The role of molecular filaments in the origin of the prestellar core mass function and stellar initial mass function

Ph André,D Arzoumanian,P Palmeirim,V Könyves,Y Shimajiri

doi:10.1051/0004-6361/201935915

Abstract

Context. The origin of the stellar initial mass function (IMF) is one of the most debated issues in astrophysics. Aims. Here we explore the possible link between the quasi-universal filamentary structure of star-forming molecular clouds and the origin of the IMF. Methods. Based on our recent comprehensive study of filament properties from Herschel Gould Belt survey observations, we derive, for the first time, a good estimate of the filament mass function (FMF) and filament line mass function (FLMF) in nearby molecular clouds. We use the observed FLMF to propose a simple toy model for the origin of the prestellar core mass function (CMF), relying on gravitational fragmentation of thermally supercritical but virialized filaments. Results. We find that the FMF and the FLMF have very similar shapes and are both consistent with a Salpeter-like power-law function (dN/dlog Mline ∝ Mline−1.5±0.1) in the regime of thermally supercritical filaments (Mline > 16 M⊙ pc−1). This is a remarkable result since, in contrast, the mass distribution of molecular clouds and clumps is known to be significantly shallower than the Salpeter power-law IMF, with dN/dlog Mcl ∝ Mcl−0.7. Conclusions. Since the vast majority of prestellar cores appear to form in thermally transcritical or supercritical filaments, we suggest that the prestellar CMF and by extension the stellar IMF are at least partly inherited from the FLMF through gravitational fragmentation of individual filaments.

Highlights

The origin of the stellar initial mass function (IMF) is a fundamental problem in modern astrophysics which is still highly debated (e.g., Offner et al 2014)
This picture is deterministic in the sense that stellar masses are directly inherited from the distribution of prestellar core masses resulting from cloud fragmentation prior to protostellar collapse, in agreement with the observed similarity between the prestellar core mass function (CMF) and the system IMF (e.g., Motte et al 1998; Alves et al 2007; Könyves et al 2015)
This is a remarkable result since, in contrast, the mass distribution of molecular clouds and clumps is observed to be significantly shallower than the Salpeter power-law IMF, namely dN/dlog Mcl ∝ Mc−l0.7 (Blitz 1993; Kramer et al 1998)

Summary

Introduction

The origin of the stellar initial mass function (IMF) is a fundamental problem in modern astrophysics which is still highly debated (e.g., Offner et al 2014). Most prestellar cores lie very close to the crests (i.e., within the inner 0.1 pc portion) of their parent filaments (e.g., Könyves et al 2019; Ladjelate et al 2019) These findings support a filamentary paradigm in which lowmass star formation occurs in two main steps (André et al 2014; Inutsuka et al 2015): (1) multiple large-scale compressions of cold interstellar material in supersonic magneto-hydrodynamic (MHD) flows generate a cobweb of ∼0.1 pc-wide filaments within sheet-like or shell-like molecular gas layers in the ISM and (2) the densest molecular filaments fragment into prestellar cores (and protostars) by gravitational instability near or above the critical line mass, Mline,crit, corresponding to Σcgraist ∼ Mline,crit/Wfil ∼ 160 M pc−2 in gas surface density (AV ∼ 7.5) or nH2 ∼ 2 × 104 cm−3 in volume density.

Observations of the filament line mass function

Role of filaments in the prestellar CMF

Findings

Concluding remarks