Deep near-infrared adaptive-optics observations of a young embedded cluster at the edge of the RCW 41 H II region

¹ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
e-mail: benoit.neichel@lam.fr
² Laboratorio de Astrofísica Teórica e Observacional, Universidade Estadual de Santa Cruz, Rodovia Jorge Amado km16, 45662-900 Ilhéus BA, Brazil
³ ONERA (Office National d’Études et de Recherches Aérospatiales), BP 72, 92322 Châtillon, France

Received: 4 December 2014
Accepted: 6 February 2015

Abstract

Aims. We investigate the star formation activity in a young star forming cluster embedded at the edge of the RCW 41 H ii region. As a complementary goal, we aim to demonstrate the gain provided by wide-field adaptive optics (WFAO) instruments to study young clusters.

Methods. We used deep, JHK_s images from the newly commissioned Gemini-GeMS/GSAOI instrument, complemented with Spitzer IRAC observations, in order to study the photometric properties of the young stellar cluster. GeMS is a WFAO instrument that delivers almost diffraction-limited images over a field of ~2′ across. The exquisite angular resolution allows us to reach a limiting magnitude of J ~ 22 for 98% completeness. The combination of the IRAC photometry with our JHK_s catalog is used to build color−color diagrams, and select young stellar object (YSO) candidates. The JHK_s photometry is also used in conjunction with pre-main sequence evolutionary models to infer masses and ages. The K-band luminosity function is derived, and then used to build the initial mass function (IMF) of the cluster.

Results. We detect the presence of 80 YSO candidates. Those YSOs are used to infer the cluster age, which is found to be in the range 1 to 5 Myr. More precisely, we find that 1/3 of the YSOs are in a range between 3 to 5 Myr, while 2/3 of the YSO are ≤3 Myr. When looking at the spatial distribution of these two populations, we find evidence of a potential age gradient across the field that suggests sequential star formation. We construct the IMF and show that we can sample the mass distribution well into the brown dwarf regime (down to ~0.01 M_⊙). The logarithmic mass function rises to peak at ~0.3 M_⊙, before turning over and declining into the brown dwarf regime. The total cluster mass derived is estimated to be 78 ± 18 M_⊙, while the ratio derived of brown dwarfs to star is 18 ± 5%. When comparing it with other young clusters, we find that the IMF shape of the young cluster embedded within RCW 41 is consistent with those of Trapezium, IC 348, or Chamaeleon I, except for the IMF peak, which happens to be at higher mass. This characteristic is also seen in clusters like NGC 6611 or even Taurus. These results suggest that the medium-to-low mass end of the IMF possibly depends on environment.