### Abstract

We revisit the relation between magnetic-field strength (B) and gas density (ρ) for contracting interstellar clouds and fragments (or, cores), which is central in observationally determining the dynamical importance of magnetic fields in cloud evolution and star formation. Recently, it has been claimed that a relation B∝ρ^{2/3} is statistically preferred over B∝ρ^{1/2} in molecular clouds, when magnetic-field detections and non-detections from Zeeman observations are combined. This finding has unique observational implications on cloud and core geometry: the relation B∝ρ^{2/3} can only be realized under spherical contraction. However, no indication of spherical geometry can be found for the objects used in the original statistical analysis of the B-ρ relation. We trace the origin of the inconsistency to simplifying assumptions in the statistical model used to arrive at the B∝ρ^{2/3} conclusion and to an underestimate of observational uncertainties in the determination of cloud and core densities. We show that, when these restrictive assumptions are relaxed, B∝ρ^{1/2} is the preferred relation for the (selfgravitating) molecular-cloud data, as theoretically predicted four decades ago.

Original language | English (US) |
---|---|

Pages (from-to) | 4384-4396 |

Number of pages | 13 |

Journal | Monthly Notices of the Royal Astronomical Society |

Volume | 451 |

Issue number | 4 |

DOIs | |

State | Published - Apr 24 2015 |

### Fingerprint

### Keywords

- Diffusion
- ISM: clouds
- ISM: magnetic fields
- MHD
- Methods: statistical
- Stars: formation

### ASJC Scopus subject areas

- Astronomy and Astrophysics
- Space and Planetary Science

### Cite this

*Monthly Notices of the Royal Astronomical Society*,

*451*(4), 4384-4396. https://doi.org/10.1093/mnras/stv1133

**Magnetic field-gas density relation and observational implications revisited.** / Tritsis, A.; Panopoulou, G. V.; Mouschovias, T. Ch; Tassis, K.; Pavlidou, V.

Research output: Contribution to journal › Article

*Monthly Notices of the Royal Astronomical Society*, vol. 451, no. 4, pp. 4384-4396. https://doi.org/10.1093/mnras/stv1133

}

TY - JOUR

T1 - Magnetic field-gas density relation and observational implications revisited

AU - Tritsis, A.

AU - Panopoulou, G. V.

AU - Mouschovias, T. Ch

AU - Tassis, K.

AU - Pavlidou, V.

PY - 2015/4/24

Y1 - 2015/4/24

N2 - We revisit the relation between magnetic-field strength (B) and gas density (ρ) for contracting interstellar clouds and fragments (or, cores), which is central in observationally determining the dynamical importance of magnetic fields in cloud evolution and star formation. Recently, it has been claimed that a relation B∝ρ2/3 is statistically preferred over B∝ρ1/2 in molecular clouds, when magnetic-field detections and non-detections from Zeeman observations are combined. This finding has unique observational implications on cloud and core geometry: the relation B∝ρ2/3 can only be realized under spherical contraction. However, no indication of spherical geometry can be found for the objects used in the original statistical analysis of the B-ρ relation. We trace the origin of the inconsistency to simplifying assumptions in the statistical model used to arrive at the B∝ρ2/3 conclusion and to an underestimate of observational uncertainties in the determination of cloud and core densities. We show that, when these restrictive assumptions are relaxed, B∝ρ1/2 is the preferred relation for the (selfgravitating) molecular-cloud data, as theoretically predicted four decades ago.

AB - We revisit the relation between magnetic-field strength (B) and gas density (ρ) for contracting interstellar clouds and fragments (or, cores), which is central in observationally determining the dynamical importance of magnetic fields in cloud evolution and star formation. Recently, it has been claimed that a relation B∝ρ2/3 is statistically preferred over B∝ρ1/2 in molecular clouds, when magnetic-field detections and non-detections from Zeeman observations are combined. This finding has unique observational implications on cloud and core geometry: the relation B∝ρ2/3 can only be realized under spherical contraction. However, no indication of spherical geometry can be found for the objects used in the original statistical analysis of the B-ρ relation. We trace the origin of the inconsistency to simplifying assumptions in the statistical model used to arrive at the B∝ρ2/3 conclusion and to an underestimate of observational uncertainties in the determination of cloud and core densities. We show that, when these restrictive assumptions are relaxed, B∝ρ1/2 is the preferred relation for the (selfgravitating) molecular-cloud data, as theoretically predicted four decades ago.

KW - Diffusion

KW - ISM: clouds

KW - ISM: magnetic fields

KW - MHD

KW - Methods: statistical

KW - Stars: formation

UR - http://www.scopus.com/inward/record.url?scp=84940116935&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84940116935&partnerID=8YFLogxK

U2 - 10.1093/mnras/stv1133

DO - 10.1093/mnras/stv1133

M3 - Article

AN - SCOPUS:84940116935

VL - 451

SP - 4384

EP - 4396

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 4

ER -