Widespread acetaldehyde near the Galactic Centre

Chengalur, J. N.; Kanekar, Nissim

doi:10.1051/0004-6361:20030577

Cited by 42 publications

(43 citation statements)

References 28 publications

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“…CH 3 CHO emission is found to arise from Sgr B2(N), extending toward the south-west. These features are in good agreement with the strongest part of the c-C 2 H 4 O 1 1,1 -1 1,0 emission imaged by Chengalur & Kanekar (2003) with the GMRT. Given that its relative abundance to H 2 CO is considerably smaller than the ratio of 10 4 as expected from pure gas-phase models for the production of these molecules (Lee et al 1996), Chengalur & Kanekar suggested that grain chemistry is likely to be important for the enhanced CH 3 CHO; its wide-spread distribution is probably related to the presence of numerous shocks in Sgr B2.…”

Section: The Imaging Of the C 2 H 4 O Isomeric Tripletsupporting

confidence: 83%

Interferometric Observations of Complex Organic Molecules

Liu

2006

IAU

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Abstract. Rich molecular complexity has been shown to exist in star forming regions primarily through millimeter to submillimeter single-dish spectral line surveys or searches over the years. With a few case studies, we demonstrate that interferometric observations are a powerful tool for advancing our knowledge of the chemical processes related to the formation of complex organic molecules in these regions. In particular, interferometers are sensitive to compact structures, such as those of the so called "hot molecular core" sources where complex organics are almost exclusively found. The high angular resolutions achieved by interferometers allow us to better spatially discriminate chemical differentiation and, possibly, evolutionary effects.

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Section: The Imaging Of the C 2 H 4 O Isomeric Tripletsupporting

confidence: 83%

Interferometric Observations of Complex Organic Molecules

Liu

2006

IAU

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“…In an UV photon experiment performed at 100 K, the destruction of CH 3 CN was faster than at 12 K, but the same end products were seen. This suggests that the reactions were driven more by the radiation dose than the sample temperature (Hudson & Moore Note.-The chemical bonding energies were obtained at the MP2/ aug-cc-pVTZ level of theory (Frisch et al 2004;Dunning 1989;Kendall et al 1992;Woon & Dunning 1993 (Chengalur & Kanekar 2003). Such shocks have been presumed to be responsible for the formation and distribution of large aldehyde molecules toward this region (Hollis et al 2004a(Hollis et al , 2004b.…”

Section: Discussionmentioning

confidence: 99%

Interstellar Isomers: The Importance of Bonding Energy Differences

Remijan

Hollis

Lovas

et al. 2005

ApJ

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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“…Interestingly, Chengalur & Kanekar (2003) observed that CH 3 CHO is more widespread toward the Galactic center than most other complex organic molecules. They argue that the molecule could be produced by shock-induced disruption on dust mantles.…”

Section: B18 Ch 3 Chomentioning

confidence: 99%

Molecules atz= 0.89

Müller

Beelen

Guèlin

et al. 2011

A&A

163

284

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We present the results of a 7 mm spectral survey of molecular absorption lines originating in the disk of a z = 0.89 spiral galaxy located in front of the quasar PKS 1830−211. Our survey was performed with the Australia Telescope Compact Array and covers the frequency interval 30-50 GHz, corresponding to the rest-frame frequency interval 57-94 GHz. A total of 28 different species, plus 8 isotopic variants, were detected toward the south-west absorption region, located about 2 kpc from the center of the z = 0.89 galaxy, which therefore has the largest number of detected molecular species of any extragalactic object so far. The results of our rotation diagram analysis show that the rotation temperatures are close to the cosmic microwave background temperature of 5.14 K that we expect to measure at z = 0.89, whereas the kinetic temperature is one order of magnitude higher, indicating that the gas is subthermally excited. The molecular fractional abundances are found to be in-between those in typical Galactic diffuse and translucent clouds, and clearly deviate from those observed in the dark cloud TMC 1 or in the Galactic center giant molecular cloud Sgr B2. The isotopic ratios of carbon, nitrogen, oxygen, and silicon deviate significantly from the solar values, which can be linked to the young age of the z = 0.89 galaxy and a release of nucleosynthesis products dominated by massive stars. Toward the north-east absorption region, where the extinction and column density of gas is roughly one order of magnitude lower than toward the SW absorption region, only a handful of molecules are detected. Their relative abundances are comparable to those in Galactic diffuse clouds. We also report the discovery of several new absorption components, with velocities spanning between −300 and +170 km s −1 . Finally, the line centroids of several species (e.g., CH 3 OH, NH 3 ) are found to be significantly offset from the average velocity. If caused by a variation in the proton-to-electron mass ratio μ with redshift, these offsets yield an upper limit | Δμ μ | < 4×10 −6 , which takes into account the kinematical noise produced by the velocity dispersion measured from a large number of molecular species.

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Widespread acetaldehyde near the Galactic Centre

Cited by 42 publications

References 28 publications

Interferometric Observations of Complex Organic Molecules

Interferometric Observations of Complex Organic Molecules

Interstellar Isomers: The Importance of Bonding Energy Differences

Molecules atz= 0.89

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