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Showing 1-10 of about 10 results.
Spectroscopically Confirmed Lyα Emitters from Redshift 5 to 7 behind 10 Galaxy Cluster LensesFuller, S.Lemaux, B. C.Bradač, M.Hoag, A.Schmidt, K. B.Huang, K.Strait, V.Mason, Charlotte A.Treu, T.Pentericci, L.Trenti, M.Henry, A.Malkan, M.DOI: info:10.3847/1538-4357/ab959fv. 896156
Fuller, S., Lemaux, B. C., Bradač, M., Hoag, A., Schmidt, K. B., Huang, K., Strait, V., Mason, Charlotte A., Treu, T., Pentericci, L., Trenti, M., Henry, A., and Malkan, M. 2020. "Spectroscopically Confirmed Lyα Emitters from Redshift 5 to 7 behind 10 Galaxy Cluster Lenses." The Astrophysical Journal 896:156. https://doi.org/10.3847/1538-4357/ab959f
ID: 157798
Type: article
Authors: Fuller, S.; Lemaux, B. C.; Bradač, M.; Hoag, A.; Schmidt, K. B.; Huang, K.; Strait, V.; Mason, Charlotte A.; Treu, T.; Pentericci, L.; Trenti, M.; Henry, A.; Malkan, M.
Abstract: We present 36 spectroscopically confirmed intrinsically UV-faint Lyα-emitting galaxies from follow-up observations with Keck/DEep Imaging Multi-Object Spectrograph of gravitationally lensed high-redshift candidates. Candidates were selected to be between 5 ≲ z ≲ 7 from photometric data using Hubble Space Telescope and Spitzer imaging surveys. We performed an integrated photometric redshift probability cut >1% between 5 25 Å at 3σ at the fiducial depth of our survey, and only those galaxies with EW(Lyα) > 25 Å, and only objects with mAB < 26.8, we found the Lyα emitter (LAE) fraction to be flat or modestly increase from 0.26 ± 0.04 to 0.30 ± 0.04. These values are consistent with a rising LAE fraction with redshift out to z ∼ 6, but at z ∼ 6.5, there is some tension between our results and results from surveys at intrinsically brighter luminosities. We conclude that intrinsically fainter galaxies have Lyα emission, and there is a steep drop in the LAE fraction from our high-redshift sample at z ∼ 6.5 and from similar galaxies at z ∼ 7.5. This likely indicates we are witnessing the tail end of the epoch of reionization, as such a drop is not expected due to changes of intrinsic galaxy properties between these redshifts.
Measuring the properties of reionized bubbles with resolved Lya spectraMason, Charlotte A.Gronke, MaxDOI: info:10.1093/mnras/staa2910v. 4991395–1405
Mason, Charlotte A. and Gronke, Max. 2020. "Measuring the properties of reionized bubbles with resolved Lya spectra." Monthly Notices of the Royal Astronomical Society 499:1395– 1405. https://doi.org/10.1093/mnras/staa2910
ID: 158755
Type: article
Authors: Mason, Charlotte A.; Gronke, Max
Abstract: Identifying and characterizing reionized bubbles enables us to track both their size distribution, which depends on the primary ionizing sources, and the relationship between reionization and galaxy evolution. We demonstrate that spectrally resolved z ? 6 Lyman-alpha (Lya) emission can constrain properties of reionized regions. Specifically, the distance from a source to a neutral region sets the minimum observable Lya velocity offset from systemic. Detection of flux on the blue side of the Lya resonance implies the source resides in a large, sufficiently ionized region that photons can escape without significant resonant absorption, and thus constrains both the sizes of and the residual neutral fractions within ionized bubbles. We estimate the extent of the region around galaxies which is optically thin to blue Lya photons, analogous to quasar proximity zones, as a function of the source's ionizing photon output and surrounding gas density. This optically thin region is typically ? 0.3-=pMpc in radius (allowing transmission of flux ? -250-=km-=s-1), ? 20 per-=cent of the distance to the neutral region. In a proof-of-concept, we demonstrate the z ? 6.6 galaxy COLA1 - with a blue Lya peak - likely resides in an ionized region >0.7-=pMpc, with residual neutral fraction ), ? 20 per-=cent of the distance to the neutral region. In a proof-of-concept, we demonstrate the z ? 6.6 galaxy COLA1 - with a blue Lya peak - likely resides in an ionized region >0.7-=pMpc, with residual neutral fraction -5.5. To ionize its own proximity zone we infer COLA1 has a high ionizing photon escape fraction (fesc > 0.50), relatively steep UV slope (ß < -1.79), and low line-of-sight gas density (˜0.5 times the cosmic mean), suggesting it is a rare, underdense line-of-sight.
