arXiv subjects

Dan Coe

Publications and source records attributed to Dan Coe.

At least 37 records · Page 2Linked to original sources

arXiv2026

VENUS: Two Faint Little Red Dots Separated by $\sim70\,\mathrm{pc}$ Hidden in a Single Lensed Galaxy at $z\sim7$

We report the identification of a pair of faint little red dots (LRDs), dubbed Red Eyes, in a strongly-lensed galaxy at $z\sim7$ behind the PLCKG004.5-10.5 cluster, identified from the JWST Treasury program VENUS. Red Eyes are spatially resolved on the image plane with distinct colors, while the critical curve lies far north of Red Eyes, clearly requiring two different LRDs rather than a single LRD. Red Eyes is an extremely close pair of LRDs separated by $\sim70\,\mathrm{pc}$ in the source plane with a magnification of $μ\sim20$, which consistently explains another counter-image detected to the north-west. Red Eyes is hosted in a typical star-forming galaxy with $M_{\mathrm{UV,int}}\sim -19$, but its own UV emission is very faint ($M_{\mathrm{UV,int}} \gtrsim -16$). Moreover, Red Eyes does not reside at the galaxy center but lies at an offset position of approximately one effective radius $R_{\mathrm{e}}$ away from the galaxy center. If observed without lensing, Red Eyes would appear as a typical star-forming galaxy at $z\sim 7$ with $M_{\mathrm{UV}}\sim -19$, showing no apparent LRD signatures in either morphology or SED. These results suggest that multiple off-center LRDs, similar to Red Eyes, may be commonly hidden in a typical high-$z$ star-forming galaxy. In this case, various plausible scenarios may emerge, one of which is that intermediate-mass black holes (IMBHs) with $M_\mathrm{BH}\sim10^{4\text{--}6}\,M_\odot$ may form in star clusters on a stellar disk and contribute to the growth of the central supermassive black hole via mergers, with some IMBHs detectable as luminous LRDs in a sufficiently active and massive phase.

astro-ph.GA↗

arXiv2025

High-Redshift Galaxy Candidates at z > 6 as Revealed by JWST Observations of MACS0647

We present a catalog of 57 high-redshift $z>6$ galaxy candidates, including 14 spectroscopic confirmations ($z = 6.10$ -- 9.25), 2 Little Red Dots ($z = 4.77$, 5.81), and 2 interlopers ($z = 3.23$, 3.72), based on \JWST\ NIRCam imaging (7 filters), NIRSpec spectroscopy (PRISM and G395H), and archival \HST\ imaging (17 filters) of the strong lensing galaxy cluster MACS0647. Our highest redshift confirmation ($z = 9.25$) is an Extremely Blue Galaxy (presented in~\citealt{Yanagisawa2024}), and here we identify a spectral turnover likely due to damped Lyman-$α$. We identify an overdensity of galaxies with spectroscopic redshifts $z = 6.1$, confirming the $z \sim 6$ overdensity identified in \HST\ images. In one of these galaxies, our high-resolution G395H spectroscopy reveals two spatially resolved components with a velocity difference of $\sim$90 km/s; if these components are gravitationally bound, this would imply a dynamical mass on the order of $\sim 10^8\ M_\odot$ given their projected separation. We present spectral line fluxes, widths, and derived physical properties, including stellar masses ($10^8 - 10^9 \ \mathrm{M}_{\odot}$) and metallicities ($10\% - 40\% \ \mathrm{Z}_{\odot}$) for our spectroscopic sample. We note half of our NIRSpec data was obtained with standard 3-slitlet nods and half was obtained with single slitlets yielding similar results, demonstrating the power to observe more sources on a densely packed NIRSpec MSA.

astro-ph.GA↗

arXiv2025

Little red dot variability over a century reveals black hole envelope via a giant Einstein cross

