P. Ferruit (ESA JWST project scientist)! Slide #1
Acknowledgements Thanks for giving me the opportunity to present the NIRSpec instrument. All along this presentation you will see the results of work conducted by a large number of teams in Europe, USA and Canada. Many elements of this presentation are based on existing presentations prepared by other members of the NIRSpec team as well as of the JWST project, the other instrument teams and STScI. Slide #2
Before we really start jwst.nasa.gov The flight instruments in the payload module (ISIM). The electronic boxes in their compartment. To get a better idea of the scale! The telescope with all the mirrors in place! (with protective covers) Slide #3
Table of contents NIRSpec The origin, the team and the hardware. NIRSpec The instrument - Spectral configurations and modes. NIRSpec - Multi-object spectroscopy mode (MOS). NIRSpec - Integral field spectroscopy mode (IFU). NIRSpec - Fixed slit spectroscopy mode (SLIT). Exoplanet transit spectroscopy. Conclusion. Backup slides (JWST visibility constraints). Slide #4
The origin Artist view D. Hardy Artist view R. Hurt JWST will be one of the major space-based observatories of the next decade and its science goals encompass a very broad set of topics. From P. Oesch et al. 2016 From Ellerbroek et al. 201 Charnay et al. arxiv:1510.01706 3D spectroscopy YSO disk-jet system Modeling GJ1214b Spectroscopy will be a key tool to achieve JWST science goals. Slide #5
The origin Artist view D. Hardy Artist view R. Hurt To achieve JWST science goals a near-infrared spectrograph was needed in the instrument suite. It should be capable of: Deep multi-object spectroscopy at low, medium (around 1000) resolution over a wide field of view. Spatially-resolved, single-object spectroscopy at high (a few thousands) spectral resolution over a small (a few arc seconds) field of view. High-contrast slit spectroscopy at various spectral resolutions, including an aperture for extra-solar planet transit observations. Slide #6
The origin NIRSpec is part of the European contribution to the JWST mission. ASWG recommendation in January 2000. Becomes part of ESA contribution in the following year. NIRSpec = Near-infrared Spectrograph Provided by the European Space Agency. Built by an industrial consortium led by Airbus Defence and Space. Slide #7
The team Built for ESA by an industrial consortium led by Airbus Defence and Space (Astrium GMBH at the time). NASA-provided the detectors and micro-shutter arrays. Slide #8
The hardware Figure credit: B. Dorner, PhD, 2012 Spectrograph region, including detectors Fore-optics region apertures Size: ~ 1.9 m x 1.3 m x 0.7 m Mass: < 220 kg Slide #9
The hardware NIRSpec flight model was delivered to NASA at the end of 2013. See also: Birkmann et al., proceedings of the SPIE, Volume 9143 (2014) Slide #10
The hardware NIRSpec was integrated JWST s payload module (ISIM) in 2014. The ISIM and the instruments are now ready for their integration on the telescope. NIRSpec Slide #11
The instrument Artist view D. Hardy Artist view R. Hurt To achieve JWST science goals a near-infrared spectrograph was needed in the instrument suite. It should be capable of: Deep multi-object spectroscopy at low, medium (around 1000) resolution over a wide field of view. Spatially-resolved, single-object spectroscopy at high (a few thousands) spectral resolution over a small (a few arc seconds) field of view. High-contrast slit spectroscopy at various spectral resolutions, including an aperture for extra-solar planet transit observations. Slide #12
The instrument Slide #13
JWST NIRSpec The instrument Yes this is a NIRSpec presentation but do not forget that in JWST, spectroscopy comes in many flavors. Always take a careful look and pick the instrument and the mode most suited to your science objectives. Instrument Type Wavelength (microns) Spectral resolution Field of view NIRISS slitless 1.0-2.5 ~150 2.2 x 2.2 NIRCam slitless 2.4-5.0 ~2000 2.2 x 2.2 NIRSpec MOS 0.6-5.3 100/1000/[2700] 9 square arcmin. NIRSpec IFU 0.6-5.3 100/1000/2700 3 x 3 MIRI IFU 5.0-28.8 2000-3500 >3 x >3.9 NIRSpec SLIT 0.6-5.3 100/1000/2700 Single object MIRI SLIT 5.0-10.0 60-140 Single object NIRSpec Aperture 0.6-5.3 100/1000/2700 Single object NIRISS Aperture 0.6-2.5 700 Single object Note: MIRI also has slitless spectroscopy capabilities over its imager field of view and over the 5.0-10.0 micron range. Slide #14
