IMF-aware N-body forward modelling of membership selection functions for young open clusters
Abstract
We present an IMF-aware N-body forward-modelling framework, in which the stellar initial mass function (IMF) is an explicit input, to quantify the membership selection functions of open clusters, namely completeness and contamination as functions of magnitude. Accurate derivation of the IMF requires correcting for these selection effects, which otherwise distort the inferred present-day mass function. Our framework simulates clusters with IMF slopes α2 = −2.7, −2.3, −1.9, converts them into synthetic Gaia observations, adds mock field populations, and recovers members with HDBSCAN to mimic observational membership selection. Applying this framework to 35 young open clusters (ages ≲100 Myr, distances ≲600 pc), we find declining completeness towards the faint limit; older, more expanded, and more diffuse models have lower completeness and higher contamination. For a given cluster, models with flatter IMFs yield modestly but systematically lower global completeness and higher contamination, despite initial cluster masses calibrated to the same observed member count. These models undergo more stellar evolution mass loss and expand more, resulting in lower projected stellar densities; their lower completeness is consistent with more diffuse clusters being harder to separate from field stars. Corrections derived from a mismatched IMF largely recover the total star counts but leave a larger distortion in the shape of the present-day luminosity function than those derived with the correct IMF. Because membership recovery is tied to a cluster's structural evolution and the specific membership algorithm used, our findings emphasize that selection functions should be inferred jointly with the IMF rather than assumed in advance.
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BibTeX
@misc{shen2026imfaware,
title = {{IMF-aware N-body forward modelling of membership selection functions for young open clusters}},
author = {Yue-Yue Shen and Chao Liu and Zepeng Zheng and Long Wang and Xiaoying Pang and Bo Zhang and Hao Tian and Yang Xiang},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.25200},
eprint = {2610.25200},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.25200},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - IMF-aware N-body forward modelling of membership selection functions for young open clusters
AU - Yue-Yue Shen
AU - Chao Liu
AU - Zepeng Zheng
AU - Long Wang
AU - Xiaoying Pang
AU - Bo Zhang
AU - Hao Tian
AU - Yang Xiang
PY - 2026
DA - 2026/10/18
PB - arXiv
DO - 10.48550/arxiv.2610.25200
UR - https://arxiv.org/abs/2610.25200
AB - We present an IMF-aware N-body forward-modelling framework, in which the stellar initial mass function (IMF) is an explicit input, to quantify the membership selection functions of open clusters, namely completeness and contamination as functions of magnitude. Accurate derivation of the IMF requires correcting for these selection effects, which otherwise distort the inferred present-day mass function. Our framework simulates clusters with IMF slopes α_2 = −2.7, −2.3, −1.9, converts them into synthetic Gaia observations, adds mock field populations, and recovers members with HDBSCAN to mimic observational membership selection. Applying this framework to 35 young open clusters (ages ≲100 Myr, distances ≲600 pc), we find declining completeness towards the faint limit; older, more expanded, and more diffuse models have lower completeness and higher contamination. For a given cluster, models with flatter IMFs yield modestly but systematically lower global completeness and higher contamination, despite initial cluster masses calibrated to the same observed member count. These models undergo more stellar evolution mass loss and expand more, resulting in lower projected stellar densities; their lower completeness is consistent with more diffuse clusters being harder to separate from field stars. Corrections derived from a mismatched IMF largely recover the total star counts but leave a larger distortion in the shape of the present-day luminosity function than those derived with the correct IMF. Because membership recovery is tied to a cluster's structural evolution and the specific membership algorithm used, our findings emphasize that selection functions should be inferred jointly with the IMF rather than assumed in advance.
ER -