A deep near-infrared survey of the chamaeleon I dark cloud core

We have carried out a deep near-infrared imaging survey to search for low-mass young stellar objects (YSOs) in the densest star-forming core of the Chamaeleon I dark cloud. Our observations cover an area of 30 arcmin(2), including an early B9 star (HD 97300) and an outflow source (HM 23). The 10 sigma limiting magnitudes are 18.1, 17.0, and 16.2 mag at J, H, and K, respectively, which is sensitive enough to provide a census of the embedded stellar population down to substellar objects in the cloud. Source classification is performed based on the near-infrared (NIR) color-color diagram. Many of the YSO candidates with NIR excesses are more than 7 mag fainter than typical T Tauri stars in the same cloud. Some of them are even fainter than the known brown dwarfs in the Pleiades. The luminosities of newly identified YSO candidates and the recent evolutionary models for very low mass objects suggest that they appear to be substellar, if their typical age is assumed to be similar to that of classic T Tauri stars or, namely, 1 Myr with an upper limit of 10 Myr. Therefore it is highly likely that young brown dwarfs form in this molecular cloud core. The J-band luminosity function of the YSO candidates does not appear to turn over down to the completeness limit. In the Chamaeleon I dark cloud core, stars form in a clustered mode characterized by both a high star formation efficiency and high stellar density such as in the rho Oph core.