Implications of [ITAL]Submillimeter Wave Astronomy Satellite[/ITAL] Observations for Interstellar Chemistry and Star Formation

Bergin, Edwin A.; Melnick, Gary J.; Stauffer, J. R.; Ashby, M. L. N.; Chin, G.; Erickson, N. R.; Goldsmith, P. F.; Harwit, Martin; Howe, J. E.; Kleiner, S. C.; Koch, David; Neufeld, David A.; Patten, B. M.; Plume, R.; Schieder, R.; Snell, R. L.; Tolls, Volker; Wang, Z.; Winnewisser, G.; Zhang, Y. F.

doi:10.1086/312843

Cited by 144 publications

(118 citation statements)

References 38 publications

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“…Charnley 1997), i.e. orders of magnitude relative to the values inferred in cold molecular clouds and PDRs (Melnick & Bergin 2005), where H 2 O ice is expected to be efficiently formed upon hydrogenation of atomic oxygen depleted on mantles in cold environments (Bergin et al 2000;Hollenbach et al 2009). If the gas attains sufficiently high temperatures (T g ∼ 300 K), H 2 O will be further enhanced in the gas phase via neutral-neutral reactions (e.g.…”

Section: Model Uncertaintiesmentioning

confidence: 98%

“…Assuming a gas-phase O i abundance typical of translucent clouds (χ Oi = 2.5 × 10 −4 relative to H, Cartledge et al 2001;Lis et al 2001), N H ≈ 6.5 × 10 22 cm −2 , or A v ∼ 30 mag. Since oxygen depletion may be enhanced for those columns (Bergin et al 2000), the allowed range is A v ≈ 30−60 mag. This extinction is at least half of that required to account for the silicate absorption at 10 μm.…”

Section: H 18mentioning

confidence: 99%

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Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H₂O, H₂¹⁸O, OH,¹⁸OH, O I, HCN, and NH₃

González-Alfonso

Fischer

Graciá-Carpio

et al. 2012

A&A

152

166

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Full range Herschel/PACS spectroscopy of the (ultra)luminous infrared galaxies NGC 4418 and Arp 220, observed as part of the SHINING key programme, reveals high excitation in H 2 O, OH, HCN, and NH 3 . In NGC 4418, absorption lines were detected with E lower > 800 K (H 2 O), 600 K (OH), 1075 K (HCN), and 600 K (NH 3 ), while in Arp 220 the excitation is somewhat lower. While outflow signatures in moderate excitation lines are seen in Arp 220 as have been seen in previous studies, in NGC 4418 the lines tracing its outer regions are redshifted relative to the nucleus, suggesting an inflow withṀ 12 M yr −1 . Both galaxies have compact and warm (T dust 100 K) nuclear continuum components, together with a more extended and colder component that is much more prominent and massive in Arp 220. A chemical dichotomy is found in both sources: on the one hand, the nuclear regions have high H 2 O abundances, ∼10 −5 , and high HCN/H 2 O and HCN/NH 3 column density ratios of 0.1−0.4 and 2−5, respectively, indicating a chemistry typical of evolved hot cores where grain mantle evaporation has occurred. On the other hand, the high OH abundance, with OH/H 2 O ratios of ∼0.5, indicates the effects of X-rays and/or cosmic rays. The nuclear media have high surface brightnesses ( 10 13 L /kpc 2 ) and are estimated to be very thick (N H 10 25 cm −2 ). While NGC 4418 shows weak absorption in H 18 2 O and 18 OH, with a 16 O-to-18 O ratio of 250−500, the relatively strong absorption of the rare isotopologues in Arp 220 indicates 18 O enhancement, with 16 O-to-18 O of 70−130. Further away from the nuclear regions, the H 2 O abundance decreases to 10 −7 and the OH/H 2 O ratio is reversed relative to the nuclear region to 2.5−10. Despite the different scales and morphologies of NGC 4418, Arp 220, and Mrk 231, preliminary evidence is found for an evolutionary sequence from infall, hot-core like chemistry, and solar oxygen isotope ratio to high velocity outflow, disruption of the hot core chemistry and cumulative high mass stellar processing of 18 O.

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Section: Model Uncertaintiesmentioning

confidence: 98%

Section: H 18mentioning

confidence: 99%

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H₂O, H₂¹⁸O, OH,¹⁸OH, O I, HCN, and NH₃

González-Alfonso

Fischer

Graciá-Carpio

et al. 2012

A&A

152

166

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“…5 and Table 2. Unless a very long static phase (16t ff ) is assumed, the models labeled AT tend to overpredict the O 2 abundance, implying that the majority of oxygen should be locked up in molecules such as water and CO before the prestellar core stage (Yıldız et al 2013;Bergin et al 2000).…”

Section: O 2 and Ortho-para Ratio Of Hmentioning

confidence: 99%

Reconstructing the history of water ice formation from HDO/H₂O and D₂O/HDO ratios in protostellar cores

