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Two images of the Seyfert galaxy NGC 6552 obtained with the F560W filter: the image on the left was observed with a single integration of 200 groups, while the image on the right was offset using APT and was observed with eight integrations of 25 groups. Both images have the same total integration time of 555 s.
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The detectors in the Mid-Infrared Instrument (MIRI) of the James Webb Space Telescope (JWST) are arsenic-doped silicon impurity band conduction (Si:As IBC) devices and are direct descendants of the Spitzer IRAC long wavelength arrays (channels 3 and 4). With appropriate data processing, they can provide excellent performance. In this paper we discu...
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The detectors in the Mid-Infrared Instrument (MIRI) of the James Webb Space Telescope (JWST) are arsenic-21 doped silicon impurity band conduction (Si:As IBC) devices and are direct descendants of the Spitzer IRAC22 long wavelength arrays (channels 3 and 4). With appropriate data processing, they can provide excellent per-23 formance. In this paper...
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... The first stage of the MRS pipeline 45,84 , which performs the detectorlevel corrections and transforms the ramps to slope detector images, was run with especial attention to identify and correct the cosmic-ray showers. We turned on the find_showers keyword of the jump pipeline step and used 60 s and 400 pixels for the time_masked_after_shower and max_extended_radius keywords. ...
The rapid assembly of the first supermassive black holes is an enduring mystery. Until now, it was not known whether quasar ‘feeding’ structures (the ‘hot torus’) could assemble as fast as the smaller-scale quasar structures. We present JWST/MRS (rest-frame infrared) spectroscopic observations of the quasar J1120+0641 at z = 7.0848 (well within the epoch of reionization). The hot torus dust was clearly detected at λrest ≃ 1.3 μm, with a black-body temperature of Tdust=1,413.5−7.4+5.7\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${T}_{{{{\rm{dust}}}}}=\text{1,413.5}_{-7.4}^{+5.7}$$\end{document} K, slightly elevated compared to similarly luminous quasars at lower redshifts. Importantly, the supermassive black hole mass of J1120+0641 based on the Hα line (accessible only with JWST), MBH = 1.52 ± 0.17 × 10⁹ M⊙, is in good agreement with previous ground-based rest-frame ultraviolet Mg ii measurements. Comparing the ratios of the Hα, Paα and Paβ emission lines to predictions from a simple one-phase Cloudy model, we find that they are consistent with originating from a common broad-line region with physical parameters that are consistent with lower-redshift quasars. Together, this implies that J1120+0641’s accretion structures must have assembled very quickly, as they appear fully ‘mature’ less than 760 Myr after the Big Bang.
... Total exposure times and the breakdown into groups and integrations are shown in Table 1. 4. DATA PROCESSING This section describes the data processing for SMILES, which is broadly similar to the reductions described in previous works (e.g. Yang et al. 2023b;Morrison et al. 2023;Pérez-González et al. 2024b). Data reduction is done using v1.12.5 of the JWST Calibration Pipeline (Bushouse et al. 2023) with CRDS 4 version 11.17.7 and CRDS context 1188. ...
... Stage 1 (calwebb detector1) of the JWST pipeline performs detector-level processing on raw ramp data, including corrections for non-linearity, reset anomaly, first and last frame effects, dark subtraction, and jump detection specific to the MIRI imager. Based on pre-flight ground-based and commissioning data (see also Yang et al. 2021, for MIRI data reduction simulations), we adopt the default parameters in the pipeline for this step; a detailed discussion of the non-ideal behaviors and the corrections implemented in stage 1 of the pipeline is presented in Morrison et al. (2023). As noted in that work, several artifacts are not currently addressed in the pipeline, including persistence, the cruciform feature of the PSF at F560W and F770W, interpixel capacitance, column and row striping, the first exposure effect, and the brighter-fatter effect (Argyriou et al. 2023b). ...
