High and Intermediate-Mass Young Stellar Objects in the Large Magellanic Cloud

Archival Spitzer IRAC and MIPS observations of the Large Magellanic Cloud (LMC) have been used to search for young stellar objects (YSOs). We have carried out independent aperture photometry of these data and merged the results from different passbands to produce a photometric catalog. To verify our methodology we have also analyzed the data from the SAGE and SWIRE Legacy programs; our photometric measurements are in general agreement with the photometry released by these programs. A detailed completeness analysis for our photometric catalog of the LMC show that the 90% completeness limits are, on average, 16.0, 15.0, 14.3, 13.1, and 9.2 mag at 3.6, 4.5, 5.8, 8.0, and 24 μm, respectively. Using our mid-infrared photometric catalogs and two simple selection criteria, [4.5]−[8.0]>2.0 to exclude normal and evolved stars and [8.0]>14−([4.5]−[8.0]) to exclude background galaxies, we have identified a sample of 2,910 sources in the LMC that could potentially be YSOs. We then used the Spitzer observations complemented by optical and near-infrared data to carefully assess the nature of each source. To do so we simultaneously considered multi-wavelength images and photometry to assess the source morphology, spectral energy distribution (SED) from the optical through the mid-infrared wavelengths, and the surrounding interstellar environment to determine the most likely nature of each source. From this examination of the initial sample, we suggest 1,172 sources are most likely YSOs. We have also identified 1,075 probable background galaxies, consistent with the expected number estimated from the SWIRE survey. Spitzer IRS observations of 269 of the brightest YSOs from our sample have confirmed that &95% are indeed YSOs. Examination of color-color and color-magnitude diagrams shows no simple criteria in color-magnitude space that can unambiguously separate the LMC YSOs from all AGB/post-AGB stars, planetary nebulae, and background galaxies. Astronomy Department, University of Illinois, 1002 W. Green Street, Urbana, IL 61801; [email protected],[email protected] Visiting astronomer, Cerro Tololo Inter-American Observatory