Linking ice and gas in the λ Orionis Barnard 35A cloud

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Context. Dust grains play an important role in the synthesis of molecules in the interstellar medium, from the simplest species, such as H2, to complex organic molecules. How some of these solid-state molecules are converted into gas-phase species is still a matter of debate. Aims. Our aim is to directly compare ice and gas abundances of methanol (CH3OH) and carbon monoxide (CO) obtained from near-infrared (2.5-5 μm) and millimetre (1.3 mm) observations and to investigate the relationship between ice, dust, and gas in low-mass protostellar envelopes. Methods. We present Submillimeter Array (SMA) and Atacama Pathfinder EXperiment (APEX) observations of gas-phase CH3OH (JK = 5K-4K), 13CO, and C18O (J = 2-1) towards the multiple protostellar system IRAS 05417+0907, which is located in the B35A cloud, λ Orionis region. We use archival IRAM 30 m data and AKARI H2O, CO, and CH3OH ice observations towards the same target to compare ice and gas abundances and directly calculate CH3OH and CO gas-to-ice ratios. Results. The CO isotopologue emissions are extended, whereas the CH3OH emission is compact and traces the giant molecular outflow emanating from IRAS 05417+0907. A discrepancy between sub-millimetre dust emission and H2O ice column density is found for B35A-4 and B35A-5, similar to what has previously been reported. B35A-2 and B35A-3 are located where the sub-millimetre dust emission peaks and show H2O column densities lower than that of B35A-4. Conclusions. The difference between the sub-millimetre continuum emission and the infrared H2O ice observations suggests that the distributions of dust and H2O ice differ around the young stellar objects in this dense cloud. The reason for this may be that the four sources are located in different environments resolved by the interferometric observations: B35A-2, B35A-3, and, in particular, B35A-5 are situated in a shocked region that is plausibly affected by sputtering and heating, which in turn impacts the sub-millimetre dust emission pattern, while B35A-4 is situated in a more quiescent part of the cloud. Gas and ice maps are essential for connecting small-scale variations in the ice composition with the large-scale astrophysical phenomena probed by gas observations.

TidsskriftAstronomy and Astrophysics
Antal sider17
StatusUdgivet - 2021

Bibliografisk note

Funding Information:
Acknolw edgements. The authors wish to thank Bo Reipurth for fruitful discussions on HH 175 and Alison Craigon, Zak Smith, Jennifer Noble for providing the reduced IRAM 30 m data. The authors also wish to acknowledge the significance of Mauna Kea to the indigenous Hawaiian people and the anonymous reviewer for the careful reading of the manuscript and the useful comments. This work is based on observations with the Submillimeter Array, Mauna Kea, Hawaii, program code: 2018A-S033, with the Atacama Pathfinder Experiment, Llano Chajnantor, Chile, program code: 0102.F-9304. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. The Atacama Pathfinder EXperiment (APEX) telescope is a collaboration between the Max Planck Institute for Radio Astronomy, the European Southern Observatory, and the Onsala Space Observatory. Swedish observations on APEX are supported through Swedish Research Council grant No 2017-00648. The study is also based on data from the IRAM Science Data Archive, obtained by H.J.Fraser with the IRAM 30 m telescope under project ID 088-07. Finally, this work is based on archival data from the AKARI satellite, a JAXA project with the participation of the European Space Agency (ESA). The group of J.K.J. acknowledges the financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 646908) through ERC Consolidator Grant “S4F”. The research of LEK is supported by research grant (19127) from VILLUM FONDEN. H.J.F. gratefully acknowledges the support of STFC for Astrochemistry at the OU under grant Nos ST/P000584/1 and ST/T005424/1 enabling her participation in this work.

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© 2021 ESO.

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