The Near-Infrared Spectrograph (NIRSpec) is one of four science instruments on board the James Webb Space Telescope (JWST), which began routine operations in July 2022. As JWST's primary spectroscopic instrument for faint, distant targets, NIRSpec plays a central role in several of the mission's core science goals. Its signature multi-object spectroscopy (MOS) mode enables the simultaneous acquisition of spectra for up to a hundred targets across the field of view, using a micro-shutter array (MSA) comprised of nearly 250,000 individually addressable micro-electromechanical shutters. The MSA is susceptible to occasional electrical shorts, which produce unwanted infrared glow in MOS exposures, rendering them unusable and wasting valuable observatory time. Mitigation requires promptly identifying the affected shutter(s) and masking the corresponding row(s) or column(s) to prevent future activation. However, masking shutters unnecessarily reduces NIRSpec's multiplexing capacity, so it is important to minimize the extent of masking while reliably suppressing the short's effects. More than two years of operations have informed refinements in technical procedures and operational decision-making around short mitigation. This experience also supports new efforts to identify and unmask previously affected rows or columns where shorts have since disappeared, enabling the recovery of multiplexing capacity that would otherwise remain lost. As MSA technology matures toward use in future missions such as the Habitable Worlds Observatory, operational strategies developed for NIRSpec remain relevant beyond JWST. This paper provides an overview of MSA shorts mitigation operations, summarizes shorts observed since the completion of commissioning, and describes the evolving contingency procedures that have enabled continued science productivity from this unique payload.

The Near Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope affords the astronomical community an unprecedented space-based Multi-Object Spectroscopy (MOS) capability through the use of a programmable array of micro-electro-mechanical shutters. Launched in December 2021 and commissioned along with a suite of other observatory instruments throughout the first half of 2022, NIRSpec has been carrying out scientific observations since the completion of commissioning. These observations would not be possible without a rigorous program of engineering operations to actively monitor and maintain NIRSpec's hardware health and safety and enhance instrument efficiency and performance. Although MOS is only one of the observing modes available to users, the complexity and uniqueness of the Micro-Shutter Assembly (MSA) that enables it has presented a variety of engineering challenges, including the appearance of electrical shorts that produce contaminating glow in exposures. Despite these challenges, the NIRSpec Multi-Object Spectrograph continues to perform robustly with no discernible degradation or significant reduction in capability. This paper provides an overview of the NIRSpec micro-shutter subsystem's state of health and operability and presents some of the developments that have taken place in its operation since the completion of instrument commissioning.

We present a statistical study of 180 dust continuum sources identified in 33 massive cluster fields by the ALMA Lensing Cluster Survey (ALCS) over a total of 133 arcmin$^{2}$ area, homogeneously observed at 1.2 mm. ALCS enables us to detect extremely faint mm sources by lensing magnification, including near-infrared (NIR) dark objects showing no counterparts in existing {\it Hubble Space Telescope} and {\it Spitzer} images. The dust continuum sources belong to a blind sample ($N=141$) with S/N $\gtrsim$ 5.0 (a purity of $>$ 0.99) or a secondary sample ($N=39$) with S/N= $4.0-5.0$ screened by priors. With the blind sample, we securely derive 1.2-mm number counts down to $\sim7$ $\mu$Jy, and find that the total integrated 1.2mm flux is 20.7$^{+8.5}_{-6.5}$ Jy deg$^{-2}$, resolving $\simeq$ 80 % of the cosmic infrared background light. The resolved fraction varies by a factor of $0.6-1.1$ due to the completeness correction depending on the spatial size of the mm emission. We also derive infrared (IR) luminosity functions (LFs) at $z=0.6-7.5$ with the $1/V_{\rm max}$ method, finding the redshift evolution of IR LFs characterized by positive luminosity and negative density evolution. The total (=UV+IR) cosmic star-formation rate density (SFRD) at $z>4$ is estimated to be $161^{+25}_{-21}$ % of the established measurements, which were almost exclusively based on optical$-$NIR surveys. Although our general understanding of the cosmic SFRD is unlikely to change beyond a factor of 2, these results add to the weight of evidence for an additional ($\approx 60$ %) SFRD component contributed by the faint-mm population, including NIR dark objects.

