A Search for O_2 in CO-depleted Molecular Cloud Cores with Herschel

Abstract

The general lack of molecular oxygen in molecular clouds is an outstanding problem in astrochemistry. Extensive searches with SWAS, Odin and Herschel have only produced two detections; upper limits to the O_2 abundance in the remaining sources observed are about 1000 times lower than predicted by chemical models. Previous atomic oxygen observations and inferences from observations of other molecules indicated that high abundances of O atoms might be present in dense cores exhibiting large amounts of CO depletion. Theoretical arguments concerning the oxygen gas-grain interaction in cold dense cores suggested that, if O atoms could survive in the gas after most of the rest of the heavy molecular material has frozen out on to dust, then O_2 could be formed efficiently in the gas. Using Herschel HIFI we searched a small sample of four depletion cores - L1544, L694-2, L429, Oph D - for emission in the low excitation O_2 N_J=3_3-1_2 line at 487.249 GHz. Molecular oxygen was not detected and we derive upper limits to its abundance in the range N(O_2)/N(H_2) = (0.6 - 1.6)x10^{-7}. We discuss the absence of O_2 in the light of recent laboratory and observational studies.

arXiv commentAccepted for publication in ApJ

References in corpus (32)

• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
• Cold Dark Clouds: The Initial Conditions for Star Formation
• Probing the evolutionary status of starless cores through N2H+ and N2D+ observations
• Molecular ions in L1544. II. The ionization degree
• Water, O2 and Ice in Molecular Clouds
• N2H+ and C18O Depletion in a Cold Dark Cloud
• Laboratory evidence for efficient water formation in interstellar ices
• First detection of water vapor in a pre-stellar core
• Experimental evidence for water formation on interstellar dust grains by hydrogen and oxygen atoms
• The Degree of CO Depletion in Pre-stellar Cores
• Herschel Measurements of Molecular Oxygen in Orion
• Survey of ortho-H2D+(1_{1,0}-1_{1,1}) in dense cloud cores
• HI Narrow Self-Absorption in Dark Clouds: Correlations with Molecular Gas and Implications for Cloud Evolution and Star Formation
• Molecular oxygen in the rho Ophiuchi cloud
• Desorption of CO and O2 interstellar ice analogs
• Nitrogen chemistry and depletion in starless cores
• Detection of interstellar hydrogen peroxide
• Molecular freeze-out as a tracer of the thermal and dynamical evolution of pre- and protostellar cores
• Multi-line detection of O2 toward rho Oph A
• Wavelength-dependent UV photodesorption of pure N2 and O2 ices
• Disappearance of N2H+ from the Gas Phase in the Class 0 Protostar IRAM 04191
• Freeze-out and coagulation in pre-protostellar collapse
• Deep observations of O2 toward a low-mass protostar with Herschel-HIFI
• Deuterated formaldehyde in rho Ophiuchi A
• Sticking of molecules on non-porous amorphous water ice
• Hydrogen cyanide and isocyanide in prestellar cores
• A New Determination of the Binding Energy of Atomic Oxygen on Dust Grain Surfaces: Experimental Results and Simulations
• Herschel HIFI observations of O${}_2$ toward Orion: special conditions for shock enhanced emission
• Herschel Search for O2 Toward the Orion Bar
• Gas-grain models for interstellar anion chemistry
• Herschel HIFI Observations of the Sgr A +50 km/s Cloud. Deep Searches for O2 in Emission and Foreground Absorption
• Search for HOOH in Orion

Cited by in corpus (9)

• Astrochemistry and compositions of planetary systems
• A sensitive 3 mm line survey of L483: a broad view of the chemical composition of a core around a Class 0 object
• The KOSMA-$\tau$ PDR Model -- I. Recent updates to the numerical model of photo-dissociated regions
• Gas and dust in the star-forming region rho Oph A: II. The gas in the PDR and in the dense cores
• Influence of galactic arm scale dynamics on the molecular composition of the cold and dense ISM II. Molecular oxygen abundance
• A gas-phase primordial origin of O2 in comet 67P/Churyumov-Gerasimenko
• Constraints on the non-thermal desorption of methanol in the cold core LDN 429-C
• Deep search for hydrogen peroxide toward pre- and protostellar objects -- Testing the pathway of grain surface water formation
• Chemical constraints on the dynamical evolution of the cold core L694