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We present a new method to determine the star formation rate density (SFRD) of the Universe at |$z \gtrsim 5$| that includes the contribution of dust-obscured star formation. For this purpose, we use a [C  ii ] (158 |$\mu$| m) selected sample of galaxies serendipitously identified in the fields of known |$z\gtrsim 4.5$| objects to characterise the fraction of obscured star formation rate (SFR). The advantage of a [C  ii ] selection is that our sample is SFR-selected, in contrast to an ultraviolet (UV)-selection that would be biased towards unobscured star formation. We obtain a sample of 23 [C  ii ] emitters near star-forming (SF) galaxies and quasi-stellar objects (QSOs) – three of which we identify for the first time – using previous literature and archival Atacama Large Millimeter/submillimeter Array data. 18 of these serendipitously identified galaxies have sufficiently deep rest-UV data and are used to characterise the obscured fraction of the star formation in galaxies with SFRs |$\gtrsim 30\ \text{M}_{\odot } \ \text{yr}^{-1}$|⁠. We find that [C  ii ] emitters identified around SF galaxies have |$\approx$| 63 per cent of their SFR obscured, while [C  ii ] emitters around QSOs have |$\approx$| 93 per cent of their SFR obscured. By forward modelling existing wide-area UV luminosity function (LF) determinations, we derive the intrinsic UV LF using our characterisation of the obscured SFR. Integrating the intrinsic LF to |$M_{\mathrm{ UV}}$| = |$-$| 20, we find that the obscured SFRD contributes to |$\gt 3~{{\ \rm per\ cent}}$| and |$\gt 10~{{\ \rm per\ cent}}$| of the total SFRD at |$z \sim 5$| and |$z \sim 6$| based on our sample of companions galaxies near SF galaxies and QSOs, respectively. Our results suggest that dust obscuration is not negligible at |$z\gtrsim 5$|⁠ , further underlining the importance of far-infrared observations of the |$z\gtrsim 5$| Universe. [ABSTRACT FROM AUTHOR]

We present new determinations of the rest-UV luminosity functions (LFs) at z = 2â€"9 to extremely low luminosities (>âˆ'14 mag) from a sample of >2500 lensed galaxies found behind the Hubble Frontier Fields (HFF) clusters. For the first time, we present faint-end slope results from lensed samples that are fully consistent with blank-field results over the redshift range z = 2â€"9, while reaching to much lower luminosities than possible from the blank-field studies. Combining the deep lensed sample with the large blank-field samples allows us to set tight constraints on the faint-end slope α of the z = 2â€"9 UV LFs and its evolution. We find a smooth flattening in α from âˆ'2.28 ± 0.10 (z = 9) to âˆ'1.53 ± 0.03 (z = 2) with cosmic time (dα / dz = âˆ'0.11 ± 0.01), fully consistent with dark matter halo buildup. We utilize these new results to present new measurements of the evolution in the UV luminosity density ρ UV brighter than âˆ'13 mag from z ∼ 9 to z ∼ 2. Accounting for the star formation rate (SFR) densities to faint luminosities implied by our LF results, we find that unobscured star formation dominates the SFR density at z ≳ 4, with obscured star formation dominant thereafter. Having shown we can quantify the faint-end slope α of the LF accurately with our lensed HFF samples, we also quantify the apparent curvature in the shape of the UV LF through a curvature parameter δ. The constraints on the curvature δ strongly rule out the presence of a turn-over brighter than âˆ'13.1 mag at z ∼ 3, âˆ'14.3 mag at z ∼ 6, and âˆ'15.5 mag at all other redshifts between z ∼ 9 and z ∼ 2. [ABSTRACT FROM AUTHOR]

