Search

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]

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 discovery of four surprisingly bright (H160 ∼ 26-27 mag AB) galaxy candidates at z ∼ 9-10 in the complete HST CANDELS WFC3/IR GOODS-N imaging data, doubling the number of z ∼ 10 galaxy candidates that are known, just ∼500 Myr after the big bang. Two similarly bright sources are also detected in a reanalysis of the GOODS-S data set. Three of the four galaxies in GOODS-N are significantly detected at 4.5σ-6.2σ in the very deep Spitzer/IRAC 4.5 μm data, as is one of the GOODS-S candidates. Furthermore, the brightest of our candidates (at z = 10.2 ± 0.4) is robustly detected also at 3.6 μm (6.9σ), revealing a flat UV spectral energy distribution with a slope β = –2.0 ± 0.2, consistent with demonstrated trends with luminosity at high redshift. Thorough testing and use of grism data excludes known low-redshift contamination at high significance, including single emission-line sources, but as-yet unknown low redshift sources could provide an alternative solution given the surprising luminosity of these candidates. Finding such bright galaxies at z ∼ 9-10 suggests that the luminosity function for luminous galaxies might evolve in a complex way at z > 8. The cosmic star formation rate density still shows, however, an order-of-magnitude increase from z ∼ 10 to z ∼ 8 since the dominant contribution comes from low-luminosity sources. Based on the IRAC detections, we derive galaxy stellar masses at z ∼ 10, finding that these luminous objects are typically 109M☼. This allows for a first estimate of the cosmic stellar mass density at z ∼ 10 resulting in M☼ Mpc–3 for galaxies brighter than MUV ∼ –18. The remarkable brightness, and hence luminosity, of these z ∼ 9-10 candidates will enable deep spectroscopy to determine their redshift and nature, and highlights the opportunity for the James Webb Space Telescope to map the buildup of galaxies at redshifts much earlier than z ∼ 10. [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 search for z ~ 10 galaxies over ~160 arcmin² of Wide-Field Camera 3 (WFC3)/IR data in the Chandra Deep Field South, using the public HUDF09, Early Release Science, and CANDELS surveys, that reach to 5σ depths ranging from 26.9 to 29.4 in H160 AB mag. z ≳ 9.5 galaxy candidates are identified via J125 - H160 > 1.2 colors and non-detections in any band blueward of J125. Spitzer Infrared Array Camera (IRAC) photometry is key for separating the genuine high-z candidates from intermediate-redshift (z ~ 2-4) galaxies with evolved or heavily dust obscured stellar populations. After removing 16 sources of intermediate brightness (H160 ~ 24-26 mag) with strong IRAC detections, we only find one plausible z ~ 10 galaxy candidate in the whole data set, previously reported in Bouwens et al.. The newer data cover a 3x larger area and provide much stronger constraints on the evolution of the UV luminosity function (LF). If the evolution of the z ~ 4-8 LFs is extrapolated to z ~ 10, six z ~ 10 galaxies are expected in our data. The detection of only one source suggests that the UV LF evolves at an accelerated rate before z ~ 8. The luminosity density is found to increase by more than an order of magnitude in only 170 Myr from z ~ 10 to z ~ 8. This increase is ≥4x larger than expected from the lower redshift extrapolation of the UV LF. We are thus likely witnessing the first rapid buildup of galaxies in the heart of cosmic reionization. Future deep Hubble Space Telescope WFC3/IR data, reaching to well beyond 29 mag, can enable a more robust quantification of the accelerated evolution around z ~ 10. [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 present the census of H  |$\beta$|  + [ |${\rm O\, {\small III}}$| ] |$4960,5008\rm{\mathring{\rm\,A}}$| emitters at |$6.8\lt z\lt 9.0$| from the JWST FRESCO survey over 124 arcmin |$^2$| in the GOODS-North and GOODS-South fields. Our unbiased spectroscopic search results in 137 spectroscopically confirmed galaxies at |$6.8\lt z\lt 9.0$| with observed [ |${\rm O\, {\small III}}$| ] fluxes |$f_{\rm { [{\rm O\, {\small III}}]}}\gtrsim 1\times 10^{-18}\ \rm {ergs}\ \rm {s}^{-1} \ \rm {cm}^{-2}$|⁠. The rest-frame optical line ratios of the median stacked spectrum (median |$M_{\rm {UV}}=-19.65^{+0.59}_{-1.05}$|⁠) indicate negligible dust attenuation, low metallicity (⁠|$12+\log (\rm {O/H})= 7.2-7.7$|⁠) and a high ionization parameter |$\log _{10}U \simeq -2.5$|⁠. We find a factor |$\times 1.3$| difference in the number density of |$6.8\lt z\lt 9.0$| galaxies between GOODS-South and GOODS-North, which is caused by a single overdensity at |$7.0\lt z\lt 7.2$| in GOODS-North. The bright end of the UV luminosity function of spectroscopically confirmed [ |${\rm O\, {\small III}}$| ] emitters is in good agreement with HST dropout-selected samples. Discrepancies between the observed [ |${\rm O\, {\small III}}$| ] LF, [ |${\rm O\, {\small III}}$| ]/UV ratio, and [ |${\rm O\, {\small III}}$| ] equivalent widths, and that predicted by theoretical models, suggest burstier star-formation histories and/or more heterogeneous metallicity and ionizing conditions in |$z\gt 7$| galaxies. We report a rapid decline of the [ |${\rm O\, {\small III}}$| ] luminosity density at |$z\gtrsim 6\!-\!7$| which cannot be explained by the evolution of the cosmic star-formation rate density. Finally we find that FRESCO detects in only 2h galaxies likely accounting for |$\sim 10-20{{\ \rm per\ cent}}$| of the ionizing budget at |$z=7\!-\!8$| (assuming an escape fraction of |$10{{\ \rm per\ cent}}$|⁠), raising the prospect of directly detecting a significant fraction of the sources of reionization with JWST. [ABSTRACT FROM AUTHOR]