"Little red dots" (LRDs) represent a new population of astronomical objects uncovered by JWST whose nature remains debated. Although many LRDs are suspected as active galactic nuclei (AGN), they show little variability on days-years timescales. We report the discovery of two gravitationally lensed LRDs at redshift $\sim$4.3 behind the cluster RXCJ2211-0350, one of which (RX1) is quadruply imaged with time delays spanning $\sim$130 years. RX1 exhibits intrinsic color and brightness variations of up to 0.7 magnitude among its images. These changes are consistent with blackbody-temperature variations of a photosphere, indicating long-term variability analogous to Cepheid-like pulsations but in a far more extended ($R \sim 2000$ AU) and massive ($M \gtrsim 10^6 \, M_{\odot}$) systems. These results suggest LRDs as a distinct class of AGN with stellar-like envelopes.

astro-ph.GA↗

arXiv2025

VENUS: When Red meets Blue -- A multiply imaged Little Red Dot with an apparent blue companion behind the galaxy cluster Abell 383

We report the discovery of a doubly-imaged Little Red Dot (LRD) candidate behind the galaxy cluster Abell 383, which we dub A383-LRD1. Initially classified as a dropout galaxy in HST imaging with several ground-based emission line detections placing it at $z_{\mathrm{spec}}=6.027$, new JWST/NIRCam observations taken as part of the cycle 4 VENUS survey now reveal that the source consists of two underlying components: A red point-source with a V-shaped SED consistent with LRD selection criteria, and a nearby ($\sim 380$ pc) compact blue companion which was the main contributor to the previous rest-frame UV detections. Based on lensing symmetry and its SED, the LRD appears to lie at a similar redshift as well. The magnification of the two images of A383-LRD1 is $μ_{\mathrm{A}}=16.2\pm1.2$ and $μ_\mathrm{B}=9.0\pm0.6$, respectively, and the predicted time delay between them is $Δt_{\mathrm{grav}}=5.20\pm0.14$ yr ($\sim0.7$ yr in the rest-frame). After correcting for the lensing magnification, we derive an absolute magnitude of $M_{\mathrm{UV,LRD}}=-16.8\pm 0.3$ for the LRD, and $M_{\mathrm{UV,BC}}=-18.2\pm 0.2$ for the blue companion. We perform SED fits to both components, revealing the LRD to be best fitted with a black hole star (BH*) model and a substantial host galaxy, and the blue companion with an extremely young, emission-line dominated star-forming nebula. A383-LRD1 represents the second known multiply-imaged LRD detected to date, following A2744-QSO1, and to our knowledge, the first LRD system with a confirmed detection of [C $_{II}$]$\lambda158 \ μ$m emission from ALMA observations. Thanks to lensing magnification, this system opens a unique door to study the relation between a LRD, its host galaxy, and its environment, and represents a prime candidate for deep JWST spectroscopy and high-resolution ALMA follow-up observations.

astro-ph.GA↗

arXiv2025

Dissecting Reionisation with the Cosmic Star Formation and Active Galactic Nuclei Luminosity History

The combination of the $z=0-13.5$ cosmic star formation history and active galactic nuclei (AGN) luminosity history as inferred by the James Webb Space Telescope is connected to the cosmic spectral energy distribution (CSED) to explore the sources of reionisation. We compute the redshift evolution of the corresponding cosmic ionising photon emissivity, the neutral fraction and the cosmic microwave background optical depth. We use the generative SED modelling code ProSpect to bracket the ionising emissivity between escape fractions of $f_{\mathrm{esc}} = 1 - 100\%$ for both the stars and AGN. Stars alone could have achieved reionisation by $z\approx 6$ with $f_{\mathrm{esc}} \gtrsim 30\%$ for solar metallicity ($Z=0.02$) stars or $f_{\mathrm{esc}} \gtrsim 10\%$ for metal-poor ($Z=10^{-4}$) stars. On the other hand, AGN by themselves would have struggled to produce sufficiently many ionising photons even with $f_{\mathrm{esc}} = 100\%$. A hybrid model containing both stars and AGN is explored where we find best fit (median$\pm 1σ$) $f_{\mathrm{esc}}=$ $12\%$ ($14^{+9}_{-7}\%$) for the stars and $f_{\mathrm{esc}}=$ $63\%$ ($60^{+28}_{-32}\%$) for the AGN, maintained at all redshifts. In essence, the joint growth of stellar mass and supermassive black holes produces neither more nor fewer ionising photons than needed to reionise $\gtrsim 99\%$ of the intergalactic medium by $z\approx 6$.

