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Improved selection criteria for H ii regions, based on IRAS sources.

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
Source :
Monthly Notices of the Royal Astronomical Society. May2018, Vol. 476 Issue 3, p3981-3990. 10p.
Publication Year :
2018

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. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
00358711
Volume :
476
Issue :
3
Database :
Academic Search Index
Journal :
Monthly Notices of the Royal Astronomical Society
Publication Type :
Academic Journal
Accession number :
132660227
Full Text :
https://doi.org/10.1093/mnras/sty518