We present the JWST cycle 1 53.8 h medium program FRESCO, short for 'First Reionization Epoch Spectroscopically Complete Observations'. FRESCO covers 62 arcmin2 in each of the two GOODS/CANDELS fields for a total area of 124 arcmin2 exploiting JWST 's powerful new grism spectroscopic capabilities at near-infrared wavelengths. By obtaining ∼2 h deep NIRCam/grism observations with the F 444 W filter, FRESCO yields unprecedented spectra at R ∼ 1600 covering 3.8–5.0 µm for most galaxies in the NIRCam field of view. This setup enables emission line measurements over most of cosmic history, from strong PAH lines at z ∼ 0.2–0.5, to Pa α and Pa β at z ∼ 1–3, He  i and [S  iii ] at z ∼ 2.5–4.5, H α and [N  ii ] at z ∼ 5–6.5, up to [O  iii ] and H β for z ∼ 7–9 galaxies. FRESCO's grism observations provide total line fluxes for accurately estimating galaxy stellar masses and calibrating slit-loss corrections of NIRSpec/MSA spectra in the same field. Additionally, FRESCO results in a mosaic of F 182 M, F 210 M , and F 444 W imaging in the same fields to a depth of ∼28.2 mag (5σ in 0 |${_{.}^{\prime\prime}}$| 32 diameter apertures). Here, we describe the overall survey design and the key science goals that can be addressed with FRESCO. We also highlight several, early science results, including: spectroscopic redshifts of Lyman break galaxies that were identified almost 20 yr ago, the discovery of broad-line active galactic nuclei at z > 4, and resolved Pa α maps of galaxies at z ∼ 1.4. These results demonstrate the enormous power for serendipitous discovery of NIRCam/grism observations. [ABSTRACT FROM AUTHOR]

We utilize a two-color Lyman-break selection criterion to search for z ∼ 9-10 galaxies over the first 19 clusters in the CLASH program. A systematic search yields three z ∼ 9-10 candidates. While we have already reported the most robust of these candidates, MACS1149-JD, two additional z ∼ 9 candidates are also found and have H160-band magnitudes of ∼26.2-26.9. A careful assessment of various sources of contamination suggests ≲1 contaminants for our z ∼ 9-10 selection. To determine the implications of these search results for the luminosity function (LF) and star formation rate density at z ∼ 9, we introduce a new differential approach to deriving these quantities in lensing fields. Our procedure is to derive the evolution by comparing the number of z ∼ 9-10 galaxy candidates found in CLASH with the number of galaxies in a slightly lower-redshift sample (after correcting for the differences in selection volumes), here taken to be z ∼ 8. This procedure takes advantage of the fact that the relative volumes available for the z ∼ 8 and z ∼ 9-10 selections behind lensing clusters are not greatly dependent on the details of the lensing models. We find that the normalization of the UV LF at z ∼ 9 is just that at z ∼ 8, which is ∼1.4× lower than extrapolating z ∼ 4-8 LF results. While consistent with the evolution in the UV LF seen at z ∼ 4-8, these results marginally favor a more rapid evolution at z > 8. Compared to similar evolutionary findings from the HUDF, our result is less insensitive to large-scale structure uncertainties, given our many independent sightlines on the high-redshift universe. [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]

