arXiv subjects

Charlotte Mason

Publications and source records attributed to Charlotte Mason.

53 records · Page 3Linked to original sources

arXiv2022

The archival discovery of a strong Lyman-$α$ and [CII] emitter at z = 7.677

We report the archival discovery of Lyman-$α$ emission from the bright ultraviolet galaxy Y002 at $z=7.677$, spectroscopically confirmed by its ionized carbon [CII] 158$μ$m emission line. The Ly$α$ line is spatially associated with the rest-frame UV stellar emission ($M_{\rm UV}$~-22, 2x brighter than $M^\star_{\rm UV}$) and it appears offset from the peak of the extended [CII] emission at the current ~1" spatial resolution. We derive an estimate of the unobscured SFR(UV)=$(22\pm1)\,M_\odot$ yr$^{-1}$ and set an upper limit of SFR(IR)$<15\,M_\odot$ yr$^{-1}$ from the far-infrared wavelength range, which globally place Y002 on the SFR(UV+IR)-L([CII]) correlation observed at lower redshifts. In terms of velocity, the peak of the Ly$α$ emission is redshifted by $Δv$(Ly$α$)~500 km s$^{-1}$ from the systemic redshift set by [CII] and a high-velocity tail extends to up to ~1000 km s$^{-1}$. The velocity offset is up to ~3.5x higher than the average estimate for similarly UV-bright emitters at z~6-7, which might suggest that we are witnessing the merging of two clumps. A combination of strong outflows and the possible presence of an extended ionized bubble surrounding Y002 would likely facilitate the escape of copious Ly$α$ light, as indicated by the large equivalent width EW(Ly$α$)=$24^{+5}_{-6}$ Å. Assuming that [CII] traces the neutral hydrogen, we estimate a HI gas fraction of $M({\rm HI})/M_\star\gtrsim8$ for Y002 as a system and speculate that patches of high HI column densities could contribute to explain the observed spatial offsets between Ly$α$ and [CII] emitting regions. The low dust content, implied by the non-detection of the far-infrared continuum emission at rest-frame ~160 $μ$m, would be sufficient to absorb any potential Ly$α$ photons produced within the [CII] clump as a result of large HI column densities.

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arXiv2022

The Impact of the First Galaxies on Cosmic Dawn and Reionization

The formation of the first galaxies during cosmic dawn and reionization (at redshifts $z=5-30$), triggered the last major phase transition of our universe, as hydrogen evolved from cold and neutral to hot and ionized. The 21-cm line of neutral hydrogen will soon allow us to map these cosmic milestones and study the galaxies that drove them. To aid in interpreting these observations, we upgrade the publicly available code {\tt 21cmFAST}. We introduce a new, flexible parametrization of the additive feedback from: an inhomogeneous, $H_2$-dissociating (Lyman-Werner; LW) background; and dark matter -- baryon relative velocities; which recovers results from recent, small-scale hydrodynamical simulations with both effects. We perform a large, "best-guess" simulation as the 2021 installment of the Evolution of 21-cm Structure (EOS) project. This improves the previous release with a galaxy model that reproduces the observed UV luminosity functions (UVLFs), and by including a population of molecular-cooling galaxies. The resulting 21-cm global signal and power spectrum are significantly weaker, primarily due to a more rapid evolution of the star-formation rate density required to match the UVLFs. Nevertheless, we forecast high signal-to-noise detections for both HERA and the SKA. We demonstrate how the stellar-to-halo mass relation of the unseen, first galaxies can be inferred from the 21-cm evolution. Finally, we show that the spatial modulation of X-ray heating due to relative velocities provides a unique acoustic signature that is detectable at $z \approx 10-15$ in our fiducial model. Ours are the first public simulations with joint inhomogeneous LW and relative-velocity feedback across the entire cosmic dawn and reionization.

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arXiv2021

Inferring the IGM Neutral Fraction at z ~ 6-8 with Low-Luminosity Lyman Break Galaxies

