The expected yield of potentially Earth-like planets is a useful metric for designing future exoplanet-imaging missions. Recent yield studies of direct-imaging missions have focused primarily on yield methods and trade studies using "toy" models of missions. Here we increase the fidelity of these calculations substantially, adopting more realistic exoplanet demographics as input, an improved target list, and a realistic distribution of exozodi levels. Most importantly, we define standardized inputs for instrument simulations, use these standards to directly compare the performance of realistic instrument designs, include the sensitivity of coronagraph contrast to stellar diameter, and adopt engineering-based throughputs and detector parameters. We apply these new high-fidelity yield models to study several critical design trades: monolithic vs segmented primary mirrors, on-axis vs off-axis secondary mirrors, and coronagraphs vs starshades. We show that as long as the gap size between segments is sufficiently small (ă 0.1% of telescope diameter), there is no difference in yield for coronagraph-based missions with monolithic off-axis telescopes and segmented off-axis telescopes, assuming that the requisite engineering constraints imposed by the coronagraph can be met in both scenarios. We show that there is currently a factor of "2 yield penalty for coronagraph-based missions with on-axis telescopes compared to off-axis telescopes, and note that there is room for improvement in coronagraph designs for on-axis telescopes. We also reproduce previous results in higher fidelity showing that the yields of coronagraph-based missions continue to increase with aperture size while the yields of starshade-based missions turnover at large apertures if refueling is not possible. Finally, we provide absolute yield numbers with uncertainties that include all major sources of astrophysical noise to guide future mission design.

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 − 5.3µm and higher resolution (R = 500− 1340 or R = 1320− 3600) grating spectroscopy over 0.7 − 5.2µm, both in singleobject mode employing any one of five fixed slits, or a 3.1×3.2 arcsec 2 integral field unit, or in multiobject mode employing a novel programmable micro-shutter device covering a 3.6×3.4 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.

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.

We have performed deep imaging of a diverse sample of 26 low surface brightness galaxies (LSBGs) in the optical and the near-infrared. Using stellar population synthesis models, we find that it is possible to place constraints on the ratio of young to old stars (which we parameterise in terms of the average age of the galaxy), as well as the metallicity of the galaxy, using optical and near-infrared colours. LSBGs have a wide range of morphologies and stellar populations, ranging from older, high metallicity earlier types to much younger and lower metallicity late type galaxies. Despite this wide range of star formation histories, we find that colour gradients are common in LSBGs. These are most naturally interpreted as gradients in mean stellar age, with the outer regions of LSBGs having younger ages than their inner regions. In an attempt to understand what drives the differences in LSBG stellar populations, we compare LSBG average ages and metallicities with their physical parameters. Strong correlations are seen between a LSBG's star formation history and its K band surface brightness, K band absolute magnitude and gas fraction. These correlations are consistent with a scenario in which the star formation history of a LSBG primarily correlates with its surface density and its metallicity correlates both with its mass and surface density.Comment: 29 pages; 5 figures; re-submitted to MNRAS after replying to referee's repor

We describe how the James Webb Space Telescope (JWST) Near-Infrared Spectrograph's (NIRSpec's) detectors will be read out, and present a model of how noise scales with the number of multiple non-destructive reads samplingup-the-ramp. We believe that this noise model, which is validated using real and simulated test data, is applicable to most astronomical near-infrared instruments. We describe some non-ideal behaviors that have been observed in engineering grade NIRSpec detectors, and demonstrate that they are unlikely to affect NIRSpec sensitivity, operations, or calibration. These include a HAWAII-2RG reset anomaly and random telegraph noise (RTN). Using real test data, we show that the reset anomaly is: (1) very nearly noiseless and (2) can be easily calibrated out. Likewise, we show that large-amplitude RTN affects only a small and fixed population of pixels. It can therefore be tracked using standard pixel operability maps.

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The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST) offers the first opportunity to use integralfield 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 µm for a contiguous 3.1 × 3.2 sky area at spectral resolutions of R ≈ 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.

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