astro-ph.GA↗

arXiv2025

Globular Clusters in the Galaxy Cluster MACS0416 at z = 0.397

We present a photometric analysis of globular clusters (GCs) in the massive galaxy cluster MACS J0416.1-2403 (z = 0.397) using deep JWST/NIRCam imaging from the PEARLS program. PSF photometry was performed in the short wavelength filters F090W, F115W, F150W, and F200W, yielding a catalog of approximately 3 x 10^3 unresolved, point-like sources consistent with a GC population. Artificial star tests indicate 80% completeness at F200W = 30.36 mag. The color-magnitude diagrams show a narrow GC sequence well reproduced by PARSEC single-stellar-population models spanning ages of 5-9 Gyr and metallicities from [M/H] = -2.0 to +0.2, consistent with evolved GC systems at this redshift. The globular cluster luminosity function (GCLF) follows a log-normal form truncated by incompleteness at the faint end. The brightest sources extend slightly beyond the locus of classical GCs, suggesting a small number of UCD-like systems or stripped nuclei, while the bulk of the population exhibits the luminosities and colors expected for mature globular clusters at z ~ 0.4.

astro-ph.GA↗

arXiv2025

PEARLS: NuSTAR and XMM-Newton Extragalactic Survey of the JWST North Ecliptic Pole Time-domain Field III

The James Webb Space Telescope (JWST) North Ecliptic Pole (NEP) Time-Domain Field (TDF) has been monitored by NuSTAR and XMM-Newton with a regular cadence for five years starting in 2019. The survey has accumulated 3.5Ms of NuSTAR exposure and 228 ks quasi-simultaneous XMM-Newton observations covering 0.31 deg^2. This paper presents the results from the most recent two-years' 2Ms NuSTAR and 166 ks XMM observations in NuSTAR cycles 8 and 9. These observations reached a 20%-area flux of 2.20 x 10^-14 erg cm^-2 s^-1 in the 8-24 keV band. 75 NuSTAR sources and 274 XMM-Newton sources are detected at 99% reliability level. The logN-logS measured in cycles 8+9 are consistent with those measured in the previous cycle 5+6 NuSTAR NEP survey, but in a larger area (0.3 deg^2 compared with 0.19 deg^2). The slope of the cycles 8+9 8-24 keV logN-logS curve is flatter than other works (α89 = 1.13 +/- 0.46), but is consistent with the Euclidean value of α = 1.50. In addition, we found ~36% of the NuSTAR sources to be heavily obscured (NH >= 10^23 cm^-2). The Compton-thick (NH >= 10^24 cm^-2) (CT-) AGN fraction is 9+18-8% in the NEP-TDF, which is consistent with the measurements in previous surveys.

astro-ph.HE↗

arXiv2025

Using gravitational lensing to probe for bright quintessential galaxies in the Epoch of Reionization

Understanding the properties of the first generation of galaxies is an ongoing challenge in observational astrophysics. While advances in deep field observation have led to the identification of large numbers of galaxies within the Epoch of Reionization, there are very few observed galaxies at this range that are sufficiently bright for high signal-to-noise spectroscopy. To this end, we analyse HST and ground-based photometry of five candidate strongly lensed galaxies, all projected behind the cores of massive clusters and with similarly red optical-NIR colors. All are characterized by a drop-off in their spectra between the near-infrared and optical wavelengths, corresponding to a Lyman-break that sets a lower bound on their redshifts. Using the open-source SED modeling software Prospector, we characterize two of these galaxies as high-z (z $\sim$ 6.5-7) while the other three are low-z (z $\sim$ 2) despite all five having similar apparent magnitudes at the observed wavelengths. We demonstrate that for the brightest dropout candidates we can distinguish high-z galaxies from red or dusty low-z galaxies using limited photometric data. The bright sources enable deep constraints on the dropout color which, in combination with flat continua measured in redder bands, require high-z solutions when searching the parameter space. At the time of writing this work significantly increases the number of m_AB < 24 galaxies at or above a redshift of 6, and provides a path forward for future analysis on the early era of galaxy formation

