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Timothy Carleton

Publications and source records attributed to Timothy Carleton.

At least 19 recordsLinked to original sources

The Roman eXtreme Deep Field (RXDF)

The Roman eXtreme Deep Field (RXDF) program is one of the five General Astrophysics Survey (GAS) programs approved for observing time with the Nancy Grace Roman Space Telescope in Cycles 1 and 2. It has been allocated 386.41 hours to carry out an imaging survey to AB = 30 mag (5-sigma) over ~140x larger area than the Hubble eXtreme Deep Field (HXDF) full-depth area (ACS+WFC3/IR). The RXDF will cover the full Roman wavelength range with 7 bands, reaching AB = 30 mag in RZYJH, 29 mag in F, and 28 mag in K, over a full-depth area of 678.75 arcmin^2 embedded in a total area of 1,243 arcmin^2, and far exceeding the depths of the Roman Core Community Surveys (CCS). The RXDF is within the Euclid Ultra Deep Field (EUDF) near the North Ecliptic Pole (NEP), a strategic long-term field for generational space facilities, with a wealth of multi-wavelength data including extensive coverage from the James Webb Space Telescope (JWST) NEXUS Treasury program. The observations will cover 3 epochs at a 1-year cadence, each epoch divided into 3 sub-epochs ~10 days apart, enabling time-domain studies on time baselines from ~10 days to over ~2 years. The RXDF is uniquely positioned to address critical questions in reionization, large scale structure (LSS), growth of supermassive black holes (SMBHs), little red dots (LRDs), and high-z supernovae (SNe); the volumes probed by HST+JWST are too small at these extreme depths, and even the deepest CCS tiers are too shallow. In addition to our key objectives, a wealth of additional science will be enabled by engaging the community with our rapidly released datasets, revolutionizing a wide range of science for a lasting legacy. This short document, which is converted from the approved RXDF proposal, aims to provide the community with a summary of the program.

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The Koi Pond: A Strongly Lensed Protocluster Core hosting a Diverse Population of DSFGs

We present James Webb Space Telescope (JWST) and Atacama Large Millimeter Array (ALMA) observations of PJ0846+15, \textit{The Koi Pond}, a strongly lensed protocluster core at Cosmic Noon. This field offers a magnified view of 11 dusty star-forming galaxies (DSFGs) all at $z=2.67$ (within $\Delta V=800$ km s$^{-1}$) spanning a projected extent of $>300$ kpc lensed by a $z=0.77$ foreground cluster. NIRCam and ALMA Band 6 continuum measurements map the stellar distribution and thermal dust emission respectively at a spatial resolution of $\sim$0.15$^{\prime\prime}$. This analysis reveals a diverse population of DSFGs, with evidence of both interacting and non-interacting systems exhibiting a wide range of morphological features including spiral arms, bars, bulges, clumps/stellar clusters, tidal tails/debris and displaced molecular gas reservoirs. Comparing the rest-frame J- band continuum (F444W) vs (i-J) color (F277W$-$F444W), we find a wide range of values, suggesting a $>$1-dex spread in stellar mass and a dust attenuation reddening of $\Delta A_{\mathrm{V}} > 1$ mag. The DSFG members exhibit varying dust sizes relative to the stellar emission, ranging from compact dusty cores to galaxy-wide emission. Resolved color maps of individual sources showing a spread as high as F277W$-$F444W$=2$ mag suggesting complex stellar-to-dust geometry. Although gas-rich mergers are identified in the core, the most red and dust emitting members are disks exhibiting clumpy structure indicating secular growth can drive these starburst events. Such a remarkable range in properties within this sample suggest DSFGs in protocluster core environments follow diverse evolutionary pathways towards their transition into quiescent, elliptical cluster galaxies.

