arXiv subjects

Marusa Bradac

Publications and source records attributed to Marusa Bradac.

At least 37 records · Page 2Linked to original sources

arXiv2024

Early Results from GLASS-JWST XXIII: The transmission of Lyman-alpha from UV-faint z ~ 3-6 galaxies

Lyman-alpha (Ly$α$) emission from galaxies can be used to trace neutral hydrogen in the epoch of reionization, however, there is a degeneracy between the attenuation of Ly$α$ in the intergalactic medium (IGM) and the line profile emitted from the galaxy. Large shifts of Ly$α$ redward of systemic due to scattering in the interstellar medium can boost Ly$α$ transmission in the IGM during reionization. The relationship between Ly$α$ velocity offset from systemic and other galaxy properties is not well-established at high-redshift or low luminosities, due to the difficulty of observing emission lines which trace systemic redshift. Rest-frame optical spectroscopy with JWST/NIRSpec has opened a new window into understanding of Ly$α$ at z>3. We present a sample of 12 UV-faint galaxies ($-20 \lesssim$ MUV $\lesssim -16$) at $3 \lesssim z \lesssim 6$, with Ly$α$ velocity offsets, $Δv_{\mathrm{Ly}α}$, measured from VLT/MUSE and JWST/NIRSpec from the GLASS-JWST Early Release Program. We find median $Δv_{\mathrm{Ly}α}$ of 205 km s$^{-1}$ and standard deviation 75 km s$^{-1}$, compared to 320 and 170km s$^{-1}$ for MUV < -20 galaxies in the literature. Our new sample demonstrates the previously observed trend of decreasing Ly$α$ velocity offset with decreasing UV luminosity and optical line velocity dispersion, extends to MUV $\gtrsim$ -20, consistent with a picture where the Ly$α$ profile is shaped by gas close to the systemic redshift. Our results imply that during reionization Ly$α$ from UV-faint galaxies will be preferentially attenuated, but that detecting Ly$α$ with low $Δv_{\mathrm{Ly}α}$ can be an indicator of large ionized bubbles.

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arXiv2023

High-Redshift Galaxy Candidates at $z = 9-10$ as Revealed by JWST Observations of WHL0137-08

We report the discovery of four galaxy candidates observed 450 - 600 Myr after the Big Bang with photometric redshifts between z ~ 8.3 - 10.2 measured using the JWST NIRCam imaging of the galaxy cluster WHL0137-08 observed in 8 filters spanning 0.8-5.0 micron, plus 9 Hubble filters spanning 0.4-1.7 micron. One candidate is gravitationally lensed with a magnification of ~8, while the other three are located in a nearby NIRCam module with expected magnifications of <~ 1.1. Using SED fitting, we estimate the stellar masses of these galaxies are typically in the range log M*/Msun = 8.3 - 8.7. All appear young with mass-weighted ages < 240 Myr, low dust content A_V < 0.15 mag, and specific star formation rates sSFR ~0.25 - 10 /Gyr for most. One z ~ 9 candidate is consistent with an age < 5 Myr and a sSFR ~10 /Gyr, as inferred from a strong F444W excess, implying [OIII]+H-beta rest-frame equivalent width ~2000 Angstrom, although an older z ~ 10 object is also allowed. Another z ~ 9 candidate is lensed into an arc 2.4 arcsec long with a magnification of ~8. This arc is the most spatially-resolved galaxy at z ~ 9 known to date, revealing structures ~30 pc across. Follow-up spectroscopy of WHL0137-08 with JWST/NIRSpec will be useful to spectroscopically confirm these high-redshift galaxy candidates and to study their physical properties in more detail.

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arXiv2023

JWST reveals a possible $z \sim 11$ galaxy merger in triply-lensed MACS0647$-$JD

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 ($β\sim-2.6$), 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 ($β\sim-2$), 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 $1-5\rmμm$, out to $4300\,Å$ 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.

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arXiv2023

Early Results from GLASS-JWST. XXI: Rapid assembly of a galaxy at z=6.23 revealed by its C/O abundance

The abundance of carbon relative to oxygen (C/O) is a promising probe of star formation history in the early universe, as the ratio changes with time due to production of these elements by different nucleosynthesis pathways. We present a measurement of $\log{\mathrm{(C/O)}} = -1.01\pm0.12$ (stat) $\pm0.15$ (sys) in a $z=6.23$ galaxy observed as part of the GLASS-JWST Early Release Science Program. Notably, we achieve good precision thanks to the detection of the rest-frame ultraviolet O III], C III], and C IV emission lines delivered by JWST/NIRSpec. The C/O abundance is $\sim$0.8 dex lower than the solar value and is consistent with the expected yield from core-collapse supernovae, indicating that longer-lived intermediate mass stars have not fully contributed to carbon enrichment. This in turn implies rapid buildup of a young stellar population with age $\lesssim100$ Myr in a galaxy seen $\sim$900 million years after the Big Bang. Our chemical abundance analysis is consistent with spectral energy distribution modeling of JWST/NIRCam photometric data, which indicates a current stellar mass $\log\,\mathrm{M}_* / \mathrm{M_{sun}} = 8.4^{+0.4}_{-0.2}$ and specific star formation rate sSFR $\simeq 20$ Gyr$^{-1}$. These results showcase the value of chemical abundances and C/O in particular to study the earliest stages of galaxy assembly.

