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Abstract Supernovae (SNe) may be the dominant channel by which dust grains accumulate in galaxies during the first Gyr of cosmic time as formation channels important for lower-redshift galaxies, e.g., asymptotic giant branch stars and grain growth, may not have had sufficient time to take over. SNe produce fewer small grains, leading to a flatter attenuation law. In this work, we fit observations of 138 spectroscopically confirmedz > 6 galaxies adopting standard spectral energy distribution (SED) modeling assumptions and compare standard attenuation law prescriptions to a flat attenuation law. Compared to SMC dust, flat attenuation close to what may be expected from dust produced in SNe yields up to 0.5 mag higherA_Vand 0.4 dex larger stellar masses. It also finds better fits to the rest-frame UV photometry with lower ${\chi }_{\mathrm{UV}}^2$, allowing the observed UV luminosities taken from the models to be fainter by 0.2 dex on average. The systematically fainter observed UV luminosities for fixed observed photometry could help resolve current tension between the ionizing photon production implied by JWST observations and the redshift evolution of the neutral hydrogen fraction. Given these systematic effects and the physical constraint of cosmic time itself, fairly flat attenuation laws that could represent the properties of dust grains produced by SNe should be a standard consideration in fitting to the SEDs ofz > 6 galaxies. 

Abstract Measurements of galaxy rotation curves provide direct measurements of the distribution of baryonic and dark matter in galaxies. Here, we present spectroscopic confirmation and one such rotation curve for az = 0.5325 galaxy observed with Keck I/MOSFIRE as a filler target for the Web Epoch of Reionization Survey. The rotation curve was derived from Hα6563 Å emission out to a galactocentric radius of approximately 24 kpc. The target's rotation curve is well fit by an arctangent curve, that when combined with broadbanned photometric constraints on the galaxy’s stellar mass, predicts a dark matter fraction consistent with results from the literature forz ∼ 0.5. We constrain the estimate for this galaxy's dark matter fraction to be 93%, out to a galactocentric radius of 30 kpc. 

Abstract We present the COSMOS Spectroscopic Redshift Compilation encompassing ∼20 yr of spectroscopic redshifts within a 10 deg²area centered on the 2 deg²COSMOS legacy field. This compilation contains 487,666 redshifts of 266,284 unique objects from 138 individual programs up toz ∼ 8 with median stellar mass ∼10^8.4–10¹⁰M_⊙(redshift dependent). Rest-frameNUVrJcolors and star formation rate–stellar mass correlations show that the compilation primarily contains low-to-intermediate-mass star-forming and massive, quiescent galaxies atz < 1.25 and mostly low-mass bursty star-forming galaxies atz > 2. Sources in the compilation cover a diverse range of environments, including protoclusters such as “Hyperion.” The full compilation is 50% spectroscopically complete byi ∼ 23.4 mag andK_s ∼ 21.6 mag; however, this is redshift dependent. Spatially, the compilation is >50% (>30%) complete within the central (outer) region limited toi < 24 mag andK_s < 22.5 mag, separately. We demonstrate how the compilation can be used to validate photometric redshifts and investigate calibration metrics. By training self-organizing maps on COSMOS2020/Classic and projecting the compilation onto it, we find key subpopulations currently lacking spectroscopic coverage, includingz < 1 intermediate-mass quiescent and low-/intermediate-mass bursty star-forming galaxies,z ∼ 2 massive quiescent galaxies, andz > 3 massive star-forming galaxies. This highlights how combining self-organizing maps with our compilation can provide guidance for future spectroscopic observations to get a complete spectroscopic view of galaxy populations. Lastly, the compilation will undergo periodic data releases incorporating new spectroscopic redshifts and providing a lasting legacy resource for the community. 

Abstract We present the first results from the Web Epoch of Reionization LyαSurvey (WERLS), a spectroscopic survey of Lyαemission using Keck I/MOSFIRE and LRIS. WERLS targets bright (J< 26) galaxy candidates with photometric redshifts of 5.5 ≲z≲ 8 selected from pre-JWST imaging embedded in the Epoch of Reionization (EoR) within three JWST deep fields: CEERS, PRIMER, and COSMOS-Web. Here, we report 11z∼ 7–8 Lyαemitters (LAEs; three secure and eight tentative candidates) detected in the first five nights of WERLS MOSFIRE data. We estimate our observed LAE yield is ∼13%, which is broadly consistent with expectations assuming some loss from redshift uncertainty, contamination from sky OH lines, and that the Universe is approximately half-ionized at this epoch, whereby observable Lyαemission is unlikely for galaxies embedded in a neutral intergalactic medium. Our targets are selected to be UV-bright, and span a range of absolute UV magnitudes with −23.1 <M_UV< −19.8. With two LAEs detected atz= 7.68, we also consider the possibility of an ionized bubble at this redshift. Future synergistic Keck+JWST efforts will provide a powerful tool for pinpointing beacons of reionization and mapping the large-scale distribution of mass relative to the ionization state of the Universe. 

Abstract We report the discovery of 15 exceptionally luminous 10 ≲z≲ 14 candidate galaxies discovered in the first 0.28 deg²of JWST/NIRCam imaging from the COSMOS-Web survey. These sources span rest-frame UV magnitudes of −20.5 >M_UV> −22, and thus constitute the most intrinsically luminousz≳ 10 candidates identified by JWST to date. Selected via NIRCam imaging, deep ground-based observations corroborate their detection and help significantly constrain their photometric redshifts. We analyze their spectral energy distributions using multiple open-source codes and evaluate the probability of low-redshift solutions; we conclude that 12/15 (80%) are likely genuinez≳ 10 sources and 3/15 (20%) likely low-redshift contaminants. Three of ourz∼ 12 candidates push the limits of early stellar mass assembly: they have estimated stellar masses ∼ 5 × 10⁹M_⊙, implying an effective stellar baryon fraction ofϵ_⋆∼ 0.2−0.5, whereϵ_⋆≡M_⋆/(f_bM_halo). The assembly of such stellar reservoirs is made possible due to rapid, burst-driven star formation on timescales < 100 Myr where the star formation rate may far outpace the growth of the underlying dark matter halos. This is supported by the similar volume densities inferred forM_⋆∼ 10¹⁰M_⊙galaxies relative toM_⋆∼ 10⁹M_⊙—both about 10⁻⁶Mpc⁻³—implying they live in halos of comparable mass. At such high redshifts, the duty cycle for starbursts would be of order unity, which could cause the observed change in the shape of the UV luminosity function from a double power law to a Schechter function atz≈ 8. Spectroscopic redshift confirmation and ensuing constraints of their masses will be critical to understand how, and if, such early massive galaxies push the limits of galaxy formation in the Lambda cold dark matter paradigm.