We present a Bayesian inference on the neutral hydrogen fraction of the intergalactic medium (IGM), $x_{\textrm{HI}}$, at $z \sim$ 6-8 using the properties of Lyman break galaxies during the Epoch of Reionization. We use large samples of LBG candidates at $5.5 \leq z \leq 8.2$ with spectroscopy from Keck/DEIMOS and Keck/MOSFIRE. For each galaxy, we incorporate either the Lyman-$α$ equivalent width (EW) for detections or the EW limit spectrum for nondetections to parameterize the EW distribution at various ultraviolet brightnesses for a given redshift. Using our reference sample of galaxy candidates from the ionized universe at $z$ $\sim$ 6.0, we are able to infer $x_{\textrm{HI}}$ at two redshifts: $z$ $\sim$ 6.7 and $z$ $\sim$ 7.6. This work includes intrinsically faint, gravitationally lensed galaxies at $z$ $\sim$ 6.0 in order to constrain the intrinsic faint-end Ly$α$ EW distribution and provide a comparable population of galaxies to counterparts in our sample that are at higher redshift. The inclusion of faint galaxy candidates, in addition to a more sophisticated modelling framework, allows us to better isolate effects of the interstellar medium and circumgalactic medium on the observed Lyman-$α$ distribution from those of the IGM. We infer an upper limit of $x_{\textrm{HI}}$ $\leq$ 0.25 at $z$ = 6.7 $\pm$ 0.2 and a neutral fraction of $x_{\textrm{HI}}$ = $0.83^{+0.08}_{-0.11}$ at $z$ = 7.6$\pm$ 0.6, both within 1$σ$ uncertainty, results which favor a moderately late and rapid reionization.

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arXiv2021

Lyman-alpha transmission properties of the intergalactic medium in the CoDaII simulation

The decline in abundance of Lyman-$α$ (Ly$α$) emitting galaxies at $z \gtrsim 6$ is a powerful and commonly used probe to constrain the progress of cosmic reionization. We use the CoDaII simulation, which is a radiation hydrodynamic simulation featuring a box of $\sim 94$ comoving Mpc side length, to compute the Ly$α$ transmission properties of the intergalactic medium (IGM) at $z\sim 5.8$ to $7$. Our results mainly confirm previous studies, i.e., we find a declining Ly$α$ transmission with redshift and a large sightline-to-sightline variation. However, motivated by the recent discovery of blue Ly$α$ peaks at high redshift, we also analyze the IGM transmission on the blue side, which shows a rapid decline at $z\gtrsim 6$ of the blue transmission. This low transmission can be attributed not only to the presence of neutral regions but also to the residual neutral hydrogen within ionized regions, for which a density even as low as $n_{\rm HI}\sim 10^{-9}\,\mathrm{cm}^{-3}$ (sometimes combined with kinematic effects) leads to a significantly reduced visibility. Still, we find that $\sim 1\%$ of sightlines towards $M_{\mathrm{1600AB}}\sim -21$ galaxies at $z\sim 7$ are transparent enough to allow a transmission of a blue Ly$α$ peak. We discuss our results in the context of the interpretation of observations.

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arXiv2021

The Evolution of the Lyman-Alpha Luminosity Function During Reionization

The time frame in which hydrogen reionization occurred is highly uncertain, but can be constrained by observations of Lyman-alpha (Ly$α$) emission from distant sources. Neutral hydrogen in the intergalactic medium (IGM) attenuates Ly$α$~photons emitted by galaxies. As reionization progressed the IGM opacity decreased, increasing Ly$α$~visibility. The galaxy Ly$α$~luminosity function (LF) is thus a useful tool to constrain the timeline of reionization. In this work, we model the Ly$α$~LF as a function of redshift, $z=5-10$, and average IGM neutral hydrogen fraction, $\overline{x}_\textsc{hi}$. We combine the Ly$α$~luminosity probability distribution obtained from inhomogeneous reionization simulations with a model for the UV LF to model the Ly$α$~LF. As the neutral fraction increases, the average number density of Ly$α$~emitting galaxies decreases, and are less luminous, though for $\overline{x}_\textsc{hi} \lesssim 0.4$ there is only a small decrease of the Ly$α$~LF. We use our model to infer the IGM neutral fraction at $z=6.6, 7.0, 7.3$ from observed Ly$α$~LFs. We conclude that there is a significant increase in the neutral fraction with increasing redshift: $\overline{x}_\textsc{hi}(z=6.6)=0.08^{+ 0.08}_{- 0.05}, \, \overline{x}_\textsc{hi}(z=7.0)=0.28 \pm 0.05$ and $\overline{x}_\textsc{hi}(z=7.3)=0.83^{+ 0.06}_{- 0.07}$. We predict trends in the Ly$α$~luminosity density and Schechter parameters as a function of redshift and the neutral fraction. We find that the Ly$α$~luminosity density decreases as the universe becomes more neutral. Furthermore, as the neutral fraction increases, the faint-end slope of the Ly$α$~LF steepens, and the characteristic Ly$α$~luminosity shifts to lower values, concluding that the evolving shape of the Ly$α$~LF -- not just its integral -- is an important tool to study reionization.