... Backgrounds in MIRI are a combination of sky background (dominated by zodi at shorter wavelengths, then thermal emission and scattering from the telescope at ≳ 15 µm ( Figure 10; Glasse et al. 2015;Rigby et al. 2023b) and detector effects that can cause large-scale gradients, row/column striping and tree rings that are largely static in detector coordinates for a given dataset (Morrison et al. 2023). As discussed in (Dicken et al. 2024), these latter effects are likely residuals from the current flat fielding and/or the dark/reset anomaly correction in stage 1. ...
The James Webb Space Telescope (JWST) is revolutionizing our view of the Universe through unprecedented sensitivity and resolution in the infrared, with some of the largest gains realized at its longest wavelengths. We present the Systematic Mid-infrared Instrument (MIRI) Legacy Extragalactic Survey (SMILES), an eight-band MIRI survey with Near-Infrared Spectrograph (NIRSpec) spectroscopic follow-up in the GOODS-S/HUDF region. SMILES takes full advantage of MIRI's continuous coverage from $5.6-25.5\,\mu$m over a $\sim34$ arcmin$^2$ area to greatly expand our understanding of the obscured Universe up to cosmic noon and beyond. This work, together with a companion paper by Rieke et al., covers the SMILES science drivers and technical design, early results with SMILES, data reduction, photometric catalog creation, and the first data release. As part of the discussion on early results, we additionally present a high-level science demonstration on how MIRI's wavelength coverage and resolution will advance our understanding of cosmic dust using the full range of polycyclic aromatic hydrocarbon (PAH) emission features from $3.3-18\,\mu$m. Using custom background subtraction, we produce robust reductions of the MIRI imaging that maximize the depths reached with our modest exposure times ($\sim0.6 - 2.2$ ks per filter). Included in our initial data release are (1) eight MIRI imaging mosaics reaching depths of $0.2-18\,\mu$Jy ($5\sigma$) and (2) a $5-25.5\,\mu$m photometric catalog with over 3,000 sources. Building upon the rich legacy of extensive photometric and spectroscopy coverage of GOODS-S/HUDF from the X-ray to the radio, SMILES greatly expands our investigative power in understanding the obscured Universe.
... The MIRI imager (MIRIM) uses a Si:As blocked impurity band conduction detector with 1032 × 1024 pixel 2 . Not all pixels are exposed to the incoming light (Ressler et al. 2015;Morrison et al. 2023). What is commonly addressed as the imager is the largest part on the right side of the detector with a Field of View (FoV) of about 74 × 113 arcsec 2 (nominal pixel scale of 110 mas pixel −1 ; Bouchet et al. 2015), but also the topleft region, which is designed for Lyot coronography, is also used for imaging, adding extra coverage in each exposure. ...
... We downloaded the level-1b, uncalibrated (_uncal) products from the Mikulski Archive for Space Telescopes. 14 These exposures were processed using a development version of the JWST pipeline 15 (Bushouse et al. 2023) through the stages 1 and 2 to obtain the level-2b (_cal) fits files, fully calibrated and unresampled images (see Morrison et al. 2023, andD. Dickens et al. 2024, in preparation). ...
... At faint magnitudes, the QFIT increases and the RADXS distribution becomes broader because the signal-to-noise ratio of the sources decreases, and so objects becomes progressively poorly measured, but the points are mostly centered at RADXS ∼ 0. Very-bright stars in the short-wavelength filters show an increasing QFIT and a positive trend for the RADXS. This behavior is likely due to a combination of various factors, including saturation, nonlinearity (although it is expected to be small; Morrison et al. 2023) and, most importantly, brighter-fatter (there is more flux just outside the core of the star, meaning the object is "fatter" than what the ePSF predicts; Argyriou et al. 2023, see also Section 3.3). Similar trends have been found for the NIRISS detector (Libralato et al. 2023). ...
