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A Near-Infrared Study of the NGC 7538 Star-forming Region

Ojha, D. K. and Tamura, M. and Nakajima, Y. and Fukagawa, M. and Sugitani, K. and Nagashima, C. and Nagayama, T. and Nagata, T. and Sato, S. and Vig, S. and Ghosh, S. K. and Pickles, A. J. and Momose, M. and Ogura, K. (2004) A Near-Infrared Study of the NGC 7538 Star-forming Region. Astrophysical Journal, 616 (2). pp. 1042-1057. ISSN 0004-637X. doi:10.1086/425068.

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We present subarcsecond (FWHM ~ 0farcs7), near-infrared (NIR) JHKs-band images and a high-sensitivity radio continuum image at 1280 MHz, using SIRIUS on the University of Hawaii 88 inch (2.2 m) telescope and the Giant Metrewave Radio Telescope (GMRT). The NIR survey covers an area of ~24 arcmin^2 with 10 σ limiting magnitudes of ~19.5, 18.4, and 17.3 in the J, H, and Ks bands, respectively. Our NIR images are deeper than any JHK surveys to date for the larger area of the NGC 7538 star-forming region. We construct JHK color-color and J - H/J and H - K/K color-magnitude diagrams to identify young stellar objects (YSOs) and to estimate their masses. Based on these color-color and color-magnitude diagrams, we identified a rich population of YSOs (Class I and Class II) associated with the NGC 7538 region. A large number of red sources (H - K > 2) have also been detected around NGC 7538. We argue that these red stars are most probably pre-main-sequence stars with intrinsic color excesses. Most of the YSOs in NGC 7538 are arranged from the northwest toward the southeast regions, forming a sequence in age: a diffuse H II region (northwest and oldest, where most of the Class II and Class I sources are detected), a compact IR core (center), and regions with an extensive IR reflection nebula and a cluster of red young stars (southeast and south). We find that the slope of the Ks-band luminosity function of NGC 7538 is lower than the typical values reported for young embedded clusters, although equally low values have also been reported in the W3 Main star-forming region. From the slope of the Ks-band luminosity function and the analysis by Megeath and coworkers, we infer that the embedded stellar population is composed of YSOs with an age of ~1 Myr. Based on the comparison of models of pre-main-sequence stars with the observed color-magnitude diagram, we find that the stellar population in NGC 7538 is primarily composed of low-mass pre-main-sequence stars similar to those observed in the W3 Main star-forming region. The radio continuum image from the GMRT observations at 1280 MHz shows an arc-shaped structure due to the interaction between the H II region and the adjacent molecular cloud. The ionization front at the interface between the H II region and the molecular cloud is clearly delineated by comparing the radio continuum, molecular line, and NIR images.

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Tamura, M.0000-0002-6510-0681
Additional Information:© 2004. The American Astronomical Society. Received 2004 April 16; accepted 2004 August 11. It is a pleasure to thank the anonymous referee for a most thorough reading of this paper and several useful comments and suggestions, which greatly improved the scientific content of the paper. We thank the staff of the University of Hawaii 2.2 m telescope for supporting the first run of SIRIUS. D. K. O. was supported by the Japan Society for the Promotion of Science through a fellowship, during which most of this work was done. We acknowledge support by Grants-in-Aid (10147207, 12309010, and 13573001) from the Ministry of Education, Culture, Sports, Science, and Technology. We thank the staff of the GMRT who made the radio observations possible. The GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research (India). We thank Francesco Palla for providing us with the PMS grids. We thank Annie Robin for letting us use her model of stellar population synthesis. We thank Chris Davis for providing us with the FITS images of his H_2, narrowband K continuum, and CO molecular line observations of NGC 7538. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)UNSPECIFIED
Ministry of Education, Culture, Sports, Science and Technology (MEXT)10147207
Ministry of Education, Culture, Sports, Science and Technology (MEXT)12309010
Ministry of Education, Culture, Sports, Science and Technology (MEXT)13573001
Subject Keywords:infrared: stars; ISM: clouds; ISM: individual (NGC 7538) ; open clusters and associations: general; stars: formation; stars: pre-main sequence
Issue or Number:2
Record Number:CaltechAUTHORS:20170408-133608208
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Official Citation:D. K. Ojha et al 2004 ApJ 616 1042
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75865
Deposited By: 1Science Import
Deposited On:13 Apr 2017 19:49
Last Modified:15 Nov 2021 16:55

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