the infrared sky: background considerations for jwst
DESCRIPTION
The Infrared Sky: Background Considerations for JWST. Dean C. Hines & Christine Chen MIRI Instrument Team. The Visible (Optical) Sky. The Visible vs the Infrared Sky. The Visible vs the Infrared Sky. Infrared Background Sources. - PowerPoint PPT PresentationTRANSCRIPT
04/22/23DCH-1
JWST/MIRI
Space Telescope Science Institute
The Infrared Sky: BackgroundThe Infrared Sky: BackgroundConsiderations for JWSTConsiderations for JWST
Dean C. Hines & Christine ChenMIRI Instrument Team
04/22/23DCH-2
JWST/MIRI
Space Telescope Science Institute
The Visible (Optical) SkyThe Visible (Optical) Sky
04/22/23DCH-3
JWST/MIRI
Space Telescope Science Institute
The Visible The Visible vsvs the Infrared Sky the Infrared Sky
04/22/23DCH-4
JWST/MIRI
Space Telescope Science Institute
The Visible The Visible vsvs the Infrared Sky the Infrared Sky
04/22/23DCH-5
JWST/MIRI
Space Telescope Science Institute
Infrared Background SourcesInfrared Background Sources
Three primary sources of diffuse light in the astronomical sky– Extragalactic – light from unresolved objects (galaxies and QSOs)– Galactic – mostly star-light reprocessed by material in the
Interstellar Medium (ISM)– Solar System – sun light reprocessed by material within the solar
system These astronomical components are highly wavelength dependent
– Visible and near-Infrared (NIR) – dominated by scattered/reflected light but with some thermal NIR emission from very hot dust
– Longer wavelengths – dominated by thermal emission from warm dust and by broad solid-state and giant molecular emission features
Emission from the telescope and stray light also contribute to the background– Not a large issue for HST (except for NICMOS > 1.8µm)– For JWST, this is an issue for most wavelengths, and becomes a
dominant source for MIRI
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JWST/MIRI
Space Telescope Science Institute
HST vsHST vs JWSTJWST
JWST
Glasse et al. (2010)
Diffuse Galactic + Zodi
HST ThermalEmission
HST
Because JWST operates much colder than HST (~39-46K vs ~290K), diffusegalactic and zodiacal emission dominate the background for ≤ 16µm
NICMOS Instrument Handbook
04/22/23DCH-7
JWST/MIRI
Space Telescope Science Institute
Zodi + Galaxy + Exgal
Galaxy + Exgal
Exgal
COBE/DIRBECOBE/DIRBE
All of the images use 4 decade logarithmic color scales.
The lowest level is 3.95 kJy/sr at 3.5 microns, 6.67 kJy/sr at 2.2 microns, and 7.08 kJy/sr at 1.25 microns for the upper and middle images, but 0.395 kJy/sr for the lower image.
Blue = 1.25 µmGreen = 2.2 µmRed = 3.5 µm
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JWST/MIRI
Space Telescope Science Institute
Thermal Emission from Zodi DustThermal Emission from Zodi Dust
Blue = 12 µm; Green = 60 µm; Red = 100 µm
IRAS
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JWST/MIRI
Space Telescope Science Institute
Thermal Emission from Zodi DustThermal Emission from Zodi Dust
Blue = 12 µm; Green = 60 µm; Red = 100 µm
IRAS
04/22/23DCH-10
JWST/MIRI
Space Telescope Science Institute
Thermal Emission from Zodi DustThermal Emission from Zodi Dust
Blue = 65 µm; Green = 90 µm; Red = 140 µm
Akari
04/22/23DCH-11
JWST/MIRI
Space Telescope Science Institute
Zodi Dust Bands (IRAS)Zodi Dust Bands (IRAS)
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JWST/MIRI
Space Telescope Science Institute
Zodi Bands & SpectrumZodi Bands & Spectrum
Optical
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JWST/MIRI
Space Telescope Science Institute
Taurus Taurus SpitzerSpitzer 24µm 24µm
Residual Zodiacal Dust Band Emission after subtraction of a smooth zodiacal background model based on COBE/DIRBE data.
ZodiacalDust Bands
7.7˚
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JWST/MIRI
Space Telescope Science Institute
Galactic ISM (COBE)Galactic ISM (COBE)
Blue = 60 µm; Green = 100 µm; Red = 240 µm
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JWST/MIRI
Space Telescope Science Institute
Galactic ISM (COBE)Galactic ISM (COBE)
Green = 100 µm; Red = 240 µm
04/22/23DCH-16
JWST/MIRI
Space Telescope Science Institute
PAH Emission from the ISMPAH Emission from the ISM
PAH Emission Features — 3.29, 6.2, 7.7, 8.7, 11.3, and 12.7 µm
Wavelength (µm)
04/22/23DCH-17
JWST/MIRI
Space Telescope Science Institute
Emission from the GalaxyEmission from the Galaxy
PAH Emission Features — 3.29, 6.2, 7.7, 8.7, 11.3, and 12.7 µm
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JWST/MIRI
Space Telescope Science Institute
Zodi + GalacticZodi + Galactic
04/22/23DCH-19
JWST/MIRI
Space Telescope Science Institute
Zodi + GalacticZodi + Galactic
04/22/23DCH-20
JWST/MIRI
Space Telescope Science Institute
ConclusionsConclusions The Infrared Sky is much different in structure and brightness
compared the visible sky At visible wavelengths, the background is dominated by light
scattered from dust in the solar system (HST also contends with geocoronal emission and earthshine)
The infrared background is dominated by emission from dust in the solar system and the galaxy, plus broad-band emission features from PAHs associated with diffuse galactic dust
These astronomical background sources will dominate the JWST background for ≤ 16µm, and will still be important for longer wavelengths
The background will vary in time as our view of the zodiacal emission changes during the year
STScI is working with the Spitzer Science Center (SSC) to develop a background model appropriate for JWST
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JWST/MIRI
Space Telescope Science Institute
Fin
04/22/23DCH-22
JWST/MIRI
Space Telescope Science Institute
WISEWISE
04/22/23DCH-23
JWST/MIRI
Space Telescope Science Institute
All of the images use 4 decade logarithmic color scales. The lowest level is 3.95 kJy/sr at 3.5 microns, 6.67 kJy/sr at 2.2 microns, and 7.08 kJy/sr at 1.25 microns for the upper and middle images, but 0.395 kJy/sr for the lower image.
The lowest level is 223.2 kJy/sr at 240 microns, 555.3 kJy/sr at 100 microns, and 508.2 kJy/sr at 60 microns for the upper and middle images, but 30.7 kJy/sr for the lower image.