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Magnetic field versus gas density, in different physical conditions

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Abstract

A search is made here for possible variations in the behavior of magnetic field valuesB at various gas density valuesn, when comparing low density gas versus high density gas, and when comparing compressed gas versus quiescent gas.

  1. (a)

    For thequiescent microturbulent interstellar gas (e.g., clouds, interclumps — see TableI), the statistical relationB ~n kyieldsk = 0.46 ± 0.07 forhigh gas densityn > 100 cm−3, andk = 0.17 ± 0.03 forlow gas densityn < 100 cm−3 (see Figure 1).

  2. (b)

    For thecompressed macroturbulent interstellar gas (e.g., masers, expanding shells — see Table II), the statistical relationB ~n KyieldsK = 0.61 ± 0.09 forhigh gas densityn > 100 cm−3, andK = 0.37 ± 0.2 forlow gas densityn < 100 cm−3 (see Figure 2).

  3. (c)

    The separation betweenlow density gas andhigh density gas is statistically significant. The 2 different physical behaviors (below and above the break at 100 cm−3) are confirmed statistically (about 2 to 4 sigma away for the quiescent gas alone; about 3 to 6 sigma away for the combined quiescent plus compressed gas).

  4. (d)

    The separation betweencompressed gas andquiescent gas is not statistically significant now (see Figure 3). Atn > 100 cm−3, a comparison of quiescent gas versus compressed gas shows no statistically significant differences in behavior (they are only about 1 sigma away). Atn < 100 cm−3, a comparison of quiescent versus compressed gas also shows no statistically significant differences in behavior (less than 1 sigma away).

  5. (e)

    A relation between the densityn and the galactic-wide Star Formation Rate (SFR) can be made for galactic magnetic fields, i.e.: (SFR) ~n n. For galactic-wide parameters using quiescent, low densityn < 100 cm−3, and the known relationshipsB ~n k/jwithk = 0.17,B ~ (SFR)j withj = 0.13, then one gets here a lawSFR ~n k/jwith an exponentk/j = 1.3. This is in rough accord with known data for the Milky Way and for NGC6946.

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  1. J.C.M.T. Group, Herzberg Institute of Astrophysics, National Research Council of Canada, room 2069, 100 Sussex Drive, K1A 0R6, Ottawa, Ontario, Canada

    J. P. Vallée

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Vallée, J.P. Magnetic field versus gas density, in different physical conditions. Astrophys Space Sci 234, 1–10 (1995). https://doi.org/10.1007/BF00627277

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