James Colbert

We present far-ultraviolet (FUV) images and catalogs from the Hubble Space Telescope (HST) Advanced Camera for Surveys/Solar Blind Channel (ACS/SBC) F150LP (∼1600 Å) of three extragalactic fields: GOODS-S, GOODS-N, and COSMOS. The data comprise 365 orbits of high-resolution imaging of 151 pointings covering an area of 44.7 arcmin ² to typical depths of FUV ≈ 28.7 AB (3 σ , 0 . ″ 5-diameter aperture). We provide a new model of the spatially varying dark “glow” created from all 365 orbits of data, and we scale and subtract it from all pointings. We provide drizzled image mosaics, weight maps, and exposure time maps matched in coordinates and pixel scale to the Hubble Legacy Fields frame and original COSMOS tiles. Galaxy photometry is measured within isophotes defined with existing deep Hubble F606W or F814W optical filters. We detect 1068 FUV sources and provide catalogs of all optical detections, and we include matched IDs to existing 3D-HST and CANDELS catalogs. The redshift distribution of FUV-detected galaxies peaks at z ∼ 0.6 and falls until z = 1.2, where the Lyman limit shifts redward of any filter transmission. These data fill the redshift gap of high-resolution FUV imaging between z ∼ 0 and z > 1, allowing for studies of star-forming regions, dust properties, the FUV extragalactic background, and Lyman continuum emission from z > 1.2 galaxies.

We consider the application of an übercalibration -like relative flux calibration to the grism observations of the Roman High Latitude Wide Area Survey (HLWAS). We propose a simplified model of the calibration with (i) an independent flat field for each detector in each exposure of the focal plane. In addition, we include two wavelength dependent components: (ii) a single wavelength throughput curve, modulated by (iii) a simple parabolic model for the throughput as a function of a source’s focal plane position. We consider the impact of the dither scale, as well as the calibrator star magnitude cuts. We show that the width of the calibration residuals can be reduced to less than 1.5 mmag, or 0.15% in flux, within the optimal dither range 50″–240″. This wide range allows for significant flexibility in optimizing other parts of the observing program without diminishing the effectiveness of the relative flux calibration. We also discuss some improvements to the methodology that must be strongly considered before the calibration can be applied to real data. Finally, although we focused on the spectroscopic component of the HLWAS here, our formalism and results should carry over to the imaging surveys as well.

Environment plays a crucial role in shaping galaxy formation, yet the impact of overdensities on the internal chemical structure of galaxies at cosmic noon is still under debate. Here, we present spatially resolved gas-phase metallicity gradients for 42 star-forming galaxies in three massive protoclusters at z ∼ 2.3, derived from Hubble Space Telescope slitless grism spectroscopy from the MAMMOTH-Grism survey. We find that the majority (29 of 42, ∼69%) of these protocluster members exhibit positive (inverted) metallicity gradients, a fraction significantly higher than observed in field galaxies of similar mass and redshift. By examining correlations with global properties, we show that these positive gradients are strongly associated with galaxies that are metal-deficient relative to the field mass–metallicity relation, particularly among the massive population ( log ( M * / M ⊙ ) > 9.95 ). These trends suggest that galaxies in dense protocluster environments experience substantial, enhanced inflows of pristine gas toward their central regions, which dilute the central metallicity and produce the observed inverted gradients. Our results provide observational evidence that environmental effects actively regulate gas accretion and chemical redistribution during the peak epoch of cosmic star formation.

We present the Parallel Application of Slitless Spectroscopy to Analyze Galaxy Evolution (PASSAGE) spectroscopic redshift catalog in the COSMOS field. PASSAGE is a JWST Cycle 1 Near Infrared Imager and Slitless Spectrograph (or NIRISS) wide-field slitless spectroscopy pure-parallel survey, obtaining near-infrared spectra of thousands of extragalactic sources. Fifteen out of 63 PASSAGE fields fall within the Hubble Space Telescope COSMOS footprint, of which 11 overlap with COSMOS-Web, a JWST treasury survey providing additional space-based photometry. We present our custom line-finding algorithm and visual inspection effort used to identify emission lines and derive the spectroscopic redshifts for line-emitting sources in PASSAGE. The line-finding algorithm identifies between ∼200 and 950 line-emitting candidates per field, of which typically 47% were identified as true emission lines post visual inspection. We identify 2183 emission-line sources at 0.08 ≲ z ≲ 4.7, 1896 of which have available COSMOS photometric redshifts. We find excellent redshift agreement between the COSMOS photometric redshifts and the PASSAGE spectroscopic redshifts for strong (signal-to-noise ratio > 5), multi-line-emitting sources. This agreement weakens for PASSAGE single-line emitters with ambiguous identities. These single-line emitters are likely misidentified around 18% of the time based on comparisons to photometric redshifts. We derive stellar masses using PASSAGE photometry and spectroscopic redshifts, in broad agreement with existing COSMOS-Web stellar masses, but with some discrepancy driven by redshift disagreements. We publicly release this spectroscopic redshift catalog, which will enable community-led science in prime extragalactic fields and serve as a crucial dataset for validating Euclid and Roman spectroscopy.

