[Paper Review] The initial mass function of young open clusters in the Galaxy: A preliminary result

Beomdu Lim, Hwankyung Sung+2 more|arXiv (Cornell University)|Nov 1, 2015

Stellar, planetary, and galactic studies4 citations

TL;DR

This study presents a preliminary analysis of the initial mass function (IMF) in 16 young Galactic open clusters using a homogeneous photometric survey, revealing that massive, dense clusters exhibit a shallower IMF slope and higher maximum stellar masses, suggesting environmental control over star formation rather than universality.

ABSTRACT

The initial mass function (IMF) is an essential tool with which to study star formation processes. We have initiated the photometric survey of young open clusters in the Galaxy, from which the stellar IMFs are obtained in a homogeneous way. A total of 16 famous young open clusters have preferentially been studied up to now. These clusters have a wide range of surface densities (log sigma = -1 to 3 [stars pc^2] for stars with mass larger than 5M_sun) and cluster masses (M_cl = 165 to 50,000M_sun), and also are distributed in five different spiral arms in the Galaxy. It is possible to test the dependence of star formation processes on the global properties of individual clusters or environmental conditions. We present a preliminary result on the variation of the IMF in this paper.

Motivation & Objective

• To investigate the universality of the initial mass function (IMF) across young open clusters in the Galaxy.
• To assess whether cluster properties such as mass and surface density influence the IMF through a homogeneous data set.
• To test the hypothesis that star formation processes are environmentally dependent rather than universal.
• To establish a consistent framework for IMF derivation using photometric data from the Sejong Open Cluster Survey.
• To explore the relationship between cluster mass and maximum stellar mass in young clusters.

Proposed method

• Conducted a homogeneous photometric survey of 16 young open clusters across the Galactic disk using multi-band imaging.
• Constructed Hertzsprung-Russell (HR) diagrams from the photometric data to derive stellar masses and luminosities.
• Fitted the IMF in the high-mass regime (>1 M☉) using the power-law slope Γ to quantify IMF shape.
• Correlated IMF slope Γ with cluster surface density and total mass to assess environmental dependence.
• Compared observed M_max–M_cl relations with theoretical models from Elmegreen (2000), Larson (2003), Bonnell et al. (2003), and Weidner & Kroupa (2004).
• Analyzed spatial distribution across spiral arms to assess Galactic environment effects on IMF variations.

Experimental results

Research questions

• RQ1 Does the initial mass function (IMF) vary systematically across different young open clusters in the Galaxy?
• RQ2 How does the IMF slope (Γ) depend on cluster surface density and total mass?
• RQ3 Is there a correlation between the maximum stellar mass (M_max) and the total cluster mass (M_cl)?
• RQ4 To what extent is star formation in young clusters influenced by local environmental conditions such as Galactic location and cluster density?
• RQ5 How do observed IMF trends compare with theoretical predictions of deterministic mass formation?

Key findings

• The IMF slope (Γ) in the high-mass regime (>1 M☉) is shallower in massive, dense clusters compared to less massive, sparse clusters.
• A clear correlation exists between cluster mass (M_cl) and maximum stellar mass (M_max), with M_max increasing with M_cl.
• The observed M_max–M_cl relation is consistent with theoretical models from Elmegreen (2000), Larson (2003), Bonnell et al. (2003), and Weidner & Kroupa (2004).
• Massive, dense clusters are predominantly located in the inner Galaxy, while less massive, sparse clusters are more common in the outer Galaxy.
• The observed variations in IMF slope and M_max suggest that star formation processes are likely controlled by local environmental conditions rather than being universal.
• The use of a homogeneous photometric survey minimizes data inhomogeneity issues that may have contributed to conflicting results in prior IMF studies.