Several theories have been proposed to describe the formation of black hole seeds in the early Universe and to explain the emergence of very massive black holes observed in the first thousand million years after the Big Bang(1-3). Models consider different seeding and accretion scenarios(4-7), which require the detection and characterization of black holes in the first few hundred million years after the Big Bang to be validated. Here we present an extensive analysis of the JWST-NIRSpec spectrum of GN-z11, an exceptionally luminous galaxy at z=10.6, revealing the detection of the [Neiv]lambda 2423 and CII*lambda 1335 transitions (typical of active galactic nuclei), as well as semi-forbidden nebular lines tracing gas densities higher than 10(9)cm(-3), typical of the broad line region of active galactic nuclei. These spectral features indicate that GN-z11 hosts an accreting black hole. The spectrum also reveals a deep and blueshifted CIV lambda 1549 absorption trough, tracing an outflow with velocity 800-1,000kms(-1), probably driven by the active galactic nucleus. Assuming local virial relations, we derive a black hole mass of log(M-BH/M-circle dot) = 6.2 +/- 0.3, accreting at about five times the Eddington rate. These properties are consistent with both heavy seeds scenarios and scenarios considering intermediate and light seeds experiencing episodic super-Eddington phases. Our finding explains the high luminosity of GN-z11 and can also provide an explanation for its exceptionally high nitrogen abundance.

ABSTRACT We present an interstellar medium and stellar population analysis of three spectroscopically confirmed z > 7 galaxies in the Early Release Observations JWST/NIRCam and JWST/NIRSpec data of the SMACS J0723.3−7327 cluster. We use the Bayesian spectral energy distribution-fitting code prospector with a flexible star formation history (SFH), a variable dust attenuation law, and a self-consistent model of nebular emission (continuum and emission lines). Importantly, we self-consistently fit both the emission line fluxes from JWST/NIRSpec and the broad-band photometry from JWST/NIRCam, taking into account slit-loss effects. We find that these three z=7.6–8.5 galaxies (M⋆ ≈ 108 M⊙) are young with rising SFHs and mass-weighted ages of 3–4 Myr, though we find indications for underlying older stellar populations. The inferred gas-phase metallicities broadly agree with the direct metallicity estimates from the auroral lines. The galaxy with the lowest gas-phase metallicity (Zgas= 0.06 Z⊙) has a steeply rising SFH, is very compact (<0.2 kpc), and has a high star formation rate surface density (ΣSFR ≈ 22 M⊙ yr−1 kpc−2), consistent with rapid gas accretion. The two other objects with higher gas-phase metallicities show more complex multicomponent morphologies on kpc scales, indicating that their recent increase in star formation rate is driven by mergers or internal, gravitational instabilities. We discuss effects of assuming different SFH priors or only fitting the photometric data. Our analysis highlights the strength and importance of combining JWST imaging and spectroscopy for fully assessing the nature of galaxies at the earliest epochs.

We present 12 new AGN at 410^44 erg/s, among galaxies in the redshift range 410%.

We analyse the gas-phase metallicity properties of a sample of low stellar mass (log M*/M_sun<= 9) galaxies at 36, with galaxies significantly less enriched (with a median offset in log(O/H) of ~ 0.5 dex, significant at ~ 5 sigma) than predicted given their M* and SFR. These observations are consistent with an enhanced stochasticity in the star-formation history, and/or with an increased efficiency in metal removals by outflows, prompting us to reconsider the nature of the relationship between M*, O/H, and SFR in the early Universe.

