSO redshift and measured their relative abundance and spatial distribution in the four LBC fields, each covering ∼8 × 8 physical Mpc at z ∼ 6. The same selection criteria were then applied to z-band-selected sources in the ∼1 deg 2 wide-and-deep Subaru-XMM Newton Deep Survey (SXDS) to derive the expected number of dropouts over a blank LBC-sized field (∼0.14 deg 2 after removing masked regions). Results. The four observed QSO fields host more candidates than expected in a blank field. By defining objects with z AB < 25 and i − z > 1.4 that are undetected in the r-band as i-band dropouts, we found 16, 10, 9, and 12 dropouts in SDSS J1030+0524, SDSS J1148+5251, SDSS J1048+4637, and SDSS J1411+1217, respectively, whereas only 4.3 such objects are expected over a 0.14 deg 2 blank field. This corresponds to overdensity significances of 3.3, 1.9, 1.7, and 2.5σ, respectively, after accounting for cosmic variance and for the contamination by bluer objects in our dropout samples produced by photometric errors. By considering the total number of dropouts in the four LBC fields and comparing it with what is expected in four blank fields of 0.14 deg 2 each, we find that high-z QSOs reside in overdense environments at the 3.7σ level. This is the first direct and unambiguous measurement of the large-scale structures around z ∼ 6 QSOs.

The ALMA-ALPINE [CII] survey is aimed at characterizing the properties of a sample of normal star-forming galaxies (SFGs). The ALMA Large Program to INvestigate (ALPINE) features 118 galaxies observed in the [CII]-158 μm line and far infrared (FIR) continuum emission during the period of rapid mass assembly, right after the end of the HI reionization, at redshifts of 4 <  z <  6. We present the survey science goals, the observational strategy, and the sample selection of the 118 galaxies observed with ALMA, with an average beam minor axis of about 0.85″, or ∼5 kpc at the median redshift of the survey. The properties of the sample are described, including spectroscopic redshifts derived from the UV-rest frame, stellar masses, and star-formation rates obtained from a spectral energy distribution (SED) fitting. The observed properties derived from the ALMA data are presented and discussed in terms of the overall detection rate in [CII] and FIR continuum, with the observed signal-to-noise distribution. The sample is representative of the SFG population in the main sequence at these redshifts. The overall detection rate in [CII] is 64% for a signal-to-noise ratio (S/N) threshold larger than 3.5 corresponding to a 95% purity (40% detection rate for S/N >  5). Based on a visual inspection of the [CII] data cubes together with the large wealth of ancillary data, we find a surprisingly wide range of galaxy types, including 40% that are mergers, 20% extended and dispersion-dominated, 13% compact, and 11% rotating discs, with the remaining 16% too faint to be classified. This diversity indicates that a wide array of physical processes must be at work at this epoch, first and foremost, those of galaxy mergers. This paper sets a reference sample for the gas distribution in normal SFGs at 4 <  z <  6, a key epoch in galaxy assembly, which is ideally suited for studies with future facilities, such as the James Webb Space Telescope (JWST) and the Extremely Large Telescopes (ELTs).

We present the physical extent of [C II] 158 μm line-emitting gas from 46 star-forming galaxies at z=4-6 from the ALMA Large Program to INvestigate C II at Early Times (ALPINE). Using exponential profile fits, we measure the effective radius of the [C II] line ( [ ] r e, C II ) for individual galaxies and compare them with the rest-frame ultraviolet (UV) continuum (r e,UV ) from Hubble Space Telescope images. The effective radius [ ] r e, C II exceeds r e,UV by factors of ∼2-3, and the ratio of [ ] r r e, C e,UV II increases as a function of M star . We do not find strong evidence that the [C II] line, rest-frame UV, and far-infrared (FIR) continuum are always displaced over ;1 kpc scale from each other. We identify 30% of isolated ALPINE sources as having an extended [C II] component over 10 kpc scales detected at 4.1σ-10.9σ beyond the size of rest-frame UV and FIR continuum. One object has tentative rotating features up to ∼10 kpc, where the 3D model fit shows the rotating [C II]-gas disk spread over 4 times larger than the rest-frame UV-emitting region. Galaxies with the extended [C II] line structure have high star formation rate, high stellar mass (M star ), low Lyα equivalent width, and more blueshifted (redshifted) rest-frame UV metal absorption (Lyα line), as compared to galaxies without such extended [C II] structures. Although we cannot rule out the possibility that a selection bias toward luminous objects may be responsible for such trends, the star-formation-driven outflow also explains all these trends. Deeper observations are essential to test whether the extended [C II] line structures are ubiquitous to high-z star-forming galaxies.

We present the Hubble Deep UV Legacy Survey (HDUV), a 132-orbit imaging program with the WFC3/UVIS camera on board the Hubble Space Telescope (HST). The HDUV extends and builds on the few previous UV imaging surveys in the two GOODS/CANDELS-Deep fields to provide deep images over a total area of ∼100 arcmin 2 in the two filters F275W and F336W. Our release also includes all the F275W imaging data taken by the CANDELS survey, which were aligned using a novel approach and combined with the HDUV survey data. By reaching depths of 27.5-28.0 mag (5σ in 0 4 apertures), these are the deepest high-resolution UV data over such a large area taken to date. Such unique UV imaging enables a wide range of science by the community. A few of the main goals of the HDUV survey are as follows: (1) to provide a complete sample of faint star-forming galaxies at z∼1-3; (2) to constrain the ionizing photon escape fraction from galaxies at z∼2-3; and (3) to track the build-up of bulges and the disappearance of clumpy disk galaxies through reliable internal stellar population properties at sub-kiloparsec resolution out to z∼3. The addition of the HDUV data further enhances the legacy value of the two GOODS/CANDELS-Deep fields, which now include deep 11-band HST imaging, as well as very deep ancillary data from X-ray to radio, enabling unique multi-wavelength studies. Here, we provide an overview of the survey design, describe the data reduction, and highlight a few basic analyses of the images that are available to the community as high-level science products, via the Mikulski Archive for Space Telescopes.