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PACS Science and Performance Requirements

PACS Science and Performance Requirements. A. Poglitsch. Herschel/PACS Science Drivers. Detailed in PACS Science Requirements Document:

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PACS Science and Performance Requirements

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  1. PACS Science andPerformance Requirements A. Poglitsch Scientific/Performance Requirements

  2. Herschel/PACS Science Drivers Detailed in PACS Science Requirements Document: • Investigations of the distant universe, studying the history of star formation and activity in galaxies through extensive surveys and dedicated follow-up observations • Studies of the origins of stars through photometric and spectroscopic surveys of star forming regions and pre-stellar condensations • Physics and chemistry of the interstellar medium (Galactic/extragalactic) • Solar system studies Scientific/Performance Requirements

  3. Extragalactic Photometric Surveys (I) • Survey a ‘large’ region at a wavelength near 170µm to the confusion limit (“resolving the FIR background”). The Herschel confusion limit (“5s”) at this wavelength is predicted to be below or near 10mJy by different models • Simultaneously survey at a shorter wavelength to provide SED information, with the goal of covering the same area to the same depth as at 170 µm, and to reach the confusion limit at shorter wavelengths over smaller areas, if feasible • Provide large sample sizes (at least thousands of objects) required in order to detect rare objects and provide sufficient statistics even after binning objects into redshift, color etc. groups Scientific/Performance Requirements

  4. Extragalactic Photometric Surveys (II) • Map contiguous regions without gaps or significant depth variations • Provide the best possible positional accuracy. The identification of faint far-infrared galaxies is nontrivial and positional errors of several arcsec can already be detrimental. For good detections, the PACS internal positional error should be less than 1 arcsec, in order to be an insignificant contribution to the the total Herschel/PACS pointing accuracy • Allow execution of programme within expected time allocation of order 103 h ( FOV / sensitivity) Scientific/Performance Requirements

  5. Individual Galaxies (I) • Provide simultaneous dual-band photometry at 170µm and one shorter wavelength, and thepossibility to obtain photometry in total for three different bands in the 60 to 200µm range. • Asmaller shortest wavelength would be desirable (but not required) for SED characterization andAGN/starburst discrimination • Obtain continuous maps over larger regions • Provide spectroscopy of individual lines anywhere in the 60 to 210µm range, covering instantaneously a range of 1000-2000km/s with a resolution element of 150-300km/s. The detectionlimit should reach ~10-18 W/m2in practical times to achieve the scientific goals Scientific/Performance Requirements

  6. Individual Galaxies (II) • Provide the possibility to obtain complete 60-210µm spectra at this resolution for brighter sources • Obtain spectral line maps. Spatial multiplexing increases mapping speed and ensures correct spectroscopy even for slightly mistargeted sources, as might occur due to inaccurate (far-infrared!) positions or Herschel pointing errors. These advantages are considered more important than those of increased spectral multiplexing (i.e. increased instantaneous wavelength range).  FOV/sensitivity Scientific/Performance Requirements

  7. Star Formation and the Galactic ISM (I) • Survey at 170µm large areas (up to square degrees, either contiguous or in patches preselectedfrom other observations) to a depth somewhat shallower than for the extragalactic surveys (5s, 10 mJy to a few tens of mJy) • Simultaneously cover a shorter wavelength, with the goal of reaching the same depth over thesame area. In a situation limited by cirrus confusion, deeper integrations may in fact be chosento take advantage of the lower confusion limit in the shorter band. Scientific/Performance Requirements

  8. Star Formation and the Galactic ISM (II) • Preserve the image quality of the Hesrchel telescope. • Especially for crowded cluster cores, the intended lowering ofthe Hesrchel telescope diffraction limited wavelength to the goal of 85µm or below will directlyboost the quality of the data at these wavelengths • Limiting the strength of PSF wings and sidelobes due tooptical effects or cross-talk is important because of the presence of strong contrasts • Provide SED photometry for three points spread across the 60...200µm range. For study of thewarmest sources, it is desirable (but not required) to include a photometric point below 60µm toget below the peak of the SED Scientific/Performance Requirements