SuperBoRG: Exploration of Point Sources at z ~ 8 in HST Parallel FieldsMorishita, T.Stiavelli, M.Trenti, M.Treu, T.Roberts-Borsani, G. W.Mason, Charlotte A.Hashimoto, T.Bradley, L.Coe, D.Ishikawa, Y.DOI: info:10.3847/1538-4357/abba83v. 90450
Morishita, T., Stiavelli, M., Trenti, M., Treu, T., Roberts-Borsani, G. W., Mason, Charlotte A., Hashimoto, T., Bradley, L., Coe, D., and Ishikawa, Y. 2020. "SuperBoRG: Exploration of Point Sources at z ~ 8 in HST Parallel Fields." The Astrophysical Journal 904:50. https://doi.org/10.3847/1538-4357/abba83
ID: 158857
Type: article
Authors: Morishita, T.; Stiavelli, M.; Trenti, M.; Treu, T.; Roberts-Borsani, G. W.; Mason, Charlotte A.; Hashimoto, T.; Bradley, L.; Coe, D.; Ishikawa, Y.
Abstract: To extend the search for quasars in the epoch of reionization beyond the tip of the luminosity function, we explore point-source candidates at redshift z ~ 8 in SuperBoRG, a compilation of ~0.4 deg2 archival medium-deep (mF160W ~ 26.5 ABmag, 5s) parallel infrared (IR) images taken with the Hubble Space Telescope (HST). Initial candidates are selected by using the Lyman-break technique. We then carefully analyze source morphology, and robustly identify three point sources at z ~ 8. Photometric redshift analysis reveals that they are preferentially fit by extragalactic templates, and we conclude that they are unlikely to be low-z interlopers, including brown dwarfs. A clear IRAC ch2 flux excess is seen in one of the point sources, which is expected if the source has strong Hß+[O III] emission with a rest-frame equivalent width of ~3000 Å. Deep spectroscopic data taken with Keck/MOSFIRE, however, do not reveal Lya emission from the object. In combination with the estimated Hß+[O III] equivalent width, we place an upper limit on its Lya escape fraction of ${f}_{\mathrm{esc},\mathrm{Ly}\alpha }\lesssim 2 \% $ . We estimate the number density of these point sources as ~1 × 10-6 Mpc-3 mag-1 at MUV ~ -23 mag. The final interpretation of our results remains inconclusive: extrapolation from low-z studies of faint quasars suggests that ?100× survey volume may be required to find one of this luminosity. The James Webb Space Telescope will be able to conclusively determine the nature of our luminous point-source candidates, while the Roman Space Telescope will probe ~200 times the area of the sky with the same observing time considered in this HST study. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555 (doi:10.17909/t9-m7tx-qb86).
Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape FractionsNaidu, Rohan P.Tacchella, SandroMason, Charlotte A.Bose, SownakOesch, Pascal A.Conroy, CharlieDOI: info:10.3847/1538-4357/ab7cc9v. 892109
Naidu, Rohan P., Tacchella, Sandro, Mason, Charlotte A., Bose, Sownak, Oesch, Pascal A., and Conroy, Charlie. 2020. "Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions." The Astrophysical Journal 892:109. https://doi.org/10.3847/1538-4357/ab7cc9
ID: 157130
Type: article
Authors: Naidu, Rohan P.; Tacchella, Sandro; Mason, Charlotte A.; Bose, Sownak; Oesch, Pascal A.; Conroy, Charlie
Abstract: The protagonists of the last great phase transition of the universe - cosmic reionization - remain elusive. Faint star-forming galaxies are leading candidates because they are found to be numerous and may have significant ionizing photon escape fractions (fesc). Here we update this picture via an empirical model that successfully predicts latest observations (e.g., the rapid drop in star-formation density (ρSFR at z > 8). We generate an ionizing spectrum for each galaxy in our model and constrain fesc by leveraging latest measurements of the reionization timeline (e.g., Lyα damping of quasars and galaxies at z > 7). Assuming a constant fesc across all sources at z > 6, we find MUV esc = 0.21-0.04+0.06 to complete reionization. The inferred Intergalactic Medium neutral fraction is [0.9, 0.5, 0.1] at z=[8.2,6.8,6.2] ± 0.2 - that is, the bulk of reionization transpires rapidly in 300 Myr, driven by the z > 8 ρSFR and favored by high neutral fractions (∼60%-90%) measured at z ∼ 7-8. Inspired by the