Astrometry is one of the main pillars of astronomy, and one of its oldest branches. Over the years, an increasing number of astrometric works by means of Hubble Space Telescope (HST) data have revolutionized our understanding of various phenomena. With the launch of JWST, it becomes almost instinctive to want to replicate or improve these results with data taken with the newest, state-of-the-art, space-based telescope. In this regard, the initial focus of the community has been on the Near-Infrared detectors on board of JWST because of their high spatial resolution. This paper begins the effort to capture and apply what has been learned from HST to the Mid-InfraRed Instrument (MIRI) of JWST by developing the tools to obtain high-precision astrometry and photometry with its imager. We describe in detail how to create accurate effective point-spread-function (ePSF) models and geometric-distortion corrections, analyze their temporal stability, and test their quality to the extent of what is currently possible with the available data in the JWST MAST archive. We show that careful data reduction provides deep insight on the performance and intricacies of the MIRI imager, and of JWST in general. In an effort to help the community devise new observing programs, we make our ePSF models and geometric-distortion corrections publicly available.
... Due to the brightness of GJ 367, we were forced to use only five groups (up-the-ramp reads) per integration to avoid saturation. The first five groups of MIRI integrations are known to be plagued by the reset switch charge decay, and all bright pixels are affected by the brighter-fatter effect (Morrison et al. 2023;Wright et al. 2023). Additionally, the last group is known to be anomalous, with a downward offset proportional to the signal in the previous group (Morrison et al. 2023). ...
... The first five groups of MIRI integrations are known to be plagued by the reset switch charge decay, and all bright pixels are affected by the brighter-fatter effect (Morrison et al. 2023;Wright et al. 2023). Additionally, the last group is known to be anomalous, with a downward offset proportional to the signal in the previous group (Morrison et al. 2023). All of these effects introduce uncorrected nonlinearity, which we attempt to compensate for using our two-step up-the-ramp fitting process (described in Kempton et al. 2023 and Appendix A). ...
We present the mid-infrared (5–12 μ m) phase curve of GJ 367b observed by the Mid-Infrared Instrument on the James Webb Space Telescope (JWST). GJ 367b is a hot ( T eq = 1370 K), extremely dense (10.2 ± 1.3 g cm ⁻³ ) sub-Earth orbiting an M dwarf on a 0.32 day orbit. We measure an eclipse depth of 79 ± 4 ppm, a nightside planet-to-star flux ratio of 4 ± 8 ppm, and a relative phase amplitude of 0.97 ± 0.10, all fully consistent with a zero-albedo planet with no heat recirculation. Such a scenario is also consistent with the phase offset of 11°E ± 5° to within 2.2 σ . The emission spectrum is likewise consistent with a blackbody with no heat redistribution and a low albedo of A B ≈ 0.1, with the exception of one anomalous wavelength bin that we attribute to unexplained systematics. The emission spectrum puts few constraints on the surface composition but rules out a CO 2 atmosphere ≳1 bar, an outgassed atmosphere ≳10 mbar (under heavily reducing conditions), or an outgassed atmosphere ≳0.01 mbar (under heavily oxidizing conditions). The lack of day–night heat recirculation implies that 1 bar atmospheres are ruled out for a wide range of compositions, while 0.1 bar atmospheres are consistent with the data. Taken together with the fact that most of the dayside should be molten, our JWST observations suggest that the planet must have lost the vast majority of its initial inventory of volatiles.
... The stage 1 PIPELINE has a "Jump" step to mask out jumps caused by cosmic rays (Morrison et al. 2023). However, this step is not able to detect all of the corrupted jumps in the data sets impacted by this issue. ...
... The background emission dominates the source emission in all MIRI bands except F560W because the former rises strongly toward longer wavelengths. Upon viewing the images produced by stage 2, we noted some obvious "stripe-like" noise patterns in the vertical and/or horizontal directions (e.g., Figure 4 left; Morrison et al. 2023). To remove such noise, we first calculated the median of the pixels in each row, adopting a sigma clip (2σ) to avoid pixels illuminated by sources. ...
... Also, its flux in the three dithers declines chronologically. Therefore, we consider this source as a detector artifact, i.e., latent (persistence), which is common among IR detectors (e.g., Rieke 2007; Morrison et al. 2023). By carefully inspecting the three dithers, we find additional fainter sources in these observations with similar behaviors. ...