  9. Star Formation and the Galactic ISM (III) • Cover a wavelength range of at least 60-210µm in spectroscopy mode, allowing both single lineand range spectroscopy. • Provide spectroscopy for a FOV of several beams instantaneously for observations of complextargets and efficient mapping • Spectroscopically observe bright sources  FOV/ sensitivity / dynamic range Scientific/Performance Requirements

  10. Stars • Spectroscopically observe bright sources (maximum about 10000Jy at 60µm). Note: In case thisgoal induces design conflicts with faint source observations, faint sources must have absolutepriority • For studies of features in bright sources rapidly cover (spectrophotometrically) the full 60-210µmwavelength range, at the expense of high resolution fidelity Scientific/Performance Requirements

  11. Solar System Objects • Obtain all types of observations (photometry, line spectroscopy, range spectroscopy, chopping/ nodding) also on (moving) solar system targets. This is primarily a requirement on the Herschel pointing system, but also on PACS observing modes • Observe bright sources. Goals are that PACS should be able to obtain observations of Uranus in imaging mode for calibration. All outer planets should be observable in spectroscopy mode (extended sources, brightness temperature ~140K for Jupiter/ Saturn, Mars is even warmer but smaller). Note: In case this goal induces design conflicts with faint source observations, faint sources must have absolute priority Scientific/Performance Requirements

  12. Required Photometer Capabilities • Instantaneous FOV: 3.5’ x 1.75’, Nyquist sampled • 3 wavelength bands:60 – 85 µm, 85 – 130 µm, 130 – 210 µm • Dual-band photometry observing modes • Targeted point source photometry (on-array chopping/ nodding) • Targeted compact object mapping mode (off-array chopping / nodding) • Extended object / survey mapping mode (scanning; if necessary/applicable with chopping) • Chopper throw commandable 0…±4 arcmin Scientific/Performance Requirements

  13. Photometer Performance Requirements • Image quality • blur: telescope limited (instrument-internal Strehl >90%) • distortion: ±1 pixel; alignment: <1/3 pixel • Sensitivity (point source detection) • requirement: 5 mJy (5s), 1h of integration • goal: 3 mJy (5s), 1h of integration • Dynamic range • detection from 3 mJy to >1000 Jy (goal: 3000 Jy) • contrast of up to 1:500 in one field • Post-detection bandwidth • requirement: 0.5 - 5 Hz • goal: 0.05 - 5 Hz Scientific/Performance Requirements

  14. Required Spectrometer Capabilities • Wavelength range: <60µm – >205µm • Resolution: 150…300 km/s • Instantaneous velocity coverage: 1000…2000 km/s • Instantaneous FOV: ~ 1’ x 1’ • Spectroscopic observing modes • Targeted compact source spectroscopy (chopping/nodding; individual lines or wavelength ranges / SED) • Spectral line mapping of extended sources (chopping/nodding, wavelength switching) • Full spectral and spatial sampling must be possible Scientific/Performance Requirements

  15. Spectrometer Performance Requirements • Image quality • blur: telescope limited (instrument-internal Strehl >90%) • distortion: ±1 pixel; alignment: <1/4 pixel • Sensitivity (point source detection) • requirement: 3x10-18 W/m2 (5s), 1h of integration • goal: 2x10-18 W/m2 (5s), 1h of integration • Dynamic range • detection from ~1x10-18 W/m2 to >10-13 W/m2 • contrast of up to 1:100 in one field • spectral ghosts <1% • Post-detection bandwidth • requirement: 5 Hz • goal: 10 Hz Scientific/Performance Requirements

  16. Verification of Required Performance • Many of the instrument requirements are achieved by design (and have been subject of previous reviews) • Performance-relevant quantities that need verification by testing (on ground and/or in orbit) include • Sensitivity (including radiation effects) • Optical performance (PSF, spectral resolution, distortion, position accuracy) • Calibration accuracy (photometric, wavelength) • Suppression of “systematics” [fringing, inhomogeneity in filters, “structure” in optics (including telescope), …] at the10-4…<10-5 level of the background • Verification of AOT design/optimisation regarding • Scientific needs • Instrument limitations Scientific/Performance Requirements

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