emergent sample of Lyman Continuum (LyC) leakers spanning z ∼ 0-6.6 that overwhelmingly displays higher- than-average star-formation surface density (ΣSFR), we propose a physically motivated model relating fesc to ΣSFR and find fesc ∝ ΣSFR0.4±0.1. Since ΣSFR falls by ∼2.5 dex between z = 8 and z = 0, our model explains the humble upper limits on fesc at lower redshifts and its required evolution to fesc ∼ 0.2 at z > 6. Within this model, strikingly, ∼ 0.2 at z > 6. Within this model, strikingly, UV /M) > 8 (the "oligarchs") account for ≳80% of the reionization budget - a stark departure from the canonical "democratic" reionization led by copious faint sources. In fact, faint sources (MUV > -16) must be relegated to a limited role in order to ensure high neutral fractions at z = 7-8. Shallow faint-end slopes of the UV luminosity function (αUV > -2) and/or fesc distributions skewed toward massive galaxies produce the required late and rapid reionization. We predict that LyC leakers like COLA1 (z = 6.6, fesc ∼ 30%, MUV = -21.5) will become increasingly common toward z ∼ 6 and that the drivers of reionization do not lie hidden across the faint end of the luminosity function but are already known to us.
Hubble Frontier Field photometric catalogues of Abell 370 and RXC J2248.7-4431: multiwavelength photometry, photometric redshifts, and stellar propertiesBradač, MarušaHuang, Kuang-HanFontana, AdrianoCastellano, MarcoMerlin, EmilianoAmorín, RicardoHoag, AustinStrait, VictoriaSantini, PaolaRyan, Russell E.Casertano, StefanoLemaux, Brian C.Lubin, Lori M.Schmidt, Kasper B.Schrabback, TimTreu, Tommasovon der Linden, AnjaMason, Charlotte A.Wang, XinDOI: info:10.1093/mnras/stz2119v. 48999–107
Bradač, Maruša, Huang, Kuang-Han, Fontana, Adriano, Castellano, Marco, Merlin, Emiliano, Amorín, Ricardo, Hoag, Austin, Strait, Victoria, Santini, Paola, Ryan, Russell E., Casertano, Stefano, Lemaux, Brian C., Lubin, Lori M., Schmidt, Kasper B., Schrabback, Tim, Treu, Tommaso, von der Linden, Anja, Mason, Charlotte A., and Wang, Xin. 2019. "Hubble Frontier Field photometric catalogues of Abell 370 and RXC J2248.7-4431: multiwavelength photometry, photometric redshifts, and stellar properties." Monthly Notices of the Royal Astronomical Society 489:99– 107. https://doi.org/10.1093/mnras/stz2119
ID: 154645
Type: article
Authors: Bradač, Maruša; Huang, Kuang-Han; Fontana, Adriano; Castellano, Marco; Merlin, Emiliano; Amorín, Ricardo; Hoag, Austin; Strait, Victoria; Santini, Paola; Ryan, Russell E.; Casertano, Stefano; Lemaux, Brian C.; Lubin, Lori M.; Schmidt, Kasper B.; Schrabback, Tim; Treu, Tommaso; von der Linden, Anja; Mason, Charlotte A.; Wang, Xin
Abstract: This paper presents multiwavelength photometric catalogues of the last two Hubble Frontier Fields (HFFs), the massive galaxy clusters Abell 370 and RXC J2248.7-4431. The photometry ranges from imaging performed on the Hubble Space Telescope to ground-based Very Large Telescope and Spitzer/Infrared Array Camera, in collaboration with the ASTRODEEP team, and using the ASTRODEEP pipeline. While the main purpose of this paper is to release the catalogues, we also perform, as a proof of concept, a brief analysis of z > 6 objects selected using dropout method, as well as spectroscopically confirmed sources and multiple images in both clusters. While dropout methods yield a sample of high-z galaxies, the addition of longer wavelength data reveals that as expected the samples have substantial contamination at the ̃30-45 per cent level by dusty galaxies at lower redshifts. Furthermore, we show that spectroscopic redshifts are still required to unambiguously determine redshifts of multiply imaged systems. Finally, the now publicly available ASTRODEEP catalogues were combined for all HFFs and used to explore stellar properties of a large sample of 20 000 galaxies across a large photometric redshift range. The powerful magnification provided by the HFF clusters allows for an exploration of the properties of galaxies with intrinsic stellar masses as low as M* ≳ 107 M and intrinsic star formation rates ̃0.1-1 M yr-1 at z > 6.