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arXiv2023

Early results from GLASS-JWST. XIV: A spectroscopically confirmed protocluster 650 million years after the Big Bang

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-$σ$ 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.

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arXiv2023

Spectroscopy from Photometry: A Population of Extreme Emission Line Galaxies at $1.7 \lesssim z \lesssim 6.7$ Selected with JWST Medium Band Filters

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 $\text{[OIII] + H}β$ and H$α$ 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}α) = 893 $ Å and $ EW(\text{[OIII] + H}β) = 1255 $ Å, and includes some objects with $EW(\text{[OIII] + H}β) \sim 3000$ Å. 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.

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arXiv2023

Early results from GLASS-JWST XIV: A first morphological atlas of the 1 < z < 5 Universe in the rest-frame optical

We present a rest-frame optical morphological analysis of galaxies observed with the NIRCam imager on the James Webb Space Telescope (JWST) as part of the GLASS-JWST Early Release Science program. We select 388 sources at redshifts $0.8 < z < 5.4$ and use the seven 0.9--5\micron\ NIRCam filters to generate rest-frame $gri$ composite color images, and conduct visual morphological classification. Compared to HST-based work we find a higher incidence of disks and bulges than expected at $z>1.5$, revealed by rest frame optical imaging. We detect 123 clear disks (58 at $z>1.5$) of which 76 have bulges. No evolution of bulge fraction with redshift is evident: 61\% at $z<2$ ($N=110$) versus 60\% at $z\geq2$ ($N=13$). A stellar mass dependence is evident, with bulges visible in 80\% of all disk galaxies with mass $> 10^{9.5}\, {\rm M}_{\odot}$ ($N=41$) but only 52\% at $M < 10^{9.5}\, {\rm M}_{\odot}$ ($N=82$). We supplement visual morphologies with non-parametric measurements of Gini and Asymmetry coefficients in the rest-frame $i$-band. Our sources are more asymmetric than local galaxies, with slightly higher Gini values. When compared to high-z rest-frame ultraviolet measurements with Hubble Space Telescope, JWST shows more regular morphological types such as disks, bulges and spiral arms at $z>1.5$, with smoother (i.e. lower Gini) and more symmetrical light distributions.

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arXiv2023

Early Results from GLASS-JWST XXII: Rest frame UV-optical spectral properties of Lyman-alpha emitting galaxies at 3 $<$ z $<$ 6

Ly$α$ emission is possibly the best indirect diagnostic of Lyman continuum (LyC) escape since the conditions that favor the escape of Ly$α$ photons are often the same that allows for the escape of LyC photons. In this work, we present the rest UV-optical spectral characteristics of 11 Ly$α$ emitting galaxies at 3 $<$ z $<$ 6 - the optimal redshift range chosen to avoid the extreme IGM attenuation while simultaneously studying galaxies close enough to the epoch of reionization. From a combined analysis of JWST/NIRSpec and MUSE data, we present the Ly$α$ escape fraction and study their correlations with other physical properties of galaxies that might facilitate Ly$α$ escape. We find that our galaxies have low masses (80\% of the sample with $\rm log_{10} \ M_{\star} < 9.5\ M_{\odot}$), compact sizes (median $\rm R_e \sim 0.7 \ kpc $), low dust content, moderate [OIII]/[OII] flux ratios (mean $\sim$ 6.8 $\pm$ 1.2), and moderate Ly$α$ escape fraction (mean $\rm f_{esc}^{Lyα} \ \sim$ 0.11). Our sample show characteristics that are broadly consistent with the low redshift galaxies with Ly$α$ emission, which are termed as "analogs" of high redshift population. We predict the Lyman continuum escape fraction in our sample to be low (0.03-0.07), although larger samples in the post-reionization epoch are needed to confirm these trends.