astro-ph.GA↗

arXiv2025

Unveiling the Cosmic Gems Arc at $z\sim10$ with JWST NIRCam

We present recent JWST NIRCam imaging observations of SPT0615-JD (also known as the Cosmic Gems Arc), lensed by the galaxy cluster SPT-CL J0615-5746. The 5 arcsec long arc is the most highly magnified $z>10$ galaxy known. It straddles the lensing critical curve and reveals five star clusters with radii of $\sim 1$ pc or less. We measure the full arc to have F200W 24.5 AB mag, consisting of two mirror images, each 25.3 AB mag with a median magnification of $μ\sim 60^{+17}_{-8}$ (delensed 29.7 AB mag, $M_{UV} = -17.8$). The galaxy has an extremely strong Lyman break F115W$-$F200W $>3.2$ mag ($2σ$ lower limit), is undetected in all bluer filters ($< 2σ$), and has a very blue continuum slope redward of the break ($β= -2.7 \pm 0.1$). This results in a photometric redshift $z_{phot} = 10.2 \pm 0.2$ (95% confidence) with no significant likelihood below $z<9.8$. Based on spectral energy distribution fitting to the total photometry, we estimate an intrinsic stellar mass of $M_{*} \sim 2.4 - 5.6 \times 10^{7} M_{\odot}$, young mass-weighted age of $\sim 21 - 79$ Myr, low dust content ($A_V < 0.15$), and a low metallicity of $\lesssim 1\%~Z_{\odot}$. We identify a fainter third counterimage candidate within 2.2 arcsec of the predicted position, lensed to AB mag 28.4 and magnified by $μ\sim 2$, suggesting the fold arc may only show $\sim 60$% of the galaxy. SPT0615-JD is a unique laboratory to study star clusters observed within a galaxy just 460 Myr after the Big Bang.

astro-ph.GA↗

arXiv2025

The Distribution of Quenched Galaxies in the Massive z = 0.87 Galaxy Cluster El Gordo

El Gordo (ACT-CL J0102$-$4915) is a massive galaxy cluster with two major mass components at redshift $z=0.87$. Using SED fitting results from JWST/NIRCam photometry, the fraction of quenched galaxies in this cluster was measured in two bins of stellar mass: $9<\log{({M_*}/\mathrm{M}_{\odot})}<10$ and $10\leq\log{({M_*}/\mathrm{M}_{\odot})}<12$. While there is no correlation between the quenched fraction and angular separation from the cluster's overall center of mass, there is a correlation between the quenched fraction and angular separation from the center of the nearest of the two mass components for the less-massive galaxies. This suggests that environmental quenching processes are in place at $z\sim1$, and that dwarf galaxies are more affected by those processes than massive galaxies.

astro-ph.GA↗

arXiv2025

First direct carbon abundance measured at $z>10$ in the lensed galaxy MACS0647$-$JD

Investigating the metal enrichment in the early universe helps us constrain theories about the first stars and study the ages of galaxies. The lensed galaxy MACS0647$-$JD at $z=10.17$ is the brightest galaxy known at $z > 10$. Previous work analyzing JWST NIRSpec and MIRI data yielded a direct metallicity $\rm{12+log(O/H)}=7.79\pm0.09$ ($\sim$ 0.13 $Z_\odot$) and electron density $\rm{log}(n_e / \rm{cm^{-3}}) = 2.9 \pm 0.5$, the most distant such measurements to date. Here we estimate the direct C/O abundance for the first time at $z > 10$, finding a sub-solar ${\rm log(C/O)}=-0.44^{+0.06}_{-0.07}$. This is higher than other $z>6$ galaxies with direct C/O measurements, likely due to higher metallicity. It is also slightly higher than galaxies in the local universe with similar metallicity. This may suggest a very efficient and rapid burst of star formation, a low effective oxygen abundance yield, or the presence of unusual stellar populations including supermassive stars. Alternatively, the strong CIII]${\rm λλ}$1907,1909 emission ($14\pm 3\,{Å}$ rest-frame EW) may originate from just one of the two component star clusters JDB ($r \sim 20$ pc). Future NIRSpec IFU spectroscopic observations of MACS0647$-$JD will be promising for disentangling C/O in the two components to constrain the chemistry of individual star clusters just 460 Myr after the Big Bang.