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Spectral Energy Distributions of Globular Clusters in VV191a

We investigate globular cluster (GC) candidates associated with the elliptical galaxy VV191a using JWST NIRCam and archival HST imaging. Beginning with an initial catalog of over 500 candidate sources, we apply morphological filtering, photometric redshift selection, and spectral energy distribution (SED) fitting using BAGPIPES to isolate a refined sample of 61 probable GCs, including a high-confidence subset of 20 objects. The derived age distribution is concentrated between ~ 6-10 Gyr, with a peak near ~ 8 Gyr, while metallicities are predominantly near and super-solar. Unlike many GC systems in elliptical galaxies, the VV191a sample does not exhibit a clear bimodal metallicity distribution. Derived stellar masses span a broad range and suggest significant degeneracies related to dust attenuation and foreground contamination from the overlapping spiral galaxy VV191b. These results support the presence of an evolved GC population in VV191a while highlighting limitations imposed by broadband SED fitting and foreground contamination

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PEARLS: NuSTAR and XMM-Newton Extragalactic Survey of the JWST North Ecliptic Pole Time Domain Field VI: Multiwavelength SED Analysis

We model spectral energy distributions of 261 X-ray sources to $z \sim 5$ in the North Ecliptic Pole Time Domain Field, extending prior XMM-Newton and NuSTAR analyses. Using the star-forming main sequence (SFMS) and black hole accretion rate (BHAR) frameworks, we find that SFRs generally lie below the SFMS while most BHARs exceed the population average, as expected for X-ray-selected samples. There is a strong correlation ($\rho=+0.73$) between SFR relative to the SFMS and specific AGN luminosity, $L_{AGN}/M_*$; galaxies with the highest $L_{AGN}/M_*$ exist at or above the SFMS. X-ray luminosity correlates with SFR ($\rho=+0.80$), revealing a star-forming and X-ray luminous "cold quasar" population consistent with dramatic, short-timescale accretion episodes. Low-mass galaxies show BHARs well above the population averaged value for their mass whereas high-mass galaxies' SMBHs accrete at the population averaged BHAR, suggesting "growth spurt" and "maintenance-mode" accretion, respectively. Traditional AGN classifications (obscured, unobscured, or radio-loud) do not reveal these distinctions, demonstrating the X-ray perspective's unique ability to identify rare AGN phases that are critical for the instantaneous link between galaxies and their SMBHs.

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PEARLS: Two Distinct Populations of AGN Hosts Moving Between Star Formation and Quiescence

We present the results of AGN--host-galaxy decomposition using JWST/NIRCam, HST/ACS, and HST/WFC3 imaging of the North Ecliptic Pole Time Domain Field (NEP-TDF). The light-profiles of 36 NIRCam-selected AGN candidates are modeled for measurement of their point sources, and point source-subtracted host-galaxy emission is used in SED modeling for star formation rate (SFR) estimation. Offsets from the canonical star-forming main sequence (SFMS) show that the host galaxies form two distinct groups distinguished by their star formation: a ``bridge'' between the moderate SFRs of radio sources and low SFRs of X-ray sources, and a cleanly-separated ``branch'' above $\Delta \rm SFMS = -1$ whose SFR trends positively with AGN fraction. Branch galaxies include late-type galaxies with X-ray and radio detections and more dominant point sources that are most certainly AGN, while bridge galaxies have predominantly early-type morphologies with weaker point sources that may be due to compact stellar bulges. Both groups show evidence of recent transition between star formation and quiescence, but neither group shows preference for higher or lower stellar mass or redshift, suggesting that star formation in NIRCam-selected AGN-hosts is more strongly determined by AGN activity than by stellar mass.

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Comparative Bayesian SED Fitting of PEARLSDG

The initial distance to PEARLSDG estimated from the Tip of the Red Giant Branch suggested it was an exotic isolated quiescent dwarf galaxy. We combine recent and archival Hectospec spectroscopy to place it at $z = 0.02843 \pm 0.00012$ ($D \approx 124$\,Mpc) within a galaxy group, revising the distance from 30\,Mpc to $\sim$124\,Mpc. We then carry out {\sc Prospector} SED fitting using parametric and non-parametric star-formation histories sampled with \texttt{dynesty}, \texttt{nautilus}, and \texttt{emcee}, recovering metallicity $\log(Z/Z_\odot) = -0.44^{+0.35}_{-0.06}$, stellar mass $\log_{10}(M_*/M_\odot) = 9.25^{+0.02}_{-3.73}$, and dust attenuation $\hat{\tau}_V = 0.67^{+0.02}_{-0.05}$. The updated metallicity places PEARLSDG squarely on the standard mass--metallicity relation, resolving its former outlier status, with its quenched star-formation history consistent with environmental quenching in a group setting.