Before the end of the Epoch of Reionization, the Hydrogen in the Universe was predominantly neutral. This leads to a strong attenuation of Ly α lines of z ≳ 6 galaxies in the intergalactic medium. Nevertheless, Ly α has been detected up to very high redshifts (z ∼ 9) for several especially UV luminous galaxies. Here, we test to what extent the galaxy's local environment might impact the Ly α transmission of such sources. We present an analysis of dedicated Hubble Space Telescope (HST) imaging in the CANDELS/EGS field to search for fainter neighbours around three of the most UV luminous and most distant spectroscopically confirmed Ly α emitters: EGS-zs8-1, EGS-zs8-2, and EGSY-z8p7 at z spec = 7.73, 7.48, and 8.68, respectively. We combine the multiwavelength HST imaging with Spitzer data to reliably select z ∼ 7–9 galaxies around the central, UV-luminous sources. In all cases, we find a clear enhancement of neighbouring galaxies compared to the expected number in a blank field (by a factor ∼3–9×). Our analysis thus reveals ubiquitous overdensities around luminous Ly α emitting sources in the heart of the cosmic reionization epoch. We show that our results are in excellent agreement with expectations from the Dragons simulation, confirming the theoretical prediction that the first ionized bubbles preferentially formed in overdense regions. While three UV luminous galaxies already have spectroscopic redshifts, the majority of the remaining fainter, surrounding sources are yet to be confirmed via spectroscopy. JWST follow-up observations of the neighbouring galaxies identified here will thus be needed to confirm their physical association and to map out the ionized regions produced by these sources. [ABSTRACT FROM AUTHOR]

We assemble a large comprehensive sample of 2534 z ∼ 2, 3, 4, 5, 6, 7, 8, and 9 galaxies lensed by the six clusters from the Hubble Frontier Fields (HFF) program. Making use of the availability of multiple independent magnification models for each of the HFF clusters and alternatively treating one of the models as the “truth,” we show that the median magnification factors from the v4 parametric models are typically reliable to values of 30â€"50, and in one case to 100. Using the median magnification factor from the latest v4 models, we estimate the UV luminosities of the 2534 lensed z ∼ 2â€"9 galaxies, finding sources as faint as âˆ'12.4 mag at z ∼ 3 and âˆ'12.9 mag at z ∼ 7. We explicitly demonstrate the power of the surface densityâ€"magnification relations ÎŁ(z) versus ÎĽ in the HFF clusters to constrain both distant galaxy properties and cluster lensing properties. Based on the ÎŁ(z) versus ÎĽ relations, we show that the median magnification estimates from existing public models must be reliable predictors of the true magnification ÎĽ to ÎĽ < 15 (95% confidence). We also use the observed ÎŁ(z) versus ÎĽ relations to derive constraints on the evolution of the luminosity function faint-end slope from z ∼ 7 to z ∼ 2, showing that faint-end slope results can be consistent with blank-field studies if, and only if, the selection efficiency shows no strong dependence on the magnification factor ÎĽ. This can only be the case if very low-luminosity galaxies are very small, being unresolved in deep lensing probes. [ABSTRACT FROM AUTHOR]

We present the spectroscopic confirmation of the brightest known gravitationally lensed Lyman-break galaxy in the Epoch of Reionization (EoR), A1703-zD1, through the detection of [C  ii ] 158  |$\mu$| m at a redshift of z  = 6.8269 ± 0.0004. This source was selected behind the strong lensing cluster Abell 1703, with an intrinsic luminosity and a very blue Spitzer /Infrared Array Camera (IRAC) [3.6]–[4.5] colour, implying high equivalent width line emission of [O  iii ] + Hβ. [C  ii ] is reliably detected at 6.1σ cospatial with the rest-frame ultraviolet (UV) counterpart, showing similar spatial extent. Correcting for the lensing magnification, the [C  ii ] luminosity in A1703-zD1 is broadly consistent with the local |$L_{\rm [C\, {\small II}]}$| –star formation rate (SFR) relation. We find a clear velocity gradient of 103 ± 22 km  |$\rm s^{-1}$| across the source that possibly indicates rotation or an ongoing merger. We furthermore present spectral scans with no detected [C  ii ] above 4.6σ in two unlensed Lyman-break galaxies in the Extended Groth Strip (EGS)-Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field at z ∼ 6.6–6.9. This is the first time that the Northern Extended Millimeter Array (NOEMA) has been successfully used to observe [C  ii ] in a 'normal' star-forming galaxy at z > 6, and our results demonstrate its capability to complement the Atacama Large Millimeter/submillimeter Array (ALMA) in confirming galaxies in the EoR. [ABSTRACT FROM AUTHOR]

