Young and embedded clusters in Cygnus-X: evidence for building up the IMF?

TL;DR

This study investigates the low-mass stellar populations in young clusters of Cygnus-X north, revealing a potentially evolving initial mass function (IMF) and evidence for clusters building up their IMF by accreting low-mass stars during early stages.

Contribution

First deep near-IR survey of low-mass stars in Cygnus-X north, characterizing multiple young clusters and their IMFs, and proposing a scenario of IMF build-up during early cluster evolution.

Findings

Identified a uniform log-normal IMF with a characteristic mass of ~0.32 M$_\odot$.

Older clusters show IMF slopes consistent with the Salpeter value.

Evidence of clusters gradually building their IMF by accreting low-mass stars in early stages.

Abstract

We provide a new view on the Cygnus-X north complex by accessing for the first time the low mass content of young stellar populations in the region. CFHT/WIRCam camera was used to perform a deep near-IR survey of this complex, sampling stellar masses down to ~0.1 M$_\odot$. Several analysis tools, including a extinction treatment developed in this work, were employed to identify and uniformly characterise a dozen unstudied young star clusters in the area. Investigation of their mass distributions in low-mass domain revealed a relatively uniform log-normal IMF with a characteristic mass of 0.32$\pm$0.08 M$_\odot$ and mass dispersion of 0.40$\pm$0.06. In the high mass regime, their derived slopes showed that while the youngest clusters (age < 4 Myr) presented slightly shallower values with respect to the Salpeter's, our older clusters (4 Myr < age < 18 Myr) showed IMF compliant values and a slightly denser stellar population. Although possibly evidencing a deviation from an 'universal' IMF, these results also supports a scenario where these gas dominated young clusters gradually 'build up' their IMF by accreting low-mass stars formed in their vicinity during their first ~3 Myr, before the gas expulsion phase, emerging at the age of ~4 Myr with a fully fledged IMF. Finally, the derived distances to these clusters confirmed the existence of at least 3 different star forming regions throughout Cygnus-X north complex, at distances of 500-900 pc, 1.4-1.7 kpc and 3.0 kpc, and revealed evidence of a possible interaction between some of these stellar populations and the Cygnus-OB2 association.