Star Formation in the Outer Galaxy (SFOG)

There have been many observational studies of star formation using the Spitzer Space Telescope in regions in the solar neighborhood, and massive regions in the inner parts of the Galaxy. However, the outer Galaxy, which is intermediate in metallicity between the inner Galactic disk and the Magellanic Clouds, and at much lower volume densities, has not been as systematically studied. The extension of the Spitzer and Herschel Galactic surveys to the outer Galaxy, plus the WISE all-sky survey, has now made this possible. We are using techniques developed in studies of nearby star formation and massive regions such as Cygnus-X and W49 to locate young stellar objects in the outer Galaxy, and using model-fitting to determine their properties such as luminosity and mass, and studying their clustering properties. Comparing the results to star formation regions in other parts of the Galaxy will provide information on how dynamical processes and environmental factors can affect the mechanisms that influence the fragmentation of molecular clouds and star formation efficiency. The results will have applications to the study of star formation in other galaxies, where global properties can be observed but we cannot resolve individual clusters or stars in the infrared. This study will provide a database of outer Galaxy star formation which can be used to select objects to follow up with JWST.

Conferences and Posters

"A WISE GLIMPSE of Star Formation in the Outer Milky Way", Omoruyi, O., Winston, E., & Hora, J., AAS Abstracts #233, 233, #154.03
"A GLIMPSE of Star Formation in the Outer Galaxy", Winston, E., Hora, J. L., and Tolls, V., 2018, AAS, 231, #114.01

Image Release

Star formation in the G104.52+1.24 Region in the SMOG field

Papers and Data

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

Abstract:
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
A Census of Star Formation in the Outer Galaxy: The GLIMPSE360 Field
Winston, E., Hora, J. L., and Tolls, V., 2020, AJ, 160, 68, arXiv: (arXiv:2006.03080)

Abstract:
We have conducted a study of star formation in the outer Galaxy from 65° < l < 265° in the region observed by the GLIMPSE360 program. This Spitzer warm mission program mapped the plane of the outer Milky Way with IRAC at 3.6 and 4.5 μm. We combine the IRAC, WISE, and 2MASS catalogs and our previous results from another outer Galaxy survey and identify a total of 47,338 Young Stellar Objects (YSOs) across the field spanning >180° in Galactic longitude. Using the DBSCAN method on the combined catalog, we identify 618 clusters or aggregations of YSOs having 5 or more members. We identify 10,476 Class I, 29,604 Class II, and 7,325 anemic Class II/Class III YSOs. The ratio of YSOs identified as members of clusters was 25,528/47,338, or 54%. We found 100 of the clusters identified have previously measured distances in the WISE H II survey. We used these distances in our spectral energy distribution (SED) fitting of the YSOs in these clusters, of which 96 had YSOs with <3σ fits. We used the derived masses from the SED model fits to estimate the initial mass function (IMF) in the inner and outer Galaxy clusters: dividing the clusters by Galactocentric distances, the slopes were Γ = 1.87±0.31 above 3 M_☉ for R_Gal<11.5 kpc and Γ= 1.15±0.4 above 3 M_☉ for R_Gal>11.5 kpc. The slope of the combined IMF was found to be Γ = 1.92±0.42 above 3 M_☉. These values are consistent with each other within the uncertainties, and with literature values in the inner Galaxy high-mass star formation regions. The slopes are likely also consistent with a universal Salpeter IMF.
SFOG Dataverse page - Contains the figure sets from the paper, including 3-color images of the clusters and images with the YSOs overlayed. Also included are the FITS file cutouts for each cluster, and data for the tables.
Data tables in the paper:
- Table 1: SFOG Field YSOs - contains positions, photometry, for all SFOG YSOs
- Table 2: SFOG YSO Classifications - SFOG YSO number, positions, and evolutionary class & method
- Table 3: SFOG Field YSOs: SIMBAD matches - SIMBAD associations for all SFOG YSO with matches within 2 arcsec
- Table 4: SFOG YSO Cluster Descriptions. Cluster number, name, # of YSOs, position, size, WISE H II association, Skiff 2014 stars in cluster, and SIMBAD associations.
- Table 5: SFOG Field YSO SED Fitter Results - Contains average parameters from SEDFitter for YSOs modeled
Figure Sets:
- Plots of 2014yCat....1.2023S OB stars on YSO clusters, with cluster hulls
- Color images of regions around clusters with IRAC and WISE images, plus overlayed YSO positions (Complete Figures 9 and 10)