The instrument JWST/NIRSpec - spectral configurations 1 μm 2 μm 3 μm 4 μm 5 μm Low spectral resolution configuration Medium and high spectral resolution configurations 0.6 μm 5.3 μm 0.7 μm 1.2 μm 1.0 μm 1.8 μm 1.7 μm 3.1 μm 2.9 μm 5.2 μm At low spectral resolution, full coverage of the 0.6-5.3 micron range in one shot. R ~30-300 (low). Configurations that can be obtained thanks to a combination of filters and dispersers installed on two wheels (FWA and GWA) At medium and high spectral resolution, several exposures are necessary to cover the full wavelength range of NIRSpec. R ~1000 and ~2700. Slide #15
The instrument Again JWST offers a large variety of configurations. And NIRSpec proposes its share Slide #16
The instrument Nice emission-line diagnostics for galaxy assembly fans Classical diagnostics available in the near-infrared instruments Classical lines moving into the mid-infrared domain Slide #17
The instrument Or nice molecular bands / signatures for Y-dwarfs aficionados From C. Alves de Oliveira @JWST 2015 Slide #18
The instrument NIRSpec MOS field of view of 9 square arc minutes divided in 4 distinct quadrants, each with its associated array of microshutters for target selection. Slide #19
The instrument A complex field-of view layout / Competing for detector real estate MOS and IFU are competing for detector real estate. Mutually exclusive modes. A specific area is dedicated to the SLIT mode. 4 slits (+ one on the other side) MOS spectra SLIT spectra MOS+SLIT mode MOS spectra Slide #20
The instrument A complex field-of view layout / Competing for detector real estate MOS and IFU are competing for detector real estate. Mutually exclusive modes. A specific area is dedicated to the SLIT mode. IFU aperture IFU spectra SLIT spectra IFU 30 slices IFU spectra IFU+SLIT mode Slide #21
Multi-object spectroscopy (MOS) The challenge of multi-object spectroscopy Letting the light from selected objects go through while blocking the light from all the other objects. A configurable mask was needed. Using 4 arrays of 365x171 micro-shutters each, provided by NASA GSFC. This gives us a total of almost 250 000 small apertures that can be individually opened/ closed MEMS device 105x204 micron shutters We typically need > 85-90 % of the shutters operable. Slide #22
Multi-object spectroscopy (MOS) An unusual MOS: a regular grid of apertures. à à Finding the best combination of pointing parameters (RA, DEC, PA) AND the best list of targets. A dedicated tool is being developed for the preparation of the observations. In yellow: nonoperable shutters (cannot be opened) Only basic data processing applied Conceptual example on a very crowded field! Omega Centauri. http://www.stsci.edu/jwst/science/sodrm/highlightspecdensestellarfields.pdf Slide #23
Multi-object spectroscopy (MOS) An unusual MOS: a regular grid of apertures. à When observing a sample of objects, there will be a distribution of objects positions within the apertures. à For compact objects, better centering = more photons make it through the aperture, more accurate radiometric calibration. à Depending on the orientation of the telescope (known once the observation is scheduled), the list of observable objects may change. à Proposed sample will have to be able to cover for this feature. WORK IN PROGRESS, STAY TUNED. Only basic data processing applied Current version of the proposal preparation tools for JWST (same as HST): http://www.stsci.edu/hst/proposing/apt Slide #24
Example of MOS test data Opening a collection of dashed-slits. Only basic data processing applied Data obtained before the replacement of the detectors by new ones with much improved cosmetics! Slide #25