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Hidden in Plain Sight: Searching for Globular Clusters Within JWST Observations of the PLCK G165.7+67.0 Galaxy Cluster

Although the James Webb Space Telescope (JWST) has received much attention for its ability to search deeper into the cosmos than ever before, it also enhances our capability to study objects closer to us in the Universe. We apply a methodology of subtracting intracluster light to the PLCK G165.7+67.0 (G165; $z$ = 0.35) cluster, revealing a population of unresolved point-like sources including globular clusters (GCs). By applying a fitting algorithm in color space used to select galaxy cluster members, we uncover over 900 globular cluster candidates from our point source sample. We also identify candidates by estimating the contribution of interlopers to the point source sample, yielding an estimate of 793$\pm$ 83 globular cluster candidates. We find the color-selected sources to be approximately correlated spatially with the intracluster light and lensing mass of the cluster. The observed luminosity function of the sources shows a turnover point fainter than the completeness limit, so we use fixed-parameter curve fitting models to predict a K-corrected turnover point between $-9.4 \leq M_{\rm F200W} \leq -10.7$ mag, although we predict the expected K-corrected turnover point should be closer to $-7.7 \leq M_{\rm F200W} \leq -8.4$ mag. We discuss the dynamical state of this disturbed galaxy cluster with a bimodal mass distribution using the spatial distribution of GC candidates and find that the radial profiles of our color-selected GC candidates are very consistent with the lensing-derived surface mass density at $>$50 kpc.

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Connection Between Dwarf Galaxies and Globular Clusters: Insights from the Perseus Cluster Using Subaru Imaging and Keck Spectroscopy

We present a systematic study of 189 dwarf galaxies and their globular cluster (GC) systems in the Perseus cluster, based on deep Subaru Hyper Suprime-Cam imaging and Keck spectroscopy, supplemented by literature data. This constitutes the largest sample of dwarfs in a single galaxy cluster to date with simultaneous deep imaging, spectroscopic coverage, and GC measurements, while uniquely spanning a broad and continuous range of galaxy properties. We find an anti-correlation between GC specific mass and galaxy stellar mass for dwarfs in Perseus similar to observations in other clusters. At fixed stellar mass, dwarfs with lower surface brightness or larger effective radius tend to be more GC-rich -- suggesting either high GC formation efficiency in an earlier compact-galaxy phase, or less efficient GC disruption. The correlation between GC richness and axis ratio in Perseus is weaker than in other environments. We find some connection between GC richness and infall time, but not with the clear correlations found in Virgo, Coma, and cosmological simulations. More complete observations are needed to test for cluster-to-cluster variations in galaxy and GC evolutionary histories. This work demonstrates the potential of new wide-field imaging and spectroscopy surveys for understanding GCs and dwarf galaxies, and highlights the need for further work in theoretical modeling.

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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 ({\alpha}89 = 1.13 +/- 0.46), but is consistent with the Euclidean value of {\alpha} = 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.

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SKYSURF-11: A New Zodiacal Light Model Optimized for Optical Wavelengths

We present an improved zodiacal light model, optimized for optical wavelengths, using archival Hubble Space Telescope (HST) imaging from the SKYSURF program. The Kelsall et al. 1998 model used infrared imaging from the Diffuse Infrared Background Experiment (DIRBE) on board the Cosmic Background Explorer to create a 3D structure of the interplanetary dust cloud. However, this model cannot accurately represent zodiacal light emission outside of DIRBE's nominal wavelength bandpasses, the bluest of which is 1.25 micron. We present a revision to this model (called ZodiSURF) that incorporates analytical forms of both the scattering phase function and albedo as a function of wavelength, which are empirically determined across optical wavelengths (0.3-1.6 micron) from over 5,000 HST sky surface brightness (sky-SB) measurements. This refined model results in significantly improved predictions of zodiacal light emission at these wavelengths and for Sun angles greater than 80 deg. Fits to HST data show an uncertainty in the model of ~4.5%. Remarkably, the HST sky-SB measurements show an excess of residual diffuse light (HST Sky - ZodiSURF - Diffuse Galactic Light) of 0.013 +/- 0.006 MJy/sr. We suggest that a very dim spherical dust cloud may need to be included in the zodiacal light model, which we present here as a toy model.