astro-ph.GA↗

arXiv2025

JWST's PEARLS: A z=6 quasar in a train-wreck galaxy merger system

We present JWST NIRSpec integral field spectroscopy observations of the z=5.89 quasar NDWFS J1425+3254 from 0.6-5.3 microns, covering the rest-frame ultraviolet and optical at a spectral resolution of R~100. The quasar has a black hole mass of $M_{\rm{BH}}=(1.4\substack{+3.1\\-1.0})\times10^9 M_\odot$ and an Eddington ratio of $L_{\rm{Bol}}/L_{\rm{Edd}}=0.3\substack{+0.6\\-0.2}$, as implied from the broad Balmer H$α$ and H$β$ lines. The quasar host has significant ongoing obscured star formation, as well as a quasar-driven outflow with velocity $6050\substack{+460\\-630}$ km/s and ionised outflow rate of $1650\substack{+130\\-1230}M_\odot$yr$^{-1}$. This is possibly one of the most extreme outflows in the early Universe. The data also reveal that two companion galaxies are merging with the quasar host. The north-eastern companion galaxy is relatively old and very massive, with a luminosity-weighted stellar age of $65\substack{+9\\-4}$ Myr, stellar mass of $(3.6\substack{+0.6\\-0.3})\times10^{11} M_\odot$, and star-formation rate (SFR) of ~15-30 $M_\odot$yr$^{-1}$. A bridge of gas connects this companion galaxy and the host, confirming their ongoing interaction. A second merger is occurring between the quasar host and a much younger companion galaxy to the south, with a stellar age of $6.7\pm1.8$ Myr, stellar mass of $(1.9\pm0.4)\times10^{10} M_\odot$, and SFR of ~40-65 $M_\odot$yr$^{-1}$. There is also another galaxy in the field, likely in the foreground at z=1.135, which could be gravitationally lensing the quasar with magnification $1<μ<2$, and, thus, <0.75 mag. Overall, the system is a 'train-wreck' merger of three galaxies, with star formation and extreme quasar activity that were likely triggered by these ongoing interactions.

astro-ph.GA↗

arXiv2025

Lonely Little Red Dots: Challenges to the AGN-nature of little red dots through their clustering and spectral energy distributions

Observations with the James Webb Space Telescope (JWST) reveal a previously unseen population of compact red objects, known as ``little red dots`` (LRDs). We study a new photometrically selected sample of 124 LRDs in the redshift range $z$ $\sim$ 3 - 10 selected from NIRCam coverage of the CEERS, NEP-TDF, JADES and JEMS surveys. For JADES, the NEP-TDF and CEERS, we compare SED models with and without AGN components and analyse the impact of an AGN component on the goodness of fit using the Bayesian information criterion (BIC). We find that whilst the $χ^{2}$ of the majority of models containing AGN components is improved compared to models without AGN components, we show that the BIC suggests models without AGN are a more appropriate fit to LRD SEDs, especially when MIRI data is available. We also measure LRD clustering in the CEERS field, JADES field, and NEP-TDF, where we compare the spatial distribution of LRDs and galaxies with Kolmogorov-Smirnov tests of equality of distribution. We find that the neighbourhood of LRDs tends to be less dense compared to galaxies at all selections and masses and at similar redshifts. We further measure upper limit estimates for the halo masses of LRDs using abundance matching. Whilst the population of LRDs could be a mixture of several different inherent populations, as a whole it does appear that these systems are mostly hosting compact galaxies or star clusters in formation.

