NGC 2264 contains ~400 brown dwarfs in the mass range 0.02-0.08 M☉ Samuel Pearson, Aleks Scholz, Paula Teixeira, Koraljka Mužić, Víctor Almendros-Abad sp246@st-Andrews.ac.uk We spectroscopically confirm 13 brown dwarfs, the first in NGC 2264. We find that requiring brown dwarf candidates to display additional criteria for youth significantly increases the success rate of follow up spectroscopy. We estimate that NGC 2264 contains 200-600 brown dwarfs in the mass range of 0.02-0.08 M☉and determine the slope of the sub-stellar mass function to be 𝛼= 0.43!".$% &".'(. These values are consistent with those measures for other young clusters. This points to a uniform sub- stellar mass function across all star-forming environments. Results The origin of brown dwarfs and the substellar mass function have long been subjects of debate. The perquisite for making progress on these issues is to have large and well characterised samples of young brown dwarfs in diverse star-forming regions. NGC 2264 is an ideal region to achieve this due to its large population of ~1500 stellar members, relative proximity of 719 ± 16 pc, and low foreground extinction. NGC 2264 provides a perfect laboratory to study star and brown dwarf formation. Introduction We have used deep multi-wavelength, multi- epoch data to build a catalogue of brown dwarf candidates in NGC 2264. Our brown dwarf candidates were initially identified by their near-infrared colours but were also required to display additional indications of youth, including variability, the presence of a disc, Gaia kinematics, rotation period and extinction. We used KMOS on the VLT to obtain follow up spectroscopy for a small sub- sample of our candidates in order to determine their spectral type, extinction and the confirmation rate of our candidates. Methodology The first spectroscopically confirmed brown dwarfs in NGC 2264 arXiv:2108.07633 The slope of the substellar mass function is 𝛼= 0.43 for a power law of the form !" !# ∝𝑚$% The majority of our confirmed brown dwarfs are very young (<0.5 Myr) Using indicators of youth significantly improves spectroscopic follow up efficiency. The substellar mass function for the three KMOS fields in NGC 2264 (see below figure), represented with three equally size log-mass bins in the range of 0.02-0.08 M☉. For more details see Sect. 5.2. arXiv:2108.07633 Absolute J-band magnitude vs. effective temperature for the 32 low- mass stars and brown dwarfs (M2-M8) identified in this study (red) as well as the Venuti et al. (2018) sample of spectroscopically confirmed NGC 2264 cluster members (blue). For more details see Sect. 4. arXiv:2108.07633 Above: A deep I-band image of NGC 2264. The three fields that were observed with KMOS/VLT are overplotted in white. Confirmed brown dwarfs are marked in red. Left: The KMOS spectra for the 13 sources identified as brown dwarfs in NGC 2264. For details on the spectral fitting see Sect. 3. arXiv:2108.07633 The slope of the Spitzer/IRAC SED (αIRAC) can be used to identify disc baring sources (Lada et al. 2006). A disc is a strong indication of youth. Confirmed brown dwarfs (≥M6) are shown in red, the early-mid M stars (M2-M5.5) in blue, the contaminants in yellow, and the full Pearson 2020 catalogue in grey.