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We present galaxy MACS0416-Y1 at z$_{\rm{spec}} = 8.312$ as observed by the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). MACS0416-Y1 has been shown to have extreme dust properties, thus, we study the physical properties and star formation histories of its resolved components. Overall, we find that MACS0416-Y1 is undergoing a star formation burst in three resolved clumps. The central clump is less massive compared to the other clumps and possibly formed in the merging process of the two larger clumps. Although the star formation history indicates an ongoing star formation burst, this gas-rich galaxy shows comparable star formation efficiency to cosmic noon galaxies. Using NIRSpec prism spectroscopy, we measure metallicity, $12 +\log\rm{(O/H)} = 7.76\pm0.03$ , ionisation parameter, $\log U = -2.48\pm0.03$, and electron temperature $\rm{T}_e = 18000\pm 4000 K $. The emission line ratios of the galaxy indicate an evolved Interstellar medium (ISM) similar to $z\sim2$ star-forming galaxies. Further, we find possible presence of ionisation from an active galactic nuclei (AGN) using emission line diagnostics, however, we do not detect broad line component in H$\beta$ emission line. As this gas-rich galaxy is undergoing a major merger, we hypothesise that the high dust temperature in MACS0416-Y1 is caused by the star formation burst or a possible narrow-line AGN., Comment: Submitted to ApJL

The epoch of reionisation progressed through the emission of ionising photons from galaxies to their local intergalactic medium. In this work, we characterise the dwarf star-forming galaxies as candidates for the source of ionising photons that drove EoR. We investigate the ionising properties and star formation histories of star-forming dwarf galaxies at the last stages of EoR at $4.8<\rm{z}<7$ using observations from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). The magnification due to gravitational lensing allows us to probe large dynamic ranges in stellar mass ($2\times 10^{6}\leq\rm{M}_*/\rm{M}_\odot\leq5\times 10^{9}$) and UV magnitudes ($-22.68\leq$M$_{UV}\leq=-15.95$).We find a median UV slope \buv of $-2. 56\pm0.23$ and the production efficiency of ionising photons $\log$ \xiion $=25.39\pm0.6$ for the full sample ($4.8<\rm{z}<7$) with a median stellar mass of $6.3\pm0.5\times10^{7} \rm{M}_\odot$. We find both \buv and \xiion are marginally correlated with the stellar mass of the galaxy, indicating a possible greater contribution of dwarf galaxies to the reionisation of the Universe. We find that on average, galaxies in our sample are experiencing a recent rise/burst of star formation which translates to a higher scatter in \xiion and a large scatter in H$\alpha$ equivalent widths. Finally, we investigate the trends of H$\alpha$ and [OIII]+H$\beta$ EWs with UV magnitude and find M$_{UV}$ is correlated between H$\alpha$ but not with [OIII]+H$\beta$ EWs indicating low metallicities and recent burst in the UV faint galaxies., Comment: Accepted For Publication in MNRAS

Spatially resolved studies are key to understanding when, where, and how stars form within galaxies. Using slitless grism spectra and broadband imaging from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS) we study the spatially resolved properties of a strongly lensed ($\mu$ = 5.4$\pm$1.8) z = 0.8718 galaxy pair consisting of a blue face-on galaxy (10.2 $\pm$ 0.2 log($M/M_\odot$)) with multiple star-forming clumps and a dusty red edge-on galaxy (9.9 $\pm$ 0.3 log($M/M_\odot$)). We produce accurate H$\alpha$ maps from JWST/NIRISS grism data using a new methodology that accurately models spatially varying continuum and emission line strengths. With spatially resolved indicators, we probe star formation on timescales of $\sim$ 10 Myr (NIRISS H$\alpha$ emission line maps) and $\sim$ 100 Myr (UV imaging and broadband SED fits). Taking the ratio of the H$\alpha$ to UV flux ($\eta$), we measure spatially resolved star formation burstiness. We find that in the face-on galaxy both H$\alpha$ and broadband star formation rates (SFRs) drop at large galactocentric radii by a factor of $\sim$ 4.7 and 3.8 respectively, while SFR over the last $\sim$ 100 Myrs has increased by a factor of 1.6. Additionally, of the 20 clumps identified in the galaxy pair we find that 7 are experiencing bursty star formation, while 10 clumps are quenching and 3 are in equilibrium (either being in a state of steady star formation or post-burst). Our analysis reveals that the blue face-on galaxy disk is predominantly in a quenching or equilibrium phase. However, the most intense quenching within the galaxy is seen in the quenching clumps. This pilot study demonstrates what JWST/NIRISS data can reveal about spatially varying star formation in galaxies at Cosmic Noon., Comment: MNRAS Accepted, 15 pages, 12 figures

Strong gravitational lensing in galaxy clusters has become an essential tool in astrophysics, allowing us to directly probe the dark matter distribution and study magnified background sources. The precision and reliability of strong lensing models rely heavily on the number and quality of multiple images of background sources with spectroscopic redshifts. We present an updated strong lensing model of the galaxy cluster MACS J0416.1-2403 with the largest sample of multiple images with spectroscopic redshifts in a galaxy cluster field to date. Furthermore, we aim to demonstrate the effectiveness of JWST particularly its NIRISS camera, for strong lensing studies. We use the JWST 's NIRCam imaging and NIRSpec and NIRISS spectroscopy from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). The cluster mass model is constrained using Lenstool software. Our new dataset, used for constraining the lens model, comprises 303 secure multiple images from 111 background sources and includes systems with previously known MUSE redshift and systems for which we obtained spectroscopic redshift for the first time using NIRISS and NIRSpec spectroscopy. The total number of secure spectroscopic systems is >20% higher than in the previous strong lensing studies of this cluster. The derived strong lensing model can reproduce multiple images with the root-mean-square distance of 0.53''. We also provide a full catalogue with 415 multiple images, including less reliable candidates. We furthermore demonstrate the effectiveness of JWST particularly NIRISS, for strong lensing studies. As NIRISS F115W, F150W, and F200W grism spectroscopy captures at least two of the [OII] {\lambda}3727, [OIII] {\lambda}{\lambda}4959, 5007, and H{\alpha} lines at 1

We report an updated mass and magnification model of galaxy cluster Abell 370 using new NIRCam and NIRISS data from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). Using Lenstool and a combination of archival HST and MUSE data with new JWST data as constraints, we derive an improved gravitational lensing model and extract magnifications of background galaxies with uncertainties. Using our best fit model, we perform a search for new multiply imaged systems via predicted positions. We report no new multiply imaged systems with identifiable redshifts, likely due to already very deep HST and Spitzer data, but confirm a $z\sim8$ multiply imaged system by measuring its redshift with NIRISS and NIRSpec spectra. We find that the overall shape of the critical curve for a source at $z = 9.0$ is similar to previous models of Abell 370, with small changes. We investigate the $z\sim8$ galaxy with two images observable with an apparent magnitude in the F125W band of $26.0\pm0.2$ and $25.6\pm0.1$. After correcting for the magnifications of the images, 7.2$^{+0.2}_{-1.2}$ and 8.7$^{+0.4}_{-0.4}$, we use SED fitting to find an intrinsic stellar mass of log($M^*/M_{\odot})$ = 7.35$^{+0.04}_{-0.05}$, intrinsic SFR of 3.5$^{+2.2}_{-1.4}$ M$_{\odot}$/yr, and $M_{UV}$ of -21.3$^{+0.2}_{-0.2}$, which is close to the knee of the luminosity function at that redshift. Our model, and corresponding magnification, shear, and convergence maps are available on request and will be made publicly available on MAST in a CANUCS data release (DOI: 10.17909/ph4n-6n76)., Comment: 15 pages

