A Caltech Library Service

The Spitzer Survey of the Small Magellanic Cloud: Discovery of Embedded Protostars in the H II Region NGC 346

Simon, Joshua D. and Bolatto, Alberto D. and Whitney, Barbara A. and Robitaille, Thomas P. and Shah, Ronak Y. and Makovoz, David and Stanimirović, Snežana and Barbá, Rodolfo H. and Rubio, Mónica (2007) The Spitzer Survey of the Small Magellanic Cloud: Discovery of Embedded Protostars in the H II Region NGC 346. Astrophysical Journal, 669 (1). pp. 327-336. ISSN 0004-637X.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


We use Spitzer Space Telescope observations from the Spitzer Survey of the Small Magellanic Cloud (S^(3)MC) to study the young stellar content of N66, the largest and brightest H II region in the SMC. In addition to large numbers of normal stars, we detect a significant population of bright, red infrared sources that we identify as likely to be young stellar objects (YSOs). We use spectral energy distribution (SED) fits to classify objects as ordinary (main-sequence or red giant) stars, asymptotic giant branch stars, background galaxies, and YSOs. This represents the first large-scale attempt at blind source classification based on Spitzer SEDs in another galaxy. We firmly identify at least 61 YSOs, with another 50 probable YSOs; only one embedded protostar in the SMC was reported in the literature prior to the S^(3)MC. We present color selection criteria that can be used to identify a relatively clean sample of YSOs with IRAC photometry. Our fitted SEDs indicate that the infrared-bright YSOs in N66 have stellar masses ranging from 2 to 17 M_☉, and that approximately half of the objects are stage II protostars, with the remaining YSOs roughly evenly divided between stage I and stage III sources. We find evidence for primordial mass segregation in the H II region, with the most massive YSOs being preferentially closer to the center than lower mass objects. Despite the low metallicity and dust content of the SMC, the observable properties of the YSOs appear consistent with those in the Milky Way. Although the YSOs are heavily concentrated within the optically bright central region of N66, there is ongoing star formation throughout the complex, and we place a lower limit on the star formation rate of 3.2 × 10^(-3) M_☉ yr^(-1) over the last ~1 Myr.

Item Type:Article
Related URLs:
URLURL TypeDescription
Bolatto, Alberto D.0000-0002-5480-5686
Robitaille, Thomas P.0000-0002-8642-1329
Additional Information:© 2007 The American Astronomical Society. Print publication: Issue 1 (2007 November 1); received 2007 March 2; accepted for publication 2007 July 10. We would like to thank the anonymous referee for a careful reading of the paper that produced valuable feedback. J. D. S. gratefully acknowledges the support of a Millikan Fellowship provided by the California Institute of Technology. This research was partially funded by NASA through an award issued by JPL/ Caltech (NASA-JPL Spitzer grant 1264151 awarded to Cycle 1 project 3316). B. W. was supported by NASA Astrophysics Theory Program grant NNG 05-GH35G and the Spitzer Theoretical Research Program under subcontract 1290701, M. R. was supported by the Chilean Center for Astrophysics FONDAP No. 15010003, and financial support from FONDECYT No. 1050052 is acknowledged by R. H. B. We thank You-Hua Chu, Robert Gruendl, Lynne Hillenbrand, Jacco van Loon, Adam Leroy, and Bob Benjamin for helpful conversations, and we also thank Dimitrios Gouliermis for providing us with the HST photometry in advance of publication. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. 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 NASA and the National Science Foundation. This research has also made use of NASA’s Astrophysics Data System Bibliographic Services and the SIMBAD database, operated at CDS, Strasbourg, France.
Funding AgencyGrant Number
Caltech Millikan FellowshipUNSPECIFIED
Fondo de Financiamiento de Centros de Investigación en Áreas Prioritarias (FONDAP)15010003
Fondo Nacional de Desarrollo Científico y Tecnologico (FONDECYT)1050052
Subject Keywords:H II regions; infrared: stars; ISM: individual (N66); Magellanic Clouds; stars: formation; stars: pre-main sequence
Issue or Number:1
Record Number:CaltechAUTHORS:20100211-153202885
Persistent URL:
Official Citation:The Spitzer Survey of the Small Magellanic Cloud: Discovery of Embedded Protostars in the H II Region NGC 346 Joshua D. Simon, Alberto D. Bolatto, Barbara A. Whitney, Thomas P. Robitaille, Ronak Y. Shah, David Makovoz, Snežana Stanimirović, Rodolfo H. Barbá, and Mónica Rubio 2007 ApJ 669 327-336 doi: 10.1086/521544
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17461
Deposited By: Jason Perez
Deposited On:12 Feb 2010 19:37
Last Modified:09 Mar 2020 13:19

Repository Staff Only: item control page