Hot Expanding Shells in the Envelope of the Sagittarius B2 Molecular Cloud

Martı́n-Pintado, J.; Gaume, R. A.; Rodriguez‐fernandez, Nemesio; Vicente, P. de; Wilson, Thomas L.

doi:10.1086/307399

Cited by 58 publications

(58 citation statements)

References 50 publications

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“…(2) Mehringer & Menten (1997) argue that the quasi-thermal 44 GHz methanol emission (which is spatially correlated with the CH 3 CHO emission) probably arises from shocked gas at the boundaries of expanding ionized shells around the young stars in the molecular cloud. (3) Martín-Pintado et al (1999) have found a large number of hot expanding shells produced by massive evolved stars in the region between Sgr B2 (M) and Sgr B2 (AA), from which we detect bright CH 3 CHO emission. Again, the expansion of these hot shells into the parent molecular cloud is likely to result in the formation of shocks.…”

Section: Resultsmentioning

confidence: 58%

Widespread acetaldehyde near the Galactic Centre

Chengalur

Kanekar

2003

A&A

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Abstract. We present Giant Meterwave Radio Telescope images of the 1065 MHz emission from the 1 11 → 1 10 rotational transition of acetaldehyde (CH 3 CHO) in the molecular cloud complex Sgr B2. Our observations are unique in that they have a high spatial resolution (∼4 ), while still being sensitive to large-scale emission. Most complex organic molecules in this cloud (e.g. acetone, methyl formate, acetic acid) are concentrated in a very small core, ∼0.1 pc across. In contrast, acetaldehyde is found to be spread over a region at least 100 times larger in extent. The line emission is confined to regions with radio continuum emission and correlates well (in both position and velocity) with formaldehyde absorption towards this continuum; this is consistent with earlier single dish results suggesting that it is likely to be weakly mased. Our observations also suggest that grain mantle destruction by shocks plays an important role in the observed gas phase abundance of CH 3 CHO in Sgr B2.

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Section: Resultsmentioning

confidence: 58%

Widespread acetaldehyde near the Galactic Centre

Chengalur

Kanekar

2003

A&A

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“…This will produce new shocks in the surrounding gas and dust, which may release volatile molecules from the icy grain mantles (Flower & Pineau des Forêts 1994) and consequently increase the ammonia abundance again. This line of reasoning is supported by the significantly high NH 3 abundance seen to the north and south-western borders of the SW region, a trend also found in the molecular cloud around the WR nebula NGC 2359 (Rizzo et al 2001a), and the Galactic Center (Flower et al 1995;Martín-Pintado et al 1999). The young stellar objects formed in the SW region will probably suffer photo-evaporation and heating of their envelopes.…”

Section: Triggered Star Formation In the Sw Regionmentioning

confidence: 83%

Ammonia observations in the LBV nebula G79.29+0.46

Rizzo

Palau

Jiménez-Esteban

et al. 2014

A&A

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Context. The surroundings of luminous blue variable (LBV) stars are excellent laboratories to study the effects of their high UV radiation, powerful winds, and strong ejection events onto the surrounding gas and dust. Aims. We aim at determining the physical parameters of the dense gas near G79.29+0.46, an LBV-candidate located at the centre of two concentric infrared rings, which may interact with the infrared dark cloud (IRDC) G79.3+0.3. Methods. The Effelsberg 100 m telescope was used to observe the NH 3 (1, 1) and (2, 2) emission in a field of view of 7 × 7 including the infrared rings and a part of the IRDC. In addition, we observed particular positions in the NH 3 (3,3) transition toward the strongest region of the IRDC, which is also closest to the ring nebula. Results. We report here the first coherent ring-like structure of dense NH 3 gas associated with an evolved massive star. It is well traced in both ammonia lines, surrounding an already known infrared ring nebula; its column density is two orders of magnitude lower than the IRDC. The NH 3 emission in the IRDC is characterized by a low and uniform rotational temperature (T rot ∼10 K) and moderately high opacities in the (1, 1) line. The rest of the observed field is spotted by warm or hot zones (T rot >30 K) and characterized by optically thin emission of the (1, 1) line. The NH 3 abundances are about 10 −8 in the IRDC, and 10 −10 -10 −9 elsewhere. The warm temperatures and low abundances of NH 3 in the ring suggest that the gas is being heated and photo-dissociated by the intense UV field of the LBV star. An outstanding region is found to the south-west (SW) of the LBV star within the IRDC. The NH 3 (3, 3) emission at the centre of the SW region reveals two velocity components tracing gas at temperatures >30 K. Of particular interest is the northern edge of the SW region, which coincides with the border of the ring nebula and a region of strong 6 cm continuum emission; here, the opacity of the (1, 1) line and the NH 3 abundance do not decrease as expected in a typical clump of an isolated cold dark cloud. This strongly suggests some kind of interaction between the ring nebula (powered by the LBV star) and the IRDC. We finally discuss the possibility of NH 3 evaporation from the dust grain mantles due to the already known presence of low-velocity shocks in the area. Conclusions. The detection of the NH 3 associated with this LBV ring nebula, as well as the special characteristics of the northern border of the SW region, confirm that the surroundings of G79.29+0.46 constitute an exemplary scenario, which merits to be studied in detail by other molecular tracers and higher angular resolutions.