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arXiv2021

Improving $z\sim7-11$ Galaxy Property Estimates with JWST/NIRCam Medium-Band Photometry

The past decade has seen impressive progress in the detection of $z>7$ galaxies with the Hubble Space Telescope, however little is known about their properties. The James Webb Space Telescope will revolutionise the high-$z$ field by providing NIR (i.e., rest-frame optical) data of unprecedented depth and spatial resolution. Measuring galaxy quantities such as resolved stellar ages or gas metallicity gradients traditionally requires spectroscopy, as broad-band imaging filters are generally too coarse to fully isolate diagnostics such as the 4000 Å (rest-frame) break, continuum emission from aged stars, and key emission lines (e.g., [OII], [OIII], H$β$). However, in this paper, we show that adding NIRCam images through a strategically chosen medium-band filter to common wide-band filters sets adopted by ERS and GTO programs delivers tighter constraints on these galactic properties. To constrain the choice of filter, we perform a systematic investigation of which combinations of wide-band filters from ERS and GTO programs and single medium-band filters offer the tightest constraints on several galaxy properties at redshifts $z\sim7-11$. We employ the JAGUAR extragalactic catalogs to construct statistical samples of physically-motivated mock photometry and conduct SED-fitting procedures to evaluate the accuracy of galaxy property (and photo-$z$) recovery with a simple star-formation history model. We find that adding $>4.1 μ$m medium filters at comparable depth to the broad-band filters can significantly improve photo-$z$s and yield close to order-of-magnitude improvements in the determination of quantities such as stellar ages, metallicities, SF-related quantities and emission line fluxes at $z\sim8$. For resolved sources, the proposed approach enables spatially-resolved determination of these quantities that would be prohibitive with slit spectroscopy.

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arXiv2021

RELICS-DP7: Spectroscopic Confirmation of a Dichromatic Primeval Galaxy at z ~ 7

We report the discovery of a spectroscopically-confirmed strong Lyman-$α$ emitter at $z=7.0281\pm0.0003$, observed as part of the Reionization Cluster Lensing Survey (RELICS). This galaxy, dubbed "Dichromatic Primeval Galaxy" at $z\sim7$ (DP7), shows two distinct components. While fairly unremarkable in terms of its ultraviolet (UV) luminosity ($\sim0.3L^{\ast}_{UV}$, where $L^{\ast}_{UV}$ is the characteristic luminosity), DP7 has one of the highest observed Lyman-$α$ equivalent widths (EWs) among Lyman-$α$ emitters at $z>6$ ($>200$ Angstrom in the rest frame). The strong Lyman-$α$ emission generally suggests a young metal-poor, low-dust galaxy; however, we find that the UV slope $β$ of the galaxy as a whole is redder than typical star-forming galaxies at these redshifts, $-1.13\pm 0.84$, likely indicating, on average, a considerable amount of dust obscuration, or an older stellar population. When we measure $β$ for the two components separately, however, we find evidence of differing UV colors, suggesting two separate stellar populations. Also, we find that Lyman-$α$ is spatially extended and likely larger than the galaxy size, hinting to the possible existence of a Lyman-$α$ halo. Rejuvenation or merging events could explain these results. Either scenario requires an extreme stellar population, possibly including a component of Population III stars, or an obscured Active Galactic Nucleus. DP7, with its low UV luminosity and high Lyman-$α$ EW, represents the typical galaxies that are thought to be the major contribution to the reionization of the Universe, and for this reason DP7 is an excellent target for follow-up with the James Webb Space Telescope.

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arXiv2020

Effects of self-consistent rest-ultraviolet colours in semi-empirical galaxy formation models

