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Astron. Astrophys. 356, L13-L16 (2000)

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5. Implications for the structure of the local ISM

Because we have not yet reached a quantitative conclusion about the suspected correlation between [FORMULA] and [FORMULA]RM, it is not possible to give a full discussion of the implications that these polarization data have for the small-scale structure of the warm ISM. However, the data discussed here show the great promise that high-resolution, multi-band polarization data hold for the study of the ISM, especially on small scales where pulsars and extragalactic radio sources cannot give much information.

Fortunately, more and more sensitive radio polarization data (in different regions of sky) are forthcoming. In addition, information must be obtained about the electron density in the warm ISM on the relevant scales (e.g. through H[FORMULA] measurements), as well as on the other components in the ISM (like e.g. the HI).

While we fully realize the preliminary nature of the conclusions presented, we feel justified to speculate somewhat on the possible implications of the `canals'. Structure in RM reflects structure in [FORMULA] and/or [FORMULA] in the ISM. However, as the RM is an integral over the entire line of sight, the large [FORMULA]RM/RM values that are implied by our observations may give a very specific message. In particular, we consider it unlikely that the large [FORMULA]RM/RM values are produced mainly by variations in electron density. Instead, they may be indicating a turbulent ISM with varying (reversing) magnetic field structures, as modeled in recent MHD simulations (see e.g. Mac Low & Ossenkopf 2000; Vázquez-Semadeni & Passot 1999).

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© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000