Analytical core mass function (CMF) from filaments: Under which circumstances can filament fragmentation reproduce the CMF?

TL;DR

This paper models how filamentary molecular clouds fragment into cores, incorporating magnetic support, to explain the observed core mass function and the two-step star formation process.

Contribution

It extends the Hennebelle & Chabrier fragmentation theory to filamentary environments, including magnetic effects, and predicts hierarchical fragmentation patterns.

Findings

Filament geometry induces hierarchical fragmentation into core groups.

Magnetic support prevents excessive fragmentation in high mass per unit length filaments.

The model aligns with observed two-step star formation in filaments.

Abstract

Observations suggest that star formation in filamentary molecular clouds occurs in a two-step process, with the formation of filaments preceding that of prestellar cores and stars. Here, we apply the gravo-turbulent fragmentation theory of Hennebelle & Chabrier 08, 09, 13 to a filamentary environment, taking into account magnetic support. We discuss the induced geometrical effect on the cores, with a transition from 3D geometry at small scales to 1D at large ones. The model predicts the fragmentation behavior of a filament for a given mass per unit length (MpL) and level of magnetization. This CMF for individual filaments is then convolved with the distribution of filaments to obtain the final system CMF. The model yields two major results: (i) the filamentary geometry naturally induces a hierarchical fragmentation process, first into groups of cores, separated by a length equal to a few filament Jeans lengths, i.e. a few times the filament width. These groups then fragment into individual cores. (ii) Non-magnetized filaments with high MpL are found to fragment excessively, at odd with observations. This is resolved by taking into account the magnetic field treated simply as additional pressure support). The present theory suggests two complementary modes of star formation: while small (spherical or filamentary) structures will collapse directly into prestellar cores, according to the standard Hennebelle-Chabrier theory, the large (filamentary) ones, the dominant population according to observations, will follow the afore-described two-step process.