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]

We present Atacama Large Millimeter/Submillimeter Array (ALMA) [C  ii ] and ∼158 |$\rm \mu m$| continuum observations of REBELS-25, a massive, morphologically complex ultra-luminous infrared galaxy (ULIRG; L IR = |$1.5^{+0.8}_{-0.5} \times 10^{12}$| L⊙) at z  = 7.31, spectroscopically confirmed by the Reionization Era Bright Emission Line Survey (REBELS) ALMA Large Programme. REBELS-25 has a significant stellar mass of |$M_{*} = \mbox{$ 8^{+4}_{-2} \times 10^{9} $}{} ~\mbox{M$_\odot $}{}$|⁠. From dust-continuum and ultraviolet observations, we determine a total obscured + unobscured star formation rate of SFR |$= \mbox{$199^{+101}_{-63}$}{} ~ \mbox{M$_\odot $}~ \mbox{${\rm yr}$}^{-1}$|⁠. This is about four times the SFR estimated from an extrapolated main sequence. We also infer a [C  ii ]-based molecular gas mass of |$M_{{\rm H}_{2}} = \mbox{$5.1^{+5.1}_{-2.6} \times 10^{10}$}{} ~\mbox{M$_\odot $}{}$|⁠ , implying a molecular gas depletion time of |$t_{\rm depl, {\rm H}_{2}} = \mbox{$0.3^{+0.3}_{-0.2} $}{}$| Gyr. We observe a [C  ii ] velocity gradient consistent with disc rotation, but given the current resolution we cannot rule out a more complex velocity structure such as a merger. The spectrum exhibits excess [C  ii ] emission at large positive velocities (∼500 km s−1), which we interpret as either a merging companion or an outflow. In the outflow scenario, we derive a lower limit of the mass outflow rate of 200 |$\mbox{M$_\odot $}~ \mbox{${\rm yr}$}^{-1}$|⁠ , which is consistent with expectations for a star-formation-driven outflow. Given its large stellar mass, SFR, and molecular gas reservoir ∼700 Myr after the big bang, we explore the future evolution of REBELS-25. Considering a simple, conservative model assuming an exponentially declining star formation history, constant star formation efficiency, and no additional gas inflow, we find that REBELS-25 has the potential to evolve into a galaxy consistent with the properties of high-mass quiescent galaxies recently observed at z ∼ 4. [ABSTRACT FROM AUTHOR]

We present new z ∼ 8 galaxy candidates from a search over ∼95 arcmin2 of WFC3/IR data, tripling the previous search area for bright z ∼ 8 galaxies. Our analysis uses newly acquired WFC3/IR imaging data from the CANDELS Multi-Cycle Treasury program over the GOODS-South field. These new data are combined with existing deep optical Advanced Camera for Surveys (ACS) imaging to search for relatively bright (MUV < –19.5 mag) z ∼ 8 galaxy candidates using the Lyman break technique. These new candidates are used to determine the bright end of the UV luminosity function (LF) of star-forming galaxies at z ∼ 7.2-8.7, i.e., a cosmic age of 600 ± 80 Myr. To minimize contamination from lower redshift galaxies, we make full use of all optical ACS data and impose strict non-detection criteria based on an optical χ2opt flux measurement. In the whole search area, we identify 16 candidate z ∼ 8 galaxies, spanning a magnitude range H160, AB = 25.7-27.9 mag. The new data show that the UV LF is a factor ∼1.7 lower at MUV < –19.5 mag than determined from the HUDF09 and Early Release Science (ERS) data alone. Combining this new sample with the previous candidates from the HUDF09 and ERS data allows us to perform the most accurate measurement of the z ∼ 8 UV LF yet. Schechter function fits to the combined data result in a best-fit characteristic magnitude of M*(z = 8) = –20.04 ± 0.46 mag. The faint-end slope is very steep, though quite uncertain, with α = –2.06 ± 0.32. A combination of wide-area data with additional ultra-deep imaging will be required to significantly reduce the uncertainties on these parameters in the future. [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]

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]