We present a study on stellar properties of Lyman-alpha (Ly$\alpha$) emitters at 5 $< z <$ 8.2. We use 247 photometrically-selected, lensed, high-redshift, low luminosity galaxy candidates with spectroscopic follow-up. Of these, 38 are confirmed spectroscopically to be between 5 $< z <$ 8.2 via detection of Ly$\alpha$. For each galaxy and candidate, we estimate stellar mass, star formation rate, specific star formation rate, and mass-weighted age with spectral energy distribution fitting. We also measure the UV $\beta$ slope and luminosity using values from photometry. We find no strong correlation between Ly$\alpha$ equivalent width and any of these properties, as well as no significant difference between the physical properties of Ly$\alpha$ emitters and candidates without Ly$\alpha$ detected. This lack of expected trends may be explained by a combination of the evolving opacity of the IGM at these redshifts as well as the unique phase space probed by our lensed sample. Via tests on other galaxy samples which show varying strengths of correlations, we conclude that if there exist any relationships between Ly$\alpha$ EW and physical properties in the underlying population of faint galaxies, they are weak correlations. We also present the results of a spectroscopic search for CIII] emission in confirmed Ly$\alpha$ emitters at $z \sim 7$, finding no CIII] detections, but putting constraints on strong AGN activity and extreme nebular emission., Comment: v2, 14 pages, 8 figures, accepted to MNRAS after minor updates

The most distant galaxies detected by JWST are assembling in a Universe that is less than 5\% of its present age. At these times, the progenitors of galaxies like the Milky Way are expected to be about 10,000 times less massive than they are now, with masses quite comparable to that of massive globular clusters seen in the local Universe. Composed today primarily of old stars and correlating with the properties of their parent dark matter halos, the first globular clusters are thought to have formed during the earliest stages of galaxy assembly. In this article we explore the connection between star clusters and galaxy assembly by showing JWST observations of a strongly lensed galaxy at zspec = 8.304, exhibiting a network of massive star clusters (the 'Firefly Sparkle') cocooned in a diffuse arc. The Firefly Sparkle exhibits the hallmarks expected of a future Milky Way-type galaxy captured during its earliest and most gas-rich stage of formation. The mass distribution of the galaxy seems to be concentrated in ten distinct clusters, with individual cluster masses that straddle the boundary between low-mass galaxies and high-mass globular clusters. The cluster ages suggest that they are gravitationally bound with star formation histories showing a recent starburst possibly triggered by the interaction with a companion galaxy at the same redshift at a projected distance of $\sim$2 kpc away from the Firefly Sparkle. The central star cluster shows nebular-dominated spectra consistent with high temperatures and a top-heavy initial mass function, the product of formation in a very metal poor environment. Combined with abundance matching that suggests that this is likely to be a progenitor of galaxies like our own, the Firefly Sparkle provides an unprecedented case study of a Milky Way-like galaxy in the earliest stages of its assembly in only a 600 million year old Universe., Comment: submitted, comments are welcome! 36 pages, 9 figures

We present a measurement of the mass-metallicity relation (MZR) at cosmic noon, using the JWST near-infrared wide-field slitless spectroscopy obtained by the GLASS-JWST Early Release Science program. By combining the power of JWST and the lensing magnification by the foreground cluster A2744, we extend the measurements of the MZR to the dwarf mass regime at high redshifts. A sample of 50 galaxies with several emission lines is identified across two wide redshift ranges of $z=1.8-2.3$ and $2.6-3.4$ in the stellar mass range of $\log{(M_*/M_\odot)}\in [6.9, 10.0]$. The observed slope of MZR is $0.223 \pm 0.017$ and $0.294 \pm 0.010$ at these two redshift ranges, respectively, consistent with the slopes measured in field galaxies with higher masses. In addition, we assess the impact of the morphological broadening on emission line measurement by comparing two methods of using 2D forward modeling and line profile fitting to 1D extracted spectra. We show that ignoring the morphological broadening effect when deriving line fluxes from grism spectra results in a systematic reduction of flux by $\sim30\%$ on average. This discrepancy appears to affect all the lines and thus does not lead to significant changes in flux ratio and metallicity measurements. This assessment of the morphological broadening effect using JWST data presents, for the first time, an important guideline for future work deriving galaxy line fluxes from wide-field slitless spectroscopy, such as Euclid, Roman, and the Chinese Space Station Telescope., Comment: 19 pages, 6 figures, accepted for publication in ApJL

We present a new sample of 158 galaxies at redshift $z>7.5$ selected from deep \jwst\ NIRCam imaging of five widely-separated sightlines in the CANUCS survey. Two-thirds of the pointings and 80\% of the galaxies are covered by 12 to 14 NIRCam filters, including seven to nine medium bands, providing accurate photometric redshifts and robustness against low redshift interlopers. A sample of 28 galaxies at $z>7.5$ with spectroscopic redshifts shows a low systematic offset and scatter in the difference between photometric and spectroscopic redshifts. We derive the galaxy UV luminosity function at redshifts 8 to 12, finding a slightly higher normalization than previously seen with \hst\ at redshifts 8 to 10. We observe a steeper decline in the galaxy space density from $z=8$ to $12$ than found by most \jwst\ Cycle 1 studies. In particular, we find only eight galaxies at $z>10$ and none at $z>12.5$, with no $z>10$ galaxies brighter than F277W AB=28 or $M_{\rm UV}=-20$ in our unmasked, delensed survey area of 53.4 square arcminutes. We attribute the lack of bright $z>10$ galaxies in CANUCS compared to GLASS and CEERS to intrinsic variance in the galaxy density along different sightlines. The evolution in the CANUCS luminosity function between $z=8$ and $12$ is comparable to that predicted by simulations that assume a standard star formation efficiency, without invoking any special adjustments., Comment: 30 pages, 12 figures, ApJ, in press

Early JWST observations that targeted so-called double-break sources (attributed to Lyman and Balmer breaks at $z>7$), reported a previously unknown population of very massive, evolved high-redshift galaxies. This surprising discovery led to a flurry of attempts to explain these objects' unexpected existence including invoking alternatives to the standard $\Lambda$CDM cosmological paradigm. To test these early results, we adopted the same double-break candidate galaxy selection criteria to search for such objects in the JWST images of the CAnadian NIRISS Unbiased Cluster Survey (CANUCS), and found a sample of 19 sources over five independent CANUCS fields that cover a total effective area of $\sim60\,$arcmin$^2$ at $z\sim8$. However, (1) our SED fits do not yield exceptionally high stellar masses for our candidates, while (2) spectroscopy of five of the candidates shows that while all five are at high redshifts, their red colours are due to high-EW emission lines in star-forming galaxies rather than Balmer breaks in massive, evolved systems. Additionally, (3) field-to-field variance leads to differences of $\sim 1.5$ dex in the maximum stellar masses measured in the different fields, suggesting that the early single-field JWST observations may have suffered from cosmic variance and/or sample bias. Finally, (4) we show that the presence of even a single massive outlier can dominate conclusions from small samples such as those in early JWST observations. In conclusion, we find that the double-break sources in CANUCS are not sufficiently massive or numerous to warrant questioning the standard $\Lambda$CDM paradigm., Comment: V3 Accepted for publication in MNRAS, 13 pages (+5 in Appendix), 7 figures (+4), 1 table (+2)

