Recent near-infrared power-spectra and panchromatic Extragalactic Background Light (EBL) measurements provide upper limits on the integrated near-infrared surface brightness (SB > ∼ 31mag arcsec −2 at 2µm) that may come from Population III (Pop III) stars and possible accretion disks around resulting stellar-mass black holes (BHs) in the epoch of First Light, broadly taken from z 7-17. Physical parameters for zero metallicity Pop III stars at z > ∼ 7 can be estimated from MESA stellar evolution models through helium-depletion, and for BH accretion disks from quasar microlensing results and multicolor accretion models. Second-generation non-zero metallicity stars can form at higher multiplicity, so that BH accretion disks may be fed by Roche-lobe overflow from lower-mass companions in their AGB stage. The near-infrared SB constraints can be used to calculate the number of caustic transits behind lensing clusters that the James Webb Space Telescope (JWST) and the next generation 25-39 m ground-based telescopes may detect for both Pop III stars and stellar mass BH accretion disks. Because Pop III stars and stellar mass BH accretion disks have sizes of a few×10 −11 arcsec at z > ∼ 7, typical caustic magnifications can be µ 10 4 -10 5 , with rise times of hours and decline times of < ∼ 1 year for cluster transverse velocities of v T < ∼ 1000 km s −1 . Microlensing by intracluster medium objects can modify transit magnifications, and lengthen visibility times. Depending on BH masses, accretion-disk radii and feeding efficiencies, stellar-mass BH accretion-disk caustic transits could outnumber those from Pop III stars. To observe Pop III caustic transits directly may require monitoring 3-30 lensing clusters to AB < ∼ 29 mag over a decade or more. Such a program must be started with JWST at the start of Cycle 1, and -depending on the role of microlensing in the Intra Cluster Light (ICL) -should be continued for decades with the next generation 25-39 m ground-based telescopes, where both JWST and the ground-based facilities each will play a unique and strongly complementary role.

While most of the inter-galactic medium (IGM) today is permeated by ionized hydrogen, it was largely filled with neutral hydrogen for the first 700 million years after the Big Bang. The process that ionized the IGM (cosmic reionization) is expected to be spatially inhomogeneous, with fainter galaxies playing a significant role. However, we still have only a few direct constraints on the reionization process. Here we report the first spectroscopic confirmation of two galaxies and very likely a third galaxy in a group (hereafter EGS77) at redshift z = 7.7, merely 680 Myrs after the Big Bang. The physical separation among the three members is < 0.7 Mpc. We estimate the radius of ionized bubble of the brightest galaxy to be about 1.02 Mpc, and show that the individual ionized bubbles formed by all three galaxies likely overlap significantly, forming a large yet localized ionized region, which leads to the spatial inhomogeneity in the reionization process. It is striking that two of three galaxies in EGS77 are quite faint in the continuum, thanks to our selection of reionizing sources using their Lyman-α line emission. Indeed, one is the faintest spectroscopically confirmed galaxy yet discovered at such high redshifts. Our observations provide direct constraints in the process of cosmic reionization, and allow us to investigate the properties of sources responsible for reionizing the universe.

We give an overview and describe the rationale, methods, and first results from NIRCam images of the JWST “Prime Extragalactic Areas for Reionization and Lensing Science” (PEARLS) project. PEARLS uses up to eight NIRCam filters to survey several prime extragalactic survey areas: two fields at the North Ecliptic Pole (NEP); seven gravitationally lensing clusters; two high redshift protoclusters; and the iconic backlit VV 191 galaxy system to map its dust attenuation. PEARLS also includes NIRISS spectra for one of the NEP fields and NIRSpec spectra of two high-redshift quasars. The main goal of PEARLS is to study the epoch of galaxy assembly, active galactic nucleus (AGN) growth, and First Light. Five fields—the JWST NEP Time-Domain Field (TDF), IRAC Dark Field, and three lensing clusters—will be observed in up to four epochs over a year. The cadence and sensitivity of the imaging data are ideally suited to find faint variable objects such as weak AGN, high-redshift supernovae, and cluster caustic transits. Both NEP fields have sightlines through our Galaxy, providing significant numbers of very faint brown dwarfs whose proper motions can be studied. Observations from the first spoke in the NEP TDF are public. This paper presents our first PEARLS observations, their NIRCam data reduction and analysis, our first object catalogs, the 0.9–4.5 μm galaxy counts and Integrated Galaxy Light. We assess the JWST sky brightness in 13 NIRCam filters, yielding our first constraints to diffuse light at 0.9–4.5 μm. PEARLS is designed to be of lasting benefit to the community.

Galaxies at high redshifts are a valuable tool for studying cosmic dawn, therefore it is crucial to reliably identify these galaxies. Here, we present an unambiguous and first simultaneous detection of both the Lyα emission and the Lyman break from a =  z 7.512 0.004 galaxy, observed in the Faint Infrared Grism Survey (FIGS). These spectra, taken with the G102 grism on the Hubble Space Telescope (HST), show a significant emission line detection 2 . The line flux is nearly a factor of four higher than that in the archival MOSFIRE spectroscopic observations. This is consistent with other recent observations, implying that groundbased near-infrared spectroscopy underestimates the total emission line fluxes, and if confirmed, can have strong implications for reionization studies that are based on ground-based Lyα measurements. A 4σ detection of the NV line in one PA also suggests a weak active galactic nucleus (AGN), and if confirmed, would make this source the highest-redshift AGN yet found. These observations from HST thus clearly demonstrate the sensitivity of the FIGS survey, and the capability of grism spectroscopy for studying the epoch of reionization.

Energetic feedback due to active galactic nuclei (AGNs) is likely to play an important role in the observed antihierarchical trend in the evolution of galaxies, and yet the energy injected into the circumgalactic medium by this process is largely unknown. One promising approach to constrain this feedback is through measurements of spectral distortions in the cosmic microwave background due to the thermal Sunyaev-Zeldovich (tSZ) effect, whose magnitude is directly proportional to the energy input by AGNs. With current instruments, making such measurements requires stacking large numbers of objects to increase signal-to-noise. While one possible target for such stacks is AGNs themselves, these are relatively scarce sources that contain contaminating emission that complicates tSZ measurements. Here we adopt an alternative approach and co-add South Pole Telescope SZ (SPT-SZ) survey data around a large set of massive quiescent elliptical galaxies at  z 0.5, which are much more numerous and less contaminated than active AGNs, yet are subject to the same feedback processes from the AGNs they hosted in the past. We use data from the Blanco Cosmology Survey and VISTA Hemisphere Survey to create a large catalog of galaxies split up into two redshift bins: one with 3394 galaxies at   z 0.5 1.0 and one with 924 galaxies at   z 1.0 1.5, with typical stellar masses of´ M 1.5 10 . 11We then co-add the emission around these galaxies, resulting in a measured tSZ signal at s 2.2 significance for the lower redshift bin and a contaminating signal at s 1.1 for the higher redshift bin. To remove contamination due to dust emission, we use SPT-SZ source counts to model a contaminant source population in both the SPT-SZ bands and Planck highfrequency bands for a subset of 937 galaxies in the low-redshift bin and 240 galaxies in the high-redshift bin. This increases our detection to s 3.6 for low redshifts and s 0.9 for high redshifts. We find the mean angularly integrated Compton-y values to be- 60 erg, respectively. These numbers are higher than expected from simple theoretical models that do not include AGN feedback, and serve as constraints that can be applied to current simulations of massive galaxy formation.