Star formation in dense clusters

TL;DR

This paper presents a core-clump accretion model with stochastic stopping to explain star formation in dense clusters, successfully reproducing the observed initial mass function and star formation timescales.

Contribution

It introduces a novel accretion model that accounts for environmental effects and matches the observed stellar initial mass function in dense clusters.

Findings

Model reproduces the stellar initial mass function from 0.01 to >10 solar masses.

Maximum protostar luminosity indicates the age and mass of the oldest protostar.

Protostar luminosity distribution matches observations if birthrate is constant.

Abstract

A model of core-clump accretion with equally likely stopping describes star formation in the dense parts of clusters, where models of isolated collapsing cores may not apply. Each core accretes at a constant rate onto its protostar, while the surrounding clump gas accretes as a power of protostar mass. Short accretion flows resemble Shu accretion, and make low-mass stars. Long flows resemble reduced Bondi accretion and make massive stars. Accretion stops due to environmental processes of dynamical ejection, gravitational competition, and gas dispersal by stellar feedback, independent of initial core structure. The model matches the field star IMF from 0.01 to more than 10 solar masses. The core accretion rate and the mean accretion duration set the peak of the IMF, independent of the local Jeans mass. Massive protostars require the longest accretion durations, up to 0.5 Myr. The maximum protostar luminosity in a cluster indicates the mass and age of its oldest protostar. The distribution of protostar luminosities matches those in active star-forming regions if protostars have a constant birthrate but not if their births are coeval. For constant birthrate, the ratio of YSOs to protostars indicates the star-forming age of a cluster, typically ~1 Myr. The protostar accretion luminosity is typically less than its steady spherical value by a factor of ~2, consistent with models of episodic disk accretion.