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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.

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Forecasting the Observable Rates of Gravitationally Lensed Supernovae for the PASSAGES Dusty Starbursts

More than 60 years have passed since the first formal suggestion to use strongly-lensed supernovae to measure the expansion rate of the Universe through time-delay cosmography. Yet, fewer than 10 such objects have ever been discovered. We consider the merits of a targeted strategy focused on lensed hyperluminous infrared galaxies -- among the most rapidly star-forming galaxies known in the Universe. With star formation rates (SFRs) $\sim {200 - 6000}~\textrm{M}_\odot~\textrm{yr}^{-1}$, the $\sim 30$ objects in the Planck All-Sky Survey to Analyze Gravitationally-lensed Extreme Starbursts (PASSAGES) are excellent candidates for a case study, in particular, and have already led to the discovery of the multiply-imaged SN H0pe. Considering their lens model-corrected SFRs, we estimate their intrinsic supernova rates to be an extraordinary ${1.8 - 65}~\textrm{yr}^{-1}$ (core-collapse) and ${0.2 - 6.4}~\textrm{yr}^{-1}$ (Type Ia). Moreover, these massive starbursts typically have star-forming companions which are unaccounted for in this tally. We demonstrate a strong correlation between Einstein radius and typical time delays, with cluster lenses often exceeding several months (and therefore most favorable for high-precision $H_0$ inferences). A multi-visit monitoring campaign with a sensitive infrared telescope (namely, JWST) is necessary to mitigate dust attenuation. Still, a porous interstellar medium and clumpy star formation in these extreme galaxies might produce favorable conditions for detecting supernovae as transient point sources. Targeted campaigns of known lensed galaxies to discover new lensed supernovae can greatly complement wide-area cadenced surveys. Increasing the sample size helps to realize the potential of supernova time-delay cosmography to elucidate the Hubble tension through a single-step measurement, independent of other $H_0$ techniques.

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PEARLS: Globular Clusters and Ultra-Compact Dwarfs in the El Gordo Galaxies at z=0.87

JWST/NIRCam 0.9 to 2.0 micron images reveal a population of point sources around the major galaxies in the El Gordo cluster at redshift z=0.87. Their distribution in the color--magnitude diagrams shows a narrow sequence well separated from field-galaxy contamination and consistent with their identification as ultra-compact dwarf galaxies (UCDs) or luminous globular clusters (GCs). The point-source sequence is more luminous by almost a magnitude than the corresponding sequence in Abell 2744 at z=0.31, matching the predicted evolutionary change for GC/UCDs over the 4-Gyr difference in lookback time between these two clusters. Deeper observations should allow direct JWST imaging of GC/UCD populations, even without the help of lensing, up to z ~ 1.4, a lookback time of more than 9 Gyr. Such observations would directly reveal the evolution of these compact stellar systems two-thirds of the way back to the Big Bang.

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SKYSURF VIII -- Modeling SKYSURF Completeness Data for Comparison to the Hubble Space Telescope Exposure Time Calculator

Accurately assessing image source completeness is critical for interpreting measurements on telescope data. Using the Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) data from the Hubble Space Telescope ($HST$) archival project "SKYSURF", we model galaxy completeness as a function of the exposure time and background of an image. This is accomplished by adding simulated objects with varying magnitudes and sizes into these images, and determining the detection rate for each set of parameters. The fifty percent completeness results are then compared to the Exposure Time Calculator (ETC), in order to assess the differences between the STSCI ETC and our analysis of the archival data. Ultimately, we find that, for extended galaxies, the ETC predicts a 1-2 magnitudes fainter completeness limit than our data. We believe the difference is due to the ETC's flat surface brightness profiles being less accurate at predicting for extended sources compared to our more realistic profiles.

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A long time ago in an LAE far, far away: a signpost of early reionization or a nascent AGN at $z=13$?

