SYNISM

The Dust-Gas Synergy in the ISM

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 Obiettivo del progetto (Objective)

'Interstellar dust is a fundamental component of the interstellar medium (ISM). By mediating key processes such as the absorption of stellar radiation, which is then re-emitted at infrared-mm wavelengths, it provides the necessary conditions (e.g., cloud cooling) for star formation to occur. Thus, dust determines the very processes that govern galaxy evolution. Dust is a ubiquitous component of the ISM in nearly all types of galaxies, even those at very high redshifts, where the dust has had little time to form. However, dust is an evolving component of the ISM, which responds to the local conditions. If we are to understand the processes that govern galaxy evolution it is therefore essential that we understand the evolving nature of dust in its relationship with the physical and dynamical conditions of the local ISM. The aim of this project is to study the evident synergy between interstellar gas and dust and to quantify the factors that drive dust evolution. This will be achieved by combining observations of a sample of photo-dissociation regions covering a range of local physical conditions, using the unique capabilities from ESA's newest IR space observatory, the Herschel space telescope, together with cutting edge expertise.'

Introduzione (Teaser)

The interstellar medium is the reservoir out of which stars are born and into which stars inject newly created elements as they age. New technological developments have enabled EU-funded scientists to probe processes never before observed.

Descrizione progetto (Article)

Herschel space observatory, European Space Agency's cutting-edge observatory, carries the largest, most powerful infrared telescope ever flown in space. It is the first space observatory to cover the entire range from far-infrared to sub-millimetre wavelengths. With Herschel's observations, scientists working on the 'The dust-gas synergy in the ISM' (SYNISM) project were able to deeply explore the interstellar medium.

About 99% of the interstellar medium is atomic and molecular gas and only 1% consists of tiny pieces of solid particles of dust. This dust plays a key role in the processes that regulate the formation of stars, and in the synthesis of complex molecules present in space. However, dust is an evolving component of the interstellar medium, and its evolution is intimately related to the gas's physical conditions. It is this circular dependence that has previously made dust-gas studies so complex. Dust grains absorb visible and ultraviolet light, thus heating up and radiating in infrared and submiilimetre wavelengths, now accessible with Herschel.

By tapping these unexploited wavelengths, the SYNISM scientists were able to see phenomena beyond the reach of other observatories. Specifically, they were able to study photodissociation regions (PDRs) at an unprecedented level of detail. These regions of the interstellar medium are at the edge of molecular clouds, the dense regions where stars form, and are the source of most non-stellar infrared emission. Structures such as filaments that are in nearby PDRs are easily observable due to the spatial resolution of the Herschel telescope.

Using the Herschel detectors, the SYNISM scientists were able to unveil this symbiotic system. The physical conditions prevailing around PDRs' fine structure were determined based on observations of emission lines which were the fingerprints of atoms and molecules. Theoretical models were also used by SYNISM scientists to interpret emission lines observe, and compared with the dust emission. The SYNISM scientists linked variations in gas physical properties with the changes in dust in the dense interstellar medium where stars form.

The results of the SYNISM study have improved our understanding of processes that govern galaxy evolution.