We analyse FIR dust continuum measurements for 14 galaxies (redshift z ≈ 7) in the ALMA Reionization Era Bright Emission Line Survey (REBELS) Large Program to derive their physical properties. Our model uses three input data, i.e. (a) the UV spectral slope, β, (b) the observed UV continuum flux at 1500 Å, F 1500, (c) the observed continuum flux at |$\approx 158\, \mu$| m, F 158, and considers Milky Way (MW) and SMC extinction curves, along with different dust geometries. We find that REBELS galaxies have 28−90.5 per cent of their star formation obscured; the total (UV+IR) star formation rates are in the range |$31.5 \lt {\rm SFR}/({\rm M}_\odot \, {\rm yr}^{-1}) \lt 129.5$|⁠. The sample-averaged dust mass and temperature are |$(1.3\pm 1.1)\times 10^7 \, \mathrm{M}_\odot$| and 52 ± 11 K, respectively. However, in some galaxies dust is particularly abundant (REBELS-14, |$M^{\prime }_{\rm d} \approx 3.4 \times 10^7 \, \mathrm{M}_\odot$|⁠), or hot (REBELS-18, |$T^{\prime }_{\rm d} \approx 67$| K). The dust distribution is compact (<0.3 kpc for 70 per cent of the galaxies). The inferred dust yield per supernova is |$0.1 \le y_{\rm d}/\, \mathrm{M}_\odot \le 3.3$|⁠ , with 70 per cent of the galaxies requiring |$y_{\rm d} \lt 0.25 \, \mathrm{M}_\odot$|⁠. Three galaxies (REBELS-12, 14, 39) require |$y_{\rm d} \gt 1 \, \mathrm{M}_\odot$|⁠ , which is likely inconsistent with pure SN production, and might require dust growth via accretion of heavy elements from the interstellar medium. With the SFR predicted by the model and a MW extinction curve, REBELS galaxies detected in [C  ii ] nicely follow the local L CII−SFR relation, and are approximately located on the Kennicutt–Schmidt relation. The sample-averaged gas depletion time is |$0.11\, y_{\rm P}^{-2}$| Gyr, where y P is the ratio of the gas-to-stellar distribution radius. For some systems, a solution simultaneously matching the observed (β, F 1500, F 158) values cannot be found. This occurs when the index Im  = (F 158/ F 1500)/(β − βint), where βint is the intrinsic UV slope, exceeds |$I_m^{*}\approx 1120$| for an MW curve. For these objects, we argue that the FIR and UV emitting regions are not co-spatial, questioning the use of the IRX–β relation. [ABSTRACT FROM AUTHOR]

The James Webb Space Telescope will allow to spectroscopically study an unprecedented number of galaxies deep into the reionization era, notably by detecting [O  iii ]λλ4959, 5007, and H β nebular emission lines. To efficiently prepare such observations, we photometrically select a large sample of galaxies at z ∼ 8 and study their rest-frame optical emission lines. Combining data from the GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS) survey and from HST we perform spectral energy distribution (SED) fitting, using synthetic SEDs from a large grid of photoionization models. The deep Spitzer /IRAC data combined with our models exploring a large parameter space enables to constrain the [O  iii ] + H β fluxes and equivalent widths for our sample, as well as the average physical properties of z ∼ 8 galaxies, such as the ionizing photon production efficiency with |$\log (\xi _\mathrm{ion}/\mathrm{erg}^{-1}\mathrm{Hz})\ge 25.77$|⁠. We find a relatively tight correlation between the [O  iii ] + H β and UV luminosity, which we use to derive for the first time the [O  iii ]λλ4959, 5007 + H β luminosity function (LF) at z ∼ 8. The z ∼ 8 [O  iii ] + H β LF is higher at all luminosities compared to lower redshift, as opposed to the UV LF, due to an increase of the [O  iii ] + H β luminosity at a given UV luminosity from z ∼ 3 to z ∼ 8. Finally, using the [O  iii ] + H β LF, we make predictions for JWST /NIRSpec number counts of z ∼ 8 galaxies. We find that the current wide-area extragalactic legacy fields are too shallow to use JWST at maximal efficiency for z ∼ 8 spectroscopy even at 1 h depth and JWST pre-imaging to ≳30 mag will be required. [ABSTRACT FROM AUTHOR]