Constraining the Neutral Fraction of Hydrogen in the IGM at Redshift 7.5Hoag, A.Bradač, M.Huang, K.Mason, Charlotte A.Treu, T.Schmidt, K. B.Trenti, M.Strait, V.Lemaux, B. C.Finney, E. Q.Paddock, M.DOI: info:10.3847/1538-4357/ab1de7v. 87812
Hoag, A., Bradač, M., Huang, K., Mason, Charlotte A., Treu, T., Schmidt, K. B., Trenti, M., Strait, V., Lemaux, B. C., Finney, E. Q., and Paddock, M. 2019. "Constraining the Neutral Fraction of Hydrogen in the IGM at Redshift 7.5." The Astrophysical Journal 878:12. https://doi.org/10.3847/1538-4357/ab1de7
ID: 152915
Type: article
Authors: Hoag, A.; Bradač, M.; Huang, K.; Mason, Charlotte A.; Treu, T.; Schmidt, K. B.; Trenti, M.; Strait, V.; Lemaux, B. C.; Finney, E. Q.; Paddock, M.
Abstract: We present a large spectroscopic campaign with Keck/Multi-Object Spectrometer for InfraRed Exploration (MOSFIRE) targeting Lyα emission (Lyα) from intrinsically faint Lyman-break galaxies (LBGs) behind 12 efficient galaxy cluster lenses. Gravitational lensing allows us to probe the more abundant faint galaxy population to sensitive Lyα equivalent-width limits. During the campaign, we targeted 70 LBG candidates with the MOSFIRE Y band, selected photometrically to cover Lyα over the range 7 5 emission lines in two of these galaxies and find that they are likely Lyα at z = 7.148 ± 0.001 and z = 7.161 ± 0.001. We present new lens models for four of the galaxy clusters, using our previously published lens models for the remaining clusters to determine the magnification factors for the source galaxies. Using a Bayesian framework that employs large-scale reionization simulations of the intergalactic medium (IGM) as well as realistic properties of the interstellar medium and circumgalactic medium, we infer the volume-averaged neutral hydrogen fraction, {\overline{x}}{{H}{{I}}}, in the IGM during reionization to be {\overline{x}}{{H}{{I}}}={0.88}-0.10+0.05 at z = 7.6 ± 0.6. Our result is consistent with a late and rapid reionization scenario inferred by Planck.
Constraining Lyman-alpha spatial offsets at 3 < z < 5.5 from VANDELS slit spectroscopyHoag, A.Treu, T.Pentericci, L.Amorin, R.Bolzonella, M.Bradač, M.Castellano, M.Cullen, F.Fynbo, J. P. U.Garilli, B.Guaita, L.Hathi, N.Henry, A.Jones, T.Mason, Charlotte A.McLeod, D.McLure, R.Morishita, T.Pozzetti, L.Schaerer, D.Schmidt, K. B.Talia, M.Thomas, R.DOI: info:10.1093/mnras/stz1768v. 488706–719
Hoag, A., Treu, T., Pentericci, L., Amorin, R., Bolzonella, M., Bradač, M., Castellano, M., Cullen, F., Fynbo, J. P. U., Garilli, B., Guaita, L., Hathi, N., Henry, A., Jones, T., Mason, Charlotte A., McLeod, D., McLure, R., Morishita, T., Pozzetti, L., Schaerer, D., Schmidt, K. B., Talia, M., and Thomas, R. 2019. "Constraining Lyman-alpha spatial offsets at 3 < z < 5.5 from VANDELS slit spectroscopy." Monthly Notices of the Royal Astronomical Society 488:706– 719. https://doi.org/10.1093/mnras/stz1768
ID: 154392
Type: article
Authors: Hoag, A.; Treu, T.; Pentericci, L.; Amorin, R.; Bolzonella, M.; Bradač, M.; Castellano, M.; Cullen, F.; Fynbo, J. P. U.; Garilli, B.; Guaita, L.; Hathi, N.; Henry, A.; Jones, T.; Mason, Charlotte A.; McLeod, D.; McLure, R.; Morishita, T.; Pozzetti, L.; Schaerer, D.; Schmidt, K. B.; Talia, M.; Thomas, R.
