The Evolution of Massive Young Stellar Objects in the Large Magellanic Cloud. Ii. Thermal Processing of Circumstellar Ices

Seale, Jonathan; Looney, Leslie W.; Chen, C.-H. Rosie; Chu, You‐Hua; Gruendl, R. A.

doi:10.1088/0004-637x/727/1/36

Cited by 21 publications

(44 citation statements)

References 69 publications

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“…Spectral profiles of the 15.2 μm CO 2 ice band for high-mass YSOs in the LMC are well studied with Spitzer observations (Oliveira et al 2009;Seale et al 2011). Seale et al (2011) suggest that the CO 2 ices around high-mass YSOs in the LMC are more thermally processed than those in our Galaxy.…”

Section: N(ch 3 Oh)/n(h 2 O) [%]supporting

confidence: 53%

“…The authors suggest that intense radiation field and/or warm dust temperature in the LMC could be responsible for the different molecular abundance of ices in the LMC. Observations of the 15.2 μm CO 2 ice band toward LMC highmass YSOs with Spitzer/IRS suggest that a majority of CO 2 is locked in a water-rich (polar) ice mixture, but a fraction of CO 2 in a polar ice component is lower in the LMC than in our Galaxy (Oliveira et al 2009;Seale et al 2011). In addition, these studies argued that a larger number of LMC high-mass YSOs show a CO 2 ice profile characteristic to a pure or annealed CO 2 ice component compared to Galactic similar sources, suggesting a higher degree of thermal processing of ices in the LMC.…”

Section: Introductionmentioning

confidence: 80%

“…Previous studies have reported properties of ices around embedded high-mass YSOs in the LMC (Shimonishi et al 2008(Shimonishi et al , 2010(Shimonishi et al , 2013van Loon et al 2005van Loon et al , 2010aOliveira et al 2006Oliveira et al , 2009Oliveira et al , 2011Seale et al 2009Seale et al , 2011. Shimonishi et al (2010), for example, report the results of 2.5-5.0 μm spectroscopic observations of embedded highmass YSOs in the LMC with the Infrared Camera (IRC) on board the AKARI satellite (Onaka et al 2007;Murakami et al 2007).…”

Section: Introductionmentioning

confidence: 99%

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VLT/ISAAC infrared spectroscopy of embedded high-mass YSOs in the Large Magellanic Cloud: Methanol and the 3.47μm band

Shimonishi

Dartois

Onaka

et al. 2016

A&A

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Aims. This study aims to elucidate a possible link between chemical properties of ices in star-forming regions and environmental characteristics (particularly metallicity) of the host galaxy. The Large Magellanic Cloud (LMC) is an excellent target to study properties of interstellar and circumstellar medium in a different galactic environment thanks to its proximity and low metallicity. Methods. We performed near-infrared, L-band spectroscopic observations toward embedded high-mass young stellar objects (YSOs) in the LMC with the Infrared Spectrometer And Array Camera (ISAAC) at the Very Large Telescope. The 3.2-3.7 μm spectral region, which is accessible from ground-based telescopes, is important for ice studies, since various C-H stretching vibrations of carbon bearing species fall in this region. Results. We obtained medium-resolution (R ∼ 500) spectra in the 3-4 μm range for nine high-mass YSOs in the LMC. Additionally, we analyzed archival ISAAC data of two LMC YSOs. We detected absorption bands due to solid H 2 O and CH 3 OH as well as the 3.47 μm absorption band. The properties of these bands are investigated based on comparisons with Galactic embedded sources. The 3.53 μm CH 3 OH ice absorption band for the LMC YSOs is found to be absent or very weak compared to that seen toward Galactic sources. The absorption band is weakly detected for two out of eleven objects. We estimate the abundance of the CH 3 OH ice, which suggests that solid CH 3 OH is less abundant for high-mass YSOs in the LMC than those in our Galaxy. The 3.47 μm absorption band is detected toward six out of eleven LMC YSOs. We found that the 3.47 μm band and the H 2 O ice band correlate similarly between the LMC and Galactic samples, but the LMC sources seem to require a slightly higher H 2 O ice threshold for the appearance of the 3.47 μm band. For the LMC sources with relatively large H 2 O ice optical depths, we found that the strength ratio of the 3.47 μm band relative to the water ice band is only marginally lower than those of the Galactic sources. Conclusions. We propose that grain surface reactions at a relatively high dust temperature (warm ice chemistry) are responsible for the observed characteristics of ice chemical compositions in the LMC; i.e., the low abundance of solid CH 3 OH presented in this work as well as the high abundance of solid CO 2 reported in previous studies. We suggest that this warm ice chemistry is one of the important characteristics of interstellar and circumstellar chemistry in low metallicity environments. The low abundance of CH 3 OH in the solid phase implies that formation of complex organic molecules from methanol-derived species is less efficient in the LMC. For the 3.47 μm band, the observed difference in the water ice threshold may suggest that a more shielded environment is necessary for the formation of the 3.47 μm band carrier in the LMC. On the one hand, in well-shielded regions of the LMC, our results suggest that the lower metallicity and different interstellar environment of the LMC...