The Cosmic Evolution Early Release Science Survey (CEERS), targeting the Extended Groth Strip extragalactic field, is one of the James Webb Space Telescope Director’s Discretionary Early Release Science programs. To date, all observations have been executed and include NIRCam/MIRI imaging and NIRSpec/NIRCam spectroscopic exposures. Here we discuss the MIRI imaging, which includes eight pointings, four of which provide deep imaging with the bluer bands (F560W and F770W) and four of which provide contiguous wavelength coverage in F1000W, F1280W, F1500W, and F1800W, where two of these also include coverage in F770W and F2100W. We present a summary of the data, data quality, and data reduction. The data reduction is based on the jwst calibration pipeline combined with custom modifications and additional steps designed to enhance the output quality, including improvements in astrometry and the removal of detector artifacts. We estimate the image depth of the reduced mosaics and show that these generally agree with expectations from the Exposure Time Calculator. We compare the MIRI F560W and F770W flux densities for bright sources to measurements from Spitzer/IRAC Ch3 (5.8 μ m) and Ch4 (8.0 μ m), and we find that they agree with systematic differences of <0.1 mag. For the redder MIRI bands, we assess their quality by studying the spectral energy distributions (SEDs) of Galactic stars. The SEDs are consistent with the expected Rayleigh–Jeans law with a deviation of ∼0.03 mag, indicating that the MIRI colors are reliable. We also discuss all publicly released data products (images and source catalogs), which are available on the CEERS website ( https://ceers.github.io/ ).
... MIRI observers can take multiple integrations in a single exposure, and in that case, after a virtually instantaneous reset, the pixel starts integrating signal again. The default operation of the MIRI FPE in flight is to perform two reset frames in succession to mitigate reset switch charge decay effects, i.e., once to remove the integrated signal and again to set a solid zero point (Morrison, et al. 2023). ...
... An example of a MIRI pixel ramp is shown in Fig. 3. Instead of the output level increasing linearly with frame number (time) the slope of the ramp decreases. Traditionally a correction for this non-linearity is derived by (1) fitting a polynomial to the ramp, (2) using the linear term of the fit as a proxy for what the ramp would look like if not impacted by the cause behind the non-linearity, (3) a correction is defined as the ratio of the linear term and the polynomial fit, and that as a function of the DN level at each frame time (Morrison, et al. 2023). ...
... Assuming a perfectly uniform detector illumination and a perfectly uniform response for all pixels, this would imply a single global correction, derived as per the process described in Sect. 2.3 and illustrated in Fig. 2. In this simple case the uncertainties on the non-linearity solution would be linked to read-out noise, photon-noise, dark current noise, and the reset effects impacting the start of MIRI ramps (Morrison, et al. 2023). Although one would expect the global "classical" non-linearity solution to hold for all types of illumination -and indeed it does for low-contrast extended and semi-extended sources -it fails in regions of high contrast, for example for point sources. ...
The Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) uses three Si:As impurity band conduction (IBC) detector arrays. The output voltage level of each MIRI detector pixel is digitally recorded by sampling-up-the-ramp. For uniform or low-contrast illumination, the pixel ramps become non-linear in a predictable way, but in areas of high contrast, the non-linearity curve becomes much more complex. We provide observational evidence of the Brighter-Fatter Effect (BFE) in MIRI conventional and high-contrast coronographic imaging, low-resolution spectroscopy, and medium-resolution spectroscopy data and investigate the physical mechanism that gives rise to the effect on the detector pixel raw voltage integration ramps. We use public data from the JWST/MIRI commissioning and Cycle 1 phase. We also develop a numerical electrostatic model of the MIRI detectors using a modified version of the public Poisson_CCD code. The physical mechanism behind the MIRI BFE is fundamentally different to that of CCDs and Hawaii-2RG (H2RG) detectors. This is due to the largest majority of the MIRI photo-excited electric charges not being stored at the pixels but at the input to the MIRI detector unit cell buffer amplifier capacitance. The resulting detector voltage debiasing alters the electrostatic potential inside the infrared-active layer and causes new photo-excited electrons, generated at a bright pixel, to be guided to the neighboring fainter pixels. Observationally, the debiasing-induced BFE makes the JWST MIRI data yield 10-25 % larger and 0.5-8 % brighter point sources and spectral line profiles as a function of the output level covered by the detector pixels. We find that the profile of the shrinking detector depletion region has implications for developing a pixel ramp non-linearity model for point sources observed with MIRI.
