Kinematics of the Sagittarius B2(N-LMH) Molecular Core

Hollis, J. M.; Pedelty, J. A.; Boboltz, D. A.; Liu, Sheng-Yuan; Snyder, L. E.; Palmer, Patrick; Lovas, Francis J.; Jewell, P. R.

doi:10.1086/379315

Cited by 55 publications

(65 citation statements)

References 18 publications

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“…Two distinct velocity components were detected at 64 km s −1 and 75 km s −1 , which had been previously observed for other molecules in this source (e.g., Hollis et al 2003;Belloche et al 2008a;Müller et al 2008;Belloche et al 2009). A much weaker red wing at 82 km s −1 was seen for HNCO, but it is barely detected for HOCN so it was not included in Table 3. the analysis.…”

Section: Sgr B2(n)supporting

confidence: 82%

Interstellar HOCN in the Galactic center region

Brünken¹,

Беллоче

Martín

et al. 2010

A&A

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Aims. Our aim is to confirm the interstellar detection of cyanic acid, HOCN, in the Galactic center clouds. It has previously been tentatively detected only in Sgr B2(OH). Methods. We used a complete line survey of the hot cores Sgr B2(N) and (M) in the 3 mm range, complemented by additional observations carried out with the IRAM 30 m telescope at selected frequencies in the 2 mm band and towards four additional positions in the Sgr B2 cloud complex in the 2 and 3 mm bands. The spectral survey was analysed in the local thermodynamical equilibrium approximation (LTE) by modeling the emission of all identified molecules simultaneously. This allowed us to distinguish weak features of HOCN from the rich line spectrum observed in Sgr B2(N) and (M). Lines of the more stable (by 1.1 eV) isomer isocyanic acid, HNCO, in these sources, as well as those of HOCN and HNCO towards the other positions, were analysed in the LTE approximation as well. Results. Four transitions of HOCN were detected in a quiescent molecular cloud in the Galactic center at a position offset in (RA, Dec) by (20 , 100 ) from the hot core source Sgr B2(M), confirming its previous tentative interstellar detection. Up to four transitions were detected toward five other positions in the Sgr B2 complex, including the hot cores Sgr B2(M), (S), and (N). A fairly constant abundance ratio of ∼0.3−0.8% for HOCN relative to HNCO was derived for the extended gas components, suggesting a common formation process of these isomers.

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Section: Sgr B2(n)supporting

confidence: 82%

Interstellar HOCN in the Galactic center region

Brünken¹,

Беллоче

Martín

et al. 2010

A&A

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“…Therefore, our observations indicate that B / S < 0:3/3:8. Solving for the source size assuming a Gaussian beam size of 192 arcsec 2 , we find S > 2432 arcsec 2 , or equivalently, a linear size of >100 00 (1A7), which is much larger than the typical LMH hot core diameter of $5 00 ( Hollis et al 2003). This strongly suggests that the spatial distribution of CH 3 NC is extended and would not show any significant concentration toward the LMH hot core.…”

Section: Discussionmentioning

confidence: 81%

Interstellar Isomers: The Importance of Bonding Energy Differences

Remijan

Hollis

Lovas

et al. 2005

ApJ

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100

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We present strong detections of methyl cyanide (CH 3 CN), vinyl cyanide (CH 2 CHCN), ethyl cyanide (CH 3 CH 2 CN), and cyanodiacetylene (HC 4 CN) molecules with the Green Bank Telescope (GBT) toward the Sgr B2(N) molecular cloud. Attempts to detect the corresponding isocyanide isomers were only successful in the case of methyl isocyanide (CH 3 NC ) for its J K ¼ 1 0 0 0 transition, which is the first interstellar report of this line. To determine the spatial distribution of CH 3 NC, we used archival Berkeley-Illinois-Maryland Association ( BIMA) array data for the J K ¼ 4 K 3 K (K ¼ 0 3) transitions, but no emission was detected. From ab initio calculations, the bonding energy difference between the cyanide and isocyanide molecules is >8500 cm À1 (>12,000 K ). Thus, cyanides are the more stable isomers and would likely be formed more preferentially over their isocyanide counterparts. That we detect CH 3 NC emission with a single antenna (Gaussian beam size B ¼ 1723 arcsec 2 ) but not with an interferometer ( B ¼ 192 arcsec 2 ) strongly suggests that CH 3 NC has a widespread spatial distribution toward the Sgr B2( N ) region. Other investigators have shown that CH 3 CN is present both in the LMH hot core of Sgr B2( N ) and in the surrounding medium, while we have shown that CH 3 NC appears to be deficient in the LMH hot core. Thus, largescale, nonthermal processes in the surrounding medium may account for the conversion of CH 3 CN to CH 3 NC, while the LMH hot core, which is dominated by thermal processes, does not produce a significant amount of CH 3 NC. Ice analog experiments by other investigators have shown that radiation bombardment of CH 3 CN can produce CH 3 NC, thus supporting our observations. We conclude that isomers separated by such large bonding energy differences are distributed in different interstellar environments, making the evaluation of column density ratios between such isomers irrelevant unless it can be independently shown that these species are cospatial.