We use CANUCS JWST/NIRCam imaging of galaxies behind the gravitationally-lensing cluster MACS J0417.5-1154 to investigate star formation burstiness in low-mass ($M_\star\sim10^8\ M_\odot$) galaxies at $z\sim4.7-6.5$. Our sample of 123 galaxies is selected using the Lyman break selection and photometric emission-line excess methods. Sixty per cent of the 123 galaxies in this sample have H$\alpha$-to-UV flux ratios that deviate significantly from the range of $\eta_{1500}$ values consistent with smooth and steady star formation histories. This large fraction indicates that the majority of low-mass galaxies is experiencing bursty star formation histories at high redshift. We also searched for interacting galaxies in our sample and found that they are remarkably common ($\sim40$ per cent of the sample). Compared to non-interacting galaxies, interacting galaxies are more likely to have very low H$\alpha$-to-UV ratios, suggesting that galaxy-galaxy interactions enhance star formation burstiness and enable faster quenching (with timescales of $\lesssim100$ Myr) that follows the rapid rise of star formation activity. Given the high frequency of galaxy-galaxy interactions and the rapid SFR fluctuations they appear to cause, we conclude that galaxy-galaxy interactions could be a leading cause of bursty star formation in low-mass, high-$z$ galaxies. They could thus play a significant role in the evolution of the galaxy population at early cosmological times., Comment: 20 pages, 15 figures, and 1 table. Accepted for publication in MNRAS

We report on a $\rm{[CII]}_{158\mu\rm{m}}$ search using the Atacama Large Millimeter/submillimeter Array (ALMA) on three lensed, confirmed {\lya} emitting galaxies at $z \sim 7$. Our targets are ultra-violet (UV) faint systems with stellar masses on the order of $M_{*} \sim 10^{9} M_{\odot}$. We detect a single [CII] line emission ($4\sigma$) from the brightest ($L \sim 2.4 \times 10^{10}L_{\odot}$) galaxy in our sample, MACS0454-1251. We determine a systemic redshift ($z_{\rm{[CII]}} = 6.3151 \pm 0.0005$) for MACS0454-1251 and measure a {\lya} velocity offset of $\Delta v \approx 300 \pm 70 \rm{km\,s}^{-1}$. The remaining two galaxies we detect no {\ct} but provide $3 \sigma$ upper limits on their {\ct} line luminosities which we use to investigate the $L_{\textrm{[CII]}} - \rm{SFR}$ relation. Overall our single {\ct} detection shows agreement with the relation for dwarf and local starburst galaxies. Our [CII] deficient galaxies could potentially be exhibiting low metallicities ($Z

We present measurements of stellar populations properties of a z = 9.1 gravitationally lensed galaxy MACS1149-JD1 using deep JWST NIRISS slitless spectroscopy as well as NIRISS and NIRCam imaging from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). The galaxy is split into four components. Three magnified (${\mu}$ ~ 17) star-forming components are unresolved, giving intrinsic sizes of < 50pc. In addition, the underlying extended component contains the bulk of the stellar mass, formed the majority of its stars ~ 50Myr earlier than the other three components and is not the site of the most active star formation currently. The NIRISS and NIRCam resolved photometry does not confirm a strong Balmer break previously seen in Spitzer. The NIRISS grism spectrum has been extracted for the entire galaxy and shows a clear continuum and Lyman-break, with no Lyman-${\alpha}$ detected., Comment: This is the version of the article before peer review or editing, as submitted by an author to ApJLetters

The onset of galaxy formation is thought to be initiated by the infall of neutral, pristine gas onto the first protogalactic halos. However, direct constraints on the abundance of neutral atomic hydrogen (HI) in galaxies have been difficult to obtain at early cosmic times. Here we present spectroscopic observations with JWST of three galaxies at redshifts $z=8.8 - 11.4$, about $400-600$ Myr after the Big Bang, that show strong damped Lyman-$\alpha$ absorption ($N_{\rm HI} > 10^{22}$ cm$^{-2}$) from HI in their local surroundings, an order of magnitude in excess of the Lyman-$\alpha$ absorption caused by the neutral intergalactic medium at these redshifts. Consequently, these early galaxies cannot be contributing significantly to reionization, at least at their current evolutionary stages. Simulations of galaxy formation show that such massive gas reservoirs surrounding young galaxies so early in the history of the universe is a signature of galaxy formation in progress., Comment: Submitted

We use JWST/NIRCam medium band photometry in a single pointing of the CAnadian NIRISS Unbiased Cluster Survey (CANUCS) to identify 118 Extreme Emission Line Galaxies (EELGs) over $1.7 \lesssim z \lesssim 6.7$, selected using a set of color cuts that target galaxies with extreme $\text{[OIII] + H}\beta$ and H$\alpha$ emission. We show that our medium band color selections are able to select galaxies based on emission line equivalent width (EW), which is advantageous to more commonly used selections since it does not require strong continuum emission, and can select galaxies with faint or red continuum fluxes. The median EWs of our sample is $EW(\text{H}\alpha) = 893 $ \AA\ and $ EW(\text{[OIII] + H}\beta) = 1255 $ \AA, and includes some objects with $EW(\text{[OIII] + H}\beta) \sim 3000$ \AA. These systems are mostly compact with low stellar mass (median $\log(M_\star/M_\odot) = 8.03$), low metallicity (median $Z = 0.14 Z_\odot$), little dust (median $A_V = 0.18$ mag) and high SSFR (median $SSFR = 1.18 \times 10^{-8}/yr$). Additionally, galaxies in our sample show increasing EW(\Ha) and EW(\OIIIHb) with redshift, an anti-correlation of EW(\Ha) with stellar mass, and no correlation between EW(\OIIIHb) and stellar mass. Finally, we present NIRSpec spectroscopy of 15 of the EELGs in our sample. These spectra confirm the redshifts and EWs of the EELGs calculated from the medium bands, which demonstrates the accuracy and efficiency of our color selections. Overall, we show that there are significant advantages to using medium band photometry to identify and study EELGs at a wide range of redshifts., Comment: Submitted to ApJL. 11 pages, 5 figures, animated Figure 1 is available to view here: https://www.youtube.com/watch?v=bTjjjyFRJys and available for download here: https://github.com/sunnawithers/EELG_colours/blob/main/Figure1_EELGcolours_Withers%2B2023.mp4

We present the first results on the spatial distribution of dust attenuation at $1.0

We report the discovery of a low-mass $z=5.200\pm 0.002$ galaxy that is in the process of ceasing its star formation. The galaxy, MACS0417-z5PSB, is multiply imaged with magnification factors $\sim40$ by the galaxy cluster MACS J0417.5-1154, observed as part of the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). Using observations of MACS0417-z5PSB with a JWST/NIRSpec Prism spectrum and NIRCam imaging, we investigate the mechanism responsible for the cessation of star formation of the galaxy, and speculate about possibilities for its future. Using spectrophotometric fitting, we find a remarkably low stellar mass of $\rm{M_*}=4.3\pm^{0.9}_{0.8} \times 10^{7} \rm{M_{\odot}}$, less than 1% of the characteristic stellar mass at $z\sim5$. We measure a de-lensed rest-UV half-light radius in the source plane of $30\pm^{7}_{5}$ pc, and measure a star formation rate from H$\alpha$ of $0.14\pm^{0.17}_{0.12}$ $\rm{M_{\odot}/yr}$. We find that under the assumption of a double power law star formation history, MACS0417-z5PSB has seen a recent rise in star formation, peaking $\sim10-30$ Myr ago and declining precipitously since then. Together, these measurements reveal a low-mass, extremely compact galaxy which is in the process of ceasing star formation. We investigate the possibilities of mechanisms that have led to the cessation of star formation in MACS0417-z5PSB, considering stellar and AGN feedback, and environmental processes. We can likely rule out an AGN and most environmental processes, but leave open the possibility that MACS0417-z5PSB could be a star forming galaxy in the lull of a bursty star formation history., Comment: 9 pages, 4 figures, 1 table