We report on James Webb Space Telescope (JWST) commissioning observations of the transiting exoplanet HAT-P-14 b, obtained using the Bright Object Time Series (BOTS) mode of the NIRSpec instrument with the G395H/F290LP grating/filter combination (3–5 μ m). While the data were used primarily to verify that the NIRSpec BOTS mode is working as expected, and to enable it for general scientific use, they yield a precise transmission spectrum which we find is featureless down to the precision level of the instrument, consistent with expectations given HAT-P-14 b’s small scale-height and hence expected atmospheric features. The exquisite quality and stability of the JWST/NIRSpec transit spectrum—almost devoid of any systematic effects—allowed us to obtain median uncertainties of 50–60 ppm in this wavelength range at a resolution of R = 100 in a single exposure, which is in excellent agreement with pre-flight expectations and close to the (or at the) photon-noise limit for a J = 9.094, F-type star like HAT-P-14. These observations showcase the ability of NIRSpec/BOTS to perform cutting-edge transiting exoplanet atmospheric science, setting the stage for observations and discoveries to be made in Cycle 1 and beyond.

Surveys with James Webb Space Telescope (JWST) have discovered candidate galaxies in the first 400 Myr of cosmic time. Preliminary indications have suggested these candidate galaxies may be more massive and abundant than previously thought. However, without confirmed distances, their inferred properties remain uncertain. Here we identify four galaxies located in the JWST Advanced Deep Extragalactic Survey (JADES) Near-Infrared Camera (NIRCam) imaging with photometric redshifts z 10-13. These galaxies include the first redshift z>12 systems discovered with distances spectroscopically confirmed by JWST in a companion paper. Using stellar population modelling, we find the galaxies typically contain a hundred million solar masses in stars, in stellar populations that are less than one hundred million years old. The moderate star formation rates and compact sizes suggest elevated star formation rate surface densities, a key indicator of their formation pathways. Taken together, these measurements show that the first galaxies contributing to cosmic reionisation formed rapidly and with intense internal radiation fields.

The Near-Infrared Spectrograph (NIRSpec) is one of the four focal plane instruments on the James Webb Space Telescope. In this paper, we summarize the in-orbit performance of NIRSpec, as derived from data collected during its commissioning campaign and the first few months of nominal science operations. More specifically, we discuss the performance of some critical hardware components such as the two NIRSpec Hawaii-2RG detectors, wheel mechanisms, and the microshutter array. We also summarize the accuracy of the two target acquisition procedures used to accurately place science targets into the slit apertures, discuss the current status of the spectrophotometric and wavelength calibration of NIRSpec spectra, and provide the "as measured" sensitivity in all NIRSpec science modes. Finally, we point out a few important considerations for the preparation of NIRSpec science programs.

The NIRSpec instrument on the James Webb Space Telescope (JWST) brings the first multi-object spectrograph (MOS) into space, enabled by a programmable Micro Shutter Array (MSA) of ∼250,000 individual apertures. During the 6-month Commissioning period, the MSA performed admirably, completing ∼800 reconfigurations with an average success rate of ∼96% for commanding shutters open in science-like patterns. We show that 82.5% of the unvignetted shutter population is usable for science, with electrical short masking now the primary cause of inoperable apertures. In response, we propose a plan to recheck existing shorts during nominal operations, which is expected to reduce the number of affected shutters. We also present a full assessment of the Failed Open and Failed Closed shutter populations, which both show a marginal increase in line with predictions from ground testing. We suggest an amendment to the Failed Closed shutter flagging scheme to improve flexibility for MSA configuration planning. Overall, the NIRSpec MSA performed very well during Commissioning, and the MOS mode was declared ready for science operations on schedule.