We present a comprehensive analysis of z > 8 galaxies based on ultra-deep WFC3/IR data. We exploit all the WFC3/IR imaging over the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12 program, in addition to the HUDF09 parallel field data, as well as wider area imaging over GOODS-South. Galaxies are selected based on the Lyman break technique in three samples centered around z ~ 9, z ~ 10, and z ~ 11, with seven z ~ 9 galaxy candidates, and one each at z ~ 10 and z ~ 11. We confirm a new z ~ 10 candidate (with z = 9.8 ± 0.6) that was not convincingly identified in our first z ~ 10 sample. Using these candidates, we perform one of the first estimates of the z ~ 9 UV luminosity function (LF) and improve our previous constraints at z ~ 10. Extrapolating the lower redshift UV LF evolution should have revealed 17 z ~ 9 and 9 z ~ 10 sources, i.e., a factor ~3× and 9× larger than observed. The inferred star formation rate density (SFRD) in galaxies above 0.7M☉ yr-1 decreases by 0.6 ± 0.2 dex from z ~ 8 to z ~ 9, in excellent agreement with previous estimates. From a combination of all current measurements, we find a best estimate of a factor 10× decrease in the SFRD from z ~ 8 to z ~ 10, following (1 + z)-11.4±3.1. Our measurements thus confirm our previous finding of an accelerated evolution beyond z ~ 8, and signify a very rapid build-up of galaxies with MUV < -17.7 mag within only ~200 Myr from z ~ 10 to z ~ 8, in the heart of cosmic reionization. [ABSTRACT FROM AUTHOR]

We report the discovery of seven strongly lensed lyman-break galaxy (LBG) candidates at z ~ 7 detected in hubble Space Telescope Wide Field Camera 3 (WFC3) imaging of A1703. The brightest candidate, called A1703-zD1, has an observed (lensed) magnitude of 24.0 AB (26σ) in the WFC3/IR F160W band, making it 0.2 mag brighter than the z850-dropout candidate recently reported behind the Bullet Cluster and 0.7 mag brighter than the previously brightest known z ~ 7.6 galaxy, A1689-zD1. with a cluster magnification of ~9, this source has an intrinsic magnitude of H160 = 26.4 AB, a strong z850-J125 break of 1.7 mag, and a photometric redshift of z ~ 6.7. Additionally, we find six other bright LBG candidates with H160-band magnitudes of 24.9-26.4, photometric redshifts z ~ 6.4 - 8.8, and magnifications μ ~ 3-40. stellar population fits to the advanced camera for surveys, WFC3/IR, and Spitzer/Infrared Array Camera data for A1703-zD1 and A1703-zD4 yield stellar masses (0.7 - 3.0) x 109 M⊙, stellar ages 5-180 Myr, and star formation rates ~7.8 M⊙ yr-1, and low reddening with AV ≤ 0.7. The source-plane reconstruction of the exceptionally bright candidate A1703-zD1 exhibits an extended structure, spanning ~4 kpc in the z ~ 6.7 source plane, and shows three resolved star-forming knots of radius r ~ 0.4 kpc. [ABSTRACT FROM AUTHOR]

We identify 73 z ~ 7 and 59 z ~ 8 candidate galaxies in the reionization epoch, and use this large 26-29.4 AB mag sample of galaxies to derive very deep luminosity functions to < - 18 AB mag and the star formation rate (SFR) density at z ~ 7 and z ~ 8 (just 800 Myr and 650 Myr after recombination, respectively). The galaxy sample is derived using a sophisticated Lyman-break technique on the full two-year Wide Field Camera 3/infrared (WFC3/IR) and Advanced Camera for Surveys (ACS) data available over the HUDF09 (~29.4 AB mag, 5σ), two nearby HUDF09 fields (~29 AB mag, 5σ, 14 arcmin²), and the wider area Early Release Science (~27.5 AB mag, 5σ, ~40 arcmin²). The application of strict optical non-detection criteria ensures the contamination fraction is kept low (just ~7% in the HUDF). This very low value includes a full assessment of the contamination from lower redshift sources, photometric scatter, active galactic nuclei, spurious sources, low-mass stars, and transients (e.g., supernovae). From careful modeling of the selection volumes for each of our search fields, we derive luminosity functions for galaxies at z ~ 7 and z ~ 8 to <-18 AB mag. The faint-end slopes α at z ~ 7 and z ~ 8 are uncertain but very steep at α = -2.01 ± 0.21 and α = -1.91 ± 0.32, respectively. Such steep slopes contrast to the local α ≳ - 1.4 and may even be steeper than that at z ~ ~ 4 where α = -1.73 ± 0.05. With such steep slopes (α ≲ - 1.7) lower luminosity galaxies dominate the galaxy luminosity density during the epoch of reionization. The SFR densities derived from these new z ~ 7 and z ~ 8 luminosity functions are consistent with the trends found at later times (lower redshifts). We find reasonable consistency with the SFR densities implied from reported stellar mass densities being only ~40% higher at z < 7. This suggests that (1) the stellar mass densities inferred from the Spitzer Infrared Array Camera (IRAC) photometry are reasonably accurate and (2) that the initial mass function at very high redshift may not be very different from that at later times. [ABSTRACT FROM AUTHOR]