We present results of [CII]$\,158\,\rm{\mu m}$ emission line observations, and report the spectroscopic redshift confirmation of a strongly lensed ($\mu\sim20$) star-forming galaxy, MACS0308-zD1 at $z=6.2078\pm0.0002$. The [CII] emission line is detected with a signal-to-noise ratio $>6$ within the rest-frame UV bright clump of the lensed galaxy (zD1.1) and exhibits multiple velocity components; the narrow [CII] has a velocity full-width-half-maximum (FWHM) of $110\pm20\,\rm{km/s}$, while broader [CII] is seen with an FWHM of $230\pm20\,\rm{km/s}$. The broader [CII] component is blueshifted ($-80\pm20\,\rm{km/s}$) with respect to the narrow [CII] component, and has a morphology which extends beyond the UV-bright clump. We find that while the narrow [CII] emission is most likely associated with zD1.1, the broader component is possibly associated with outflowing gas. Based on the non-detection of $\lambda_{\rm 158\,\mu m}$ dust continuum, we find that MACS0308-zD1's star-formation activity occurs in a dust-free environment with the stringent upper limit of infrared luminosity $\lesssim9\times10^{8}\,{\rm L_{\odot}}$. Targeting this strongly lensed faint galaxy for follow-up ALMA and JWST observations will be crucial to characterize the details of typical galaxy growth in the early Universe., Comment: 10 pages, 6 figures, 1 table; submitted to ApJ

We present the results of a systematic search for candidate quiescent galaxies in the distant Universe in eleven $JWST$ fields with publicly available observations collected during the first three months of operations and covering an effective sky area of $\sim145$ arcmin$^2$. We homogeneously reduce the new $JWST$ data and combine them with existing observations from the $Hubble\,Space\,Telescope$. We select a robust sample of $\sim80$ candidate quiescent and quenching galaxies at $3 < z < 5$ using two methods: (1) based on their rest-frame $UVJ$ colors, and (2) a novel quantitative approach based on Gaussian Mixture Modeling of the $NUV-U$, $U-V$, and $V-J$ rest-frame color space, which is more sensitive to recently quenched objects. We measure comoving number densities of massive ($M_\star\geq 10^{10.6} M_\odot$) quiescent galaxies consistent with previous estimates relying on ground-based observations, after homogenizing the results in the literature with our mass and redshift intervals. However, we find significant field-to-field variations of the number densities up to a factor of $2-3$, highlighting the effect of cosmic variance and suggesting the presence of overdensities of red quiescent galaxies at $z>3$, as it could be expected for highly clustered massive systems. Importantly, $JWST$ enables the robust identification of quenching/quiescent galaxy candidates at lower masses and higher redshifts than before, challenging standard formation scenarios. All data products, including the literature compilation, are made publicly available., Comment: 15 pages, 6 Figures + Appendix. Accepted for publication in ApJ on Feb, 9. Data release: - Reduced HST+JWST mosaics + photometric catalogs and Eazy-py modeling: https://erda.ku.dk/archives/7166d013c1ca1371aac3c57b9e73190d/published-archive.html - Supplementary material and tables: https://zenodo.org/record/7614908#.Y-4ZruzMLmE - MAST: https://doi.org/10.17909/g3nt-a370 - See also Gould et al. 2023

We select and characterise a sample of massive (log(M$_{*}/$M$_{\odot})>10.6$) quiescent galaxies (QGs) at $33$. We compute median rest-frame SEDs for our sample and find the median quiescent galaxy at $3

We present the first spatially resolved measurements of galaxy properties in the JWST ERO SMACS0723 field. We perform a comprehensive analysis of five $5

Using CANUCS imaging we found an apparent major merger of two $z\sim5$ ultra-low-mass galaxies ($M_\star\sim10^{7}M_\odot$ each) that are doubly imaged and magnified $\sim$12-15$\times$ by the lensing cluster MACS 0417. Both galaxies are experiencing young ($\sim$100 Myr), synchronised bursts of star formation with $\log({\rm sSFR/Gyr^{-1}} )\sim$1.3-1.4, yet SFRs of just $\sim 0.2 M_\odot\ {\rm yr}^{-1}$. They have sub-solar ($Z\sim0.2Z_\odot$) gas-phase metallicities and are connected by an even more metal-poor star-forming bridge. The galaxy that forms from the merger will have a mass of at least $M_\star\sim 2\times10^7 M_\odot$, at least half of it formed during the interaction-induced starburst. More than half of the ionizing photons produced by the system (before and during the merger) will have been produced during the burst. This system provides the first detailed look at a merger involving two high-$z$ ultra-low-mass galaxies of the type believed to be responsible for reionizing the Universe. It suggests that such galaxies can grow via a combination of mass obtained through major mergers, merger-triggered starbursts, and long-term in-situ star formation. If such high-$z$ mergers are common, then merger-triggered starbursts could be significant contributors to the ionizing photon budget of the Universe., Comment: 6 pages, 2 figures, and 1 table; accepted for publication in MNRAS Letter

We present a spectroscopic redshift catalogue of the SMACS J0723.3$-$7327 field ("Webb's First Deep Field") obtained from JWST/NIRISS grism spectroscopy and supplemented with JWST/NIRSpec and VLT/MUSE redshifts. The catalogue contains a total of 190 sources with secure spectroscopic redshifts, including 156 NIRISS grism redshifts, 123 of which are for sources whose redshifts were previously unknown. These new grism redshifts are secured with two or more spectroscopic features (64 sources), or with a single spectral feature whose identity is secured from the object's nine-band photometric redshift (59 sources). These are complemented with 17 NIRSpec and 48 MUSE redshifts, including six new NIRSpec redshifts identified in this work. In addition to the $z_{\rm cl}=0.39$ cluster galaxy redshifts (for which we provide $\sim$40 new NIRISS absorption-line redshifts), we also find three prominent galaxy overdensities at higher redshifts - at $z=1.1$, $z=1.4$, and $z=2.0$ - that were until now not seen in the JWST/NIRSpec and VLT/MUSE data. The paper describes the characteristics of our spectroscopic redshift sample and the methodology we have employed to obtain it. Our redshift catalogue is made available to the community at https://niriss.github.io/smacs0723., Comment: 19 pages, 13 figures, 3 appendices. Accepted for publication in MNRAS

We present ALMA deep spectroscopy for a lensed galaxy at $z_{\rm spec}=8.496$ with $\log(M_{\rm star}/M_{\odot})\sim7.8$ whose optical nebular lines and stellar continuum are detected by JWST/NIRSpec and NIRCam Early Release Observations in SMACS0723. Our ALMA spectrum shows [OIII]88$\mu$m and [CII]158$\mu$m line detections at $4.0\sigma$ and $4.5\sigma$, respectively. The redshift and position of the [OIII] line coincide with those of the JWST source, while the [CII] line is blue-shifted by 90 km s$^{-1}$ with a spatial offset of $0.''5$ ($\approx0.5$ kpc in source plane) from the JWST source. The NIRCam F444W image, including [OIII]$\lambda$5007 and H$\beta$ line emission, spatially extends beyond the stellar components by a factor of $>8$. This indicates that the $z=8.5$ galaxy has already experienced strong outflows whose oxygen and carbon produce the extended [OIII]$\lambda$5007 and the offset [CII] emission, which would promote ionizing photon escape and facilitate reionization. With careful slit-loss corrections and removals of emission spatially outside the galaxy, we evaluate the [OIII]88$\mu$m/$\lambda$5007 line ratio, and derive the electron density $n_{\rm e}$ by photoionization modeling to be $220^{+170}_{-100}$ cm$^{-3}$, which is comparable with those of $z\sim2-3$ galaxies. We estimate an [OIII]88$\mu$m/[CII]158$\mu$m line ratio in the galaxy of $>4$, as high as those of known $z\sim6-9$ galaxies. This high [OIII]88$\mu$m/[CII]158$\mu$m line ratio is generally explained by the high $n_{\rm e}$ as well as the low metallicity ($Z_{\rm gas}/Z_{\odot}=0.04^{+0.02}_{-0.02}$), high ionization parameter ($\log U > -2.27$), and low carbon-to-oxygen abundance ratio ($\log$(C/O) $=[-0.52:-0.24]$) obtained from the JWST/NIRSpec data; further [CII] follow-up observations will constrain the covering fraction of photodissociation regions., Comment: 27 pages, 11 figures, 5 tables. ApJ in press