We analyze nebular dust attenuation and its correlation with stellar mass ( M _* ) and ultraviolet (UV) spectral slope ( β ) in 33 lensed, low-mass star-forming galaxies at 1.4 ≤ z ≤ 2.6, using Keck/Multi-Object Spectrometer For IR Exploration (MOSFIRE) rest-frame optical spectroscopy. Located behind three massive lensing galaxy clusters A1689, MACS J1149.5+2223, and MACS J0717.5+3745, galaxies in our sample have a median stellar mass of log ( M * / M ⊙ ) = 8.3 and an intrinsic UV absolute magnitude range of −20.9 < M _UV < −13. We measure nebular dust attenuation via Balmer optical depth ( τ _B ), defined as the H α /H β ratio. We also derive physical properties from Hubble Space Telescope multiwavelength photometry and construct composite spectra using median stacking in bins of M _* and β . We find that the τ _B – β relation for the dwarf galaxies in this study is best represented by the SMC dust curve. This is consistent with previous studies of low-metallicity galaxies at similar redshifts, which show a steep attenuation curve similar to the SMC curve, in contrast to high-metallicity and more massive galaxies that exhibit a much shallower dust attenuation curve. We also investigate the relationship between nebular dust attenuation and stellar mass, E ( B − V ) _nebular − M _* , down to log ( M * / M ⊙ ) ∼ 7 . We demonstrate that this relation does not notably evolve with redshift and is consistent with what has been observed for local Sloan Digital Sky Survey (SDSS) galaxies at similar low stellar masses.

We present one of the first measurements of the mass–metallicity relation (MZR) in multiple massive protoclusters at cosmic noon, using Hubble Space Telescope (HST) G141 slitless spectroscopy from the MAMMOTH-Grism survey. We identify 63 protocluster member galaxies across three overdense structures at z = 2–3 with robust detections of [O iii ], H β , and [O ii ] emission. The sample spans gas-phase metallicities of 12 + log ( O / H ) = 8.2 − 8.6 , dust-corrected H β -based star formation rates (SFRs) of 10–250 M _⊙ yr ⁻¹ , and stellar masses of M _* ∼ 10 ^9.4 –10 ^10.5 M _⊙ , derived via spectral energy distribution fitting using deep HST and ground-based photometry. We stack spectra in five M _* bins to obtain average metallicities and SFRs. Relative to field galaxies at similar redshifts, protocluster members show elevated SFRs at M _* < 10 ^10.25 M _⊙ and a systematically shallower MZR: 12 + log ( O / H ) =(6.96 ± 0.13) + (0.143 ± 0.017) × log ( M * / M ⊙ ) . We detect a mass-dependent environmental offset: massive protocluster galaxies are metal-poor compared to field counterparts of similar mass, whereas lower-mass systems exhibit comparable or mildly enhanced metallicities. This trend is consistent with a scenario where cold-mode accretion dilutes the interstellar medium (ISM) across the full mass range, while efficient recycling of feedback-driven outflows preferentially enriches the ISM in low-mass galaxies. Finally, we assess the dependence of metallicity offsets on local overdensity and find no significant trend, likely reflecting the survey’s bias toward protocluster cores.

