A Near - Infrared L Band Survey of the Young Embedded Cluster NGC 2024

We present the results of the first sensitive L band (3.4 μm) imaging study of the nearby young embedded cluster NGC 2024. Two separate surveys of the cluster were acquired in order to obtain a census of the circumstellar disk fraction in the cluster. We detected 257 sources to the mL ≤ 12.0 completeness limit of our ∼110 arcmin primary survey region. An additional 26 sources with 12.0 < L < 14.0 were detected in the deeper survey of the central ∼6.25 arcmin region of the cluster. From an analysis of the JHKL colors of all sources in our largest area, we find an infrared excess fraction of ≥ 86%±8%. The JHKL colors suggest that the infrared excesses arise in circumstellar disks, indicating that the majority of the sources which formed in the NGC 2024 cluster are currently surrounded by, and likely formed with circumstellar disks. The excess fractions remain very high, within the errors, even at the faintest L magnitudes from our deeper surveys suggesting that disks form around the majority of the stars in very young clusters such as NGC 2024 independent of mass. From comparison with published JHKL observations of Taurus, we find the K – L excess fraction in NGC 2024 to be formally higher than in Taurus, although both fractions are quite high. Thus, existing L band observations are consistent with a high initial incidence of circumstellar disks in both NGC 2024 and Taurus. Because NGC 2024 represents a region of much NASA Florida Space Grant Fellow Visiting Astronomer, Fred Lawrence Whipple Observatory. Visiting Astronomer at the Infrared Telescope Facility which is operated by the University of Hawaii under contract to the National Aeronautics and Space Administration. Visiting Astronomer, Kitt Peak National Observatory, part of the National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. Presidential Early Career Award for Scientists and Engineers Recipient.