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A population of hypercompact H II regions identified from young H II regions
Yang, A. Y.1; Urquhart, J. S.2; Thompson, M. A.3; Menten, K. M.1; Wyrowski, F.1; Brunthaler, A.1; Tian, W. W.4,5; Rugel, M.1; Yang, X. L.6; Yao, S.6; Mutale, M.3
2021-01-22
Source PublicationASTRONOMY & ASTROPHYSICS
ISSN0004-6361
Volume645Pages:20
AbstractContext. The derived physical parameters for young HII regions are normally determined assuming the emission region to be optically thin. However, this assumption is unlikely to hold for young HII regions such as hyper-compact HII (HC HII) and ultra-compact HII (UC HII) regions and leads to underestimation of their properties. This can be overcome by fitting the SEDs over a wide range of radio frequencies.Aims. The two primary goals of this study are (1) to determine the physical properties of young HII regions from radio SEDs in the search for potential HC HII regions, and (2) to use these physical properties to investigate their evolution.Methods. We used the Karl G. Jansky Very Large Array (VLA) to observe the X-band and K-band with angular resolutions of similar to 1.7 and similar to 0.7 '', respectively, toward 114 HII regions with rising-spectra (alpha(5GHz)(1.4GHz)>0). We complement our observations with VLA archival data and construct SEDs in the range of 1-26 GHz and model them assuming an ionization-bounded HII region with uniform density.Results. Our sample has a mean electron density of n(e) = 1.6 x 10(4) cm(-3), diameter diam = 0.14 pc, and emission measure EM = 1.9 x 10(7) pc cm(-6). We identify 16 HC HII region candidates and 8 intermediate objects between the classes of HC HII and UC HII regions. The n(e), diam, and EM change, as expected, but the Lyman continuum flux is relatively constant over time. We find that about 67% of Lyman-continuum photons are absorbed by dust within these HII regions and the dust absorption fraction tends to be more significant for more compact and younger HII regions.Conclusions. Young HII regions are commonly located in dusty clumps; HC HII regions and intermediate objects are often associated with various masers, outflows, broad radio recombination lines, and extended green objects, and the accretion at the two stages tends to be quickly reduced or halted.
KeywordHII regions evolution radio continuum: stars stars: massive stars: formation
Funding OrganizationNational Key R&D Programs of China ; National Key R&D Programs of China ; National Key R&D Programs of China ; National Key R&D Programs of China ; National Key R&D Programs of China ; National Key R&D Programs of China ; National Key R&D Programs of China ; National Key R&D Programs of China
DOI10.1051/0004-6361/202038608
WOS KeywordULTRACOMPACT HII-REGIONS ; STAR-FORMING REGION ; CANDIDATE MASSIVE YSOS ; RECOMBINATION LINE ; RADIO-CONTINUUM ; MOLECULAR OUTFLOWS ; VLA OBSERVATIONS ; GALACTIC PLANE ; H2O MASERS ; RMS SURVEY
Language英语
Funding ProjectNational Key R&D Programs of China[2018YFA0404203]
Funding OrganizationNational Key R&D Programs of China ; National Key R&D Programs of China ; National Key R&D Programs of China ; National Key R&D Programs of China ; National Key R&D Programs of China ; National Key R&D Programs of China ; National Key R&D Programs of China ; National Key R&D Programs of China
WOS Research AreaAstronomy & Astrophysics
WOS SubjectAstronomy & Astrophysics
WOS IDWOS:000613034700002
PublisherEDP SCIENCES S A
Citation statistics
Document Type期刊论文
Identifierhttp://ir.bao.ac.cn/handle/114a11/79288
Collection中国科学院国家天文台
Corresponding AuthorYang, A. Y.
Affiliation1.Max Planck Inst Radio Astron, Hugel 69, D-53121 Bonn, Germany
2.Univ Kent, Ctr Astrophys & Planetary Sci, Canterbury CT2 7NH, Kent, England
3.Univ Hertfordshire, Sch Phys Astron & Math, Ctr Astrophys Res, Coll Lane, Hatfield AL10 9AB, Herts, England
4.Chinese Acad Sci, Natl Astron Observ, CAS Key Lab FAST, Beijing 100012, Peoples R China
5.Univ Chinese Acad Sci, 19A Yuquan Rd, Beijing 100049, Peoples R China
6.Peking Univ, Kavli Inst Astron & Astrophys, Beijing 100871, Peoples R China
Recommended Citation
GB/T 7714
Yang, A. Y.,Urquhart, J. S.,Thompson, M. A.,et al. A population of hypercompact H II regions identified from young H II regions[J]. ASTRONOMY & ASTROPHYSICS,2021,645:20.
APA Yang, A. Y..,Urquhart, J. S..,Thompson, M. A..,Menten, K. M..,Wyrowski, F..,...&Mutale, M..(2021).A population of hypercompact H II regions identified from young H II regions.ASTRONOMY & ASTROPHYSICS,645,20.
MLA Yang, A. Y.,et al."A population of hypercompact H II regions identified from young H II regions".ASTRONOMY & ASTROPHYSICS 645(2021):20.
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