The Initial Mass Function of the Massive Star-forming Region NGC 3603 from Near-Infrared Adaptive Optics Observations

By Y. Harayama, F. Eisenhauer, Fabrice Martins. 2007

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We study the initial mass function (IMF) of one of the most massive Galactic star-forming regions NGC 3603 to answer a fundamental question in current astrophysics: is the IMF universal, or does it vary? Using our very deep, high angular resolution JHKSL′ images obtained with NAOS-CONICA at the VLT at ESO, we have successfully revealed the stellar population down to the subsolar mass range in the core of the starburst cluster. The derived IMF of NGC 3603 is reasonably fitted by a single power law with index Γ ∼ − 0.74 within a mass range of 0.4-20 M☉, substantially flatter than the Salpeter-like IMF. A strong radial steepening of the IMF is observed mainly in the inner r≲ 30″ field, indicating mass segregation in the cluster center. We estimate the total mass of NGC 3603 to be about 1.0–1.6 × 104 M☉. The derived core density is ≥6 × 104 M☉ pc−3, an order of magnitude larger than, e.g., the Orion Nebula Cluster. The estimate of the half-mass relaxation time for solar-mass stars is about 10-40 Myr, suggesting that the intermediate- and low-mass stars have not yet been affected significantly by the dynamical relaxation in the cluster. The relaxation time for the high-mass stars can be comparable to the age of the cluster. We estimate that the stars residing outside the observed field cannot steepen the IMF significantly, indicating our IMF adequately describes the whole cluster. Analyzing thoroughly the systematic uncertainties in our IMF determination, we conclude that the power-law index of the IMF of NGC 3603 is Γ = − 0.74+ 0.62−0.47. Our result thus supports the hypothesis of a potential top-heavy IMF in massive star-forming clusters and starbursts.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/fee3a8f7b966a5ebbfe914239ea08f87ed8beca5

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Citations in the corpus

Evidence for top-heavy stellar initial mass functions with increasing density and decreasing metallicity (2012, background): “Its reported MF slope ranges from α3 = 1.9 to 2.3 (Nürnberger & Petr-Gotzens 2002; Sung & Bessell 2004; Stolte et al. 2006; Harayama et al. 2008).”
STAR FORMATION IN MASSIVE CLUSTERS VIA THE WILKINSON MICROWAVE ANISOTROPY PROBE AND THE SPITZER GLIMPSE SURVEY (2009, result): “Recent observations of young massive clusters have suggested thatΓ varies from the Salpeter value (Stolte et al. 2002; Harayama et al. 2008); if confirmed, these variations, combined with the results presented here, would lead to large variations in the estimatedstar formation rate of the Galaxy.”
The relation between the most-massive star and its parental star cluster mass (2009, unknown): “…56: Roman-Lopes & Abraham (2004); Roman-Lopes (2007), 57: Bohigas et al. (2004); Máız Apellániz et al. (2007); Wang et al. (2007), 58: Harayama (2007); Harayama et al. (2008); Schnurr et al. (2008), 59: Penny et al. (1993); Massey & Johnson (1993); Massey et al. (1995); Nelan et al. (2004);…”
Using the minimum spanning tree to trace mass segregation (2009, background): “A variation of the MF with radius will show the presence of mass segregation as a shallowing of the slope of the MF with radius (de Grijs et al. 2002a,b,c; Gouliermis et al. 2004; Sabbi et al. 2008; Kumar et al. 2008; Harayama et al. 2008).”
The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 M⊙ stellar mass limit (2010, unknown): “NGC 3603 104 ∼1.5 a, b 166 ± 20 132 ± 13 b Arches 2 × 104 2.5 ± 0.5 c, d 120–150 ≥95–120 b, d ∼1.8 b ≥185+75−45 ≥130+45−25 b R136 ≤5.5 × 104 ∼1.7 e, b 320+100−40 265+80−35 b Note. a – Harayama et al. (2008); b – this work; c – Figer (2008); d – Martins et al. (2008); e – Hunter et al. (1995).”
MOLECULAR CLOUDS TOWARD THE SUPER STAR CLUSTER NGC 3603; POSSIBLE EVIDENCE FOR A CLOUD–CLOUD COLLISION IN TRIGGERING THE CLUSTER FORMATION (2013, methodology): “Both clouds show intensity depressions toward the cluster within a radius of several pc, which includes about ten highest-mass stars having ∼100M⊙ in the cluster core within a radius of 1 pc (Stolte et al. 2004; Sung & Bessell 2004; Harayama et al. 2008).”
Peering through the veil: near-infrared photometry and extinction for the Galactic nuclear star cluster (2009, methodology): “We therefore estimated completeness directly from the data using the methodology suggested by Eisenhauer et al. (1998) and further described in Harayama et al. (2008).”