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Astron. Astrophys. 342, 233-256 (1999)

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8. Conclusions

  1. Molecular line, millimetre/submillimetre/radio continuum, and mid-IR observations are reported of the opaque fingers which cross the Eagle Nebula. These are examined, along with optical and near-IR data to measure the physical environment within the fingers, and to examine their potential for being future sites of star-formation.

  2. The fingers are surprisingly warm when viewed in the CO J = 3-2 lines, with peak temperatures approaching 60 K. The lines are however relatively narrow, and there is no compelling evidence for any molecular outflow activity. The masses of the fingertip cores determined from CO isotopomeric observations range from [FORMULA] 10 to 60 [FORMULA], and they contain 55-80% of the total mass of each of the fingers. The total mass contained in the three fingers and the nearby extended material is [FORMULA] 200 [FORMULA].

  3. The velocity fields of the gas are complex and show that the material is very clumpy. The best evidence for coherent velocity structure is along the centre finger, where a velocity gradient [FORMULA] 1.7 km s- 1 pc-1 is seen. There may be evidence for somewhat larger velocity gradients, however these are difficult to untangle from the clumpy structure of the gas.

  4. The fingers contain a number of embedded submm continuum cores. The most intense cores in each finger are found close to the tips of the fingers. The continuum spectra of these cores suggest that they are much cooler, [FORMULA] 20 K, than the gas temperatures measured by the CO observations.

  5. Detailed modelling shows that the fingers should contain dense cold cores surrounded by a sheath of warm molecular gas. These characteristics prove to be an excellent match to the observational data.

  6. The radio and morphological evidence suggest that the UV radiation field incident on the surfaces of the fingers is [FORMULA] 1700 G [FORMULA].

  7. A simple thermal and chemical model of a finger structure was developed to study their internal physical environment. This model suggests that the fingers should contain cold ([FORMULA] 20 K) dense cores near their tips, surrounded by a sheath of warm ([FORMULA] 100 K) gas. The model predictions are consistent with all of the available observations.

  8. The fingers appear to have been formed after primordial dense clumps in the original cloud (which formed NGC 6611) were irradiated by the light of its own OB stars. These primordial clumps have shielded material behind it from the photoevaporative dispersal of the cloud, leading to the formation of the finger structures. The cores appear to be at a very early stage of pre-protostellar development: there are no embedded infrared sources or molecular outflows present. The pressure inside the cores appears to be just less than that of the surrounding gas, and the consequence is that the material in the cores is being compressed by the external medium. It is well known that such characteristics are those shared by the earliest stages of objects popularly known as `protostars'. The cores in the tips of the Eagle Nebula's fingers appear to have the characteristics which are expected for objects in the very earliest stages of (pre-) protostellar activity .

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© European Southern Observatory (ESO) 1999

Online publication: December 22, 1998
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