Furuya

Dishoeck

Aikawa

2016

A&A

137

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Recent interferometer observations have found that the D 2 O/HDO abundance ratio is higher than that of HDO/H 2 O by about one order of magnitude in the vicinity of low-mass protostar NGC 1333-IRAS 2A, where water ice has sublimated. Previous laboratory and theoretical studies show that the D 2 O/HDO ice ratio should be lower than the HDO/H 2 O ice ratio, if HDO and D 2 O ices are formed simultaneously with H 2 O ice. In this work, we propose that the observed feature, D 2 O/HDO > HDO/H 2 O, is a natural consequence of chemical evolution in the early cold stages of low-mass star formation as follows: 1) majority of oxygen is locked up in water ice and other molecules in molecular clouds, where water deuteration is not efficient; and 2) water ice formation continues with much reduced efficiency in cold prestellar/protostellar cores, where deuteration processes are highly enhanced as a result of the drop of the ortho-para ratio of H 2 , the weaker UV radiation field, etc. Using a simple analytical model and gas-ice astrochemical simulations, which traces the evolution from the formation of molecular clouds to protostellar cores, we show that the proposed scenario can quantitatively explain the observed HDO/H 2 O and D 2 O/HDO ratios. We also find that the majority of HDO and D 2 O ices are likely formed in cold prestellar/protostellar cores rather than in molecular clouds, where the majority of H 2 O ice is formed. This work demonstrates the power of the combination of the HDO/H 2 O and D 2 O/HDO ratios as a tool to reveal the past history of water ice formation in the early cold stages of star formation, and when the enrichment of deuterium in the bulk of water occurred. Further observations are needed to explore if the relation, D 2 O/HDO > HDO/H 2 O, is common in low-mass protostellar sources.

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“…Unfortunately, this time range encompasses the "age" of cold cores determined by the comparison between large network chemical models and observations of more than 30 species in TMC-1CP and L134N (N) (see Wakelam et al 2006a;Garrod et al 2007;Smith et al 2004). Bergin et al (2000) found a small abundance of O 2 in the gas at all times, in agreement with observations, using a simplified version of grain surface chemistry assuming conversion of O to H 2 O and C to CH 4 , and choosing the branching ratio of the reaction H 3 O + + e − −→ H + H 2 O that equals 0.33 to reproduce the H 2 O abundance. Experimental measurements from Jensen et al (2000) showed that this branching ratio is 0.25.…”

Section: Introductionmentioning

confidence: 99%

Oxygen depletion in dense molecular clouds: a clue to a low O₂abundance?

Hincelin

Wakelam

Hersant

et al. 2011

A&A

141

154

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Context. Dark cloud chemical models usually predict large amounts of O 2 , often above observational limits. Aims. We investigate the reason for this discrepancy from a theoretical point of view, inspired by the studies of Jenkins and Whittet on oxygen depletion. Methods. We use the gas-grain code Nautilus with an up-to-date gas-phase network to study the sensitivity of the molecular oxygen abundance to the oxygen elemental abundance. We use the rate coefficient for the reaction O + OH at 10 K recommended by the KIDA (KInetic Database for Astrochemistry) experts. Results. The updates of rate coefficients and branching ratios of the reactions of our gas-phase chemical network, especially N + CN and H + 3 + O, have changed the model sensitivity to the oxygen elemental abundance. In addition, the gas-phase abundances calculated with our gas-grain model are less sensitive to the elemental C/O ratio than those computed with a pure gas-phase model. The grain surface chemistry plays the role of a buffer absorbing most of the extra carbon. Finally, to reproduce the low abundance of molecular oxygen observed in dark clouds at all times, we need an oxygen elemental abundance smaller than 1.6 × 10 −4 . Conclusions. The chemistry of molecular oxygen in dense clouds is quite sensitive to model parameters that are not necessarily well constrained. That O 2 abundance may be sensitive to nitrogen chemistry is an indication of the complexity of interstellar chemistry.

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Implications of [ITAL]Submillimeter Wave Astronomy Satellite[/ITAL] Observations for Interstellar Chemistry and Star Formation

Cited by 144 publications

References 38 publications

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H₂O, H₂¹⁸O, OH,¹⁸OH, O I, HCN, and NH₃

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H₂O, H₂¹⁸O, OH,¹⁸OH, O I, HCN, and NH₃

Reconstructing the history of water ice formation from HDO/H₂O and D₂O/HDO ratios in protostellar cores

Oxygen depletion in dense molecular clouds: a clue to a low O₂abundance?

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Implications of [ITAL]Submillimeter Wave Astronomy Satellite[/ITAL] Observations for Interstellar Chemistry and Star Formation

Cited by 144 publications

References 38 publications

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H2O, H218O, OH,18OH, O I, HCN, and NH3

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H2O, H218O, OH,18OH, O I, HCN, and NH3

Reconstructing the history of water ice formation from HDO/H2O and D2O/HDO ratios in protostellar cores

Oxygen depletion in dense molecular clouds: a clue to a low O2abundance?

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Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H₂O, H₂¹⁸O, OH,¹⁸OH, O I, HCN, and NH₃

Herschel/PACS spectroscopy of NGC 4418 and Arp 220: H₂O, H₂¹⁸O, OH,¹⁸OH, O I, HCN, and NH₃

Reconstructing the history of water ice formation from HDO/H₂O and D₂O/HDO ratios in protostellar cores

Oxygen depletion in dense molecular clouds: a clue to a low O₂abundance?