CLUSTERED STAR FORMATION IN THE SMALL MAGELLANIC CLOUD. A SPITZER/IRAC VIEW OF THE STAR-FORMING REGION NGC 602/N 90

摘要

We present Spitzer/IRAC photometry on the star-forming H Ⅱ region N 90, related to the young stellar association NGC 602 in the Small Magellanic Cloud. Our photometry revealed bright mid-infrared sources, which we classify with the use of a scheme based on templates and models of red sources in the Milky Way, and criteria recently developed from the Spitzer Survey of the SMC for the selection of candidate Young Stellar Objects (YSOs). We detected 57 sources in all four IRAC channels in a 6.2' × 4.8' field of view centered on N 90; 22 of these sources are classified as candidate YSOs. We compare the locations of these objects with the position of optical sources recently found in the same region with high-resolution HST/ACS imaging of NGC 602 by Schmalzl and coworkers, and we find that 17 candidate YSOs have one or more optical counterparts. All of these optical sources are identified as pre-main-sequence stars, thus indicating ongoing clustered star formation events in the region. The positions of the detected YSOs and their related PMS clusters give a clear picture of the current star formation in N 90, according to which the young stellar association photoionizes the surrounding interstellar medium, revealing the H Ⅱ nebula, and triggering sequential star formation events mainly along the eastern and southern rims of the formed cavity of the parental molecular cloud.