Example of MOS data And getting spectra G140M configuration. 1.3-1.7 micron source with absorption lines. Slide #26
Multi-object spectroscopy Limiting sensitivity Conservative estimates including a recipe to account for data loss due to detector cosmetics. Note the gaps between the shutters are real (pitch = 202 microns, aperture = 175 microns, 14% relative bar size) Low spectral resolution 100 njy = 1e-30 erg s-1 cm-2 Hz-1 = 1e-33 W m-2 Hz-1 = 26.4 AB mag = 24.3 K-band mag Slide #27
Multi-object spectroscopy Medium spectral resolution Slide #28
Multi-object spectroscopy High spectral resolution high Slide #29
Multi-object spectroscopy Example Simulations of a spectroscopic deep field Point-like galaxies, zodiacal light background Instrument model / IPS software PhD thesis of B. Dorner (2011) using the source catalog of Pacifici et al. 2012. CLEAR/PRISM (low spectral resolution) Single exposure of 970 s. No cosmic ray. Basic detector noise properties only (i.e. no 1/f noise). Slide #30
Multi-object spectroscopy Example Spectrum extraction pipeline applied to the simulated data Software originally developed by B. Dorner (PhD thesis, 2012). Now maintained and further developed by ESA. Used as a prototype for the support to the development of the actual pipeline by STScI. CLEAR/PRISM (low spectral resolution) High-intensities / noise at short and long wavelength are flat-fielding artifacts. Slide #31
Multi-object spectroscopy Example Another way to illustrate the sensitivity of NIRSpec i drop-out galaxies from Eyles et al. 2006 (GOODS + Spitzer IRAC imaging). Best fit SED (few 10 10 solar masses, current SFR of 9 solar masses per year; fairly evolved population) CLEAR/PRISM (low spectral resolution) Photometry data points (Eyles et al. 2006) JWST/NIRSpec limiting sensitivity in 10,000 s at low spectral resolution. Impact of detector cosmetics not included. Slide #32
Multi-object spectroscopy Example From P. Oesch et al. 2016 Slide #33
Multi-object spectroscopy Example CLEAR/PRISM (low spectral resolution) From Bunker 2015, presentation at the JWST2015 conference at ESA/ESTEC Slide #34
Integral field spectroscopy Slide #35
Integral field spectroscopy NIRSpec IFU properties Concept Advanced image slicer module (Content 1997) Manufacturer Size and weight Surrey Satellite Technology LTD (SSTL) University of Durham CfAI as a sub-contractor Size of a shoebox for a weight of less than 1kg Number of slices 30 Field of view Spaxel size Throughput Spectral Configurations (using NIRSpec spectrograph) 3 arcsec 3 arcsec 0.1 arcsec 0.1 arcsec > 50 % from 0.6 to 3.0 microns; > 80 % above 3 microns Coverage of the 0.6-5.0 µm spectral domain in one shot at 25 R 300 (using a prism) Coverage of the 0.7-5.0 µm spectral domain in four configurations at R 1000 and R 2700 (using gratings) Slide #36
Integral field spectroscopy Slide #37
Integral field spectroscopy Slide #38
Integral field spectroscopy Observations of a small sample of nearby LIRGs in the [NII]+Ha range with the VLT/VIMOS IFU. From figure 4 Bellocchi et al. 2012 Slide #39
Integral field spectroscopy Some velocity structure. From figure 4 Bellocchi et al. 2012 Slide #40
Integral field spectroscopy XL version - The object was scaled to fit in the 3 x3 NIRSpec IFU field of view (arbitrary scaling). Just for the sake of having a nice example of a spatially resolved object observed in IFU mode. compact version Object size of roughly 1 x1 Arbitrary scaling once more. More similar to the z=3 case example present in the paper. The [NII]+Ha spectra were redshifted to z=1, putting the Ha line around 1.3 microns. Mimicking an observation in the 1.0-1.8 micron band of NIRSpec (with a medium resolution grating). Only considering the [NII]+Ha line region (this is just an example ). Slide #41
Integral field spectroscopy XL version compact version Reconstructed datacubes (i.e. at NIRSpec IFU spatial resolution). Slide #42
Integral field spectroscopy Normalized to a peak value of unity Velocity structure is still clearly visible as we progress diagonally through the cube. Slide #43