ALMA observations have revealed the presence of dust in the first generations of galaxies in the Universe. However, the dust temperature T d remains mostly unconstrained due to the few available FIR continuum data at redshift |$z$| > 5. This introduces large uncertainties in several properties of high- |$z$| galaxies, namely their dust masses, infrared luminosities, and obscured fraction of star formation. Using a new method based on simultaneous [C  |$\scriptstyle \rm II$| ] 158-μm line and underlying dust continuum measurements, we derive T d in the continuum and [C  |$\scriptstyle \rm II$| ] detected |$z$| ≈ 7 galaxies in the ALMA Large Project REBELS sample. We find 39 < T d < 58 K, and dust masses in the narrow range M d = (0.9−3.6) × 107 M⊙. These results allow us to extend for the first time the reported T d(⁠|$z$|⁠) relation into the Epoch of Reionization. We produce a new physical model that explains the increasing T d(⁠|$z$|⁠) trend with the decrease of gas depletion time, t dep = M g/SFR, induced by the higher cosmological accretion rate at early times; this hypothesis yields T d ∝ (1 + |$z$|⁠)0.4. The model also explains the observed T d scatter at a fixed redshift. We find that dust is warmer in obscured sources, as a larger obscuration results in more efficient dust heating. For UV-transparent (obscured) galaxies, T d only depends on the gas column density (metallicity), |$T_{\rm d} \propto N_{\rm H}^{1/6}$| (T d ∝  Z −1/6). REBELS galaxies are on average relatively transparent, with effective gas column densities around N H ≃ (0.03−1) × 1021 cm−2. We predict that other high- |$z$| galaxies (e.g. MACS0416-Y1, A2744-YD4), with estimated T d ≫ 60 K, are significantly obscured, low-metallicity systems. In fact, T d is higher in metal-poor systems due to their smaller dust content, which for fixed L IR results in warmer temperatures. [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]

We present a study of rest-frame UV-to-optical color distributions for z ~ 4 galaxies based on the combination of deep HST/ACS+WFC3/IR data with Spitzer/IRAC imaging. In particular, we use new, ultra-deep data from the IRAC Ultradeep Field program (IUDF10), together with previous, public IRAC data over the GOODS fields. Our sample contains a total of ~2600 galaxies selected as B-dropout Lyman-break Galaxies in the HUDF and its deep parallel field HUDF09-2, as well as GOODS-North/South. This sample is used to investigate the UV continuum slopes β and Balmer break colors (J125 - [4.5]) as a function of rest-frame optical luminosity (using [4.5] to avoid optical emission lines). We find that galaxies at Mz < -21.5 (roughly corresponding to Lz~4*) are significantly redder than their lower luminosity counterparts. The UV continuum slopes and the J125 - [4.5] colors are well correlated, indicating that the dust reddening at these redshifts is better described by an SMC-like extinction curve, rather than the typically assumed Calzetti reddening. After dust correction, we find that the galaxy population shows mean stellar population ages in the range 108.5 to 109 yr, with a dispersion of ~0.5 dex, and only weak trends as a function of luminosity. Only a small fraction of galaxies shows Balmer break colors consistent with extremely young ages, younger than 100 Myr. Under the assumption of smooth star-formation histories, this fraction is 12%-19% for galaxies at Mz < -19.75. Our results are consistent with a gradual build-up of stars and dust in galaxies at z > 4 with only a small fraction of stars being formed in short, intense bursts of star-formation. [ABSTRACT FROM AUTHOR]

The ALMA Frontier Fields Survey: IV. Lensing-corrected 1.1 mm number counts in Abell 2744, MACS J0416.1-2403, and MACS J1149.5+2223 (Corrigendum) Gravitational lensing: strong, galaxies: high-redshift, submillimeter: galaxies, errata, addenda. [Extracted from the article]

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 investigate the clustering of Lyman-break galaxies (LBGs) at z ~ 4. Using the hierarchical galaxy formation model GALFORM, we predict, for the first time using a semi-analytical model with feedback from active galactic nuclei (AGN), the angular correlation function (ACF) of LBGs and find agreement within 3s with new measurements of the ACF from surveys including the Hubble eXtreme Deep Field (XDF) and Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. Our simulations confirm the conclusion reached using independent models that although the predicted ACFs reproduce the trend of increased clustering with luminosity, the dependence is less strong than observed. We find that for the detection limits of the XDF field, central LBGs at z ~ 4 predominantly reside in haloes of mass ~1011-1012 h-1 M⊙ and that satellites reside in larger haloes of mass ~1012-1013 h-1 M⊙. The model predicts fewer bright satellite LBGs at z ~ 4 than is inferred from measurements of the ACF at small scales. By analysing the halo occupation distribution (HOD) predicted by the model, we find evidence that AGN feedback affects the HOD of central LBGs in massive haloes. This is a new high-redshift test of this important feedback mechanism. We investigate the effect of photometric errors in the observations on the ACF predictions. We find that the observational uncertainty in the galaxy luminosity reduces the clustering amplitude and that this effect increases towards faint galaxies, particularly on small scales. To compare properties of model with observed LBGs, this uncertainty must be considered. [ABSTRACT FROM AUTHOR]

