2/6/2016 DCH-1 JWST/MIRI Space Telescope Science Institute The Infrared Sky: Background Considerations for JWST Dean C. Hines & Christine Chen MIRI Instrument Team

2/6/2016 DCH-2 JWST/MIRI Space Telescope Science Institute The Visible (Optical) Sky

2/6/2016 DCH-3 JWST/MIRI Space Telescope Science Institute The Visible vs the Infrared Sky

2/6/2016 DCH-4 JWST/MIRI Space Telescope Science Institute The Visible vs the Infrared Sky

2/6/2016 DCH-5 JWST/MIRI Space Telescope Science Institute Infrared 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

2/6/2016 DCH-6 JWST/MIRI Space Telescope Science Institute HST vs JWST JWST Glasse et al. (2010) Diffuse Galactic + Zodi HST Thermal Emission HST Because JWST operates much colder than HST (~39-46K vs ~290K), diffuse galactic and zodiacal emission dominate the background for ≤ 16µm NICMOS Instrument Handbook

2/6/2016 DCH-7 JWST/MIRI Space Telescope Science Institute Zodi + Galaxy + Exgal Galaxy + Exgal Exgal COBE/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 kJy/sr for the lower image. Blue = 1.25 µm Green = 2.2 µm Red = 3.5 µm

2/6/2016 DCH-8 JWST/MIRI Space Telescope Science Institute Thermal Emission from Zodi Dust Blue = 12 µm; Green = 60 µm; Red = 100 µm IRAS

2/6/2016 DCH-9 JWST/MIRI Space Telescope Science Institute Thermal Emission from Zodi Dust Blue = 12 µm; Green = 60 µm; Red = 100 µm IRAS

2/6/2016 DCH-10 JWST/MIRI Space Telescope Science Institute Thermal Emission from Zodi Dust Blue = 65 µm; Green = 90 µm; Red = 140 µm Akari

2/6/2016 DCH-11 JWST/MIRI Space Telescope Science Institute Zodi Dust Bands (IRAS)

2/6/2016 DCH-12 JWST/MIRI Space Telescope Science Institute Zodi Bands & Spectrum Optical

2/6/2016 DCH-13 JWST/MIRI Space Telescope Science Institute Taurus Spitzer 24µm Residual Zodiacal Dust Band Emission after subtraction of a smooth zodiacal background model based on COBE/DIRBE data. Zodiacal Dust Bands 7.7˚

2/6/2016 DCH-14 JWST/MIRI Space Telescope Science Institute Galactic ISM (COBE) Blue = 60 µm; Green = 100 µm; Red = 240 µm

2/6/2016 DCH-15 JWST/MIRI Space Telescope Science Institute Galactic ISM (COBE) Green = 100 µm; Red = 240 µm

2/6/2016 DCH-16 JWST/MIRI Space Telescope Science Institute PAH Emission from the ISM PAH Emission Features — 3.29, 6.2, 7.7, 8.7, 11.3, and 12.7 µm Wavelength (µm)

2/6/2016 DCH-17 JWST/MIRI Space Telescope Science Institute Emission from the Galaxy PAH Emission Features — 3.29, 6.2, 7.7, 8.7, 11.3, and 12.7 µm

2/6/2016 DCH-18 JWST/MIRI Space Telescope Science Institute Zodi + Galactic

2/6/2016 DCH-19 JWST/MIRI Space Telescope Science Institute Zodi + Galactic

2/6/2016 DCH-20 JWST/MIRI Space Telescope Science Institute Conclusions  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

2/6/2016 DCH-21 JWST/MIRI Space Telescope Science Institute Fin

2/6/2016 DCH-22 JWST/MIRI Space Telescope Science Institute WISE

2/6/2016 DCH-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 kJy/sr for the lower image.  The lowest level is kJy/sr at 240 microns, kJy/sr at 100 microns, and kJy/sr at 60 microns for the upper and middle images, but 30.7 kJy/sr for the lower image.