Galaxies throughout the last 12 Gyr of cosmic time follow a single, universal relation that connects their star-formation rates (SFRs), stellar masses ($M_\star$) and chemical abundances. Deviation from these fundamental scaling relations would imply a drastic change in the processes that regulate galaxy evolution. Observations have hinted at the possibility that this relation may be broken in the very early universe. However, until recently, chemical abundances of galaxies could be only measured reliably as far back as redshift $z=3.3$. With JWST, we can now characterize the SFR, $M_\star$, and chemical abundance of galaxies during the first few hundred million years after the Big Bang, at redshifts $z=7-10$. Here we show that galaxies at this epoch follow unique SFR-$M_\star$--main-sequence and mass-metallicity scaling relations, but their chemical abundance is a factor of three lower than expected from the fundamental-metallicity relation of later galaxies. These findings suggest that galaxies at this time are still intimately connected with the intergalactic medium and subject to continuous infall of pristine gas which effectively dilutes their metal abundances., Comment: Resubmitted version, taking reviewers comments into account

The demographics of the production and escape of ionizing photons from UV-faint early galaxies is a key unknown in discovering the primary drivers of reionization. With the advent of JWST it is finally possible to observe the rest-frame optical nebular emission from individual sub-L$^*$ z>3 galaxies to measure the production of ionizing photons, $\xi_\mathrm{ion}$. Here we study a sample of 370 z~3-7 galaxies spanning -23 0.5) in our sample, based on their photometric properties, even amongst the Lyman-alpha selected galaxies. This work demonstrates that considering the full distribution of $\xi_\mathrm{ion}$ across galaxy properties is important for assessing the primary drivers of reionization., Comment: 10 pages, 7 figures, submitted to A&A

We present the spectroscopic confirmation of a protocluster at $z=7.88$ behind the galaxy cluster Abell2744 (hereafter A2744-z7p9OD). Using JWST NIRSpec, we find seven galaxies within a projected radius of 60kpc. Although the galaxies reside in an overdensity around $>20\times$ greater than a random volume, they do not show strong Lyman-alpha emission. We place 2-$\sigma$ upper limits on the rest-frame equivalent width $<16$-$28$AA. Based on the tight upper limits to the Lyman-alpha emission, we constrain the volume-averaged neutral fraction of hydrogen in the intergalactic medium to be $x_{\rm HI} > 0.45$ (68% CI). Using an empirical $M_{\rm UV}$-$M_{\rm halo}$ relation for individual galaxies, we estimate that the total halo mass of the system is $\gtrsim 4\times10^{11}\,M_\odot$. Likewise, the line of sight velocity dispersion is estimated to be $1100 \pm 200$km/s. Using an empirical relation, we estimate the present-day halo mass of A2744-z7p9OD to be $\sim2\times10^{15}\,M_\odot$, comparable to the Coma cluster. A2744-z7p9OD is the highest redshift spectroscopically confirmed protocluster to date, demonstrating the power of JWST to investigate the connection between dark-matter halo assembly and galaxy formation at very early times with medium-deep observations at $<20$hrs total exposure time. Follow-up spectroscopy of the remaining photometric candidates of the overdensity will further refine the features of this system and help characterize the role of such overdensities in cosmic reionization., Comment: The title has been updated to reflect the published numbering; a minor change has been made to Figure 1 with regard to the MSA shutters on the rgb stamp image. NASA press release article can be found at: https://www.nasa.gov/feature/goddard/2023/webb-reveals-early-universe-prequel-to-huge-galaxy-cluster

In the first billion years after the Big Bang, sources of ultraviolet (UV) photons are believed to have ionized intergalactic hydrogen, rendering the Universe transparent to UV radiation. Galaxies brighter than the characteristic luminosity $L^{*}$ do not provide enough ionizing photons to drive this cosmic reionization. Fainter galaxies are thought to dominate the photon budget; however they are surrounded by neutral gas that prevents the escape of the Lyman-$\alpha$ photons, which has been the dominant way to identify them so far. JD1 was previously identified as a triply-imaged galaxy with a magnification factor of 13 provided by the foreground cluster Abell 2744, and a photometric redshift of $z\sim10$. Here we report the spectroscopic confirmation of this very low luminosity ($\sim0.05 L^{*}$) galaxy at $z=9.79$, observed 480 Myr after the Big Bang, by means of the identification of the Lyman break and redward continuum, as well as multiple $\gtrsim4\sigma$ emission lines, with the Near-InfraRed Spectrograph (NIRSpec) and Near-InfraRed Camera (NIRCam) instruments. The combination of the James Webb Space Telescope (JWST) and gravitational lensing shows that this ultra-faint galaxy ($M_{\rm UV}=-17.35$) -- with a luminosity typical of the sources responsible for cosmic reionization -- has a compact ($\sim$150 pc) and complex morphology, low stellar mass (10$^{7.19}$ M$_\odot$), and subsolar ($\sim$0.6 $Z_{\odot}$) gas-phase metallicity., Comment: Matched to the published Nature version of the article. 19 pages, 4 main figures, 1 supplementary figure, 1 supplementary tables. This version includes an updated version of the NIRSpec spectrum and NIRCam photometry

MACS0647$-$JD is a triply-lensed $z\sim11$ galaxy originally discovered with the Hubble Space Telescope. Here we report new JWST imaging, which clearly resolves MACS0647$-$JD as having two components that are either merging galaxies or stellar complexes within a single galaxy. Both are very small, with stellar masses $\sim10^8\,M_\odot$ and radii $r<100\,\rm pc$. The brighter larger component "A" is intrinsically very blue ($\beta\sim-2.6$), likely due to very recent star formation and no dust, and is spatially extended with an effective radius $\sim70\,\rm pc$. The smaller component "B" appears redder ($\beta\sim-2$), likely because it is older ($100-200\,\rm Myr$) with mild dust extinction ($A_V\sim0.1\,\rm mag$), and a smaller radius $\sim20\,\rm pc$. We identify galaxies with similar colors in a high-redshift simulation, finding their star formation histories to be out of phase. With an estimated stellar mass ratio of roughly 2:1 and physical projected separation $\sim400\,\rm pc$, we may be witnessing a galaxy merger 400 million years after the Big Bang. We also identify a candidate companion galaxy C $\sim3\,{\rm kpc}$ away, likely destined to merge with galaxies A and B. The combined light from galaxies A+B is magnified by factors of $\sim$8, 5, and 2 in three lensed images JD1, 2, and 3 with F356W fluxes $\sim322$, $203$, $86\,\rm nJy$ (AB mag 25.1, 25.6, 26.6). MACS0647$-$JD is significantly brighter than other galaxies recently discovered at similar redshifts with JWST. Without magnification, it would have AB mag 27.3 ($M_{UV}=-20.4$). With a high confidence level, we obtain a photometric redshift of $z=10.6\pm0.3$ based on photometry measured in 6 NIRCam filters spanning $1-5\rm\mu m$, out to $4300\,\r{A}$ rest-frame. JWST NIRSpec observations planned for January 2023 will deliver a spectroscopic redshift and a more detailed study of the physical properties of MACS0647$-$JD., Comment: 27 pages, 14 figures, accepted for publication in ApJL

