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Abstract We present in this paper (Paper II of the series) a 35 arcmin²JWST/NIRCam imaging and wide-field slitless spectroscopy mosaic centered on J0305–3150, a luminous quasar atz= 6.61. The F356W grism data reveal 124 [Oiii]+Hβemitters at 5.3 < z < 7, 53 of which constitute a protocluster spanning (10 cMpc)²across 6.5 < z < 6.8. We find no evidence of any broad-line active galactic nucleus (AGN) in individual galaxies or stacking, reporting a median HβFWHM of 585 ± 152 km s⁻¹; however, the mass–excitation diagram and “little red dot” color and compactness criteria suggest that there are a few AGN candidates on the outskirts of the protocluster. We fit the spectral energy distributions (SEDs) of the [Oiii] emitters withProspectorandBagpipesand find that none of the SED-derived properties (stellar mass, age, or star formation rate) correlate with proximity to the quasar. While there is no correlation between galaxy age and local galaxy density, we find modest correlations of local galaxy density with increasing stellar mass, decreasing 10–100 Myr star formation rate ratios, and decreasing nebular line equivalent widths. We further find that the protocluster galaxies are consistent with being more massive, being older, and hosting higher star formation rates than the field sample at the 3σlevel, distributed in a filamentary structure that supports inside-out formation of the protocluster. There is modest evidence that galaxy evolution proceeds differently as a function of the density of local environment within protoclusters during the epoch of reionization, and the central quasar has little effect on the galaxy properties of the surrounding structure. 

Abstract We present a stringent measurement of the dust-obscured star formation rate density (SFRD) atz= 4–6 from the ASPIRE JWST Cycle-1 medium and ALMA Cycle-9 large program. We obtained JWST/NIRCam grism spectroscopy and ALMA 1.2 mm continuum map along 25 independent quasar sightlines, covering a total survey area of  ∼35 arcmin²where we search for dusty star-forming galaxies (DSFGs) atz= 0–7. We identify eight DSFGs in seven fields atz= 4–6 through the detection of Hαor [O iii]λ5008 lines, including fainter lines such as Hβ, [O iii]λ4960, [N ii]λ6585, and [S ii]λλ6718,6733 for six sources. With this spectroscopically complete DSFG sample atz= 4–6 and negligible impact from cosmic variance (shot noise), we measure the infrared luminosity function (IRLF) down toL_IR ∼ 2 × 10¹¹L_⊙. We find flattening of IRLF atz= 4–6 towards the faint end (power-law slope $\alpha =0.59_{-0.45}^{+0.39}$). We determine the dust-obscured cosmic SFRD at this epoch to be $\log [{\rho }_{\mathrm{SFR},\mathrm{IR}}/(M_{\odot }{\mathrm{yr}}^{-1}{\mathrm{Mpc}}^{-3}\left)\right]=-1.52_{-0.13}^{+0.14}$. This is significantly higher than previous determinations using ALMA data in the Hubble Ultra Deep Field, which is void of DSFGs atz= 4–6 because of strong cosmic variance (shot noise). We conclude that the majority (66% ± 7%) of cosmic star formation atz ∼ 5 is still obscured by dust. We also discuss the uncertainty of SFRD propagated from far-IR spectral energy distribution and IRLF at the bright end, which will need to be resolved with future ALMA and JWST observations. 

Abstract A SPectroscopic survey of bIased halos in the Reionization Era is a quasar legacy survey primarily using JWST to target a sample of 25z > 6 quasars with NIRCam slitless spectroscopy and imaging. The first study in this series found evidence of a strong overdensity of galaxies around J0305−3150, a luminous quasar atz= 6.61, within a single NIRCam pointing obtained in JWST Cycle 1. Here we present the first results of a JWST Cycle 2 mosaic that covers 35 arcmin²with NIRCam imaging/wide-field slitless spectroscopy of the same field to investigate the spatial extent of the putative protocluster. The F356W grism data target [Oiii]+Hβat 5.3 < z < 7 and reveal a population of 124 line emitters down to a flux limit of 1.2 × 10⁻¹⁸erg s⁻¹cm⁻². Fifty-three of these galaxies lie at 6.5 < z < 6.8 spanning 10 cMpc on the sky, corresponding to an overdensity within a 2500 cMpc³volume of 12.5 ± 2.6, anchored by the quasar. Comparing to the [Oiii] luminosity function from the Emission line galaxies and Intergalactic Gas in the Epoch of Reionization project, we find a dearth of faint [Oiii] emitters at log(L/erg s⁻¹) < 42.3, which we suggest is consistent with either bursty star formation causing galaxies to scatter around the grism detection limit or modest suppression from quasar feedback. While we find a strong filamentary overdensity of [Oiii] emitters consistent with a protocluster, we suggest that we could be insensitive to a population of older, more massive Lyman break galaxies with weak nebular emission on scales >​​​​​​10 cMpc. 

