Will ALMA Reveal the True Core Mass Function of Protoclusters?

TL;DR

This study evaluates ALMA's capability to accurately characterize prestellar core masses in star-forming regions, highlighting significant uncertainties and the need for realistic simulations to interpret observations correctly.

Contribution

It provides a detailed analysis of core extraction reliability from synthetic ALMA observations, emphasizing the limitations and biases in core mass function estimation.

Findings

Core masses from synthetic ALMA maps are weakly correlated with true 3D core masses.

Less than 50% of real cores are detected in synthetic ALMA maps, especially at lower masses.

The core mass function from ALMA data is closer to the true core mass function than from column-density maps.

Abstract

Characterizing prestellar cores in star-forming regions is an important step towards the validation of theoretical models of star formation. Thanks to their sub-arcsecond resolution, ALMA observations can potentially provide samples of prestellar cores up to distances of a few kpc, where regions of massive star formation can be targeted. However, the extraction of real cores from dust-continuum observations of turbulent star-forming clouds is affected by complex projection effects. In this work, we study the problem of core extraction both in the idealized case of column-density maps and in the more realistic case of synthetic 1.3\,mm ALMA observations. The analysis is carried out on 12 regions of high column density from our 250 pc simulation. We find that derived core masses are highly unreliable, with only {\em a weak correlation between the masses of cores selected in the synthetic ALMA maps and those of the corresponding three-dimensional cores}. The fraction of real three-dimensional cores detected in the synthetic maps increases monotonically with mass and remains always below 50\%. Above $\sim 1\,M_{\odot}$, the core mass function derived from the column-density maps is steeper than that of the three-dimensional cores, while the core mass function from the synthetic ALMA maps has a slope closer to that of the real three-dimensional cores. Because of the mass uncertainties, proper guidance from realistic simulations is essential if ALMA observations of protoclusters at kpc distances are to be used to test star-formation models.