Near-Infrared Imaging of Embedded Clusters: NGC 1333

Abstract

We present the results of an extensive near-infrared (JHK) imaging survey of the NGC 1333 star forming region. Our survey covers an area more than 4 times larger than the previous imaging survey of this cloud reported by Aspin et al. [A&AS, 106, 165 (1994)] and is sufficiently sensitive to render an accurate census of the embedded stellar population in the cloud. We detected 275 sources with mK < 14.5 magnitudes within the 432 square arcminute region surveyed. The spatial distribution of these sources is found to be significantly clustered with approximately 45% of the sources contained within two adjacent stellar clusters which together occupy an area less than 16% of the entire region surveyed. From comparison with observations of nearby control fields we estimate that roughly 143 of the sources detected over the entire region are physically associated with or embedded in the NGC 1333 molecular cloud. The majority (94 or 66%) of these are also found within the boundaries of the double cluster. From analysis of the JHK colors of the stars in the NGC 1333 region we find that roughly 30% of all sources display detectable infrared excess. This corresponds to more than 50% of all the sources embedded in the cloud. The infrared-excess sources display a higher degree of clustering than the general K band source population with roughly 75% of all excess sources located within the boundaries of the double cluster. Moreover, infrared excess sources comprise roughly 60% of the sources within the cluster suggesting that it is extremely young (≤1-2×106 years). We also find that the stars in the cluster suffer from significant amounts of differential extinction indicating that the cluster is deeply embedded in molecular material. We construct the K luminosity function (KLF) for the NGC 1333 cloud and compare it to that of the control fields off the cloud. We find that background field stars dominate the KLF at faint magnitudes and that the vast majority of stars associated with the cloud are brighter than our completeness limit. We use the infrared colors to de-redden the stars in the cluster and construct their (de-reddened) K luminosity function. The resulting KLF of the NGC 1333 cluster is compared to the KLFs of the Trapezium cluster in Orion and IC 348, a rich young cluster located within the same GMC complex as NGC 1333. The KLFs of NGC 1333 and the Trapezium cluster are found to be very similar in shape and extent while the KLFs of NGC 1333 and IC 348 are found to differ. We attribute this to the effects of luminosity evolution in these young clusters and suggest that the NGC 1333 cluster is similar in age to the Trapezium cluster (i.e., ≤106 years) and significantly younger than IC 348 (i.e., <5-7×106 years). This is consistent with both the large population of excess sources and outflow sources [Hodapp & Ladd (ApJ, 1995) (in Press)] contained in the NGC 1333 cluster. However, we derive a star formation rate of 4×10-5 Msun yr-1 for NGC 1333 which is essentially the same as that characterizing IC 348 and nearly an order of magnitude lower than that found for the Trapezium cluster. The two most active star forming regions in the Perseus cloud complex have now been thoroughly surveyed with comparable sensitivities at near-infrared wavelengths. Both regions have produced embedded stellar clusters, which are forming stars at a similar rate, but which appear to be in very different stages of evolution.