Vihang Mehta

The James Webb Space Telescope (JWST) has extended the frontier of galaxy detection to redshifts z > 11, finding a high abundance of UV-bright sources that challenge theoretical models. However, most current results come from just a few fields, introducing uncertainties due to cosmic variance. Here, we constrain z ∼ 7–14 UV luminosity functions (LFs) over ∼400 arcmin ² across 36 independent sight lines from Data Release 2 of BEACON, a JWST pure-parallel NIRCam multiband imaging survey. We identify 164 7 < z < 12 galaxy candidates: 150 F090W, 14 F115W, and no robust F150W dropouts. In the 11 pointings overlapping with public JWST spectroscopy, we find no contaminants, indicating a high purity in our sample. Our z ∼ 7.5 UV LF agrees with previous bright-end measurements but yields lower number densities at −21 ≤ M _UV ≤ −19. At z ∼ 10, our measurements are lower than most photometric JWST results but match spectroscopic constraints, consistent with the high purity of our selection. The LFs at z ∼ 7.5 and 10 are consistent with pre-JWST models, while our limits at z > 13 do not rule out a possible excess. We measure significant clustering of bright ( M _UV < −20.5) galaxies at 7 < z < 10. Fields hosting such sources are approximately 3 times more likely to be overdense relative to the full survey, implying that UV-bright galaxies preferentially reside in the most massive halos at these redshifts. Comparing with seminumerical simulations, we estimate that M _UV < −20.5 galaxies inhabit halos ∼0.8 dex less massive at z ∼ 11 than at z ∼ 8, consistent with a shift to higher star formation rates. However, their observed clustering exceeds predictions from pre-JWST luminosity–halo mass relations, suggesting these sources reside in more massive halos than previously modelled and/or multiple halo occupation.

We report the detection of a previously unknown object with a single emission line within the Hubble Ultra Deep Field, using a new JWST NIRSpec technique called Multiobject Coronagraphy for Slitless Spectroscopy (MOCSS) with the G140M/F100LP observing mode. The MOCSS technique involves opening almost all the shutters on the NIRSpec microshutter array, while simultaneously closing the shutters that lie on top of known low-redshift objects, facilitating a wide-field slitless spectroscopic search without contamination from bright objects. This observational technique has enabled the detection of a strong emission line in four different dither positions and in two position angles, and thus cannot be artificial. This line is detected at 1.60 μ m with a line flux of [2.5 ± 0.3] × 10 ⁻¹⁸ erg s ⁻¹ cm ⁻² and an FWHM of 13.2 ± 2.0 Å, and does not correspond to any known source with some of the deepest Hubble Space Telescope and JWST imaging in existence. Based upon the absence of imaging detection, we place a lower limit on the observed frame equivalent width (EW) of 7620 Å on this object, which strongly limits the number of possible lines that this line can be. Given the wavelength, an EW limit that is near the ceiling of expectation, and the lack of other lines in the bandpass, this line cannot be easily explained by [O ii ] at z = 3.29, [O iii ] at z = 2.20, H α at z = 1.44, and Ly α at z = 12.16. We discuss possible active galactic nucleus and transient phenomena that could explain the finding.

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.

Understanding the complicated processes that regulate star formation and cause a galaxy to become quiescent is key to our comprehension of galaxy evolution. We used eight well-resolved star-forming z < 0.3 galaxies from the UVCANDELS survey, where a total of 10 Hubble Space Telescope bands, including UV follow-up in UVIS/F275W, allow us to reconstruct the star formation histories (SFHs) of regions across each galaxy. This approach provides a powerful tool to explore the spatiotemporal connection between star formation and galaxy evolution. The spatial and temporal profiles of stellar mass and star formation rate (SFR) surface density were obtained from the SFHs of these regions. We measure scaling relations and projected radial profiles of regions within each galaxy at the time of observation and at 1 Gyr lookback time, noting possible trends in the evolution. By comparing the change in star formation over time, we can infer the timing and location of star formation and see early signs of star formation shutting off before quenching occurs. We compared the SFR density–stellar mass density scaling relations for individual galaxies as they evolve from 1 Gyr lookback time. The correlation lines pivot around a log-stellar mass surface density of 7.25 [ M _⊙ kpc ⁻² ], which may be evidence of a self-regulating process on these scales. Radial profiles of the galaxy logarithmic specific SFR (sSFR) show an overall decrease over 1 Gyr, but five galaxies show a greater change in log(sSFR) at the outskirts than the center, indicating a possible early onset of quenching in these galaxies.

We present a spectroscopic study of low-mass galaxies (LMGs;10 ⁸ ≤ M _* / M _⊙ ≤ 10 ⁹ ) at z ∼ 0.15 in the Cosmic Evolution Survey field, and compare it to a control sample of intermediate-mass galaxies (IMGs; 10 ⁹ ≤ M _* / M _⊙ ≤ 10 ¹⁰ ) at z ∼ 0.35. We examine their star formation rates (SFRs), dust attenuation properties, and the relationship between nebular and stellar reddening. For both samples, SFRs derived from H α are strongly correlated with SFRs from fitting simple star formation histories (SFHs) to the galaxies’ spectral energy distributions. In fitting a joint SFR– M _* relation, we obtain a slope of Δ log ( SFR H α ) / Δ log ( M * / M ⊙ ) = 1.01 ± 0.03 , indicating that fair ensembles of SFHs for galaxies at these stellar masses are well described by scale-free, self-similar forms. We also examine their dust attenuation properties and the relationship between nebular and stellar reddening, exploring how these quantities vary with stellar mass and specific star formation rate (sSFR). Nebular attenuation increases with stellar mass for IMGs but is lower and less mass dependent in LMGs, consistent with their reduced dust content. In all cases, stellar continuum attenuation is lower than nebular attenuation, as expected from the two-component dust model. The nebular-to-stellar color excess ratio in both samples is consistent with the canonical factor of 2.27. The ratio is mass independent, but rises with sSFR in IMGs and remains constant in LMGs. These results suggest that in LMGs, efficient dispersal of birth clouds keeps the differential attenuation approximately constant across sSFR. Thus, although LMGs follow the same global SFR– M _* scaling as massive galaxies, their lower dust content and feedback-maintained ISM produce distinct attenuation behavior relative to IMGs.

Modern surveys present us with billions of faint galaxies for which we only have broadband images in ∼6–8 optical-to-near-infrared (NIR) filters. Galaxy star formation rates (SFRs) are difficult to estimate accurately without spectroscopic diagnostics or far-infrared (FIR) photometry, both of which are prohibitively expensive to obtain for large numbers of faint, high-redshift galaxies. Here we present the empirical relation between SFR and broadband optical-to-NIR colors learned from Spitzer MIPS and Herschel PACS/SPIRE imaging using an innovative stacking analysis that bins galaxies with similar optical-to-NIR spectral energy distributions using a self-organizing map (SOM). Stacking based on optical-to-NIR colors ensures that our FIR stacks are built from galaxies with similar intrinsic physical properties as opposed to stacking simply by stellar mass. We train a 40 × 40 SOM using 230,638 galaxies selected from the Cosmic Evolution Survey (COSMOS) field, and stack the mid-IR to FIR images from 24–500 μ m. We are able to measure the median FIR luminosities from half of the SOM cells to calibrate the SFR. In addition to investigating the common structures of optical-to-NIR properties and FIR detections labeled on the SOM, we provide calibrated SFRs for nearly half of the galaxies in the COSMOS fields down to i -band magnitude ≤25.5, and present the evolution of the galaxy main sequence for low-mass galaxies to redshift z ∼ 2.5.

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.