We have identified 274 M-type brown dwarfs in the Hubble Space Telescope's Wide Field Camera 3 pure parallel fields from the Brightest of Reionizing Galaxies (BoRG) survey for high-redshift galaxies. These are near-infrared observations with multiple lines of sight out of our Milky Way. Using these observed M-type brown dwarfs, we fitted a Galactic disc and halo model with a Markov chain Monte Carlo analysis. This modelworked best with the scalelength of the disc fixed at h = 2.6 kpc. For the scaleheight of the disc, we found z0 = 0.29+0.02-0.019 kpc and for the central number density, ρ0 = 0.29+0.20-0.13 # pc-3. For the halo, we derived a flattening parameter κ = 0.45 ± 0.04 and a power-law index p = 2.4 ± 0.07. We found the fraction of M-type brown dwarfs in the local density that belong to the halo to be fh = 0.0075+0.0025-0.0019. We found no correlation between subtype of M-dwarf and any model parameters. The total number of M-type brown dwarfs in the disc and halo was determined to be 58.2+9.81-6.70 × 109. We found an upper limit for the fraction of M-type brown dwarfs in the halo of 7+5-4 per cent. The upper limit for the total Galactic disc mass in M-dwarfs is 4.34+0.73-0.5 × 109 M⊙, assuming all M-type brown dwarfs have a mass of 80 MJ. [ABSTRACT FROM AUTHOR]

Theoretical and numerical modeling of the assembly of dark-matter halos predicts that the most massive and luminous galaxies at high redshift are surrounded by overdensities of fainter companions. We test this prediction with Hubble Space Telescope observations acquired by our Brightest-of-Reionizing Galaxies (BoRG) survey, which identified four very bright z ~ 8 candidates as Y098-dropout sources in four of the 23 non-contiguous Wide Field Camera 3 fields observed. We extend here the search for Y098-dropouts to fainter luminosities (M* galaxies with MAB ~ -20), with detections at ≥5σ confidence (compared to the 8σ confidence threshold adopted earlier) identifying 17 new candidates. We demonstrate that there is a correlation between number counts of faint and bright Y098-dropouts at ≥99.84% confidence. Field BoRG58, which contains the best bright z ~ 8 candidate (MAB = -21.3), has the most significant overdensity of faint Y098-dropouts. Four new sources are located within 70" (corresponding to 3.1 comoving Mpc at z = 8) from the previously known brighter z ~ 8 candidate. The overdensity of Y098-dropouts in this field has a physical origin to very high confidence (p > 99.975%), independent of completeness and contamination rate of the Y098-dropout selection. We modeled the overdensity by means of cosmological simulations and estimate that the principal dark-matter halo has mass Mh ≈ (4-7) x 1011 M⊙ (~5σ density peak) and is surrounded by several Mh ≈ 1011 M⊙ halos which could host the fainter dropouts. In this scenario, we predict that all halos will eventually merge into a Mh > 2 x 1014 M⊙ galaxy cluster by z = 0. Follow-up observations with ground- and space-based telescopes are required to secure the z ~ 8 nature of the overdensity, discover new members, and measure their precise redshift. [ABSTRACT FROM AUTHOR]