Searches for very-high-redshift galaxies over the past decade have yielded a large sample of more than 6,000 galaxies existing just 900-2,000 million years (Myr) after the Big Bang (redshifts 6 > z > 3; ref. 1). The Hubble Ultra Deep Field (HUDF09) data have yielded the first reliable detections of z ≈ 8 galaxies that, together with reports of a γ-ray burst at z ≈ 8.2 (refs 10, 11), constitute the earliest objects reliably reported to date. Observations of z ≈ 7-8 galaxies suggest substantial star formation at z > 9-10 (refs 12, 13). Here we use the full two-year HUDF09 data to conduct an ultra-deep search for z ≈ 10 galaxies in the heart of the reionization epoch, only 500 Myr after the Big Bang. Not only do we find one possible z ≈ 10 galaxy candidate, but we show that, regardless of source detections, the star formation rate density is much smaller (∼10%) at this time than it is just ∼200 Myr later at z ≈ 8. This demonstrates how rapid galaxy build-up was at z ≈ 10, as galaxies increased in both luminosity density and volume density from z ≈ 10 to z ≈ 8. The 100-200 Myr before z ≈ 10 is clearly a crucial phase in the assembly of the earliest galaxies. [ABSTRACT FROM AUTHOR]

We measure the UV-continuum slope β for over 4000 high-redshift galaxies over a wide range of redshifts z ∼ 4-8 and luminosities from the HST HUDF/XDF, HUDF09-1, HUDF09-2, ERS, CANDELS-N, and CANDELS-S data sets. Our new β results reach very faint levels at z ∼ 4 (–15.5 mag: ), z ∼ 5 (–16.5 mag: ), and z ∼ 6 and z ∼ 7 (–17 mag: ). Inconsistencies between previous studies led us to conduct a comprehensive review of systematic errors and develop a new technique for measuring β that is robust against biases that arise from the impact of noise. We demonstrate, by object-by-object comparisons, that all previous studies, including our own and those done on the latest HUDF12 data set, suffered from small systematic errors in β. We find that after correcting for the systematic errors (typically Δβ ∼ 0.1-0.2) all β results at z ∼ 7 from different groups are in excellent agreement. The mean β we measure for faint (–18 mag: ) z ∼ 4, z ∼ 5, z ∼ 6, and z ∼ 7 galaxies is –2.03 ± 0.03 ± 0.06 (random and systematic errors), –2.14 ± 0.06 ± 0.06, –2.24 ± 0.11 ± 0.08, and –2.30 ± 0.18 ± 0.13, respectively. Our new β values are redder than we have reported in the past, but bluer than other recent results. Our previously reported trend of bluer β's at lower luminosities is confirmed, as is the evolution to bluer β's at high redshifts. β appears to show only a mild luminosity dependence faintward of MUV, AB ∼ –19 mag, suggesting that the mean β asymptotes to ∼–2.2 to –2.4 for faint z ⩾ 4 galaxies. At z ∼ 7, the observed β's suggest non-zero, but low dust extinction, and they agree well with values predicted in cosmological hydrodynamical simulations. [ABSTRACT FROM AUTHOR]