... MIRI/MRS raw data come in the form of ramps, a sequence of detector frames where the per pixel signal (in units of Data Numbers or 'DN') rises with the increase in photo-charge collected as a function of time. These ramps are affected by a collection of electronic effects, covered in detail in Morrison, et al. (2023). The baseline data product assumed in this paper is a 2dimensional MRS detector plane 'slope' image, similar to the middle panel of Fig. 2, where the signal of each pixel has units of DN per second per pixel . ...
... One issue that arose very early in the MRS commissioning phase, while monitoring the signal in the wider gap between channels, is the fact that the MRS detector dark current seems to change drastically from one observation to the next (Morrison, et al. 2023). Currently, to address the issue of the varying dark current, the MRS calibration pipeline uses the gap region between the channels to estimate a single pedestal value (mean . ...
... The curvature of the MRS spectra on the detector result in a single cosmic ray shower appearing at multiple, separated locations in the data cube. Detector striping (discussed in Morrison, et al. (2023)) impacts the cube signal in a similar way, where brightness differences between detector columns intersect the curved MRS spectral traces. ...
The Medium-Resolution Spectrometer (MRS) provides one of the four operating modes of the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST). The MRS is an integral field spectrometer, measuring the spatial and spectral distributions of light across the 5-28 $\mu m$ wavelength range with a spectral resolving power between 3700-1300. We present the MRS' optical, spectral, and spectro-photometric performance, as achieved in flight, and report on the effects that limit the instrument's ultimate sensitivity. The MRS flight performance has been quantified using observations of stars, planetary nebulae, and planets in our Solar System. The precision and accuracy of this calibration is checked against celestial calibrators with well known flux levels and spectral features. We find that the MRS geometric calibration has a distortion solution accuracy relative to the commanded position of 8 mas at 5 $\mu m$ and 23 mas at 28 $\mu m$. The wavelength calibration is accurate to within 9 km/sec at 5 $\mu m$ and 27 km/sec at 28 $\mu m$. The uncertainty in the absolute spectro-photometric calibration accuracy is estimated at 5.6 +- 0.7 %. The MIRI calibration pipeline is able to suppress the amplitude of spectral fringes to below 1.5 % for both extended and point sources across the entire wavelength range. The MRS PSF is 60 % broader than the diffraction limit along its long axis at 5 $\mu m$ and is 15 % broader at 28 $\mu m$. The MRS flight performance is found to be better than pre-launch expectations. The MRS is one of the most subscribed observing modes of JWST and is yielding many high-profile publications. It is currently humanity's most powerful instrument for measuring the mid-infrared spectra of celestial sources and is expected to continue as such for many years to come.
Dusty star-forming galaxies emit most of their light at far-infrared to millimeter wavelengths as their star formation is highly obscured. Far-infrared and millimeter observations have revealed their dust, neutral and molecular gas properties. The sensitivity of JWST at rest-frame optical and near-infrared wavelengths now allows the study of the stellar and ionized gas content. We investigate the spatially resolved distribution and kinematics of the ionized gas in GN20, a dusty star-forming galaxy at $z$=4.0548. We present deep MIRI/MRS integral field spectroscopy of the near-infrared rest-frame emission of GN20. We detect spatially resolved out to a radius of 6 kpc, distributed in a clumpy morphology. The star formation rate derived from (144 pm 9 is only 7.7 $ 0.5 $ of the infrared star formation rate (1860 pm 90 We attribute this to very high extinction (A$_V$ = 17.2 pm 0.4 mag, or V,mixed $ = 44 pm 3 mag), especially in the nucleus of GN20, where only faint is detected, suggesting a deeply buried starburst. We identify four, spatially unresolved, clumps in the emission. Based on the double peaked profile, we find that each clump consists of at least two sub-clumps. We find mass upper limits consistent with them being formed in a gravitationally unstable gaseous disk. The ultraviolet bright region of GN20 does not have any detected emission, suggesting an age of more than 10 Myrs for this region of the galaxy. From the rotation profile of we conclude that the gas kinematics are rotationally dominated and the rot m 1.4$ is similar to low-redshift luminous infrared galaxies. From the kinematics, we cannot distinguish between a rotational profile of a large disk and a late stage merger mimicking a disk. We speculate that GN20 is in the late stage of a major merger, where the clumps in a large gas-rich disk are created by the major merger, while the central starburst is driven by the merger event.