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arXiv2023

The GLASS-JWST Early Release Science Program. III. Strong lensing model of Abell 2744 and its infalling regions

We present a new high-precision, JWST-based, strong lensing model for the galaxy cluster Abell 2744 at $z=0.3072$. By combining the deep, high-resolution JWST imaging from the GLASS-JWST and UNCOVER programs and a Director's Discretionary Time program, with newly obtained VLT/MUSE data, we identify 32 multiple images from 11 background sources lensed by two external sub-clusters at distances of ~160" from the main cluster. The new MUSE observations enable the first spectroscopic confirmation of a multiple image system in the external clumps. Moreover, the re-analysis of the spectro-photometric archival and JWST data yields 27 additional multiple images in the main cluster. The new lens model is constrained by 149 multiple images ($\sim66\%$ more than in our previous Bergamini et al. 2023 model) covering an extended redshift range between 1.03 and 9.76. The subhalo mass component of the cluster includes 177 member galaxies down to $m_{\rm F160W}=21$, 163 of which are spectroscopically confirmed. Internal velocity dispersions are measured for 85 members. The new lens model is characterized by a remarkably low scatter between predicted and observed positions of the multiple images (0.43"). This precision is unprecedented given the large multiple image sample, the complexity of the cluster mass distribution, and the large modeled area. The improved accuracy and resolution of the cluster total mass distribution provides a robust magnification map over a $\sim\!45$ arcmin$^2$ area, which is critical for inferring the intrinsic physical properties of the highly magnified, high-$z$ sources. The lens model and the new MUSE redshift catalog are released with this publication.

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arXiv2023

Early results from GLASS-JWST XVI: Discovering a bluer z~4-7 Universe through UV slopes

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 4 99% 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.

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arXiv2023

Early results from GLASS-JWST XV: properties of the faintest red sources in the NIRCAM deep fields

We present a first look at the reddest 2-5$μ\rm m$ sources found in deep images from the GLASS Early Release Science program. We undertake a general search, i.e. not looking for any particular spectral signatures, for sources detected only in bands redder than reachable with the Hubble Space Telescope, and which would likely not have been identified in pre-JWST surveys. We search for sources down to AB $\sim 27$ (corresponding to $>10σ$ detection threshold) in any of the F200W to F444W filters,with a $>1$ magnitude excess relative to F090W to F150W bands. Fainter than F444W$>25$ we find 56 such sources of which 37 have reasonably constrained spectral energy distributions to which we can fit photometric redshifts. We find the majority of this population ($\sim$ 65%) as $2 $2$μ\rm m$ boosted by a combination of the Balmer break and emission lines. The typical implied rest equivalent widths are $\sim200\unicode{0x212B}$ with some extreme objects up to $\sim 1000\unicode{0x212B}$. This is in contrast with brighter magnitudes where the red sources tend to be $z<3$ quiescent galaxies and dusty star forming objects. Our general selection criteria for red sources allow us to independently identify other phenomena as diverse as extremely low mass ($\sim 10^8$ M$_\odot$) quiescent galaxies at $z<1$, recover recently identified $z>11$ galaxies and a very cool brown dwarf.

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arXiv2022

Early Results from GLASS-JWST. I: Confirmation of Lensed $z\geqslant7$ Lyman-Break Galaxies Behind the Abell 2744 Cluster With NIRISS

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$α$ in either galaxy, but do observe tentative ($\sim2.7-3.8σ$) HeII$λ$1640 A, OIII]$λλ$1661,1666 A, and NIII]$λλ$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.

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arXiv2022

JWST Imaging of Earendel, the Extremely Magnified Star at Redshift $z=6.2$

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$μ$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 $μ> 4000$ 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.

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arXiv2022

Early results from GLASS-JWST VIII: An Extremely Magnified Blue Supergiant Star at Redshift 2.65 in the Abell 2744 Cluster Field

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.

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arXiv2022

A Highly Magnified Star at Redshift 6.2

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

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arXiv2022

Early results from GLASS-JWST. II: NIRCam extra-galactic imaging and photometric catalog

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$σ$ 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.

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arXiv2022

Early results from GLASS-JWST. III: Galaxy candidates at z$\sim$9-15

We present the results of a first search for galaxy candidates at z$\sim$9--15 on deep seven-bands NIRCam imaging acquired as part of the GLASS-JWST Early Release Science Program on a flanking field of the Frontier Fields cluster A2744. Candidates are selected via two different renditions of the Lyman-break technique, isolating objects at z$\sim$9-11, and z$\sim$9-15, respectively, supplemented by photometric redshifts obtained with two independent codes. We find five color-selected candidates at z$>$9, plus one additional candidate with photometric redshift z$_{phot}\geq$9. In particular, we identify two bright candidates at $M_{UV}\simeq -21$ that are unambiguously placed at $z\simeq 10.6$ and $z\simeq 12.2$, respectively. The total number of galaxies discovered at $z>9$ is in line with the predictions of a non-evolving LF. The two bright ones at $z>10$ are unexpected given the survey volume, although cosmic variance and small number statistics limits general conclusions. This first search demonstrates the unique power of JWST to discover galaxies at the high redshift frontier. The candidates are ideal targets for spectroscopic follow-up in Cycle$-2$.

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arXiv2022

The Sparkler: Evolved High-Redshift Globular Clusters Captured by JWST

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$μ$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}.

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