Connecting the observed rest-ultraviolet (UV) luminosities of high-$z$ galaxies to their intrinsic luminosities (and thus star formation rates) requires correcting for the presence of dust. We bypass a common dust-correction approach that uses empirical relationships between infrared (IR) emission and UV colours, and instead augment a semi-empirical model for galaxy formation with a simple -- but self-consistent -- dust model and use it to jointly fit high-$z$ rest-UV luminosity functions (LFs) and colour-magnitude relations ($M_{\mathrm{UV}}$-$β$). In doing so, we find that UV colours evolve with redshift (at fixed UV magnitude), as suggested by observations, even in cases without underlying evolution in dust production, destruction, absorption, or geometry. The observed evolution in our model arises due to the reduction in the mean stellar age and rise in specific star formation rates with increasing $z$. The UV extinction, $A_{\mathrm{UV}}$, evolves similarly with redshift, though we find a systematically shallower relation between $A_{\mathrm{UV}}$ and $M_{\mathrm{UV}}$ than that predicted by IRX-$β$ relationships derived from $z \sim 3$ galaxy samples. Finally, assuming that high $1600 Å$ transmission ($\gtrsim 0.6$) is a reliable LAE indicator, modest scatter in the effective dust surface density of galaxies can explain the evolution both in $M_{\mathrm{UV}}$-$β$ and LAE fractions. These predictions are readily testable by deep surveys with the James Webb Space Telescope.

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arXiv2020

Spectroscopically Confirmed Lyman-Alpha Emitters from Redshift 5 to 7 Behind Ten Galaxy Cluster Lenses

We present 36 spectroscopically confirmed intrinsically UV-faint Ly$α$ emitting galaxies from follow-up observations with Keck/DEIMOS of gravitationally lensed high-redshift candidates. Candidates were selected to be between $5\lesssim z \lesssim 7$ from photometric data using \textit{HST} and \textit{Spitzer} imaging surveys. We used photometric redshift information to perform an integrated photometric redshift probability cut $>1\%$ between $5 $25Å at $3σ$ at the fiducial depth of our survey, and only those galaxies with EW(Ly$α$)$>$25Å as true LAEs, and finally, only objects with $m_{AB}<26.8$, we found the LAE fraction to be flat, or modestly increase from 0.26$\pm0.04$ to 0.30$\pm0.04$. These values relative to those for lower-redshift samples are consistent with a rising LAE fraction with redshift out to $z\sim6$, but at $z\sim6.5$ there is some tension between our results and results from surveys at intrinsically brighter luminosities. We conclude intrinsically fainter galaxies have Ly$α$ emission, and there is a steep drop in the LAE fraction from our high-redshift sample at $z\sim6.5$ and from similar galaxies at $z\sim7.5$. 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.

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arXiv2019

Hubble Frontier Field Photometric Catalogues of Abell 370 and RXC J2248.7-4431: Multiwavelength photometry, photometric redshifts, and stellar properties

This paper presents multiwavelength photometric catalogues of the last two Hubble Frontier Fields (HFF), the massive galaxy clusters Abell 370 and RXC J2248.7-4431. The photometry ranges from imaging performed on the Hubble Space Telescope (HST) to ground based Very Large Telescope (VLT) and Spitzer/IRAC, 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 drop-out 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% 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 us an exploration of the properties of galaxies with intrinsic stellar masses as low as $M_* \gtrsim 10^7M_{\odot}$ and intrinsic star formation rates $\mbox{SFRs}\sim 0.1\mbox{-}1M_\odot/\mbox yr$ at z > 6.

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arXiv2019

Unveiling the Phase Transition of the Universe During the Reionization Epoch with Lyman-alpha

The epoch of reionization (6 < z < 10) marks the period in our universe when the first large galaxies grew to fruition, and began to affect the universe around them. Massive stars, and potentially accreting supermassive black holes, filled the universe with ionizing radiation, burning off the haze of neutral gas that had filled the intergalactic medium (IGM) since recombination (z~1000). The evolution of this process constrains key properties of these earliest luminous sources, thus observationally constraining reionization is a key science goal for the next decade. The measurement of Lyman-alpha emission from photometrically-identified galaxies is a highly constraining probe of reionization, as a neutral IGM will resonantly scatter these photons, reducing detectability. While significant work has been done with 8-10m telescopes, these observations require extremely large telescopes (ELTs); the flux limits available from today's 10m class telescopes are sufficient for only the brightest known galaxies (m < 26). Ultra-deep surveys with the Giant Magellan Telescope (GMT) and Thirty Meter Telescope (TMT) will be capable of detecting Lyman-alpha emission from galaxies 2-3 magnitudes fainter than today's deepest surveys. Wide-field fiber spectroscopy on the GMT combined with narrow-field AO-assisted slit spectroscopy on the TMT will be able to probe the expected size of ionized bubbles throughout the epoch of reionization, following up degree scale deep imaging surveys with the Wide Field Infrared Space Telescope. These data will provide the first resolved Lyman-alpha-based maps of the ionized intergalactic medium throughout the epoch of reionization, constraining models of both the temporal and spatial evolution of this phase change.