Galaxy clusters magnify background objects through strong gravitational lensing. Typical magnifications for lensed galaxies are factors of a few but can also be as high as tens or hundreds, stretching galaxies into giant arcs. Individual stars can attain even higher magnifications given fortuitous alignment with the lensing cluster. Recently, several individual stars at redshift $z \sim 1 - 1.5$ have been discovered, magnified by factors of thousands, temporarily boosted by microlensing. Here we report observations of a more distant and persistent magnified star at redshift $z_{\rm phot} = 6.2 \pm 0.1$, 900 Myr after the Big Bang. This star is magnified by a factor of thousands by the foreground galaxy cluster lens WHL0137--08 ($z = 0.566$), as estimated by four independent lens models. Unlike previous lensed stars, the magnification and observed brightness (AB mag 27.2) have remained roughly constant over 3.5 years of imaging and follow-up. The delensed absolute UV magnitude $M_{UV} = -10 \pm 2$ is consistent with a star of mass $M > 50 M_{\odot}$. Confirmation and spectral classification are forthcoming from approved observations with the James Webb Space Telescope, Comment: 50 pages, 11 figures (3 main text, 8 extended data). Published in Nature

The gravitationally lensed star WHL0137-LS, nicknamed Earendel, was identified with a photometric redshift $z_{phot} = 6.2 \pm 0.1$ based on images taken with the Hubble Space Telescope. Here we present James Webb Space Telescope (JWST) Near Infrared Camera (NIRCam) images of Earendel in 8 filters spanning 0.8--5.0$\mu$m. In these higher resolution images, Earendel remains a single unresolved point source on the lensing critical curve, increasing the lower limit on the lensing magnification to $\mu > 4000$ and restricting the source plane radius further to $r < 0.02$ pc, or $\sim 4000$ AU. These new observations strengthen the conclusion that Earendel is best explained by an individual star or multiple star system, and support the previous photometric redshift estimate. Fitting grids of stellar spectra to our photometry yields a stellar temperature of $T_{\mathrm{eff}} \simeq 13000$--16000 K assuming the light is dominated by a single star. The delensed bolometric luminosity in this case ranges from $\log(L) = 5.8$--6.6 $L_{\odot}$, which is in the range where one expects luminous blue variable stars. Follow-up observations, including JWST NIRSpec scheduled for late 2022, are needed to further unravel the nature of this object, which presents a unique opportunity to study massive stars in the first billion years of the universe., Comment: Accepted to ApJL. Data products, lens models, and analysis code will be available online at https://cosmic-spring.github.io

Using data from JWST, we analyze the compact sources ("sparkles") located around a remarkable $z_{\rm spec}=1.378$ galaxy (the "Sparkler") that is strongly gravitationally lensed by the $z=0.39$ galaxy cluster SMACS J0723.3-7327. Several of these compact sources can be cross-identified in multiple images, making it clear that they are associated with the host galaxy. Combining data from JWST's {\em Near-Infrared Camera} (NIRCam) with archival data from the {\em Hubble Space Telescope} (HST), we perform 0.4-4.4$\mu$m photometry on these objects, finding several of them to be very red and consistent with the colors of quenched, old stellar systems. Morphological fits confirm that these red sources are spatially unresolved even in strongly magnified JWST/NIRCam images, while JWST/NIRISS spectra show [OIII]5007 emission in the body of the Sparkler but no indication of star formation in the red compact sparkles. The most natural interpretation of these compact red companions to the Sparkler is that they are evolved globular clusters seen at $z=1.378$. Applying \textsc{Dense Basis} SED-fitting to the sample, we infer formation redshifts of $z_{form} \sim 7-11$ for these globular cluster candidates, corresponding to ages of $\sim 3.9-4.1$ Gyr at the epoch of observation and a formation time just $\sim$0.5~Gyr after the Big Bang. If confirmed with additional spectroscopy, these red, compact "sparkles" represent the first evolved globular clusters found at high redshift, could be amongst the earliest observed objects to have quenched their star formation in the Universe, and may open a new window into understanding globular cluster formation. Data and code to reproduce our results will be made available at \faGithub\href{https://niriss.github.io/sparkler.html}{http://canucs-jwst.com/sparkler.html}., Comment: Submitted to ApJL. Comments are welcome. Data and code to reproduce our results will be made available at niriss.github.io/sparkler.html

We use the GLASS-JWST Early Release Science NIRCam parallel observations to provide a first view of the UV continuum properties of NIRCam/F444W selected galaxies at 499% of the galaxies are blue star-forming galaxies with very low levels of dust (Avbeta~0.01+/-0.33). We find no statistically significant correlation for UV slope with redshift or UV magnitude. However, we find that in general galaxies at higher redshifts and fainter UV magnitudes have steeper UV slopes. We find a statistically significant correlation for UV slope with stellar mass, with galaxies with higher stellar mass showing shallower UV slopes. Individual fits to some of our galaxies reach the bluest UV slopes of beta~-3.1 allowed by stellar population models used in this analysis. Therefore, it is likely that stellar population models with higher amount of Lyman continuum leakage, AGN effects, and/or Population III contributions are required to accurately reproduce the rest-UV and optical properties of some of our bluest galaxies. This dust-free early view confirms that our current cosmological understanding of gradual mass + dust buildup of galaxies with cosmic time is largely accurate to describe the ~0.7-1.5 Gyr age window of the Universe. The abundance of a large population of UV faint dust-poor systems may point to a dominance of low-mass galaxies at z>6 playing a vital role in cosmic reionization., Comment: Accepted in ApJL

How passive galaxies form, and the physical mechanisms which prevent star formation over long timescales, are some of the most outstanding questions in understanding galaxy evolution. The properties of quiescent galaxies over cosmic time provide crucial information to identify the quenching mechanisms. Passive galaxies have been confirmed and studied out to $z\sim4$, but all of these studies have been limited to massive systems (mostly with $\log{(M_{\rm star}/M_{\odot})}>10.8$). Using James Webb Space Telescope (JWST) NIRISS grism slitless spectroscopic data from the GLASS JWST ERS program, we present spectroscopic confirmation of two quiescent galaxies at $z_{\rm spec}=2.650^{+0.004}_{-0.006}$ and $z_{\rm spec}=2.433^{+0.032}_{-0.016}$ (3$\sigma$ errors) with stellar masses of $\log{(M_{\rm star}/M_{\odot})}=10.53^{+0.18}_{-0.06}$ and $\log{(M_{\rm star}/M_{\odot})}=9.93^{+0.06}_{-0.07}$ (corrected for magnification factors of $\mu=2.0$ and $\mu=2.1$, respectively). The latter represents the first spectroscopic confirmation of the existence of low-mass quiescent galaxies at cosmic noon, showcasing the power of JWST to identify and characterize this enigmatic population., Comment: Submitted to ApJL. 8 pages, 3 figures, 1 table