Abstract: We constrain the distribution of spatially offset Lyman-alpha emission (Ly α) relative to rest-frame ultraviolet emission in ̃300 high redshift (3 2 total). Because slit spectroscopy only provides one spatial dimension, we use Bayesian inference to recover the underlying two-dimensional Ly α spatial offset distribution. We model the distribution using a two- dimensional circular Gaussian, defined by a single parameter σr,Ly α, the standard deviation expressed in polar coordinates. Over the entire redshift range of our sample (3 , the standard deviation expressed in polar coordinates. Over the entire redshift range of our sample (3 , the standard deviation expressed in polar coordinates. Over the entire redshift range of our sample (3 .}25 at = 4.5. We also find that σr,Ly α decreases significantly with redshift. Because Ly α spatial offsets can cause slit losses, the decrease in σr,Ly α with redshift can partially explain the increase in the fraction of Ly α emitters observed in the literature over this same interval, although uncertainties are still too large to reach a strong conclusion. If σr,Ly α continues to decrease into the reionization epoch, then the decrease in Ly α transmission from galaxies observed during this epoch might require an even higher neutral hydrogen fraction than what is currently inferred. Conversely, if spatial offsets increase with the increasing opacity of the intergalactic medium, slit losses may explain some of the drop in Ly α transmission observed at z > 6. Spatially resolved observations of Ly α and UV continuum at 6 < z < 8 are needed to settle the issue.
Inferences on the timeline of reionization at z ˜ 8 from the KMOS Lens-Amplified Spectroscopic SurveyMason, Charlotte A.Fontana, AdrianoTreu, TommasoSchmidt, Kasper B.Hoag, AustinAbramson, LouisAmorin, RicardoBradač, MarušaGuaita, LuciaJones, TuckerHenry, AlainaMalkan, Matthew A.Pentericci, LauraTrenti, MicheleVanzella, ErosDOI: info:10.1093/mnras/stz632v. 4853947–3969
Mason, Charlotte A., Fontana, Adriano, Treu, Tommaso, Schmidt, Kasper B., Hoag, Austin, Abramson, Louis, Amorin, Ricardo, Bradač, Maruša, Guaita, Lucia, Jones, Tucker, Henry, Alaina, Malkan, Matthew A., Pentericci, Laura, Trenti, Michele, and Vanzella, Eros. 2019. "Inferences on the timeline of reionization at z ˜ 8 from the KMOS Lens-Amplified Spectroscopic Survey." Monthly Notices of the Royal Astronomical Society 485:3947– 3969. https://doi.org/10.1093/mnras/stz632
ID: 151828
Type: article
Authors: Mason, Charlotte A.; Fontana, Adriano; Treu, Tommaso; Schmidt, Kasper B.; Hoag, Austin; Abramson, Louis; Amorin, Ricardo; Bradač, Maruša; Guaita, Lucia; Jones, Tucker; Henry, Alaina; Malkan, Matthew A.; Pentericci, Laura; Trenti, Michele; Vanzella, Eros
Abstract: Detections and non-detections of Lyman alpha (Lyα) emission from z > 6 galaxies ( 7, where Lyα redshifts to near infra-red wavelengths. Here we present a search for z > 7.2 Lyα emission in 53 intrinsically faint Lyman Break Galaxy candidates, gravitationally lensed by massive galaxy clusters, in the KMOS Lens-Amplified Spectroscopic Survey (KLASS). With integration times of ˜7-10 h, we detect no Lyα emission with signal-to-noise ratio (S/N) > 5 in our sample. We determine our observations to be 80 per cent complete for 5σ spatially and spectrally unresolved emission lines with integrated line flux >5.7 × 10-18 erg s-1 cm-2. We define a photometrically selected sub-sample of 29 targets at z = 7.9 ± 0.6, with a median 5σ Lyα EW limit of 58 Å. We perform a Bayesian inference of the average intergalactic medium (IGM) neutral hydrogen fraction using their spectra. Our inference accounts for the wavelength sensitivity and incomplete redshift coverage of our observations, and the photometric redshift probability distribution of each target. These observations, combined with samples from the literature, enable us to place a lower limit on the average IGM neutral hydrogen fraction of > 0.76 (68{{ per cent}}), > 0.46 (95{{ per cent}}) at z ˜ 8, providing further evidence of rapid reionization at z ˜ 6-8. We show that this is consistent with reionization history models extending the galaxy luminosity function to M_{UV}≲ -12, with low ionizing photon escape fractions, f_{esc} ≲ 15{{ per cent}}.