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Section: N(ch 3 Oh)/n(h 2 O) [%]supporting

confidence: 53%

Section: Introductionmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

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VLT/ISAAC infrared spectroscopy of embedded high-mass YSOs in the Large Magellanic Cloud: Methanol and the 3.47μm band

Shimonishi

Dartois

Onaka

et al. 2016

A&A

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“…The authors suggest that warm ice chemistry (grain surface reactions at a relatively high dust temperature) is responsible for the observed characteristics of ice chemical compositions in the LMC. Furthermore, detailed studies of the 15.2μm CO 2 ice band toward LMC high-mass YSOs with Spitzer suggest a higher degree of thermal processing of ices in the LMC than in our Galaxy (Oliveira et al 2009;Seale et al 2011). Since gas-grain chemistry is believed to play an important role in hot cores, the characteristic ice chemistry in the LMC would imply a diverse hot core chemistry in extragalactic environments according to their metallicities.…”

Section: Introductionmentioning

confidence: 79%

The Detection of a Hot Molecular Core in the Large Magellanic Cloud With Alma

Shimonishi

Onaka

Kawamura

et al. 2016

ApJ

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We report the first detection of a hot molecular core outside our Galaxy based on radio observations with ALMA toward a high-mass young stellar object (YSO) in a nearby low metallicity galaxy, the Large Magellanic Cloud (LMC). are detected from a compact region (∼0.1 pc) associated with a high-mass YSO, ST11. The temperature of molecular gas is estimated to be higher than 100 K based on rotation diagram analysis of SO 2 and 34 SO 2 lines. The compact source size, warm gas temperature, high density, and rich molecular lines around a high-mass protostar suggest that ST11 is associated with a hot molecular core. We find that the molecular abundances of the LMC hot core are significantly different from those of Galactic hot cores. The abundances of CH 3 OH, H 2 CO, and HNCO are remarkably lower compared to Galactic hot cores by at least 1-3 orders of magnitude. We suggest that these abundances are characterized by the deficiency of molecules whose formation requires the hydrogenation of CO on grain surfaces. In contrast, NO shows a high abundance in ST11 despite the notably low abundance of nitrogen in the LMC. A multitude of SO 2 and its isotopologue line detections in ST11 imply that SO 2 can be a key molecular tracer of hot core chemistry in metal-poor environments. Furthermore, we find molecular outflows around the hot core, which is the second detection of an extragalactic protostellar outflow. In this paper, we discuss the physical and chemical characteristics of a hot molecular core in the low metallicity environment.

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“…An example of AKARI near-infrared spectrum of a LMC's YSO is shown in Figure 1. A large number of embedded YSOs are also reported by the Spitzer/IRS observations, and midinfrared ice features are investigated in detail (Oliveira et al, 2009;Seale et al, 2011).…”

Section: Embedded Yso Samples In the Magel-lanic Cloudsmentioning

confidence: 99%