The JADES survey recently reported the discovery of JADES-GS-z13-1-LA at $z = 13$, the highest redshift Ly$\alpha$ emitter (LAE) ever observed. This observation suggests that either the intergalactic medium (IGM) surrounding JADES-GS-z13-1-LA is highly ionised, or the galaxy's intrinsic Ly$\alpha$ emission properties are extreme. We use radiative transfer simulations of reionisation that capture the distribution of ionised gas in the $z = 13$ IGM to investigate the implications of JADES-GS-z13-1-LA for reionisation. We find that if JADES-GS-z13-1-LA is a typical star forming galaxy (SFG) with properties characteristic of LAEs at $z \sim 6$, its detection suggests that the universe is $\gtrsim 5\%$ ionised by $z = 13$. We also investigate the possibility that the extreme properties of JADES-GS-z13-1-LA are driven by an AGN. Using a simple analysis based on the fact that AGN are expected to produce more ionising photons than SFGs, we estimate that the probability that JADES-GS-z13-1-LA hosts an AGN is $71\%$, $42\%$, and $15\%$ if the IGM is $< 1\%$, $\approx 5\%$ and $\approx 25\%$ ionised, respectively. We also highlight other features in the spectrum of JADES-GS-z13-1-LA that may be indicative of AGN activity, including strong Ly$\alpha$ damping wing absorption extending to $\sim 1300$ angstroms, and a possible CII*$\lambda1335$ emission line. Our findings strongly motivate dedicated follow-up observations of JADES-GS-z13-1-LA to determine whether it hosts an AGN.

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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.

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SKYSURF. X. A Novel Method for Measuring Integrated Galaxy Light

We describe the drizzling pipeline and contents of the drizzled database for Hubble Space Telescope Cycle 27-29 Archival Legacy project "SKYSURF," the largest archival project ever approved for Hubble. SKYSURF aims to investigate the extragalactic background light using all 143,914 ACSWFC, WFC3UVIS, and WFC3IR images that have been taken by Hubble since its launch in 2002. SKYSURF has produced 38,027 single-visit mosaics and 7,893 multi-visit mosaics across 28 ACSWFC, WFC3UVIS, and WFC3IR filters using nonstandard drizzling methods, which include preserving the lowest sky-level of each visit/group in the drizzled products, applying wider apertures for cosmic-ray rejection, correcting effects caused by charge transfer efficiency degradation, and removing potential light gradients from input images via sky-map subtraction. We generate source catalogs for all drizzled products with SExtractor and provide updated star-galaxy separation parameters and integrated galaxy light (IGL) estimates for 25 of the 28 SKYSURF filters (wavelength range 0.2-1.7 um) using a novel IGL fitting method made possible by the vast SKYSURF dataset. We discuss the data processing and data analysis challenges encountered, detail our solutions, and offer suggestions that may facilitate future large-scale IGL investigations with Webb, SPHEREx, and Roman.

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SKYSURF IX -- The Cosmic Optical and Infrared Background from Integrated Galaxy Light Measurements

As part of the SKYSURF Hubble Space Telescope (HST) Legacy Archival program we present galaxy number counts which yield measurements of the extragalactic background light (EBL) at 15 different wavelengths. We have processed 82,752 HST images across 23 filters into 16,686 mosaics using the same software and processing pipeline throughout. Using 17/23 filters that give reliable galaxy counts, we constrain the integrated galaxy light (IGL) with a 1.5-9\% error between 0.3 and 1.6 $\mu$m in combination with 8 bands from WAVES (Wide Area VISTA Extragalactic Survey) and DEVILS (Deep Extragalactic Visible Legacy Survey). While HST was never intended to undertake large area surveys, through extensive quality control and filtering, we were able to extract a reliable and representative sample of fields distributed across the sky. Our final catalogs cover a combined $\approx 19.6 \deg^2$, with individual filters covering areas ranging from $\approx 0.16-7.0 \deg^2$. The combination of numerous independent sight-lines and area coverage allows us to reduce cosmic variance uncertainties in deep number counts to 0.06\%-1.8\%. For the first time we are able to establish a measurement of the IGL, $\mathrm{9.07 \pm 0.35 nW m^{-2} sr^{-1}}$, at 0.59 $\mu$m using HST data. We obtain a cosmic optical background value of $ 24.45 \pm 0.50 \mathrm{nW m^{-2} sr^{-1}}$. Different techniques used to measure the COB, both directly and indirectly, have recently converged indicating that the COB arises almost exclusively from processes within galaxies. This in combination with the recent values reported from New Horizons and very high energy (VHE) constraints leaves very little room for any diffuse emission coming from outside the Milky Way.

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