Model-independent constraints on the hydrogen-ionizing emissivity at z > 6Mason, Charlotte A.Naidu, Rohan P.Tacchella, SandroLeja, JoelDOI: info:10.1093/mnras/stz2291v. 4892669–2676
Mason, Charlotte A., Naidu, Rohan P., Tacchella, Sandro, and Leja, Joel. 2019. "Model-independent constraints on the hydrogen-ionizing emissivity at z > 6." Monthly Notices of the Royal Astronomical Society 489:2669– 2676. https://doi.org/10.1093/mnras/stz2291
ID: 154621
Type: article
Authors: Mason, Charlotte A.; Naidu, Rohan P.; Tacchella, Sandro; Leja, Joel
Abstract: Modelling reionization often requires significant assumptions about the properties of ionizing sources. Here, we infer the total output of hydrogen-ionizing photons (the ionizing emissivity, \dot{N}_\textrm {ion}) at z = 4-14 from current reionization constraints, being maximally agnostic to the properties of ionizing sources. We use a Bayesian analysis to fit for a non-parametric form of \dot{N}_\textrm {ion}, allowing us to flexibly explore the entire prior volume. We infer a declining \dot{N}_\textrm {ion} with redshift at z > 6, which can be used as a benchmark for reionization models. Model-independent reionization constraints from the cosmic microwave background (CMB) optical depth and Ly α and Ly β forest dark pixel fraction produce \dot{N}_\textrm {ion} evolution ( d\log _{10}\dot{\mathbf {N}}_{ion}/ dz|_{z=6\rArr 8} = -0.31± 0.35 dex) consistent with the declining UV luminosity density of galaxies, assuming constant ionizing photon escape fraction and efficiency. Including measurements from Ly α damping of galaxies and quasars produces a more rapid decline: d\log _{10}\dot{\mathbf {N}}_{ion}/ dz|_{z=6\rArr 8} =-0.44± 0.22 dex, steeper than the declining galaxy luminosity density (if extrapolated beyond M_UV≳ -13), and constrains the mid-point of reionization to z = 6.93 ± 0.14.
The Brightest Galaxies at Cosmic Dawn from Scatter in the Galaxy Luminosity versus Halo Mass RelationRen, KevenTrenti, MicheleMason, Charlotte A.DOI: info:10.3847/1538-4357/ab2117v. 878114
Ren, Keven, Trenti, Michele, and Mason, Charlotte A. 2019. "The Brightest Galaxies at Cosmic Dawn from Scatter in the Galaxy Luminosity versus Halo Mass Relation." The Astrophysical Journal 878:114. https://doi.org/10.3847/1538-4357/ab2117
ID: 152914
Type: article
Authors: Ren, Keven; Trenti, Michele; Mason, Charlotte A.
Abstract: The Ultraviolet Luminosity Function (UVLF) is a key observable for understanding galaxy formation from cosmic dawn. There has been considerable debate on whether Schechter-like LFs (characterized by an exponential dropoff at the bright end) that describe the LF in our local universe are also a sufficient description of the LF at high redshifts (z > 6). We model the UVLF over cosmic history with a semi-empirical framework and include a log-normal scatter, Σ, in galaxy luminosities with a conditional luminosity function approach. We show that stochasticity induces a flattening or a feedback scale in the median galaxy luminosity versus halo mass relation, L c (M h ), to account for the increase of bright objects placed in lower-mass halos. We observe a natural broadening in the bright-end exponential segment of the UVLF for z > 6 if processes that regulate star formation acts on the same mass scale as at z ∼ 5, where the degree of broadening is enhanced for larger Σ. Alternatively, if the bright-end feedback is triggered at a near-constant luminosity threshold, the feedback threshold occurs at progressively lower halo masses with increasing redshift, due to galaxies being more luminous on average at a fixed halo mass from rapid halo assembly. Such feedback results in an LF shape with a bright-end closer to that of a Schechter function. We include predictions for the z > 8 UVLFs from future all-sky surveys such as WFIRST, which has the potential to both quantify the scatter and type of feedback, and provide insight behind the mechanisms that drive star formation in the early universe.