A Census of Star Formation in the Outer Galaxy: the SMOG field
Winston, E., Hora, J. L., Gutermuth, R., and Tolls, V., 2019, ApJ, 880, 9; arXiv: arXiv:1906.03267
In this paper we undertake a study of the 21 deg2 SMOG field, a Spitzer cryogenic mission Legacy program to map a region of the outer Milky Way toward the Perseus and outer spiral arms with the IRAC and MIPS instruments. We identify 4648 YSOs across the field. Using the DBSCAN method, we identify 68 clusters or aggregations of YSOs in the region, having eight or more members. We identify 1197 Class I objects, 2632 Class II objects, and 819 Class III objects, of which 45 are candidate transition disk objects, utilizing the MIPS 24 photometry. The ratio of YSOs identified as members of clusters was 2872/4648, or 62%. The ratios of Class I to Class II YSOs in the clusters are broadly consistent with those found in the inner Galactic and nearby Gould Belt young star formation regions. The clustering properties indicate that the protostars may be more tightly bound to their natal sites than the Class II YSOs, and the Class III YSOs are generally widely distributed. We further perform an analysis of the WISE data of the SMOG field to determine how the lower resolution and sensitivity of WISE affects the identification of YSOs as compared to Spitzer: we identify 931 YSOs using combined WISE and 2MASS photometry, or 20% (931/4648) of the total number identified with Spitzer. Performing the same clustering analysis finds 31 clusters that reliably trace the larger associations identified with the Spitzer data. Twelve of the clusters identified have previously measured distances from the WISE H II survey. SEDFitter modeling of these YSOs is reported, leading to an estimation of the initial mass function in the aggregate of these clusters that approximates that found in the inner Galaxy, implying that the processes behind stellar mass distribution during star formation are not widely affected by the lower density and metallicity of the outer Galaxy.
Data tables in the paper:
- SMOG Field YSO catalog: Table 1
- SMOG Field Young Stellar Objects: SIMBAD Matches within 1'': Table 2
- SMOG Field Young Stellar Objects: Cluster Descriptions: Table 3
- WISE H II Distances to Matched Clusters: Table 4
- SMOG Field Young Stellar Objects: SEDFitter Results: Table 5
- WISE and IRAC Source Matching: Table 6
- SMOG Field YSOs: WISE Photometry Table: Table 7
SMOG Dataverse page - Contains the full resolution IRAC and MIPS mosaics, and the IRAC+MIPS photometry catalog including 2MASS JHK data for the detected sources.
Other data and images from this paper can be downloaded from this URL