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Дата изменения: Tue Apr 17 22:27:54 2007
Дата индексирования: Sat Dec 22 20:44:28 2007
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Science Objectives for the Cosmic Origins Spectrograph
Claus Leitherer, Martin Barstow, Linda Dressel, Cynthia Froning, Peter Garnavich, Tony Keyes, Jeff Valenti, & the COS Science Team

Claus Leitherer

Slide Number 1 of 12

Four key science questions -- united by the theme of Cosmic Origins
· What are the origins of large-scale structure and the intergalactic medium? · How do galaxies form and evolve? · What are the interstellar origins of stars? · What are the properties of extrasolar planets

Claus Leitherer

Slide Number 2 of 12

The origins of large-scale structure and the intergalactic medium
· COS will quantify the cosmic web of matter through UV absorption-line spectroscopy. · Over 80 90% of the baryons reside in the cool and warm IGM, with 40% in the IGM with T > 106 K. · 10% of the baryons are in stars and galaxies. · COS will probe the cool photoionized IGM and the warm part (105 106 K) of the warm-hot IGM. · COS will obtain information on the physical state and distribution of ~60% of the baryonic matter. · Imaging is only sensitive to ~10% of the baryons.
Claus Leitherer Slide Number 3 of 12

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Dashed lines indicate lines of sight to QSOs accessible to COS at S/N = 20 in <5 orbits (<3 orbits for the solid lines). Factor of ~10 better sensitivity results in 50 100 more background QSOs. Unprecedented sampling of the IGM. Detection of absorbers in the most diffuse IGM. Identification of weak tracers of Z enhancement of the universe over time.
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Claus Leitherer

Formation and evolution of galaxies
· Envelopes around galaxies out to radii of 100 200 kpc are a common prediction of galaxy formation models. · Absorption-line experiments trace the low-density gas as it cools and falls onto the galaxy. · Stars and supernovae eject enriched matter into the ISM, thereby heating the gas to high temperatures. · The heated gas can escape, enriching the IGM with heavy elements. · The only method for directly measuring the properties of the escaping gas relies on searching for absorption from the wind gas against a bright background QSO.
Claus Leitherer Slide Number 5 of 12

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Observations of QSOs near dwarf galaxies reveal mass and energy transport into the IGM from unbound outflows. Origin of the mass versus metallicity relation of galaxies. Previously limited to a handful of objects with STIS. COS will increase the available number of QSO sightlines by a factor of >100.
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Claus Leitherer

Interstellar origin of stars
· COS will study the physics and chemistry in the cold gas and dust phases of the ISM. · Star forming regions are categorized as diffuse atomic, diffuse molecular, translucent, and dense molecular clouds. · Translucent clouds mark the transition between diffuse and dense molecular clouds where star and planet formation begins. · Only COS can probe sightlines dominated by translucent clouds.

Claus Leitherer

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Classification of interstellar clouds on the basis of the forms of H and C. COS can probe diffuse molecular clouds at greater optical depth than any previous UV spectrograph, and can observe translucent clouds for the first time. COS will yield extinction curves very deep in the clouds and measure grain size and composition, as well as atomic and molecular abundances.
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Claus Leitherer

Properties of extrasolar planets
· COS will investigate many transiting extra-solar planets newly found by Kepler and other missions. · UV spectroscopy is a prerequisite for understanding the physical conditions and the chemistry in the atmospheres of close-in, extra-solar planets. · STIS detected an extended atmosphere via excess absorption of background star light in HD 209458b. · The much higher sensitivity and low instrumental background of COS will enable fundamentally new advances in extra-solar planet research.
Claus Leitherer Slide Number 9 of 12

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Comparison of STIS offtransit and in-transit spectra for the Si III and H I in HD 209458b. The detection of significant hydrogen evaporation implies a transformation to planets with a hydrogenpoor atmosphere. COS will be uniquely positioned to better pursue quantification of mass loss rates by UV absorption-line spectroscopy.

Claus Leitherer

Slide Number 10 of 12

Impact of COS on astronomy in general
· Solar system: composition and structure of atmospheres of planets and their satellites. · Star formation: accretion processes and jet formation around young stars. · Stellar astrophysics: coronae and winds around cool and hot stars; geometry of binaries. · Stellar populations: age dating and IMF determinations of young and old star clusters · AGN: masses of black holes and structure and kinematics of circumnuclear gas
Claus Leitherer Slide Number 11 of 12

Unique capabilities offered by COS
· Maximum spectroscopic sensitivity in the UV. · No other NASA mission with a high-resolution, high-sensitivity spectrograph is in development. · COS is the only instrument with significant detector response around and below Ly-. · COS uses time-tag mode, where the detector time-tags each count. · COS will re-enable scientific areas that were shut out after STIS' failure.
Claus Leitherer Slide Number 12 of 12