astro-ph.GA↗

arXiv2025

Self-Consistent JWST Census of Star Formation and AGN activity at z=5.5-13.5

The cosmic star formation history (CSFH) and cosmic active galactic nuclei (AGN) luminosity history (CAGNH) are self consistently measured at $z = 5.5-13.5$. This is achieved by analyzing galaxies detected by the James Webb Space Telescope from $\approx 400 \, \mathrm{arcmin^{2}}$ fields from the PEARLS, CEERS, NGDEEP, JADES and PRIMER surveys. In particular, the combination of spectral energy distribution fitting codes, EAZY and \textsc{ProSpect}, are employed to estimate the photometric redshifts and astrophysical quantities of $3751$ distant galaxies, from which we compute the stellar mass, star formation rate and AGN luminosity distribution functions in four redshift bins. Integrating the distribution functions, we find that the CSFH rises by $\approx 1$~dex over $z = 13.5 - 5.5$ and the CAGNH rises by $\approx 1$~dex over $z = 10.5 - 5.5$. We connect our results of the CSFH and CAGNH at $z=13.5-5.5$ to that from $z= 5-0$ to determine the summary of $\gtrsim 13$ Gyr of star formation and AGN activity, from the very onset of galaxy formation to the present day.

astro-ph.GA↗

arXiv2025

Galaxy Mergers in the Epoch of Reionization I: A JWST Study of Pair Fractions, Merger Rates, and Stellar Mass Accretion Rates at $z = 4.5-11.5$

We present a full analysis of galaxy major merger pair fractions, merger rates, and mass accretion rates, thus uncovering the role of mergers in galaxy formation at the earliest previously unexplored epoch of $4.5<z<11.5$. We target galaxies with masses $\log_{10}(\mathrm{M}_*/\mathrm{M}_\odot) = 8.0 - 10.0$, utilizing data from eight JWST Cycle-1 fields (CEERS, JADES GOODS-S, NEP-TDF, NGDEEP, GLASS, El-Gordo, SMACS-0723, MACS-0416), covering an unmasked area of 189.36 $\mathrm{arcmin}^2$. We develop a new probabilistic pair-counting methodology that integrates full photometric redshift posteriors and corrects for detection incompleteness to quantify close pairs with physical projected separations between 20 and 50 kpc. Our analysis reveals an increase in pair fractions up to $z = 8$, reaching $0.211 \pm 0.065$, followed by a statistically flat evolution to $z = 11.5$. We find that the galaxy merger rate increases from the local Universe up to $z = 6$ and then stabilizes at a value of $\sim 6$ Gyr$^{-1}$ up to $z = 11.5$. The redshift evolution of both pair fractions and merger rates is well described by a power-law plus exponential model. In addition, we measure that the average galaxy increases its stellar mass due to mergers by a factor of $2.77 \pm 0.99$ from redshift $z = 10.5$ to $z = 5.0$. Lastly, we investigate the impact of mergers on galaxy stellar mass growth, revealing that mergers contribute as much as $71 \pm 25\%$ to galaxy stellar mass growth. This indicates that mergers drive about half of galaxy assembly at high redshift.

astro-ph.GA↗

arXiv2025

SAPPHIRES: Extremely Metal-Poor Galaxy Candidates with $12+{\rm log(O/H)}<7.0$ at $z\sim5-7$ from Deep JWST/NIRCam Grism Observations

Population III stars, the hypothetical first generation metal-free stars, have yet to be discovered. Even after three years of successful JWST operations, studies have shown that most galaxies identified to date at $z > 5$ exhibit a metallicity floor of $Z\gtrsim2\%\,Z_{\odot}$, possibly due to unknown selection biases toward bright galaxies or rapid metal enrichment. To address this question, we search for galaxies with low R3$=$[OIII]$\,λ$5008/H$β$ ratios as part of the JWST Cycle-3 large treasury program, the Slitless Areal Pure-Parallel HIgh-Redshift Emission Survey (SAPPHIRES). Using deep NIRCam Wide-Field Slitless Spectrscopy (WFSS) data, we report the discovery of seven extremely metal-poor galaxy candidates in the SAPPHIRES Early Data Release field, with estimated $12+{\rm log(O/H)}<7.0$ at $z\sim5-7$, including two sources with $Z<1\%\,Z_{\odot}$, significantly breaking the metallicity floor observed both locally and at high redshift. These candidates appear extremely faint ($\sim28-30\,$ F200W AB mag) and low-mass (${\rm log}(M_{*}/M_{\odot})\sim6.8-7.8$), as expected from the mass-metallicity relation. They also exhibit very blue UV slopes ($-2.6\lesssimβ\lesssim-2.0$), likely due to low dust content $A_{V}\lesssim0.2\,{\rm mag}$ or young stellar ages $\sim5-20\,{\rm Myr}$. Compared to galaxies at similar redshift, they appear exceptionally bursty in their star formation activity. Our results highlight the power of NIRCam/WFSS in identifying extremely metal-poor galaxies, from just a single pointing, with more data to come in SAPPHIRES. This underscores the potential of pure-parallel programs towards achieving JWST's primary science goal: discovering the first pristine stars and galaxies. Deep JWST/NIRSpec follow-up observations will also be essential to confirm their nature and perform detailed chemical abundance analyses.