The mechanisms of Ly α photon escape are key to understanding galaxy evolution and cosmic reionization, yet remain poorly understood. We investigate the UV-continuum sizes of 23 Ly α emitters (LAEs) at Cosmic Noon (1.7 < z < 3.3), extending previous size analyses to include fainter galaxies ( M _UV ≃ −14) using gravitational lensing. Our results show that these LAEs are unusually small for their luminosity, with a mean effective radius ( r _eff ) of 170 ± 140 pc. They follow a distinct size–luminosity relation, with an intercept at M _UV = −21 approximately three times smaller than typical star-forming galaxies (SFGs) at similar redshifts. This relation, however, is consistent with that of low-redshift Green Pea galaxies, suggesting that LAEs maintain compact sizes across redshifts. We also find that Ly α equivalent width increases with decreasing r _eff , confirming previous findings. The small sizes of LAEs lead to high star formation surface densities (ΣSFR =1–600 M _⊙ yr ⁻¹ kpc ⁻² ), clearly separating them from typical SFGs in the ΣSFR versus r _eff space. Given that high ΣSFR is linked to strong galactic outflows, our findings imply that compact morphology plays a key role in Ly α escape, likely facilitated by outflows that clear underdense channels in the intersetellar medium (ISM). Thus, these results demonstrate that compact size and high ΣSFR can help identify LAEs.

The MAMMOTH-MOSFIRE program is a deep Keck/MOSFIRE K -band spectroscopic follow-up of emission-line galaxies identified in the MAMMOTH-Grism Hubble Space Telescope/wide-field camera 3 G141 slitless spectroscopic survey, targeting the core regions of the three most massive galaxy protoclusters at cosmic noon. To introduce this program, we present a comprehensive analysis of the [N II ] λ 6584, [S II ] λλ 6717,6731, and [O I ] λ 6300 Baldwin, Philips, and Terlevich (BPT) diagnostics for a unique sample of 43 protocluster member galaxies at z ∼ 2, investigating how the overdense environment influences their interstellar medium ionization conditions. We find that, similar to their field counterparts at z ∼ 2, protocluster galaxies exhibit a systematic offset in the [N II ] BPT diagram relative to the local star-forming sequence, but no such offset in the [S II ] BPT diagram. Notably, we detect significantly elevated [O I ]/H α ratios, which can be well reproduced by photoionization models incorporating both H II regions and low-velocity shocks ( v ∼ 200 km s ⁻¹ ). We caution that neglecting shock excitation can bias abundance measurements, leading to an overestimation of nitrogen enrichment. This provides a potential explanation for the long-standing puzzle of enhanced [N II ]/H α ratios observed in z ∼ 2 galaxies. We further suggest that these shocks are likely environmentally driven, e.g., by ram pressure stripping or tidal interactions, which requires future confirmation through direct observations of features such as stripped gas tails.

During the second half of Cycle 1 of the James Webb Space Telescope (JWST), we conducted the Parallel Application of Slitless Spectroscopy to Analyze Galaxy Evolution (PASSAGE) program. PASSAGE received the largest allocation of JWST observing time in Cycle 1, 591 hr of NIRISS observations to obtain direct near-IR imaging and slitless spectroscopy. About two-thirds of this was ultimately executed, to observe 63 high-latitude fields in pure-parallel mode. These have provided more than 10,000 near-infrared grism spectrograms of faint galaxies. PASSAGE brings unique advantages in studying galaxy evolution: (a) Unbiased spectroscopic search, without prior photometric preselection. By including the typical galaxies which have low masses and strong emission lines, slitless spectroscopy is the indispensable complement to any pretargeted spectroscopy. (b) The combination of several dozen independent fields to overcome cosmic variance. (c) Near-infrared spectral coverage, spanning a wide wavelength range of up to 1.0 to 2.3 μ m, with minimal wavelength gaps, to measure multiple diagnostic rest-frame optical lines, minimizing sensitivity to dust reddening. (d) JWST’s unprecedented spatial resolution, in some cases using two orthogonal grism orientations, to overcome contamination due to blending of overlapping spectra. (e) Discovery of rare bright objects especially for detailed JWST follow-up. PASSAGE data are public immediately, and our team plans to deliver fully processed high-level data products. In this PASSAGE overview, we describe the survey and data quality, and present examples of these accomplishments in several areas of current interest in the evolution of emission-line galaxy properties, particularly at low masses.

Blocked impurity band arsenic-doped silicon detectors such as those used in the James Webb Space Telescope’s Mid-Infrared Instrument were invented in the 1980s to overcome many of the unwanted second-order effects found in the photoconductor detectors of that era. However, simply by virtue of operating the detectors at deep cryogenic temperatures (<10 K), non-ideal effects become inevitable, especially in the silicon readout integrated circuits that are hybridized with these detectors. Here, we describe a nonlinearity we have dubbed the Reset Switch Charge Decay effect. We discuss the physical origin and show the impact on both laboratory and flight data. Initial mitigation strategies show promise but are complicated by the fact that the magnitude of the effect depends on both the fluence and the flux of the incident signal, and the decay time appears to be readout speed dependent.