Invited review abstract

One of the most attempted goals of star formation theories is to determine the dominant process by which brown dwarfs form and the implications of the environment on its outcome. Current theories must be able to reproduce not only the observed shape of the IMF, but predict observable properties of clusters such as multiplicity, mass segregation, frequency and sizes of discs, accretion, etc. The new observational frontier is therefore the detection and characterization of very low mass objects in star forming regions, to confront model predictions from numerical simulations of the collapse of molecular clouds to the observed properties of YSOs. I will present the results of a major observational study aimed at uncovering the low mass population of the 1 Myr old Rho Ophiuchi molecular cloud. Candidate BDs with masses down to the planetary regime have been identified using the deepest near-IR imaging survey of the entire region (WIRCAM/CFHT), and archival Spitzer and Subaru data. A spectroscopic follow-up of these candidates has been conducted using several facilities (TNG,GTC,NTT,VLT) to ascertain their spectral types and masses, and ultimately, to construct the low-mass end of the IMF for this star forming region. I will also present preliminary results of an analogous survey targeting IC348.