Impact of the shape of the prestellar density fluctuations on the core mass function

TL;DR

This paper investigates how non-sphericity of density fluctuations influences the prestellar core mass function, revealing modest deformation effects that slightly alter the high-mass tail and slope, supporting the spherical collapse assumption in star formation models.

Contribution

It extends the ellipsoidal collapse model from cosmology to star formation, analyzing its impact on the core mass function and the validity of spherical collapse assumptions.

Findings

Ellipsoidal fluctuations cause modest deformation in prestellar cores.

Departure from sphericity increases the collapse barrier, stabilizing cores.

High-mass end of the CMF is less steep and shifted toward lower masses.

Abstract

It is well known that departure from sphericity in the geometry of primordial dark matter halos modifies their mass function. The ellipsoidal collapse model yields a better agreement with simulations of hierarchical clustering than the original, spherical model. In the present paper, we examine the same issue in the context of star formation by studying the impact of non-sphericity of density perturbations in a gravoturbulent medium on the prestellar core mass function (CMF). An important question, notably, is to find out how ellipsoidal, instead of spherical, initial density fluctuations modify both the high-mass and low-mass tails of the CMF. Our study shows that triaxial density fluctuations indeed depart from a purely spherical form but the deformation (prolateness and ellipticity) remains modest, suggesting that the usual hypothesis of spherical collapse in existing theories of the IMF is reasonable. We find that, as in the cosmological case, the departure from sphericity increases the collapse barrier, stabilizing the prestellar cores. The striking difference between the stellar case and the cosmological one for the ellipsoidal collapse model is that, although in both cases the less dense structures are the most deformed, they correspond to small scales, thus low mass halos in cosmology but to large scales, thus large mass cores in star formation. As a result, the high mass range of the CMF is the most affected by the ellipsoidal collapse, resulting in a slightly less steep slope than the one predicted with the spherical hypothesis and a peak slightly shifted toward lower masses.