The Millennium Arecibo 21 Centimeter Absorption-Line Survey. IV. Statistics of Magnetic Field, Column Density, and Turbulence

By C. Heiles, T. Troland. 2005

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We discuss observations of the magnetic field, column density, and turbulence in the cold neutral medium (CNM). The observed quantities are only indirectly related to the intrinsic astronomical ones. We relate the observed and intrinsic quantities by relating their univariate and bivariate probability distribution functions (pdf's). We find that observations of the line-of-sight component of a magnetic field do not constrain the pdf of the total field Btot very well but do constrain the median value of Btot. In the CNM, we find a well-defined median magnetic field 6.0 ± 1.8 μG. The CNM magnetic field dominates thermal motions. Turbulence and magnetism are in approximate equipartition. We find that the probability distribution of column density N⊥(H ) in the sheets closely follows N⊥(H )-1 over a range of 2 orders of magnitude, 0.026 ≲ N⊥(H ) ≲ 2.6 × 1020 cm-2. The bivariate distributions are not well enough determined to constrain structural models of CNM sheets.

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Citations in the corpus

On the relationship between molecular hydrogen and carbon monoxide abundances in molecular clouds (2010, methodology): “The particular value that we have chosen is the same as we adopted in Paper I, and is motivated by the 21 cm observations by Heiles & Troland (2005) that find a median magnetic field strength of ∼ 6µG for the cold neutral medium.”
Accretion-driven turbulence as universal process: galaxies, molecular clouds, and protostellar disks (2009, background): “Although we have Page 4 of 18 ample evidence that there are large-scale magnetic fields (Heiles & Troland 2005; Beck 2007), there is some debate whether the MRI can provide enough energy to explain the observed turbulence (Beck et al. 1996; Sellwood & Balbus 1999; Dziourkevitch et al. 2004; Piontek…”
ON THE STAR FORMATION EFFICIENCY OF TURBULENT MAGNETIZED CLOUDS (2012, methodology): “For the MHD models, we chose magnetic field strengths consistent with the range observed in clouds of that size and density (see Crutcher 1999; Heiles & Troland 2005; Crutcher et al. 2010).”
Turbulent Structure of a Stratified Supernova-driven Interstellar Medium (2005, background): “Magnetic fields may substantially thicken swept-up shells (Ferrière et al. 1991) and provide an additional pressure, which may the dominant component of the gas pressure at low temperatures (Heiles & Troland 2005; Avillez & Breitschwerdt 2004b).”
THE STAR FORMATION RATE OF TURBULENT MAGNETIZED CLOUDS: COMPARING THEORY, SIMULATIONS, AND OBSERVATIONS (2012, background): “Heiles & Troland (2005) and Crutcher et al. (2010) show that most clouds with number densities in the range 10–104 cm−3 have magneticfield strengths in the range Bz ≈ 1–10µG, with an apparent peak of the distribution at around Bz ≈ 3µG.”
Magnetic Fields in Dark Cloud Cores: Arecibo OH Zeeman Observations (2008, background): “For this assumption, the probability density function for Blos is flat between 0 and the total strength Bj j (Heiles & Troland 2005).”
Magnetic Braking and Protostellar Disk Formation: The Ideal MHD Limit (2007, background): “For reference, λ = 100 corresponds to a field strength of merely 1 µG on the core scale of 0.05 pc (for the fiducial value of sound speed), well below the median field strength (∼ 6 µG) in the cold neutral structures of HI gas (Heiles & Troland 2005).”
VERTICAL STRUCTURE OF A SUPERNOVA-DRIVEN TURBULENT, MAGNETIZED INTERSTELLAR MEDIUM (2012, background): “…energy densities dominate over the thermal energy in many interstellar environments, particularly in cold atomic and molecular gas (McKee 1990; Heiles & Troland 2005), and provide, along with high-energy particles, a crucial component of the vertical pressure that supports the ISM in…”
Physical Processes in the Interstellar Medium (2014, background): “Magnetic fields are ubiquitously observed in the interstellar gas on all scales (Crutcher et al., 2003; Heiles & Troland, 2005).”
NON-IDEAL MHD EFFECTS AND MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION (2011, background): “It is lower than the medium value of ∼ 6µG inferred for the atomic cold neutral medium (Heiles & Troland 2005).”
Turbulent molecular clouds (2012, background): “They include Zeeman measurements that sample B‖ in diffuse (mostly atomic) clouds in HI from Heiles & Troland (2005), in low-mass dense cores and molecular clouds in OH and in star-forming regions from CN (Crutcher 1999, Falgarone et al. 2008).”
Studies of Regular and Random Magnetic Fields in the ISM: Statistics of Polarization Vectors and the Chandrasekhar-Fermi Technique (2008, background): “Zeeman splitting of spectral lines provides a direct and precise derivation of the magnetic field component along the line of sight (LOS), mainly for clouds presenting strong spectral lines (Heiles & Troland 2005).”
Science with the Australian Square Kilometre Array Pathfinder (2007, background): “Zeeman splitting of the H i line can provide in situ magnetic field measurements throughout the Galactic disk (e.g. Heiles & Troland 2003, 2005).”
Cooling, Gravity, and Geometry: Flow-driven Massive Core Formation (2007, background): “…et al. (1995), Hartmann et al. (2001) envisaged the large-scale converging flows preferentially running along (dynamically dominant, e.g. Heiles & Troland 2005) magnetic field lines in the diffuse ISM, arguing that if the field lines were oriented perpendicularly, the stiffening of the…”
REGULATION OF STAR FORMATION RATES IN MULTIPHASE GALACTIC DISKS: A THERMAL/DYNAMICAL EQUILIBRIUM MODEL (2010, background): “Like other pressures, these magnetic terms are volume-weighted; both observations (Heiles & Troland 2005) and numerical simulations (Piontek & Ostriker 2005) indicate that field strengths in the warm and cold atomic medium are similar.”
Theory of Star Formation (2007, background): “Inferring the intrinsic field strength and column density from measurements of the line-of-sight components is somewhat subtle (Heiles & Troland, 2005); in particular, care must be exercised in evaluating the average value of B‖/B using logarithmic values, since 〈log B‖/B〉 < log〈B‖/B〉.”
Planck2018 results (2018, unknown): “In the cold neutral medium, the magnetic and turbulent kinetic energies are known from H i Zeeman observations to be in approximate equipartition (Heiles & Troland 2005).”
The 511 keV emission from positron annihilation in the Galaxy (2010, background): “…for projection effects, it is found that in atomic clouds, B is typically a few µG, with a slight tendency to increase with increasing density (Heiles and Troland, 2005; Troland and Heiles, 1986), while in molecular clouds, B increases approximately as the square root of density, from ∼ 10…”