|Authors||Charles J. Lada(1), August A. Muench(1), Elizabeth A. Lada(2) and Joao F. Alves(3)|
(1) Harvard-Smithsonian Center for
Astrophysics; (2) Department of Astronomy, University of Florida;
(3) European Southern Observatory
|Accepted by||Astronomical Journal|
Examining the infrared colors of all these sources we determine an infrared excess fraction of 50 ± 20% from the JHKsL' colors for both the luminosity selected and spectroscopically selected substellar samples. This finding confirms the presence of infrared excess, likely due to circumstellar disks, around a significant fraction of the cluster's substellar population, consistent with the indications of earlier observations obtained at shorter (JHKs) wavelengths. Our deep L' imaging survey also provides new information concerning the deeply embedded population of young objects located in the molecular cloud behind the cluster and revealed in an earlier L band imaging survey of the region. In particular, our present L' survey doubles the number of sources in the cluster region known to possess extremely red K-L colors. These objects exhibit K-L' colors indicative of deeply buried, possibly protostellar, objects that likely mark the site of the most recent and ongoing star formation in the region.
We find the surface density distribution of the deeply embedded population to follow that of the background molecular ridge and to be highly structured, consisting of a string of at least 5 significant subclusters. These subclusters may represent the primordial building blocks out of which the cluster was and perhaps still is being assembled. These observations may thus provide insights into the early stages of cluster formation and appear consistent with recent simulations that suggest that the Trapezium cluster may have formed from numerous but small primordial subclusters.