Search

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 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]

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]

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]

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]