We report the first gas-phase metallicity map of a distant galaxy measured with the James Webb Space Telescope (JWST). We use the NIRISS slitless spectroscopy acquired by the GLASS Early Release Science program to spatially resolve the rest-frame optical nebular emission lines in a gravitationally lensed galaxy at $z=3.06$ behind the Abell 2744 galaxy cluster. This galaxy (dubbed GLASS-Zgrad1) has stellar mass $\sim10^{8.6} M_\odot$, instantaneous star formation rate $\sim8.6$ $M_\odot$/yr (both corrected for lensing magnification), and global metallicity one-fourth solar. From its emission line maps ([O III], H$\beta$, H$\gamma$, [Ne III], and [O II]) we derive its spatial distribution of gas-phase metallicity using a well-established forward-modeling Bayesian inference method. The exquisite resolution and sensitivity of JWST/NIRISS, combined with lensing magnification, enable us to resolve this $z\sim3$ dwarf galaxy in $\gtrsim$50 resolution elements with sufficient signal, an analysis hitherto not possible. We find that the radial metallicity gradient of GLASS-Zgrad1 is strongly inverted (i.e. positive): $\Delta\log({\rm O/H})/\Delta r$ = $0.165\pm0.023$ $\mathrm{dex~kpc^{-1}}$. This inverted gradient may be due to tidal torques induced by a massive nearby ($\sim$15 kpc projected) galaxy, which can cause inflows of metal-poor gas into the central regions of GLASS-Zgrad1. These first results showcase the power of JWST wide-field slitless spectroscopic modes to resolve the mass assembly and chemical enrichment of low-mass galaxies in and beyond the peak epoch of cosmic star formation ($z\gtrsim2$). Reaching masses $\lesssim 10^9~M_\odot$ at these redshifts is especially valuable to constrain the effects of galactic feedback and environment, and is possible only with JWST's new capabilities., Comment: Accepted to ApJL. 11 pages, 4 figures, and 1 table

We present the first rest-frame optical size-luminosity relation of galaxies at $z>7$, using the NIRCam imaging data obtained by the GLASS James Webb Space Telescope Early Release Science (GLASS-JWST-ERS) program, providing the deepest extragalactic data of the ERS campaign. Our sample consist of 19 photometrically selected bright galaxies with $m_\text{F444W}\leq27.8$ at $77$. Given the limited sample size and magnitude range, we first fix the slope to that observed for larger samples in rest-frame UV using HST samples. The median size $r_0$ at the reference luminosity $M=-21$ decreases slightly from rest-frame optical ($600\pm80$ pc) to UV ($450\pm130$ pc). We then re-fit the size-luminosity relation allowing the slope to vary. The slope is consistent with $\beta\sim0.2$ for all bands except F150W, where we find a marginally steeper slope of $\beta=0.53\pm0.15$. The steep UV slope is mainly driven by the smallest and faintest galaxies. If confirmed by larger samples, it implies that the UV size-luminosity relation breaks toward the faint end as suggested by lensing studies., Comment: Accepted by ApJL, 9 pages, 3 figures, 2 tables

We present the reduced images and multi-wavelength catalog of the first JWST NIRCam extra-galactic observations from the GLASS Early Release Science Program, obtained as coordinated parallels of the NIRISS observations of the Abell 2744 cluster. Images in seven bands (F090W, F115W, F150W, F200W, F277W, F356W, F444W) have been reduced using an augmented version of the official JWST pipeline; we discuss the procedures adopted to remove or mitigate defects in the raw images. We obtain a multi--band catalog by means of forced aperture photometry on PSF-matched images at the position of F444W-detected sources. The catalog is intended to enable early scientific investigations, and it is optimized for faint galaxies; it contains 6368 sources, with limiting magnitude 29.7 at 5$\sigma$ in F444W. We release both images and catalog in order to allow the community to familiarize with the JWST NIRCam data and evaluate their merit and limitations given the current level of knowledge of the instrument., Comment: Submitted to ApJL; 9 pages, 5 figures, 2 tables

We report the discovery of an extremely magnified star at redshift $z=2.65$ in James Webb Space Telescope (JWST) NIRISS pre-imaging of the Abell 2744 galaxy-cluster field. The star's background host galaxy lies on a fold caustic of the foreground lens, and the cluster creates a pair of images of the region close to the lensed star. We identified the bright transient in one of the merging images at a distance of $\sim 0.15"$ from the critical curve, by subtracting the JWST F115W and F150W imaging from coadditions of archival Hubble Space Telescope (HST) F105W and F125W images and F140W and F160W images, respectively. Since the time delay between the two images should be only hours, the transient must be the microlensing event of an individual star, as opposed to a luminous stellar explosion which would persist for days to months. Analysis of individual exposures suggests that the star's magnification is not changing rapidly during the observations. From photometry of the point source through the F115W, F150W, and F200W filters, we identify a strong Balmer break, and modeling allows us to constrain the star's temperature to be approximately 7,000--12,000 K., Comment: 10 pages, 3 figures, submitted to ApJL

We present the first search for $z\geqslant7$, continuum-confirmed sources with NIRISS/WFS spectroscopy over the Abell 2744 Frontier Fields cluster, as part of the GLASS-JWST ERS survey. With $\sim15$ hrs of pre-imaging and multi-angle grism exposures in the F115W, F150W, and F200W filters, we describe the general data handling (i.e., reduction, cleaning, modeling, and extraction processes) and analysis for the GLASS-JWST survey. We showcase the power of JWST to peer deep into reionization, when most intergalactic hydrogen is neutral, by confirming two galaxies at $z=8.04\pm0.15$ and $z=7.90\pm0.13$ by means of their Lyman breaks. Fainter continuum spectra are observed in both the F150W and F200W bands, indicative of blue ($-1.69$ and $-1.33$) UV slopes and moderately-bright absolute magnitudes ($-20.37$ and $-19.68$ mag). We do not detect strong Ly$\alpha$ in either galaxy, but do observe tentative ($\sim2.7-3.8\sigma$) HeII$\lambda$1640 A, OIII]$\lambda\lambda$1661,1666 A, and NIII]$\lambda\lambda$1747,1749 A line emission in one, suggestive of low metallicity, star-forming systems with possible non-thermal contributions. These novel observations provide a first look at the extraordinary potential of JWST/NIRISS for confirming representative samples of bright $z\geqslant7$ sources in the absence of strong emission lines, and gain unprecedented insight into their contributions towards cosmic reionization., Comment: Accepted for publication in ApJL on 1st September 2022, after minor modifications based on the referee report. 10 pages, 3 figures, 1 table

The first few hundred Myrs at $z>10$ mark the last major uncharted epoch in the history of the Universe, where only a single galaxy (GNz11 at $z\approx11$) is currently spectroscopically confirmed. Here we present a search for luminous $z>10$ galaxies with $JWST$/NIRCam photometry spanning $\approx1-5\mu$m and covering 49 arcmin$^{2}$ from the public Early Release Science programs (CEERS and GLASS). Our most secure candidates are two $M_{\rm{UV}}\approx-21$ systems: GLASS-z12 and GLASS-z10. These galaxies display abrupt $\gtrsim1.8$ mag breaks in their spectral energy distributions, consistent with complete absorption of flux bluewards of Lyman-$\alpha$ that is redshifted to $z=12.4^{+0.1}_{-0.3}$ and $z=10.4^{+0.4}_{-0.5}$. Lower redshift interlopers such as quiescent galaxies with strong Balmer breaks would be comfortably detected at $>5\sigma$ in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up $\sim 10^9$ solar masses in stars over the $\lesssim300-400$ Myrs after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z10 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of $r_{\rm{50}}\approx0.7$ kpc. These sources, if confirmed, join GNz11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area $>10\times$ larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn epoch, with implications for just how early these galaxies began forming. This, in turn, suggests that future deep $JWST$ observations may identify relatively bright galaxies to much earlier epochs than might have been anticipated., Comment: Accepted for publication in ApJL. Analysis updated with in-flight NIRCam chip-wise zero-points -- Figure 6 shows a comparison with v1