Context . The James Webb Space Telescope (JWST) has now started its exploration of exoplanetary worlds. In particular, the Mid-InfraRed Instrument (MIRI) with its Low-Resolution Spectrometer (LRS) carries out transit, eclipse, and phase-curve spectroscopy of exoplanetary atmospheres with an unprecedented precision in a so far almost uncharted wavelength range.
Aims . The precision and significance in the detection of molecules in exoplanetary atmospheres relies on a thorough understanding of the instrument itself and on accurate data reduction methods. This paper aims to provide a clear description of the instrumental systematics that affect observations of transiting exoplanets through the use of simulations.
Methods . We carried out realistic simulations of transiting-exoplanet observations with the MIRI LRS instrument that included the model of the exoplanet system, the optical path of the telescope, the MIRI detector performances, and instrumental systematics and drifts that could alter the atmospheric features we are meant to detect in the data. After we introduce our pipeline, we show its performance on the transit of L 168-9b, a super-Earth-sized exoplanet observed during the commissioning of the MIRI instrument.
Results . This paper provides a better understanding of the data themselves and of the best practices in terms of reduction and analysis through comparisons between simulations and real data. We show that simulations validate the current data-analysis methods. Simulations also highlight instrumental effects that impact the accuracy of our current spectral extraction techniques. These simulations are proven to be essential in the preparation of JWST observation programs and help us to assess the detectability of various atmospheric and surface scenarios.
Context . The Medium Resolution integral field Spectrometer (MRS) of the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) performs spectroscopy between 5 and 28 µm, with a field of view varying from ~13 to ~56 sq. arcsec. The optics of the MRS introduce substantial distortion and this needs to be rectified in order to reconstruct the observed astrophysical scenario.
Aims . We aim to use data from the JWST/MIRI commissioning and cycle 1 calibration phase to derive the MRS geometric distortion and astrometric solution, a critical step in the calibration of MRS data. These solutions come in the form of transform matrices that map the detector pixels to spatial coordinates of a local MRS coordinate system called α / β , to the global JWST observatory coordinates V 2 and V 3 ( V 2+ V 3).
Methods . For every MRS spectral band and each slice dispersed on the detector, we fit the transform of detector pixels to α / β by a two-dimensional (2D) polynomial, using a raster of point source observations. The dispersed trace of the point source on the detector was initially estimated by fitting a one-dimensional (1D) empirical function and then iterating on the first distortion solution using forward modelling of the point spread function model based on the webbpsf python package. A polynomial transform was used to map the coordinates from α/ β to V 2+ V 3.
Results . We calibrated the distortion of all 198 discrete slices of the MIRI/MRS integral field units and derived an updated field of view (FoV) for each MRS spectral band. The precision of the distortion solution is estimated to be better than one-tenth of a spatial resolution element, with a root mean square (rms) of 10 milli-arc-second (mas) at 5 µm, to 23 mas at 27 µm. Finally, we found that the wheel positioning repeatability causes an additional astrometric rms error of 30 mas.
Conclusions . We demonstrate the application of the MRS astrometric calibration strategy and analysis for all four integral field units and all spectral bands of the MRS that enable the calibration of MRS spectra. This is a critical step in the data pipeline of every MRS observation. The distortion calibration was folded into the JWST pipeline in the Calibration Reference Data System (CRDS) context (jwst_1094.pmap), meeting the pre-launch requirement, with an estimated total astrometric uncertainty of 50 mas.
