JWST Community Lecture - NIRSpecs - P. Ferruit (March 15 ...€¦ · Slide #5 JWST/NIRSpec – The...

Slide #1

P. Ferruit (ESA JWST project

scientist)

JWST/NIRSpec

!

Slide #2

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.

SoCal JWST series - webex talk 15 March 2016

Slide #3

Before we really start…


The telescope with all the mirrors in place! (with protective covers)

The flight instruments in the payload module (ISIM).

The electronic boxes in their compartment.

To get a better idea of the scale!

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Slide #4

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 #5

JWST/NIRSpec – The origin…

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.


Artist view – R. Hurt Artist view – D. Hardy

From P. Oesch et al. 2016

3D spectroscopy – YSO disk-jet system

From Ellerbroek et al. 201 Charnay et al. arXiv:1510.01706

Modeling GJ1214b

Spectroscopy will be a key tool to achieve JWST science goals.

Slide #6




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 #7



NIRSpec = Near-infrared Spectrograph Provided by the European Space Agency. Built by an industrial consortium led by Airbus Defence and Space.

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.

Slide #8

JWST/NIRSpec – 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 #9

Figure credit: B. Dorner, PhD, 2012

Fore-optics region

Spectrograph region, including detectors

“apertures” Size: ~ 1.9 m x 1.3 m x 0.7 m Mass: < 220 kg SoCal JWST series - webex talk 15 March 2016

JWST/NIRSpec – The hardware

Slide #10


•  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 #11


•  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 #12

JWST/NIRSpec – The instrument



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 #13



Slide #14

JWST NIRSpec – The instrument

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


•  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.

Note: MIRI also has slitless spectroscopy capabilities over its imager field of view and over the 5.0-10.0 micron range.

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Configurations that can be obtained thanks to a combination of filters and dispersers installed on two wheels (FWA and GWA)

1 μm 2 μm 3 μm 5 μm4 μm

0.6 μm 5.3 μmLow spectralresolutionconfiguration

Medium andhigh spectralresolutionconfigurations

0.7 μm 1.2 μm

1.0 μm 1.8 μm1.7 μm 3.1 μm

2.9 μm 5.2 μm

JWST/NIRSpec - spectral configurations

•  At low spectral resolution, full coverage of the 0.6-5.3 micron range in one shot.

•  R ~30-300 (low). •  At medium and high spectral resolution,

several exposures are necessary to cover the full wavelength range of NIRSpec.

•  R ~1000 and ~2700.

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•  Again JWST offers a large variety of configurations.

And NIRSpec proposes its share…

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•  Nice emission-line diagnostics for galaxy assembly fans…

Slide #18



•  Or nice molecular bands / signatures for Y-dwarfs aficionados…

From C. Alves de Oliveira @JWST 2015

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NIRSpec MOS field of view of 9 square arc minutes divided in 4 distinct quadrants, each with its associated array of micro-shutters for target selection.

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•  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.

MOS spectra

MOS spectra

SLIT spectra

MOS+SLIT mode

4 slits (+ one on the other side)

Slide #21



IFU spectra

IFU spectra

SLIT spectra

IFU+SLIT mode

IFU 30 slices

IFU aperture

•  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.

Slide #22

JWST/NIRSpec 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 #23



•  An unusual MOS: a regular grid of apertures. à  Finding the best combination of pointing parameters (RA, DEC, PA)

AND the best list of targets. à  A dedicated tool is being developed for the preparation of the

observations.

Only basic data processing applied

http://www.stsci.edu/jwst/science/sodrm/highlightSpecDenseStellarFields.pdf

In yellow: non-operable shutters

(cannot be opened)

Conceptual example on a very crowded field! Omega Centauri.

Slide #24



•  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 #25

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 #26

JWST/NIRSpec Example of MOS data


!

•  And getting spectra… G140M configuration. 1.3-1.7 micron source with absorption lines.

Slide #27

JWST/NIRSpec Multi-object spectroscopy

•  Limiting sensitivity •  Conservative estimates including a

recipe to account for data loss due to detector cosmetics.


•  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

Note the gaps between the shutters are real (pitch = 202

microns, aperture = 175 microns, 14% relative bar size)

Slide #28



•  Medium spectral resolution

Slide #29



•  High spectral resolution

high

Slide #30

JWST/NIRSpec 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 #31


•  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.



High-intensities / noise at short and long wavelength are flat-fielding artifacts.

Slide #32


•  Another way to illustrate the sensitivity of NIRSpec •  i’ drop-out galaxies from Eyles et al. 2006 (GOODS + Spitzer

IRAC imaging).



JWST/NIRSpec limiting sensitivity in 10,000 s at low spectral resolution. Impact of detector cosmetics not included.

Best fit SED (few 1010 solar masses, current SFR of 9 solar masses per year; fairly evolved population)

Photometry data points (Eyles et al. 2006)

Slide #33



From P. Oesch et al. 2016

Slide #34




From Bunker 2015, presentation at the JWST2015 conference at ESA/ESTEC

Slide #35

JWST/NIRSpec Integral field spectroscopy


Slide #36



NIRSpec IFU properties

Concept Advanced image slicer module (Content 1997)

Manufacturer Surrey Satellite Technology LTD (SSTL) University of Durham – CfAI as a sub-contractor

Size and weight Size of a shoebox for a weight of less than 1kg

Number of slices 30

Field of view 3 arcsec × 3 arcsec

Spaxel size 0.1 arcsec × 0.1 arcsec

Throughput > 50 % from 0.6 to 3.0 microns; > 80 % above 3 microns

Spectral Configurations (using NIRSpec spectrograph)

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 #37



Slide #38



Slide #39



•  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 #40



•  Some velocity structure. From figure 4 – Bellocchi et al. 2012

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•  “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 #42



XL version compact version

Reconstructed datacubes (i.e. at NIRSpec IFU spatial resolution).

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Velocity structure is still clearly visible as we progress diagonally through the cube.

Normalized to a peak value of unity

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•  An example of an IFU-based point and shoot approach for moving targets.

Slide #45

JWST/NIRSpec “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 #46

JWST/NIRSpec 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 #47



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 #48



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

100 ppm

CLEAR/PRISM 0.6-5.3 microns in one shot

R~30-300

discontinuities that appear when the

host start becomes faint enough to

get an additional readout per integration

Slide #49



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

100 ppm

F290LP/G395H 2.9-5.2 microns in one shot

R~2700 1h transit

Much more balanced signal to noise ratio

curves. Still relatively easy to

get S/N of a few thousands even for “faint” host stars.

Slide #50



•  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 #51

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 #52

Backup slides


BACKUP SLIDES

Slide #53

JWST - Orbit and field-of-regard


How mobile is the telescope given that it needs to remain constantly in the shade?

Slide #54

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 #55

The James Webb Space Telescope (JWST) Orbit and field-of-regard


Periods of visibility / orientation of the field of view

Two visibility windows per year separated by

6 months

Single, longer visibility window

Small regions visible all year long (CVZ), around

the ecliptic poles

Slide #56

Visibilities and orientation during a 1-year cycle


CVZ = continuous

viewing zone around the

ecliptic poles

Slide #57

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).

CVZ: visible all year long, all orientations possible along the year, short time with the same orientation (~10 days).

Artifact from the beginning and end of a 1-year cycle

JWST Community Lecture - NIRSpecs - P. Ferruit (March 15 ...€¦ · Slide #5 JWST/NIRSpec – The...

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