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arXiv2019

Constraining the neutral fraction of hydrogen in the IGM at redshift 7.5

We present a large spectroscopic campaign with Keck/MOSFIRE targeting Lyman-alpha emission (Ly$α$) 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 Ly$α$ equivalent width limits. During the campaign we targeted 70 LBG candidates with MOSFIRE Y-band, selected photometrically to cover Ly$α$ over the range $7 5$ emission lines in 2 of these galaxies and find that they are likely Ly$α$ at $z=7.148\pm0.001$ and $z=7.161\pm0.001$. We present new lens models for 4 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, $\overline{x}_{\mathrm{HI}}$, in the IGM during reionization to be $\overline{x}_{\mathrm{HI}}=0.88^{+0.05}_{-0.10}$ at $z=7.6\pm0.6$. Our result is consistent with a late and rapid reionization scenario inferred by Planck.

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arXiv2018

Mass Modeling of Frontier Fields Cluster MACS J1149.5+2223 Using Strong and Weak Lensing

We present a gravitational lensing model of MACS J1149.5+2223 using ultra-deep Hubble Frontier Fields imaging data and spectroscopic redshifts from HST grism and VLT/MUSE spectroscopic data. We create total mass maps using 38 multiple images (13 sources) and 608 weak lensing galaxies, as well as 100 multiple images of 31 star-forming regions in the galaxy that hosts Supernova Refsdal. We find good agreement with a range of recent models within the HST field of view. We present a map of the ratio of projected stellar mass to total mass ($f_{\star}$), and find that the stellar mass fraction for this cluster peaks on the primary BCG. Averaging within a radius of 0.3 Mpc, we obtain a value of $\langle f_{\star} \rangle = 0.012^{+0.004}_{-0.003}$, consistent with other recent results for this ratio in cluster environments, though with a large global error (up to $δf_{\star} = 0.005$) primarily due to the choice of an IMF. We compare values of $f_{\star}$ and measures of star formation efficiency for this cluster to other Hubble Frontier Fields clusters studied in the literature, finding that MACS1149 has a higher stellar mass fraction than these other clusters, but a star formation efficiency typical of massive clusters.

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arXiv2017

The Grism Lens-Amplified Survey from Space (GLASS). XI. Detection of CIV in Multiple Images of $z=6.11$ Ly$α$ Emitter Behind RXCJ2248.7-4431

The CIII] and CIV rest-frame UV emission lines are powerful probes of the ionizations states of galaxies. They have furthermore been suggested as alternatives for spectroscopic redshift confirmation of objects at the epoch of reionization ($z>6$), where the most frequently used redshift indicator, Ly$α$, is attenuated by the high fraction of neutral hydrogen in the inter-galactic medium. However, currently only very few confirmations of carbon UV lines at these high redshifts exist, making it challenging to quantify these claims. Here, we present the detection of CIV$λλ$1548,1551Å in \HST\ slitless grism spectroscopy obtained by GLASS of a Ly$α$ emitter at $z=6.11$ multiply imaged by the massive foreground galaxy cluster RXJ2248. The CIV emission is detected at the 3--5$σ$ level in two images of the source, with marginal detection in two other images. We do not detect significant CIII]$λλ$1907,1909Å emission implying an equivalent width EW$_\textrm{CIII]}<20$Å (1$σ$) and $\textrm{CIV/CIII}>0.7$ (2$σ$). Combined with limits on the rest-frame UV flux from the HeII$λ$1640Å emission line and the OIII]$λλ$1661,1666Å doublet, we put constraints on the metallicity and the ionization state of the galaxy. The estimated line ratios and equivalent widths do not support a scenario where an AGN is responsible for ionizing the carbon atoms. SED fits including nebular emission lines imply a source with a mass of log(M/M$_\odot)\sim9$, SFR of around 10M$_\odot$/yr, and a young stellar population $<50$Myr old. The source shows a stronger ionizing radiation field than objects with detected CIV emission at $z<2$ and adds to the growing sample of low-mass (log(M/M$_\odot)\lesssim9$) galaxies at the epoch of reionization with strong radiation fields from star formation.