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“…For ethyl cyanide, we used in addition the constraints on the source size derived from our high angular resolution observations with the IRAM Plateau de Bure interferometer (see Table 5 of Belloche et al 2008b). The first two velocity components detected in methyl cyanide and ethyl cyanide correspond to the two hot cores embedded in Sgr B2(N) (see, e.g., Hollis et al 2003;Belloche et al 2008a). They are also seen in n-propyl cyanide.…”

Section: Comparison To Related Speciesmentioning

confidence: 88%

“…The redshifted counterpart is blended with the northern component in the single-dish beam (see Fig. 3 of Hollis et al 2003). The third velocity component is too faint to be detected in n-propyl cyanide.…”

Section: Comparison To Related Speciesmentioning

confidence: 97%

Increased complexity in interstellar chemistry: detection and chemical modeling of ethyl formate andn-propyl cyanide in Sagittarius B2(N)

Беллоче

Garrod

Müller

et al. 2009

A&A

242

300

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Context. In recent years, organic molecules of increasing complexity have been found toward the prolific Galactic center source Sagittarius B2. Aims. We wish to explore the degree of complexity that the interstellar chemistry can reach in star-forming regions. Methods. We carried out a complete line survey of the hot cores Sgr B2(N) and (M) with the IRAM 30 m telescope in the 3 mm range, plus partial surveys at 2 and 1.3 mm. We analyzed this spectral survey in the local thermodynamical equilibrium approximation. We modeled the emission of all known molecules simultaneously, which allows us to search for less abundant, more complex molecules. We compared the derived column densities with the predictions of a coupled gas-phase and grain-surface chemical code.Results. We report the first detection in space of ethyl formate (C 2 H 5 OCHO) and n-propyl cyanide (C 3 H 7 CN) toward Sgr B2(N). The detection of n-propyl cyanide is based on refined spectroscopic parameters derived from combined analyses of available laboratory spectroscopic data. For each molecule, we identified spectral features at the predicted frequencies having intensities compatible with a unique rotation temperature. For an assumed source size of 3 , our modeling yields a column density of 5.4 × 10 16 cm −2 , a temperature of 100 K, and a linewidth of 7 km s −1 for ethyl formate. n-Propyl cyanide is detected with two velocity components having column densities of 1.5 × 10 16 cm −2 and 6.6 × 10 15 cm −2 , respectively, for a source size of 3 , a temperature of 150 K, and a linewidth of 7 km s −1 . The abundances of ethyl formate and n-propyl cyanide relative to H 2 are estimated to be 3.6 × 10 −9 and 1.0 × 10 −9 , respectively. We derived column density ratios of 0.8/15/1 for the related species t-HCOOH/CH 3 OCHO/C 2 H 5 OCHO and 108/80/1 for CH 3 CN/C 2 H 5 CN/C 3 H 7 CN. Our chemical modeling reproduces these ratios reasonably well. It suggests that the sequential, piecewise construction of ethyl and n-propyl cyanide from their constituent functional groups on the grain surfaces is their most likely formation route. Ethyl formate is primarily formed on the grains by adding CH 3 to functional-group radicals derived from methyl formate, although ethanol may also be a precursor. Conclusions. The detection in Sgr B2(N) of the next stage of complexity in two classes of complex molecule, esters and alkyl cyanides, suggests that greater complexity in other classes of molecule may be present in the interstellar medium.

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Kinematics of the Sagittarius B2(N-LMH) Molecular Core

Cited by 55 publications

References 18 publications

Interstellar HOCN in the Galactic center region

Interstellar HOCN in the Galactic center region

Interstellar Isomers: The Importance of Bonding Energy Differences

Increased complexity in interstellar chemistry: detection and chemical modeling of ethyl formate andn-propyl cyanide in Sagittarius B2(N)

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