Integral field spectroscopy An example of an IFU-based point and shoot approach for moving targets. Slide #44
high-contrast slit spectroscopy A set of 5 fixed slits for high-contrast spectroscopy of individual objects Specific detector real estate (can be used in parallel to the other modes). 3 x 0.2 + 1 x 0.4 + aperture of 1.6 x1.6! Slide #45
exoplanet transit spectroscopy While optimized for faint target multi-object spectroscopy, NIRSpec features a dedicated large aperture (1.6 x 1.6 ) for exoplanet transit spectroscopy. In a more general way, exoplanet atmosphere characterisation. Ironically, one of the main worry for this mode was the saturation limit! Note that the other near-infrared instrument also have modes dedicated to exoplanet transit spectroscopy. è pick the one best suited for your needs. PASP white paper: Beichman et al. 2014 (PASP, 126,1134) Slide #46
exoplanet transit spectroscopy Most up-to-date information for NIRSpec: Ferruit et al. 2014, SPIE, 9143 Typical uncertainties of 20% (i.e. 0.2 mag). Allowing the use of the reset-read as the shortest possible exposure when computing the saturation limits. Slide #47
exoplanet transit spectroscopy Noise floor = benchmark lowest noise level that would be achieved if we had only two noise components: detector noise + shot noise from the host star. saturated discontinuities that appear when the host start becomes faint enough to get an additional readout per integration 100 ppm CLEAR/PRISM 0.6-5.3 microns in one shot R~30-300 Slide #48
exoplanet transit spectroscopy Noise floor = benchmark lowest noise level that would be achieved if we had only two noise components: detector noise + shot noise from the host star. saturated Much more balanced signal to noise ratio curves. Still relatively easy to get S/N of a few thousands even for faint host stars. 100 ppm F290LP/G395H 2.9-5.2 microns in one shot R~2700 1h transit Slide #49
exoplanet transit spectroscopy Main conclusions: Fairly easy to reach noise floor levels corresponding to 100 ppm for a 1 hour transit duration. Expecting observations to routinely reach down to noise floor levels of a few tens of ppm. Interesting wavelength coverage and range of possible spectral resolution. Of course systematics will be the key to the actual final S/N ratio that can be achieved. The success of the studies conducted by various teams on HST and Spitzer data give use good hope that for NIRSpec also we will be able to go close to the photon noise limit. Slide #50
Conclusion JWST/NIRSpec A very versatile near-infrared spectrograph with an unprecedented combination of sensitivity and spatial resolution. In the coming years NIRSpec together with the other instruments will go through JWST s remaining integration and test steps. The teams will continue working on the suite of tools necessary to prepare the observations, execute them, process the data and archive them! Thanks for your attention! Slide #51
Backup slides BACKUP SLIDES Slide #52
JWST - Orbit and field-of-regard How mobile is the telescope given that it needs to remain constantly in the shade? Slide #53
The James Webb Space Telescope (JWST) Orbit and field-of-regard At any time during the year, JWST will be able to observe an annulus corresponding to 35-40% of the sky. http://www.stsci.edu/jwst/overview/design/field-of-regard Slide #54
The James Webb Space Telescope (JWST) Orbit and field-of-regard Periods of visibility / orientation of the field of view Small regions visible all year long (CVZ), around the ecliptic poles Two visibility windows per year separated by 6 months Single, longer visibility window Slide #55
Visibilities and orientation during a 1-year cycle CVZ = continuous viewing zone around the ecliptic poles Slide #56
Visibilities and orientation during a 1-year cycle Along the ecliptic: restricted range of orientations, 2 windows per year, long time with the same orientation (~50 days). Artifact from the beginning and end of a 1- year cycle CVZ: visible all year long, all orientations possible along the year, short time with the same orientation (~10 days). Slide #57