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We present the wide field slitless spectroscopy mode of the NIRISS instrument on the James Webb Space Telescope. This mode employs two orthogonal low-resolution (resolving power ≈150) grisms in combination with a set of six blocking filters in the wavelength range 0.8–2.3 μ m to provide a spectrum of almost every source across the field-of-view. When combined with the low background, high sensitivity and high spatial resolution afforded by the telescope, this mode will enable unprecedented studies of the structure and evolution of distant galaxies. We describe the performance of the as-built hardware relevant to this mode and expected imaging and spectroscopic sensitivity. We discuss operational and calibration procedures to obtain the highest quality data. As examples of the observing mode usage, we present details of two planned Guaranteed Time Observations programs: The Canadian NIRISS Unbiased Cluster Survey and The NIRISS Survey for Young Brown Dwarfs and Rogue Planets.

Little red dots (LRDs) are a high redshift galaxy population. Despite their high number densities, their nature is still uncertain. Here we present CANUCS-LRD-z8.6, a spectroscopically confirmed little red dot at a spectroscopic redshift of z spec  = 8.6319, hosting an active galactic nucleus. Its spectrum exhibits broad H β λ 4863 Å emission, high-ionization lines (C iv, N iv]), high electron temperature, which are indicative of active galactic nucleus activity, and low metallicity ( Z  < 0.1−0.2 Z ⊙ ). The inferred black hole mass, M BH = 1 . 0 − 0.4 + 0.6 × 1 0 8 M ⊙ , poses strong constraints on current black hole formation models and simulations. Additionally, its black hole is over-massive relative to its host, deviating from local M BH  −  M * relations, suggesting an early, rapid black hole growth preceding that of its galaxy. CANUCS-LRD-z8.6 may represent an evolutionary link between early massive black holes and the luminous quasars observed at z  = 6. Little Red Dots (LRDs) are a high-redshift galaxy population with unclear nature. Here, authors show CANUCS-LRD-z8.6, a spectroscopically confirmed LRD, hosting an active galactic nucleus, and its properties provide insights for early black hole and galaxy formation.

The IRAC mapping of the NMBS-II fields program is an imaging survey at 3.6 and 4.5 m with the Spitzer Infrared Array Camera (IRAC). The observations cover three Canada-France-Hawaii Telescope Legacy Survey Deep (CFHTLS-D) fields, including one also imaged by AEGIS, and two MUSYC fields. These are then combined with archival data from all previous programs into deep mosaics. The resulting imaging covers a combined area of about 3 deg2, with at least ∼2 hr integration time for each field. In this work, we present our data reduction techniques and document the resulting coverage maps at 3.6 and 4.5 m. All of the images are W-registered to the reference image, which is either the z-band stack image of the 25% best-seeing images from the CFHTLS-D for CFHTLS-D1, CFHTLS-D3, and CFHTLS-D4, or the K-band images obtained at the Blanco 4-m telescope at CTIO for MUSYC1030 and MUSYC1255. We make all images and coverage maps described here publicly available via the Spitzer Science Center.

The most distant galaxies detected were seen when the Universe was a scant 5% of its current age. At these times, progenitors of galaxies such as the Milky Way were about 10,000 times less massive. Using the James Webb Space Telescope (JWST) combined with magnification from gravitational lensing, these low-mass galaxies can not only be detected but also be studied in detail. Here we present JWST observations of a strongly lensed galaxy at z spec  = 8.296 ± 0.001, showing massive star clusters (the Firefly Sparkle) cocooned in a diffuse arc in the Canadian Unbiased Cluster Survey (CANUCS) 1 . The Firefly Sparkle exhibits traits of a young, gas-rich galaxy in its early formation stage. The mass of the galaxy is concentrated in 10 star clusters (49–57% of total mass), with individual masses ranging from 10 5 M ⊙ to 10 6 M ⊙ . These unresolved clusters have high surface densities (>10 3 M ⊙  pc − 2 ), exceeding those of Milky Way globular clusters and young star clusters in nearby galaxies. The central cluster shows a nebular-dominated spectrum, low metallicity, high gas density and high electron temperature, hinting at a top-heavy initial mass function. These observations provide our first spectrophotometric view of a typical galaxy in its early stages, in a 600-million-year-old Universe. JWST observations of a strongly lensed low-mass galaxy in a 600-million-year-old Universe show massive star clusters (the Firefly Sparkle) cocooned in a diffuse arc in the Canadian Unbiased Cluster Survey.

