Imaging study of NGC 3372, the Carina nebula - III. The properties of G287.47−0.54 (Tr 14-N4), an embedded young cluster and its associated H2 emission★

Abstract

New deep broad- and narrow-band (JHK and Br γ at 2.17 μm and H2 at 2.12 μm) near-infrared (near-IR) images of the mid-IR source G287.47−0.54 (Tr14-N4) taken with the Baade Magellan telescope are presented and analysed along with archive 3.6–8 μ m Spitzer images. The analysis of these data demonstrates the presence of a compact (r∼ 23 arcsec, 0.3 pc), embedded IR cluster with at least 72 young members. The colour–magnitude diagram of the cluster suggests an age of approximately 105 years, consistent with the large fraction (≥32 per cent) of embedded sources found to show significant excess emission at λ > 2 μ m. The two youngest and most luminous sources are located close to the cluster nucleus. The properties of their spectral energy distributions (SEDs) indicate that these are Class I young stellar objects (YSOs) with masses in the range 7–9 M⊙ and luminosities between 400 and 800 L⊙. We derive the presence of a tilted (i∼ 40°–70°) disc of size ≥0.05 pc around one of these YSOs, #902. This object is seen directly through the dust disc only at λ≥ 2.2, with most of the observed near-IR radiation being scattered light from lobes on both sides of the disc. In contrast, the second bright YSO, #438, is seen directly even in the near-IR and also shows symmetrically elongated features that seem to be caused by scattering. The young cluster G287.47−0.54 is embedded at the head of a dust pillar and is another example of a photodissociation region (PDR) where triggered star formation occurs as a consequence of the interaction of a very massive developed cluster, in this case Tr 16, with a dense molecular core. It appears that the dense cloudlet is sticking out of the remnant giant molecular cloud located at the far side of the northern Carina nebula. Five small molecular hydrogen emission knots at 2.12 μ m with no Brγ counterpart are found in the vicinity of a CO peak, some 0.4 pc north-west of the cluster nucleus. Most probably, these are shock excited, suggesting the presence of mass outflows in the region. At present, it is unclear whether the engine of this outflow is a member of the cluster or rather it is an undetected, younger YSO deeply embedded in the molecular core.