Improved selection criteria for H ii regions, based on IRAS sources. Issue 3 (3rd March 2018)

• Record Type: Journal Article
• Authors: Yan, Qing-Zeng; Xu, Ye; Walsh, A J; Macquart, J P; MacLeod, G C; Zhang, Bo; Hancock, P J; Chen, Xi; Tang, Zheng-Hong
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 476:Issue 3(2018)
• Page Start: 3981
• Page End: 3990
• Publication Date: 2018-03-03
• Subjects: stars: evolution -- stars: massive -- stars: statistics -- H ii regions -- infrared: ISM -- infrared: stars; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty518
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: We present new criteria for selecting H ii regions from the Infrared Astronomical Satellite ( IRAS ) Point Source Catalogue (PSC), based on an H ii region catalogue derived manually from the all-sky Wide-field Infrared Survey Explorer ( WISE ). The criteria are used to augment the number of H ii region candidates in the Milky Way. The criteria are defined by the linear decision boundary of two samples: IRAS point sources associated with known H ii regions, which serve as the H ii region sample, and IRAS point sources at high Galactic latitudes, which serve as the non-H ii region sample. A machine learning classifier, specifically a support vector machine, is used to determine the decision boundary. We investigate all combinations of four IRAS bands and suggest that the optimal criterion is $\mathrm{log}\left(F_{60}/F_{12}\right)\geqq \left( -0.19 \times \mathrm{log}\left(F_{100}/F_{25}\right)+ 1.52\right)$, with detections at 60 and 100 ${\mu}$ m. This selects 3041 H ii region candidates from the IRAS PSC. We find that IRAS H ii region candidates show evidence of evolution on the two-colour diagram. Merging the WISE H ii catalogue with IRAS H ii region candidates, we estimate a lower limit of approximately 10 200 for the number of H ii regions in the Milky Way.