The multi-scale relation between magnetic field strength and gas density in the interstellar medium: observations vs simulations

Ralph Pudritz

Thursday, Dec. 5th, 14:00CET

The relation between magnetic field strength B and gas density n in the ISM is critically important for star formation on all scales- from protostellar disks to the galactic ISM. In recent submitted work (Whitworth et al 2024, submitted) we have determined the B-n relation for both observations, as well as in a wide variety of numerical simulations across many decades of physical scales. For the observations we have extended the Zeeman data of Crutcher et al (2010) to include 700 new observations using the David-Chandrasekhar-Fermi (DCF) method. Separately, we used data from 19 different published numerical simulations using a variety of codes, initial conditions, resolutions etc. for systems ranging from protostellar disk formation to multiscale galactic MHD simulations. We perform comprehensive Baysian analyses on both the observations and the simulations. For the observations, we find a break density as in the Crutcher relation, but with different power laws: B ∝ n^(0.27±0.017) for n ≤ n_o and B ∝ n^(0.54±0.18) for n > n_o, where n_o = 924^(+145−144) cm^(−3). The simulations that best match these results are global dwarf galaxy and Milky Way like galaxy simulations where the exponent is ~ 0.5 for both the dense and diffuse gas. I will discuss the physical implications of our analyses for star formation and the ISM.