Prospects – JWST, EUCLID, WFIRST

Prospects – JWST, EUCLID, WFIRST

Jeff Kruk (GSFC)[email protected]

Outline

• HST: now to 2015 and beyond…• JWST: 2015 - 2025• EUCLID(?): 2018-2023• WFIRST: XX - XX+5…

11/15/2010 2J. Kruk STScI Slitless Spectroscopy wkshp

Sky backgrounds

11/15/2010 J. Kruk STScI Slitless Spectroscopy wkshp 3

HST slitless modesInstrument FoV

(arcmin)Platescale R Bandpass

(nm)ACS WFC

grism3.4’x3.4’ 0.05” 100 550-1050

ACS SBC prisms

0.58’x0.51’ 0.025” 7996

115-180125-180

WFC3 NIR grisms

2.05’x2.27’ 0.13” 210130

800-11501075-1700

WFC3 UVIS grism

2.7’x2.7’ 0.04” 70 200-400

NIC3 prisms 0.87’x0.87’ 0.203” 200 0.8-1.21.1-1.91.4-2.5

STIS NUV prism

0.42’x0.42’ 0.024” 2500-10 115-350


JWST slitless modes

Instrument FoV (arcmin)

Platescale R Bandpass (nm)

NIRCAM 2 grisms,

Rotated 90°

2.16’x2.16’ 0.0648” 2000 2400-5000(filters in

series)

NIRSpec* prism, gratings

3.4’x3.6’ 0.1” 1001000, 2700

700-5000

*NIRSpec micro-shutters: 0.2”x0.45” - open area ratio is 0.7 if all left open


EUCLIDNIR slitless spectroscopy

• Launch in 2018 if selected, 5 year mission duration• Survey 20000 deg2

– limiting line flux 4*10-16 ergs/cm2/s• Characteristics (Laureijs et al 2010 SPIE 7731):

– 1.2m primary, 0.35m secondary obscuration– 4 grisms in wheel, identical except for 90° rotations– 1.0-2.0 microns– R=500– Focal plane: (choice still TBD?)

• 12 SCAs: 0.33”/pix 36.4’x48.5’ (0.49 sq deg)• 16 SCAs: 0.31”/pix 46.1’x46.1’ (0.59 sq deg)


WFIRST

• Launch: ?? - depends on JWST schedule• Mission duration: 5 years min, 10 years goal• Objectives:

– 10000 deg2 WL survey (30 gal/sq arcmin)– 20000 deg2 BAO survey (limiting flux 1.6 10-16)– 150 SNIa per z=0.1– (didn’t quite fit into 5 years, but close)

• EOS panel recommendations cuts time in ~half for first 5 years of mission


WFIRST characteristics(details subject to change!)

• Imager– 0.4-2.0m– 0.18”/pixel– 4x6 array of SCAs (0.25 deg2)– Filter wheel: 5 filters, R=75 prism, blank

• Spectrometers (2, w/ opposing dispersions)– 1.1-2.0m– 0.37”/pixel– 2x3 array of SCAs (0.26 deg2) each– R=270-327 per 2 pixels

• R = 200-240”, or c/R = 1500-1250km/s/arcsec


WFIRST block diagram(details almost certain to change)


WFIRST focal planes as projected onto the sky


Design Tradesgrism vs. prism

Grism pros:– zero-order gives

wavelength reference– Allows higher dispersion

Grism cons:– Zero order increases

spectral contamination– Higher dispersion not

needed for BAO; if lines resolved, S/N is reduced

– Higher orders contaminate spectra

– 1st order throughput lower than prism


Grism simulation courtesy of David Larson

Design Trades

• Dispersion– σz/(1+z) < 0.001, resolve OIII, don’t resolve Hα

• Bandpass– Redshift coverage & spectral diagnostics vs

zodiacal light– Combined w/dispersion -> length of spectral trace

• Number of roll angles, size of roll offset – 4 rolls: 0°,5°; 170°,175° found sufficient

• Don’t set 2 spectrometers exactly 180° apart


Imager sim – 225 sec


Imager simulation – 225sec 1SCA (log stretch)

Courtesy David Larson


Spectrometer simulation – 225 sec 1SCA (log stretch)


4° roll offset


Roll = 0 Roll = 4


133 ksec deep exp (SN field) asinh stretchGalaxies & stars only - no background


General issues• EUCLID, WFIRST not as clean as HST

– PSF, pixels are large compared to HST– Pointing stability, dithering, less precise than HST

• What dithering is desirable/required in this context?

• Direct images are obtained with a different instrument at different times – Use edges of traces of bright stars in field for

registration


Issues continued:calibrations

BAO needs accurate wavelengths• Optical distortion calibration is critical – not challenging

SNIa needs accurate fluxes• If from spectra, flat-field cube is critical – challenging• Would like to derive flat-field internally from the data

– Has been done for imaging instruments (Arendt et al. 2010 ApJS 186 10)

– Dimensionality of problem is higher for slitless spectrometer; will need extensive simulations to test

Persistence corrections• Can pipeline maintain continuous exposure history?

• Initial planning limited to DE programs– Need to reevaluate for larger WFIRST program


Issues cont.• Datasets are large!

– Manual processing not practical for 109 galaxies• Extract ~109 to obtain 108 emission-line galaxies

– “…it is still mandatory to check and validate the products before any science investigation can commence.” (The WFC3 IR Grism Data Reduction Cookbook – Extracting several 100 grism spectra made easy)


Issues cont.• Datasets are large!

– Manual processing not practical for 109 galaxies• Extract ~109 to obtain 108 emission-line galaxies

– “…it is still mandatory to check and validate the products before any science investigation can commence.” (The WFC3 IR Grism Data Reduction Cookbook – Extracting several 100 grism spectra made easy)

Uh Oh…..Crowd-sourcing? Doesn’t look like as much fun as

the Galaxy zoo


WFIRST - what’s next?

• Astro-2010 provided fairly strict guidance,– But details left open for further optimization

• The science goals have expanded to fill a 10-year mission.– While plausible, the nominal design life is 5 years

(so everyone starts out unhappy)• The Science Definition Team may have a big

role in defining the details. Stay tuned.


WFIRST telescope trade:

1.5m on-axis vs 1.3m off-axis


PSF - scaled by effective area Encircled Energy

Diffraction from spider arms not included

EOS observing plan

• BAO+WL: <~2 years• Sne: 0.5 years• Micro-lensing (Galactic bulge): 1.4 years• Galactic plane survey: 0.5 year• Guest-observer surveys: 1 year

– This means you!


WFIRST SDT

Deadline for applications to the WFIRST Science Definition Team: Nov 23rd, 2010

Please Apply!

Further info: http://wfirst.gsfc.nasa.gov


Documents

Prospects – JWST, EUCLID, WFIRST