astro-ph.GA↗

arXiv2025

JWSTs PEARLS: NIRCam imaging and NIRISS spectroscopy of a $z=3.6$ star-forming galaxy lensed into a near-Einstein Ring by a $z=1.258$ massive elliptical galaxy

We present the discovery, and initial lensing analysis, of a high-redshift galaxy-galaxy lensing system within the JWST-PEARLS/HST-TREASUREHUNT North Ecliptic Pole Time Domain Field (designated NEPJ172238.9+655143.1). The lensing geometry shears a $z=3.6\pm0.1$ star-forming galaxy into a near-Einstein ring with a radius of 0\farcs92, consisting of 4 primary images, around a foreground massive elliptical galaxy at $z=1.258\pm0.005$. The system is fortuitously located within the NIRISS F200W footprint of the PEARLS survey, enabling spectroscopic identification of the 8500A TiO band in the foreground galaxy and allowing tight constraints to be placed on the redshift of the background galaxy based on its continuum detection and lack of strong emission lines. We calculate magnification factors of $2.6<μ<8.4$ for the four images and a total lensing mass of $(4.08 \pm 0.07)\times10^{11}M_\odot$. SED fitting of the foreground elliptical galaxy within the Einstein radius reveals a stellar mass of $\sim1.26\times10^{11}M_\odot$, providing a mass/light ratio of 3.24. Employing simple scaling relations and assumptions, an NFW dark matter halo is found to provide the correct remaining mass within $0.12^{+0.21}_{-0.09}$dex. However, if a bottom-heavy IMF for elliptical galaxies is employed, stellar mass estimations increase and can account for the majority of the lensing mass (up to $\sim$83\%), reducing the need for dark matter. This system further demonstrates the new discovery space that the combined wavelength coverage, sensitivity and resolution of JWST now enables.

astro-ph.GA↗

arXiv2025

EPOCHS XI: The Structure and Morphology of Galaxies in the Epoch of Reionization to z ~ 12.5

We present a structural analysis of 521 galaxy candidates at 6.5 < z < 12.5, with $SNR > 10σ$ in the F444W filter, taken from the EPOCHS v1 sample, consisting of uniformly reduced deep JWST NIRCam data, covering the CEERS, JADES GOOD-S, NGDEEP, SMACS0723, GLASS and PEARLS surveys. We use standard software to fit single Sérsic models to each galaxy in the rest-frame optical and extract their parametric structural parameters (Sérsic index, half-light radius and axis-ratio), and \texttt{Morfometryka} to measure their non-parametric concentration and asymmetry parameters. We find a wide range of sizes for these early galaxies, but with a strong galaxy-size mass correlation up to $z \sim 12$ such that galaxy sizes continue to get progressively smaller in the high-redshift regime, following $R_{e} = 2.74 \pm 0.49 \left( 1 + z \right) ^{-0.79 \pm 0.08}$ kpc. Using non-parametric methods we find that galaxy merger fractions, classified through asymmetry parameters, at these redshifts remain consistent with those in literature, maintaining a value of $f_{m} \sim 0.12 \pm 0.07$ showing little dependence with redshift when combined with literature at $z > 4$. We find that galaxies which are smaller in size also appear rounder, with an excess of high axis-ratio objects. Finally, we artificially redshift a subsample of our objects to determine how robust the observational trends we see are, determining that observed trends are due to real evolutionary effects, rather than being a consequence of redshift effects.

astro-ph.GA↗