We use the high angular resolution in the near-infrared of the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope to determine YHVz color-color-selection criteria to identify and characterize 1.5 < z < 3.5 galaxies in the Hubble Ultra Deep Field 2009 (HUDF09) and Early Release Science (GOODS-South) fields. The WFC3 NIR images reveal galaxies at these redshifts that were undetected in the rest-frame UV HUDF/GOODS images, as well as true centers and regular disks in galaxies classified as highly irregular in rest-frame UV light. Across the 1.5 < z < 2.15 redshift range, regular disks are unveiled in the WFC3 images of ~25% of both intermediate and high mass galaxies, i.e., above 1010 M⊙ Meanwhile, galaxies maintaining diffuse and/or irregular morphologies in the rest-frame optical light--i.e., not yet dynamically settled--at these epochs are almost entirely restricted to masses below 1011 M⊙. In contrast at 2.25 < z < 3.5 these diffuse and/or irregular structures overwhelmingly dominate the morphological mix in both the intermediate and high mass regimes, while no regular disks, and only a small fraction (~25%) of smooth spheroids, are evident above 1011 M⊙. Strikingly, by 1.5 < z < 2.25 roughly two out of every three galaxies at the highest masses are spheroids. In our small sample, the fraction of star-forming galaxies at these mass scales decreases concurrently from ~60% to ~5%. If confirmed, this indicates that z ~ 2 is the epoch of both the morphological transformation and quenching of star formation which assemble the first substantial population of massive ellipticals. [ABSTRACT FROM AUTHOR]

ABSTRACT We present the details and early results from a deep near-infrared survey utilizing the NICMOS instrument on the Hubble Space Telescope centred around massive M* > 1011 M ⊙ galaxies at 1.7 < z < 2.9 found within the Great Observatories Origins Deep Survey (GOODS) fields North and South. The GOODS NICMOS Survey (GNS) was designed to obtain deep F160W ( H-band) imaging of 80 of these massive galaxies and other colour-selected objects such as Lyman-break dropouts, BzK objects, distant red galaxies (DRGs), extremely red objects (EROs), Spitzer-selected EROs, BX/BM galaxies, as well as flux-selected submillimetre galaxies. We present in this paper details of the observations, our sample selection, as well as a description of the properties of the massive galaxies found within our survey fields. This includes photometric redshifts, rest-frame colours and stellar masses. We furthermore provide an analysis of the selection methods for finding massive galaxies at high redshifts, including colour-selection methods and how galaxy populations selected through these colour methods overlap. We find that a single colour selection method cannot locate all of the massive galaxies, with no one method finding more than 70 per cent. We however find that the combination of these colour methods finds nearly all of the massive galaxies that would have been identified in a photometric redshift sample, with the exception of apparently rare blue massive galaxies. By investigating the rest-frame ( U− B) versus MB diagram for these galaxies, we furthermore show that there exists a bimodality in colour-magnitude space at z < 2, driven by stellar mass, such that the most massive galaxies are systematically red up to z∼ 2.5, while lower mass galaxies tend to be blue. We also discuss the number densities for galaxies with stellar masses M* > 1011 M ⊙, whereby we find an increase of a factor of 8 between z= 3 and 1.5, demonstrating that this is an epoch when massive galaxies establish most of their stellar mass. We also provide an overview of the evolutionary properties of these galaxies, such as their merger histories, and size evolution. [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]

We report the discovery of 33 Lyman-break galaxy candidates at z ∼ 8 detected in Hubble Space Telescope Wide Field Camera 3 (WFC3) imaging as part of the Brightest of Reionizing Galaxies (BoRG) pure-parallel survey. The ongoing BoRG survey currently has the largest area (274 arcmin2) with Y098 (or Y105), J125, and H160 band coverage needed to search for z ∼ 8 galaxies, about three times the current CANDELS area, and slightly larger than what will be the final CANDELS wide component with Y105 data (required to select z ∼ 8 sources). Our sample of 33 relatively bright Y098-dropout galaxies have J125-band magnitudes between 25.5 and 27.4 mag. This is the largest sample of bright (J125 ≲ 27.4) z ∼ 8 galaxy candidates presented to date. Combining our data set with the Hubble Ultra-Deep Field data set, we constrain the rest-frame ultraviolet galaxy luminosity function at z ∼ 8 over the widest dynamic range currently available. The combined data sets are well fitted by a Schechter function, i.e., , without evidence for an excess of sources at the bright end. At 68% confidence, for h = 0.7 we derive ϕ* = (4.3+3.5–2.1) × 10–4 Mpc–3, M* = –20.26+0.29–0.34, and a very steep faint-end slope α = –1.98+0.23–0.22. While the best-fit parameters still have a strong degeneracy, especially between ϕ* and M*, our improved coverage at the bright end has reduced the uncertainty of the faint-end power-law slope at z ∼ 8 compared to the best previous determination at ±0.4. With a future expansion of the BoRG survey, combined with planned ultradeep WFC3/IR observations, it will be possible to further reduce this uncertainty and clearly demonstrate the steepening of the faint-end slope compared to measurements at lower redshift, thereby confirming the key role played by small galaxies in the reionization of the universe. [ABSTRACT FROM AUTHOR]