The identification of sources driving cosmic reionization, a major phase transition from neutral hydrogen to ionized plasma around 600–800 Myr after the Big Bang 1 – 3 , has been a matter of debate 4 . Some models suggest that high ionizing emissivity and escape fractions ( f esc ) from quasars support their role in driving cosmic reionization 5 , 6 . Others propose that the high f esc values from bright galaxies generate sufficient ionizing radiation to drive this process 7 . Finally, a few studies suggest that the number density of faint galaxies, when combined with a stellar-mass-dependent model of ionizing efficiency and f esc , can effectively dominate cosmic reionization 8 , 9 . However, so far, comprehensive spectroscopic studies of low-mass galaxies have not been done because of their extreme faintness. Here we report an analysis of eight ultra-faint galaxies (in a very small field) during the epoch of reionization with absolute magnitudes between M UV  ≈ −17 mag and −15 mag (down to 0.005 L ⋆ (refs.  10 , 11 )). We find that faint galaxies during the first thousand million years of the Universe produce ionizing photons with log[ ξ ion  (Hz erg −1 )] = 25.80 ± 0.14, a factor of 4 higher than commonly assumed values 12 . If this field is representative of the large-scale distribution of faint galaxies, the rate of ionizing photons exceeds that needed for reionization, even for escape fractions of the order of 5%. An analysis of eight ultra-faint galaxies during the epoch of reionization with absolute magnitudes between −17 mag and −15  mag shows that most of the photons that reionized the Universe come from dwarf galaxies.

We present a new technique for wide and shallow observations using the near-infrared channel of Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). Wide-field near-IR surveys with HST are generally inefficient, as guide star acquisitions make it impractical to observe more than one pointing per orbit. This limitation can be circumvented by guiding with gyros alone, which is possible as long as the telescope has three functional gyros. The method presented here allows us to observe mosaics of eight independent WFC3-IR pointings in a single orbit by utilizing the fact that HST drifts by only a very small amount in the 25 s between non-destructive reads of unguided exposures. By shifting the reads and treating them as independent exposures the full resolution of WFC3 can be restored. We use this \"drift and shift\" (DASH) method in the Cycle 23 COSMOS-DASH program, which will obtain 456 WFC3 H160 pointings in 57 orbits, covering an area of 0.6 degree in the COSMOS field down to H160 = 25. When completed, the program will more than triple the area of extra-galactic survey fields covered by near-IR imaging at HST resolution. We demonstrate the viability of the method with the first four orbits (32 pointings) of this program. We show that the resolution of the WFC3 camera is preserved, and that structural parameters of galaxies are consistent with those measured in guided observations.

We present the wide field slitless spectroscopy mode of the NIRISS instrument on the James Webb Space Telescope. This mode employs two orthogonal low-resolution (resolving power ≈150) grisms in combination with a set of six blocking filters in the wavelength range 0.8–2.3 μm to provide a spectrum of almost every source across the field-of-view. When combined with the low background, high sensitivity and high spatial resolution afforded by the telescope, this mode will enable unprecedented studies of the structure and evolution of distant galaxies. We describe the performance of the as-built hardware relevant to this mode and expected imaging and spectroscopic sensitivity. We discuss operational and calibration procedures to obtain the highest quality data. As examples of the observing mode usage, we present details of two planned Guaranteed Time Observations programs: The Canadian NIRISS Unbiased Cluster Survey and The NIRISS Survey for Young Brown Dwarfs and Rogue Planets.