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“…One of the key parameters for constraining the origin of the shocks is the velocity dispersion in the GC molecular clouds. High angular-resolution observation of the envelope of Sgr B2 indicates that the warm molecular gas is highly turbulent with linewidths of ∼4 km s −1 (Martín-Pintado et al 1999). Smith et al (2000) show that MHD turbulence creates a wide range of shock velocities, but the larger amount of them should be produced with Mach numbers between 2-4.…”

Section: Grain Mantle Erosion By Shocks and Time Scales For Depletionmentioning

confidence: 99%

“…The other possible mechanisms could explain the observations if cloud-cloud collision and energetic events driven by massive stars occur on time scales of 10 5 years. In the scenario of a recent star burst in the GC as proposed to explain the fine structure lines of ionized gas (Rodríguez-Fernández & Martín-Pintado 2005), frequent energetic events associated to massive stars are expected to produce shocks with moderate velocities of ∼10 km s −1 (Martín-Pintado et al 1999) ejecting complex molecules to gas phase and a large amount of energy into the ISM.…”

Section: Grain Mantle Erosion By Shocks and Time Scales For Depletionmentioning

confidence: 99%

“…The origin of the large scale shocks is so far unclear. These shocks could be produced by cloud-cloud collisions associated with the largescale dynamics in the context of a barred potential (Hasegawa et al 1994;Hüttemeister et al 1998;Rodríguez-Fernández et al 2006), by wind-blown bubbles driven by evolved massive stars (Martín-Pintado et al 1999), or by hydrodynamic (HD) or magneto hydrodynamic turbulence (MHD) (Morris & Serabyn 1996). Since the formation of some complex organic molecules is believed to proceed in gas phase after the passage of the shocks and their abundances rapidly evolve, one could use the abundances of these molecules to gain insight into the chemistry of complex molecules in the ISM and to constrain the age of shocks in the GC (Martín-Pintado et al 2001).…”

Section: Introductionmentioning

confidence: 99%

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Organic molecules in the Galactic center

Requeña-Torres¹,

Martı́n-Pintado²,

Rodríguez-Franco

et al. 2006

A&A

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242

244

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Aims. We study the origin of large abundances of complex organic molecules in the Galactic center (GC). Methods. We carried out a systematic study of the complex organic molecules CH 3 OH, C 2 H 5 OH, (CH 3 ) 2 O, HCOOCH 3 , HCOOH, CH 3 COOH, H 2 CO, and CS toward 40 GC molecular clouds. Using the LTE approximation, we derived the physical properties of GC molecular clouds and the abundances of the complex molecules. The abundances of complex organic molecules in the GC are compared with those measured in hot cores and hot corinos, in which these complex molecules are also abundant. Results. The CH 3 OH abundance between clouds varies by nearly two orders of magnitude from 2.4×10 −8 to 1.1×10 −6 . The abundance of the other complex organic molecules relative to that of CH 3 OH is basically independent of the CH 3 OH abundance, with variations of only a factor 4-8. We find that both the abundance and the abundance ratios of the complex molecules relative to CH 3 OH in hot cores are similar to those found in the GC clouds. However, hot corinos show different abundance ratios than observed in hot cores and in GC clouds. The rather constant abundance of all the complex molecules relative to CH 3 OH suggests that all complex molecules are ejected from grain mantles by shocks. Frequent (∼10 5 years) shocks with velocities >6 km s −1 are required to explain the high abundances in gas phase of complex organic molecules in the GC molecular clouds. The rather uniform abundance ratios in the GC clouds and in Galactic hot cores indicate a similar average composition of grain mantles in both kinds of regions. The Sickle and the Thermal Radio Arches, affected by UV radiation, show different relative abundances in the complex organic molecules due to the differentially photodissociation of these molecules.

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Hot Expanding Shells in the Envelope of the Sagittarius B2 Molecular Cloud

Cited by 58 publications

References 50 publications

Widespread acetaldehyde near the Galactic Centre

Widespread acetaldehyde near the Galactic Centre

Ammonia observations in the LBV nebula G79.29+0.46

Organic molecules in the Galactic center

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