Substellar initial mass function of Trumpler 14

¹ University of Split, Faculty of Science, Ruđera Boškovića 33, 21000 Split, Croatia
² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências, Universidade de Lisboa, Ed. C8, Campo Grande, 1749-016 Lisbon, Portugal
⁴ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁵ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁶ Istituto Nazionale di Astrofisica (INAF) – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 24 July 2025
Accepted: 25 November 2025

Abstract

Context. Young, massive stellar clusters offer a prime setting to explore brown dwarf (BD) formation under high densities and intense UV radiation. Trumpler 14 (Tr 14), a ∼1 Myr old cluster located at a distance of 2.4 kpc that is particularly rich in O-type stars, is an ideal target for such a study.

Aims. Our goal is to measure the initial mass function (IMF) in the young massive, high-UV-flux cluster.

Methods. We present the deepest study to date of the IMF in Tr 14, based on Gemini Multi-Conjugate Adaptive Optics System/Gemini-South Adaptive Optics Imager imaging. We constructed the IMF using both the Besançon Galactic model and an observational control field from VISTA for background correction. Completeness was assessed using artificial star tests and applied to the IMF derivation.

Results. We estimated the IMF down to the 20% completeness limit found at ∼0.01 M_⊙. Using the control-field-based IMF as our primary result, we find a slope of α = 0.14 ± 0.19 for masses between 0.01 and 0.2 M_⊙, and α = 1.72 ± 0.04 for 0.2–4.5 M_⊙, where dN/dM ∝ M^−α. The low-mass slope is largely influenced by the incompleteness-affected lowest bin; excluding it brings our results into agreement with those for other young clusters. The resulting median for the star-to-BD ratio in the 0.03–1 M_⊙ mass range is 4.0, with a 95% confidence interval of 2.8–5.8.

Conclusions. Our analysis reveals that Tr 14 hosts a relatively flat substellar IMF, but this is strongly influenced by the lowest-mass bin, which may be affected by incompleteness. When that bin is excluded, the IMF becomes consistent with those of other regions. The star-to-BD ratio falls within the usually observed ∼3–6 range, indicating that BDs with masses above ∼0.03 M_⊙ form with similar efficiencies across environments. However, the relative lack of objects below this threshold suggests that the presence of an environment with both high stellar density and far-UV flux plays a role in shaping the IMF by suppressing the formation of BDs at masses <0.03 M_⊙.