We present a new technique for wide and shallow observations using the near-infrared channel of Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). Wide-field near-IR surveys with HST are generally inefficient, as guide star acquisitions make it impractical to observe more than one pointing per orbit. This limitation can be circumvented by guiding with gyros alone, which is possible as long as the telescope has three functional gyros. The method presented here allows us to observe mosaics of eight independent WFC3-IR pointings in a single orbit by utilizing the fact that HST drifts by only a very small amount in the 25 s between non-destructive reads of unguided exposures. By shifting the reads and treating them as independent exposures the full resolution of WFC3 can be restored. We use this “drift and shift” (DASH) method in the Cycle 23 COSMOS-DASH program, which will obtain 456 WFC3 H 160 pointings in 57 orbits, covering an area of 0.6 degree in the COSMOS field down to H 160 = 25. When completed, the program will more than triple the area of extra-galactic survey fields covered by near-IR imaging at HST resolution. We demonstrate the viability of the method with the first four orbits (32 pointings) of this program. We show that the resolution of the WFC3 camera is preserved, and that structural parameters of galaxies are consistent with those measured in guided observations.

Deep near-infrared imaging surveys allow us to select and study distant galaxies in the rest-frame optical, and have transformed our understanding of the early Universe. As the vast majority of K K - or IRAC-selected galaxies are too faint for spectroscopy, the interpretation of these surveys relies almost exclusively on photometric redshifts determined from fitting templates to the broadband photometry. The best-achieved accuracy of these redshifts,Δz/(1 + z) ≳ 0.06 Δ z / ( 1 + z ) ≳ 0.06 at z > 1.5 z > 1.5 , is sufficient for determining the broad characteristics of the galaxy population but not for measuring accurate rest-frame colors, stellar population parameters, or the local galaxy density. We have started a near-infrared imaging survey with the NEWFIRM camera on the Kitt Peak 4-m telescope to greatly improve the accuracy of photometric redshifts in the range1.5 ≲ z ≲ 3.5 1.5 ≲ z ≲ 3.5 . The survey uses five medium-bandwidth filters, which provide crude “spectra” over the wavelength range 1–1.8 μm for all objects in the27.6′ × 27.6′ 27.6 ′ × 27.6 ′ NEWFIRM field. In this first paper, we illustrate the technique by showing medium-band NEWFIRM photometry of several galaxies at1.7 < z < 2.7 1.7 < z < 2.7 from the recent near-infrared spectroscopic sample of Kriek et al.. The filters unambiguously pinpoint the location of the redshifted Balmer break in these galaxies, enabling very accurate redshift measurements. The full survey will provide similar data for∼8000 ∼ 8000 faint K K -selected galaxies at z > 1.5 z > 1.5 in the COSMOS and AEGIS fields. The filter set also enables efficient selection of exotic objects such as high-redshift quasars, galaxies dominated by emission lines, and very cool brown dwarfs; we show that late T and candidate Y dwarfs could be identified using only two of the filters.

Comparing galaxies across redshifts at fixed cumulative number density is a popular way to estimate the evolution of specific galaxy populations. This method ignores scatter in mass accretion histories and galaxy-galaxy mergers, which can lead to errors when comparing galaxies over large redshift ranges (Delta z > 1). We use abundance matching in the LCDM paradigm to estimate the median change in number density with redshift and provide a simple fit (+0.16 dex per unit Delta z) for progenitors of z = 0 galaxies. We find that galaxy descendants do not evolve in the same way as galaxy progenitors, largely due to scatter in mass accretion histories. We also provide estimates for the 1-sigma range of number densities corresponding to galaxy progenitors and descendants. Finally, we discuss some limits on number density comparisons, which arise due to difficulties measuring physical quantities (e.g., stellar mass) consistently across redshifts. A public tool to calculate number density evolution for galaxies, as well as approximate halo masses, is available online.