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arXiv2016

Detection of Lyman-Alpha Emission From a Triple Imaged z=6.85 Galaxy Behind MACS J2129.4-0741

We report the detection of Ly$α$ emission at $\sim9538$Å in the Keck/DEIMOS and \HST WFC3 G102 grism data from a triply-imaged galaxy at $z=6.846\pm0.001$ behind galaxy cluster MACS J2129.4$-$0741. Combining the emission line wavelength with broadband photometry, line ratio upper limits, and lens modeling, we rule out the scenario that this emission line is \oii at $z=1.57$. After accounting for magnification, we calculate the weighted average of the intrinsic Ly$α$ luminosity to be $\sim1.3\times10^{42}~\mathrm{erg}~\mathrm{s}^{-1}$ and Ly$α$ equivalent width to be $74\pm15$Å. Its intrinsic UV absolute magnitude at 1600Å is $-18.6\pm0.2$ mag and stellar mass $(1.5\pm0.3)\times10^{7}~M_{\odot}$, making it one of the faintest (intrinsic $L_{UV}\sim0.14~L_{UV}^*$) galaxies with Ly$α$ detection at $z\sim7$ to date. Its stellar mass is in the typical range for the galaxies thought to dominate the reionization photon budget at $z\gtrsim7$; the inferred Ly$α$ escape fraction is high ($\gtrsim 10$\%), which could be common for sub-$L^*$ $z\gtrsim7$ galaxies with Ly$α$ emission. This galaxy offers a glimpse of the galaxy population that is thought to drive reionization, and it shows that gravitational lensing is an important avenue to probe the sub-$L^*$ galaxy population.

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arXiv2015

The Galaxy UV Luminosity Function Before the Epoch of Reionization

We present a model for the evolution of the galaxy ultraviolet (UV) luminosity function (LF) across cosmic time where star formation is linked to the assembly of dark matter halos under the assumption of a mass dependent, but redshift independent, efficiency. We introduce a new self-consistent treatment of the halo star formation history, which allows us to make predictions at $z>10$ (lookback time $\lesssim500$ Myr), when growth is rapid. With a calibration at a single redshift to set the stellar-to-halo mass ratio, and no further degrees of freedom, our model captures the evolution of the UV LF over all available observations ($0\lesssim z\lesssim10$). The significant drop in luminosity density of currently detectable galaxies beyond $z\sim8$ is explained by a shift of star formation toward less massive, fainter galaxies. Assuming that star formation proceeds down to atomic cooling halos, we derive a reionization optical depth $τ= 0.056^{+0.007}_{-0.010}$, fully consistent with the latest Planck measurement, implying that the universe is fully reionized at $z=7.84^{+0.65}_{-0.98}$. In addition, our model naturally produces smoothly rising star formation histories for galaxies with $L\lesssim L_*$ in agreement with observations and hydrodynamical simulations. Before the epoch of reionization at $z>10$ we predict the LF to remain well-described by a Schechter function, but with an increasingly steep faint-end slope ($α\sim-3.5$ at $z\sim16$). Finally, we construct forecasts for surveys with \JWST~and \WFIRST and predict that galaxies out to $z\sim14$ will be observed. Galaxies at $z>15$ will likely be accessible to JWST and WFIRST only through the assistance of strong lensing magnification.

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arXiv2015

High resolution imaging and spectroscopy of the gravitational lens SDSSJ1206+4332: a natural coronagraph at $z=1.789$ and a standard ruler at $z=0.745$

We present spectroscopy and laser guide star adaptive optics (LGSAO) images of the doubly imaged lensed quasar SDSS J1206+4332. We revise the deflector redshift proposed previously to $z_{d}=0.745,$ and measure for the first time its velocity dispersion $σ=(290\pm30)$ km/s. The LGSAO data show the lensed quasar host galaxy stretching over the astroid caustic thus forming an extra pair of merging images, which was previously thought to be an unrelated galaxy in seeing limited data. Owing to the peculiar geometry, the lens acts as a natural coronagraph on the broad-line region of the quasar so that only narrow [O III] emission is found in the fold arc. We use the data to reconstruct the source structure and deflector potential, including nearby perturbers. We reconstruct the point-spread function (PSF) from the quasar images themselves, since no additional point source is present in the field of view. From gravitational lensing and stellar dynamics, we find the slope of the total mass density profile to be $γ^{\prime}=-\logρ/\log r =1.93\pm0.09.$ We discuss the potential of SDSS J1206+4332 for measuring time delay distance (and thus H$_0$ and other cosmological parameters), or as a standard ruler, in combination with the time delay published by the COSMOGRAIL collaboration. We conclude that this system is very promising for cosmography. However, in order to achieve competitive precision and accuracy, an independent characterization of the PSF is needed. Spatially resolved kinematics of the deflector would reduce the uncertainties further. Both are within the reach of current observational facilities.

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