Submillimeter Wave Astronomy Satellite and Star Formation Di Li Smithsonian Astrophysical Observatory, CfA July, 2002

Oxygen Budget in Molecular Clouds Oxygen is the third abundant element after H and He. Grains: oxygen locked up in silicates, olivine, and oxides. CO gas: limited by the carbon abundances How about O 2, H 2 O, icy mantle, and OI?

Blocked Vision Through Atmosphere

SWAS Science Objectives Where is all the oxygen in the dense interstellar medium? Are H 2 O, and to a lesser extent O 2, important coolants for molecular gas as it collapses to form stars? What are the important physical processes in the UV-illuminated surfaces of molecular clouds? What is the large scale structure of cold CI clouds?

Submillimeter-Wave Astronomy Satellite (SWAS) A NASA Small- Explorer mission Principle Investigator Gary Melnick, SAO CO Investigators Scientists from SAO, Cornell U, John Hopkins U, U Mass, and NASA AMES Center

SWAS: Observed Molecules and Transitions Transitions listed in red are ground-state transitions.

SWAS System Performance Integration Time (hrs) rms noise (K) [CI] and O 2 H 2 O and 13 CO M17

Expectations from Gas Phase Chemistry Quiescent Gas Chemistry Model -Abundance predictions after 10 6 yrs - [O 2 ]/[H 2 ] ~5x [H 2 O]/[H 2 ] ~5x10 - 7

H 2 O in Molecular Cloud Cores Antenna Temperature T A * V LSR (km/s) Ceph-ANGC 2024NGC 1333S140  Oph-A NGC6334i W3TMC-1

Analysis of H 2 O Emission in Star-Forming Regions H 2 O emission is very optically thick, but lines are close to the weak line limit: Molecular hydrogen densities typically cm -3. n crit ~ 2  10 8 cm -3.  Collisional de-excitations are unimportant and every photon created by collisional excitation eventually escapes. Lines are optically thick but effectively thin! In this limit:

H 2 O and H 2 18 O Absorption Toward Sgr B V LSR (km/s) Flux/Continuum Flux H 2 O 1 10  1 01 H 2 18 O 1 10 

H 2 O and H 2 18 O Absorption Toward Sgr B2

SWAS H 2 O Abundances from Emission Lines predictions of chemical theory

The Elusive O 2 Molecule

O 2 Abundance Upper Limits (3  ) predictions of chemical theory

What is Missing 1.Depletion onto dust grains Rate: Time scale: 2. Grain surface chemistry O+g=> H 2 O C+g=>CH 4 3. Dynamic processes associated with star formation Shocks Outflows

Gas and Grain Chemistry Pros –Depletes water –Process Oxygen into surface ice –Enhance some species, such as HC 3 N Cons –SO will disappear –Atomic oxygen may be too little

Cloud Structures: the Rho Oph Clouds

CI and CO Correlation The positive correlation is not spatial dependent, occurs in both clouds in  Ophiuchi region The turnover only happens at extremely high extinction Av>20, where 13co may also become optically thick.

Tentative Detection of O 2 Both wings have offsets from the center. 4.5 Sigma detection at outflow velocities. How significant is this?

Statistical Tests Stable performance of the system: RMS ~1/ t 0.5 still holds after hundreds of hours Number of independent channels and rms noise of our sample of spectra conform to Gaussian statistics. Fraction of scans with positive intensity have expected statistics with respect to RMS. 4.5  => O 2 Abundance ~ 10 -5

Chemical Models with Shocks Pseudo time dependent chemical model with depletion and surface chemistry Shocks release H 2 O and CO from grain surfaces and enable neutral-neutral reactions Pure gas phase chemistry. Later, depletion dominates depending on density.

Water in Other Systems Planets SWAS has measured water vapor vertical profiles of the Mars atmosphere. Water has been detected from Jupiter and Saturn. Comets comet C/1999 H1 (Lee), giving H 2 O production rate to be 8x10 28 s -1 Carbon-Rich Stars IRC10216 (CW Leonis) Expanding evaporation zone of this AGB stars deposit water into the circumstellar outflows from Kuiper belt objects— possible probe to extrasolar comets.

Conclusions SWAS has detected water in a variety of star forming regions (GMCs, dark cloud complexes, region with outflows), and in diffuse ISM. The water abundance [H 2 O]/[H 2 ] ranges from to SWAS has set significant upper limits to the abundance of molecular oxygen to these regions. [O 2 ]/[H 2 ]< (except for  Ophiuchi A). SWAS is showing that gas-phase H 2 O and O 2 are not dominant coolants or major carriers of elemental oxygen in the cold dense regions of the ISM. SWAS has made large scale CI maps of Orion, M17 and  Ophiuchi. The striking correlation between CI structures and that of the CO isotopologues suggest a clumpy cloud structure with high contrast between the clump and interclump medium. A comprehensive picture to explain SWAS data must involve chemical models with grain surface processes and possible contributions from cloud dynamics (e.g. shocks, circulation), and cloud structure (clumps). These knowledge would shed great lights on the molecular clouds, which is the birth place of young stars.