We report the discovery of a double-peaked Lyman-$\alpha$ (Ly$\alpha$) emitter (LAE) at $z=3.2177\pm0.0001$ in VLT/MUSE data. The galaxy is strongly lensed by the galaxy cluster RXC~J0018.5+1626 recently observed in the RELICS survey, and the double-peaked Ly$\alpha$ emission is clearly detected in the two counter images in the MUSE field-of-view. We measure a relatively high Ly$\alpha$ rest-frame equivalent width (EW) of $\mathrm{EW}_{\mathrm{Ly}\alpha,0}=(63\pm2)\,\mathring{\mathrm{A}}$. Additional near-infrared (NIR) spectroscopy allows us to measure the H$\beta$, [OIII]$\lambda4959\,\mathring{\mathrm{A}}$ and [OIII]$\lambda5007\,\mathring{\mathrm{A}}$ emission lines, which show moderate rest-frame EWs of the order of a few $\sim10-100\,\mathring{\mathrm{A}}$, an [OIII]$\lambda5007\,\mathring{\mathrm{A}}$/H$\beta$ ratio of $4.8\pm0.7$, and a lower limit on the [OIII]/[OII] ratio of $>5.6$. The galaxy has very blue UV-continuum slopes of $\beta_{\mathrm{FUV}}=-2.23\pm0.06$ and $\beta_{\mathrm{NUV}}=-3.0\pm0.2$, and is magnified by factors $\mu\sim7-10$ in each of the two images, thus enabling a view into a low-mass ($M_{\star}\simeq10^{7.5}\,\mathrm{M}_{\odot}$) high-redshift galaxy analog. Notably, the blue peak of the Ly$\alpha$ profile is significantly stronger than the red peak, which suggests an inflow of matter and possibly very low HI column densities in its circumgalactic gas. Combined with the high lensing magnification and image multiplicity, these properties make this galaxy a prime candidate for follow-up observations to search for LyC emission and constrain the LyC photon escape fraction., Comment: Updated to match published version

We report the archival discovery of Lyman-$\alpha$ emission from the bright ultraviolet galaxy Y002 at $z=7.677$, spectroscopically confirmed by its ionized carbon [CII] 158$\mu$m emission line. The Ly$\alpha$ 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$\alpha$ emission is redshifted by $\Delta v$(Ly$\alpha$)~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$\alpha$ light, as indicated by the large equivalent width EW(Ly$\alpha$)=$24^{+5}_{-6}$ \r{A}. 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$\alpha$ and [CII] emitting regions. The low dust content, implied by the non-detection of the far-infrared continuum emission at rest-frame ~160 $\mu$m, would be sufficient to absorb any potential Ly$\alpha$ photons produced within the [CII] clump as a result of large HI column densities., Comment: 10 pages, 4 figures. Accepted for publication in The Astrophysical Journal Letters

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-$\alpha$ 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$\alpha$ 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-$\alpha$ 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$\sigma$ uncertainty, results which favor a moderately late and rapid reionization., Comment: 11 pages, 7 figures

We present size measurements of 78 high-redshift ($z\geq 5.5$) galaxy candidates from the Reionisation Lensing Cluster Survey (RELICS). These distant galaxies are well-resolved due to the gravitational lensing power of foreground galaxy clusters, imaged by the Hubble Space Telescope (HST) and the Spitzer Space Telescope. We compute sizes using the forward-modeling code Lenstruction and account for magnification using public lens models. The resulting size-magnitude measurements confirm the existence of many small galaxies with effective radii $R_{\rm{eff}}<200$ pc in the early universe, in agreement with previous studies. In addition, we highlight compact and highly star-forming sources with star formation rate surface densities $\Sigma_\text{SFR}>10M_\odot\text{yr}^{-1}\text{kpc}^{-2}$ as possible Lyman continuum leaking candidates that could be major contributors to the process of reionisation. Future spectroscopic follow-up of these compact galaxies (e.g., with the James Webb Space Telescope) will further clarify their role in reionisation and the physics of early star formation., Comment: 10 pages, 5 figures

Although observations of high-redshift quasars demonstrate that many supermassive black holes (BHs) reached large masses within one billion years after the Big Bang, the origin of the first BHs is still a mystery. A promising way to constrain the origin of the first BHs is to explore the average properties of $z\gtrsim6$ BHs. However, typical BHs remain hidden from X-ray surveys, which is due to their relatively faint nature and the limited sensitivity of X-ray telescopes. Gravitational lensing provides an attractive way to study this unique galaxy population as it magnifies the faint light from these high-redshift galaxies. Here, we study the X-ray emission originating from 155 gravitationally-lensed $z\gtrsim6$ galaxies that were detected in the RELICS survey. We utilize Chandra X-ray observations to search for AGN in the individual galaxies and in the stacked galaxy samples. We did not identify an individual X-ray source that was undoubtedly associated with a high-redshift galaxy. We stack the signal from all galaxies and do not find a statistically significant detection. We split our sample based on stellar mass, star-formation rate, and lensing magnification and stack these sub-samples. We obtain a $2.2\sigma$ detection for massive galaxies with an X-ray luminosity of $(3.7\pm1.6)\times10^{42} \ \rm{erg \ s^{-1}}$, which corresponds to a $(3.0\pm1.3)\times10^5 \ \rm{M_{\odot}}$ BH accreting at its Eddington rate. Other stacks remain undetected and we place upper limits on the AGN emission. These limits imply that the bulk of BHs at $z\gtrsim6$ either accrete at a few percent of their Eddington rate and/or are $1-2$ orders of magnitude less massive than expected based on the stellar mass of their host galaxy., Comment: 14 pages, 5 figures, accepted for publication in The Astrophysical Journal

We report the discovery of a spectroscopically-confirmed strong Lyman-$\alpha$ 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-$\alpha$ equivalent widths (EWs) among Lyman-$\alpha$ emitters at $z>6$ ($>200$ Angstrom in the rest frame). The strong Lyman-$\alpha$ emission generally suggests a young metal-poor, low-dust galaxy; however, we find that the UV slope $\beta$ 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 $\beta$ for the two components separately, however, we find evidence of differing UV colors, suggesting two separate stellar populations. Also, we find that Lyman-$\alpha$ is spatially extended and likely larger than the galaxy size, hinting to the possible existence of a Lyman-$\alpha$ 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-$\alpha$ 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., Comment: 8 pages, 3 figures, 2 table. Accepted for publication in ApJL

We present constraints on the physical properties (including stellar mass, age, and star formation rate) of 207 $6\lesssim z \lesssim8$ galaxy candidates from the Reionization Lensing Cluster Survey (RELICS) and companion Spitzer-RELICS surveys. We measure photometry using T-PHOT and perform spectral energy distribution fitting using EA$z$Y and BAGPIPES. Of the 207 candidates for which we could successfully measure Spitzer fluxes, 23 were demoted to likely low redshift ($z<4$). Among the remaining high redshift candidates, we find intrinsic stellar masses between $1\times10^6\rm{M_{\odot}}$ and $4\times10^9\rm{M_\odot}$, and rest-frame UV absolute magnitudes between $-22.6$ and $-14.5$ mag. While our sample is mostly comprised of $L_{UV}/L^*_{UV}<1$ galaxies, there are a number of brighter objects in the sample, extending to $L_{UV}/L^*_{UV}\sim2$. The galaxies in our sample span approximately four orders of magnitude in stellar mass and star-formation rates, and exhibit ages ranging from maximally young to maximally old. We highlight 11 galaxies which have detections in Spitzer/IRAC imaging and redshift estimates $z\geq6.5$, several of which show evidence for some combination of evolved stellar populations, large contributions of nebular emission lines, and/or dust. Among these is PLCKG287+32-2013, one of the brightest $z\sim7$ candidates known (AB mag 24.9) with a Spitzer 3.6$\mu$m flux excess suggesting strong [OIII] + H-$\beta$ emission ($\sim$1000\AA\ rest-frame equivalent width). We discuss the possible uses and limits of our sample and present a public catalog of Hubble 0.4--1.6$\mu$m + Spitzer 3.6$\mu$m and 4.5$\mu$m photometry along with physical property estimates for all 207 objects in the sample. Because of their apparent brightnesses, high redshifts, and variety of stellar populations, these objects are excellent targets for follow-up with James Webb Space Telescope., Comment: 20 pages, 9 figures