The Near-Infrared Spectrograph (NIRSpec) is one the four focal plane instruments on the James Webb Space Telescope (JWST) which was launched on December 25, 2021. We present the in-flight status and performance of NIRSpec's detector system as derived from the instrument commissioning data. The instrument features two 2048 x 2048 HAWAII-2RG sensor chip assemblies (SCAs) that are operated at a temperature of about 42.8 K and are read out via a pair of SIDECAR ASICs. NIRSpec supports "Improved Reference Sampling and Subtraction" (IRS2) readout mode that was designed to meet NIRSpec's stringent noise requirements and to reduce 1/f and correlated noise. In addition, NIRSpec features subarrays optimized for bright object time series observations, e.g. for the observation of exoplanet transit around bright host stars. We focus on the dark signal as well as the read and total noise performance of the detectors.

We present an ALMA-Herschel joint analysis of sources detected by the ALMA Lensing Cluster Survey (ALCS) at 1.15 mm. Herschel/PACS and SPIRE data at 100–500 μm are deblended for 180 ALMA sources in 33 lensing cluster fields that are detected either securely (141 sources; in our main sample) or tentatively at S/N ≥ 4 with cross-matched HST/Spitzer counterparts, down to a delensed 1.15 mm flux density of ∼0.02 mJy. We performed far-infrared spectral energy distribution modeling and derived the physical properties of dusty star formation for 125 sources (109 independently) that are detected at >2σ in at least one Herschel band. A total of 27 secure ALCS sources are not detected in any Herschel bands, including 17 optical/near-IR-dark sources that likely reside at z = 4.2 ± 1.2. The 16th, 50th, and 84th percentiles of the redshift distribution are 1.15, 2.08, and 3.59, respectively, for ALCS sources in the main sample, suggesting an increasing fraction of z ≃ 1 − 2 galaxies among fainter millimeter sources (f 1150 ∼ 0.1 mJy). With a median lensing magnification factor of μ=2.6−0.8+2.6 , ALCS sources in the main sample exhibit a median intrinsic star formation rate of 94−54+84 M ⊙ yr−1, lower than that of conventional submillimeter galaxies at similar redshifts by a factor of ∼3. Our study suggests weak or no redshift evolution of dust temperature with L IR < 1012 L ⊙ galaxies within our sample at z ≃ 0 − 2. At L IR > 1012 L ⊙, the dust temperatures show no evolution across z ≃ 1–4 while being lower than those in the local universe. For the highest-redshift source in our sample (z = 6.07), we can rule out an extreme dust temperature (>80 K) that was reported for MACS0416 Y1 at z = 8.31.

The Near-Infrared Spectrograph (NIRSpec) on board of the James Webb Space Telescope will be the first multi-object spectrograph in space offering 250,000 configurable micro-shutters, apart from being equipped with an integral field unit and fixed slits. At its heart, the NIRSpec grating wheel assembly is a cryogenic mechanism equipped with six dispersion gratings, a prism, and a mirror. The finite angular positioning repeatability of the wheel causes small but measurable displacements of the light beam on the focal plane, precluding a static solution to predict the light-path. To address that, two magneto-resistive position sensors are used to measure the tip and tilt displacement of the selected GWA element each time the wheel is rotated. The calibration of these sensors is a crucial component of the model-based approach used for NIRSpec for calibration, spectral extraction, and target placement in the micro-shutters. In this paper, we present the results of the evolution of the GWA sensors performance and calibration from ground to space environments.

The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST) offers the first opportunity to use integral-field spectroscopy from space at near-infrared wavelengths. More specifically, NIRSpec's integral-field unit can obtain spectra covering the wavelength range $0.6 - 5.3~\mu$m for a contiguous 3.1 arcsec $\times$ 3.2 arcsec sky area at spectral resolutions of $R \approx 100$, 1000, and 2700. In this paper we describe the optical and mechanical design of the NIRSpec integral-field spectroscopy mode, together with its expected performance. We also discuss a few recommended observing strategies, some of which are driven by the fact that NIRSpec is a multipurpose instrument with a number of different observing modes, which are discussed in companion papers. We briefly discuss the data processing steps required to produce wavelength- and flux-calibrated data cubes that contain the spatial and spectral information. Lastly, we mention a few scientific topics that are bound to benefit from this highly innovative capability offered by JWST/NIRSpec.