Strong gravitational magnification enables the detection of faint background sources and allows researchers to resolve their internal structures and even identify individual stars in distant galaxies. Highly magnified individual stars are useful in various applications, including studies of stellar populations in distant galaxies and constraining dark matter structures in the lensing plane. However, these applications have been hampered by the small number of individual stars observed, as typically one or a few stars are identified from each distant galaxy. Here, we report the discovery of more than 40 microlensed stars in a single galaxy behind Abell 370 at redshift of 0.725 (dubbed ‘the Dragon arc’) when the Universe was half of its current age, using James Webb Space Telescope observations with the time-domain technique. These events were found near the expected lensing critical curves, suggesting that these are magnified stars that appear as transients from intracluster stellar microlenses. Through multi-wavelength photometry, we constrained their stellar types and found that many of them are consistent with red giants or supergiants magnified by factors of hundreds. This finding reveals a high occurrence of microlensing events in the Dragon arc and demonstrates that time-domain observations by the James Webb Space Telescope could lead to the possibility of conducting statistical studies of high-redshift stars. 

Abstract Low-luminosity active galactic nuclei (AGNs) with low-mass black holes (BHs) in the early universe are fundamental to understanding the BH growth and their coevolution with the host galaxies. Utilizing JWST NIRCam Wide Field Slitless Spectroscopy, we perform a systematic search for broad-line Hαemitters (BHAEs) atz≈ 4–5 in 25 fields of the A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) project, covering a total area of 275 arcmin². We identify 16 BHAEs with FWHM of the broad components spanning from ∼1000 to 3000 km s⁻¹. Assuming that the broad line widths arise as a result of Doppler broadening around BHs, the implied BH masses range from 10⁷to 10⁸M_⊙, with broad Hα-converted bolometric luminosities of 10^44.5–10^45.5erg s⁻¹and Eddington ratios of 0.07–0.47. The spatially extended structure of the F200W stacked image may trace the stellar light from the host galaxies. The Hαluminosity function indicates an increasing AGN fraction toward the higher Hαluminosities. We find possible evidence for clustering of BHAEs: two sources are at the same redshift with a projected separation of 519 kpc; one BHAE appears as a composite system residing in an overdense region with three close companion Hαemitters. Three BHAEs exhibit blueshifted absorption troughs indicative of the presence of high column density gas. We find that the broad-line-selected and photometrically selected BHAE samples exhibit different distributions in the optical continuum slopes, which can be attributed to their different selection methods. The ASPIRE broad-line Hαsample provides a good database for future studies of faint AGN populations at high redshift. 

Abstract Understanding when and how reionization happened is crucial for studying the early structure formation and the properties of the first galaxies in the Universe. Atz> 5.5, the observed intergalactic medium (IGM) optical depth shows a significant scatter, indicating an inhomogeneous reionization process. However, the nature of the inhomogeneous reionization remains debated. A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) is a JWST Cycle 1 program that has spectroscopically identified >400 [Oiii] emitters in 25 quasar fields atz> 6.5. Combined with deep ground-based optical spectroscopy of ASPIRE quasars, the ASPIRE program provides the current largest sample for IGM-galaxy connection studies during cosmic reionization. We present the first results of IGM effective optical depth measurements around [Oiii] emitters using 14 ASPIRE quasar fields. We find the IGM transmission is tightly related to reionization era galaxies to the extent that a significant excess of Lyαtransmission exists around [Oiii] emitters. We measure the stacked IGM effective optical depth of IGM patches associated with [Oiii] emitters and find they reach the same IGM effective optical depth at leastdz∼ 0.1 ahead of those IGM patches where no [Oiii] emitters are detected, supporting earlier reionization around [Oiii] emitters. Our results indicate an enhancement in IGM Lyαtransmission around [Oiii] emitters at scales beyond 25h⁻¹cMpc, consistent with the predicted topology of reionization from fluctuating UV background models. 

Abstract We characterize the multiphase circumgalactic medium (CGM) and galaxy properties atz= 6.0–6.5 in four quasar fields from the James Webb Space Telescope A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) program. We use the Very Large Telescope/X-shooter spectra of quasar J0305–3150 to identify one new metal absorber atz= 6.2713 with multiple transitions (Oi, Mgii, Feii,and Cii). They are combined with the published absorbing systems in Davies et al. at the same redshift range to form a sample of nine metal absorbers atz= 6.03–6.49. We identify eight galaxies within 1000 km s⁻¹and 350 kpc around the absorbing gas from the ASPIRE spectroscopic data, with their redshifts secured by [Oiii] (λλ4959, 5007) doublets and Hβemission lines. Our spectral energy distribution fitting indicates that the absorbing galaxies have stellar masses ranging from 10^7.2to 10^8.8M_⊙and metallicity between 0.02 and 0.4 solar. Notably, thez= 6.2713 system in the J0305–3150 field resides in a galaxy overdensity region, which contains two (tentatively) merging galaxies within 350 kpc and seven galaxies within 1 Mpc. We measure the relative abundances ofαelements to iron ([α/Fe]) and find that the CGM gas in the most overdense region exhibits a lower [α/Fe] ratio. Our modeling of the galaxy’s chemical abundance favors a top-heavy stellar initial mass function and hints that we may be witnessing the contribution of the first generation of Population III stars to the CGM at the end of the reionization epoch. 