Lyman-break galaxy (LBG) samples observed during reionization (z ≳ 6) with the Hubble Space Telescope's Wide Field Camera 3 are reaching sizes sufficient to characterize their clustering properties. Using a combined catalog from the Hubble eXtreme Deep Field and CANDELS surveys, containing N = 743 LBG candidates at z ⩾ 6.5 at a mean redshift of , we detect a clear clustering signal in the angular correlation function (ACF) at ≳ 4σ, corresponding to a real-space correlation length cMpc. The derived galaxy bias is that of dark matter halos of at z = 7.2, and highlights that galaxies below the current detection limit (MAB ∼ –17.7) are expected in lower-mass halos (M ∼ 108-1010.5 ). We compute the ACF of LBGs at z ∼ 3.8 – z ∼ 5.9 in the same surveys. A trend of increasing bias is found from (b ∼ 3.0) to (b ∼ 8.6), broadly consistent with galaxies at fixed luminosity being hosted in dark matter halos of similar mass at 4 ≲ z ≲ 6, followed by a slight rise in halo masses at z ≳ 7 (∼2σ confidence). Separating the data at the median luminosity of the sample (MUV = –19.4) shows higher clustering at for bright galaxies (cMpc, ) compared to faint galaxies (cMpc, ) implying a constant mass-to-light ratio . A similar trend is present in the sample with larger uncertainty. Finally, our bias measurements allow us to investigate the fraction of dark matter halos hosting UV-bright galaxies (the duty cycle, εDC). At values near unity are preferred, which may be explained by the shortened halo assembly time at high redshift. [ABSTRACT FROM AUTHOR]

Growing observational evidence indicates that nebular line emission has a significant impact on the rest-frame optical fluxes of z ∼ 5-7 galaxies. This line emission makes z ∼ 5-7 galaxies appear more massive, with lower specific star-formation rates (sSFRs). However, corrections for this line emission have been difficult to perform reliably because of huge uncertainties on the strength of such emission at z ≳ 5.5. In this paper, we present the most direct observational evidence thus far for ubiquitous high-equivalent-width (EW) [O III] + Hβ line emission in Lyman-break galaxies at z ∼ 7, and we present a strategy for an improved measurement of the sSFR at z ∼ 7. We accomplish this through the selection of bright galaxies in the narrow redshift window z ∼ 6.6-7.0 where the Spitzer/Infrared Array Camera (IRAC) 4.5 μm flux provides a clean measurement of the stellar continuum light, in contrast with the 3.6 μm flux, which is contaminated by the prominent [O III] + Hβ lines. To ensure a high signal-to-noise ratio for our IRAC flux measurements, we consider only the brightest (H160 < 26 mag) magnified galaxies we have identified behind galaxy clusters. It is remarkable that the mean rest-frame optical color for our bright seven-source sample is very blue, [3.6]-[4.5] = –0.9 ± 0.3. Such blue colors cannot be explained by the stellar continuum light and require that the rest-frame EW of [O III] + Hβ is greater than 637 Å for the average source. The four bluest sources from our seven-source sample require an even more extreme EW of 1582 Å. We can also set a robust lower limit of ≳ 4 Gyr–1 on the sSFR of our sample based on the mean spectral energy distribution. [ABSTRACT FROM AUTHOR]

Ultra-deep Advanced Camera for Surveys (ACS) and WFC3/IR HUDF+HUDF09 data, along with the wide-area GOODS+ERS+CANDELS data over the CDF-S GOODS field, are used to measure UV colors, expressed as the UV-continuum slope β, of star-forming galaxies over a wide range of luminosity (0.1L*z = 3 to 2L*z = 3) at high redshift (z ∼ 7 to z ∼ 4). β is measured using all ACS and WFC3/IR passbands uncontaminated by Lyα and spectral breaks. Extensive tests show that our β measurements are only subject to minimal biases. Using a different selection procedure, Dunlop et al. recently found large biases in their β measurements. To reconcile these different results, we simulated both approaches and found that β measurements for faint sources are subject to large biases if the same passbands are used both to select the sources and to measure β. High-redshift galaxies show a well-defined rest-frame UV color-magnitude (CM) relationship that becomes systematically bluer toward fainter UV luminosities. No evolution is seen in the slope of the UV CM relationship in the first 1.5 Gyr, though there is a small evolution in the zero point to redder colors from z ∼ 7 to z ∼ 4. This suggests that galaxies are evolving along a well-defined sequence in the LUV-color (β) plane (a “star-forming sequence”?). Dust appears to be the principal factor driving changes in the UV color β with luminosity. These new larger β samples lead to improved dust extinction estimates at z ∼ 4-7 and confirm that the extinction is essentially zero at low luminosities and high redshifts. Inclusion of the new dust extinction results leads to (1) excellent agreement between the star formation rate (SFR) density at z ∼ 4-8 and that inferred from the stellar mass density; and (2) to higher specific star formation rates (SSFRs) at z ≳ 4, suggesting that the SSFR may evolve modestly (by factors of ∼2) from z ∼ 4-7 to z ∼ 2. [ABSTRACT FROM AUTHOR]