We provide an overview of the design and capabilities of the near-infrared spectrograph (NIRSpec) onboard the James Webb Space Telescope. NIRSpec is designed to be capable of carrying out low-resolution ($R\!=30\!-330$) prism spectroscopy over the wavelength range $0.6-5.3\!~\mu$m and higher resolution ($R\!=500\!-1340$ or $R\!=1320\!-3600$) grating spectroscopy over $0.7-5.2\!~\mu$m, both in single-object mode employing any one of five fixed slits, or a 3.1$\times$3.2 arcsec$^2$ integral field unit, or in multiobject mode employing a novel programmable micro-shutter device covering a 3.6$\times$3.4~arcmin$^2$ field of view. The all-reflective optical chain of NIRSpec and the performance of its different components are described, and some of the trade-offs made in designing the instrument are touched upon. The faint-end spectrophotometric sensitivity expected of NIRSpec, as well as its dependency on the energetic particle environment that its two detector arrays are likely to be subjected to in orbit are also discussed.

The Near-Infrared Spectrograph (NIRSpec) is one of the four focal plane instruments on the James Webb Space Telescope which was launched on Dec. 25, 2021. We present an overview of the as-run NIRSpec commissioning campaign, with particular emphasis on the sequence of activities that led to the verification of all hardware components of NIRSpec. We also discuss the mechanical, thermal, and operational performance of NIRSpec, as well as the readiness of all NIRSpec observing modes for use in the upcoming JWST science program.

To achieve its ambitious scientific goals, the Near-Infrared Spectrograph, NIRSpec, on board the Webb Space Telescope, needs to meet very demanding throughput requirements, here quantified in terms of photon-conversion efficiency (PCE). During the calibration activities performed for the instrument commissioning, we have obtained the first in-flight measurements of its PCE and also updated the modeling of the light losses occurring in the NIRSpec slit devices. The measured PCE of NIRSpec fixed-slit and multi-object spectroscopy modes overall meets or exceeds the pre-launch model predictions. The results are more contrasted for the integral-field spectroscopy mode, where the differences with the model can reach −20%, above 4 μm, and exceed +30%, below 2 μm. Additionally, thanks to the high quality of the JWST point-spread function, our slit-losses, at the shorter wavelength, are significantly decreased with respect to the pre-flight modeling. These results, combined with the confirmed low noise performance of the detectors, make of NIRSpec an exceptionally sensitive spectrograph.

We provide an overview of the capabilities and performance of the Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST) when used in its multi-object spectroscopy (MOS) mode employing a novel Micro Shutter Array (MSA) slit device. The MSA consists of four separate 98 arcsec $\times$ 91 arcsec quadrants each containing $365\times171$ individually addressable shutters whose open areas on the sky measure 0.20 arcsec $\times$ 0.46 arcsec on a 0.27 arcsec $\times$ 0.53 arcsec pitch. This is the first time that a configurable multi-object spectrograph has been available on a space mission. The levels of multiplexing achievable with NIRSpec MOS mode are quantified and we show that NIRSpec will be able to observe typically fifty to two hundred objects simultaneously with the pattern of close to a quarter of a million shutters provided by the MSA. This pattern is fixed and regular, and we identify the specific constraints that it yields for NIRSpec observation planning. We also present the data processing and calibration steps planned for the NIRSpec MOS data. The significant variation in size of the mostly diffraction-limited instrument point spread function over the large wavelength range of 0.6-5.3 $\mu$m covered by the instrument, combined with the fact that most targets observed with the MSA cannot be expected to be perfectly centred within their respective slits, makes the spectrophotometric and wavelength calibration of the obtained spectra particularly complex. These challenges notwithstanding, the sensitivity and multiplexing capabilities anticipated of NIRSpec in MOS mode are unprecedented, and should enable significant progress to be made in addressing a wide range of outstanding astrophysical problems.