The development of low-cost, highly efficient and stable electrocatalysts for the oxygen evolution reaction (OER) is of great significance for many promising energy storage and conversion applications, including metal–air batteries and water splitting technology. Here we report a layer-structured Ca 0.5 CoO 2 nanofibers composed of interconnected ultrathin nanoplates, synthesized using an electrospinning process. The OER activity of Ca 0.5 CoO 2 can be dramatically improved by iron doping, and the overpotential of Ca 0.5 Co 1− x Fe x O 2 ( x = 0.25) is only 346 mV at a current density of 10 mA cm −2 . The mass activity and intrinsic activity of Ca 0.5 Co 0.75 Fe 0.25 O 2 at 1.6 V are, respectively, ∼18.7 and ∼11.4 times higher than those of Ca 0.5 CoO 2 . Iron doping modifies the electronic structure of Ca 0.5 CoO 2 , resulting in partial oxidation of the surface cobalt and increased amount of highly oxidative species (O 2 2− /O 2 ). Consequently, Ca 0.5 Co 0.75 Fe 0.25 O 2 nanofibers with tuned electronic states have shown great potential as cost-effective and efficient electrocatalysts for OER. 

ABSTRACT The Merian survey is mapping ∼ 850 deg2 of the Hyper Suprime-Cam Strategic Survey Program (HSC-SSP) wide layer with two medium-band filters on the 4-m Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory, with the goal of carrying the first high signal-to-noise (S/N) measurements of weak gravitational lensing around dwarf galaxies. This paper presents the design of the Merian filter set: N708 (λc = 7080 Å, Δλ = 275 Å) and N540 (λc = 5400 Å, Δλ = 210 Å). The central wavelengths and filter widths of N708 and N540 were designed to detect the $$\rm H\alpha$$ and $$\rm [OIII]$$ emission lines of galaxies in the mass range $$8\lt \rm \log M_*/M_\odot \lt 9$$ by comparing Merian fluxes with HSC broad-band fluxes. Our filter design takes into account the weak lensing S/N and photometric redshift performance. Our simulations predict that Merian will yield a sample of ∼ 85 000 star-forming dwarf galaxies with a photometric redshift accuracy of σΔz/(1 + z) ∼ 0.01 and an outlier fraction of $$\eta =2.8~{{\ \rm per\ cent}}$$ over the redshift range 0.058 < z < 0.10. With 60 full nights on the Blanco/Dark Energy Camera (DECam), the Merian survey is predicted to measure the average weak lensing profile around dwarf galaxies with lensing S/N ∼32 within r < 0.5 Mpc and lensing S/N ∼90 within r < 1.0 Mpc. This unprecedented sample of star-forming dwarf galaxies will allow for studies of the interplay between dark matter and stellar feedback and their roles in the evolution of dwarf galaxies. 

Abstract The launch of JWST opens a new window for studying the connection between metal-line absorbers and galaxies at the end of the Epoch of Reionization. Previous studies have detected absorber–galaxy pairs in limited quantities through ground-based observations. To enhance our understanding of the relationship between absorbers and their host galaxies atz> 5, we utilized the NIRCam wide-field slitless spectroscopy to search for absorber-associated galaxies by detecting their rest-frame optical emission lines (e.g., [OIII] + Hβ). We report the discovery of a Mgii-associated galaxy atz= 5.428 using data from the JWST ASPIRE program. The Mgiiabsorber is detected on the spectrum of quasar J0305–3150 with a rest-frame equivalent width of 0.74 Å. The associated galaxy has an [OIII] luminosity of 10^42.5erg s⁻¹with an impact parameter of 24.9 pkpc. The joint Hubble Space Telescope–JWST spectral energy distribution (SED) implies a stellar mass and star formation rate ofM_*≈ 10^8.8M_⊙, star-formation rate  ≈ 10M_⊙yr⁻¹. Its [OIII] equivalent width and stellar mass are typical of [OIII] emitters at this redshift. Furthermore, connecting the outflow starting time to the SED-derived stellar age, the outflow velocity of this galaxy is ∼300 km s⁻¹, consistent with theoretical expectations. We identified six additional [OIII] emitters with impact parameters of up to ∼300 pkpc at similar redshifts (∣dv∣ < 1000 km s⁻¹). The observed number is consistent with that in cosmological simulations. This pilot study suggests that systematically investigating the absorber–galaxy connection within the ASPIRE program will provide insights into the metal-enrichment history in the early Universe.