J/A+A/645/A110 Hypercompact HII regions (Yang+, 2021)
A population of hypercompact HII regions identified from young HII regions.
Yang A.Y., Urquhart J.S., Thompson M.A., Menten K.M., Wyrowski F.,
Brunthaler A., Tian W.W., Rugel M., Yang X.L., Yao S., Mutale M.
<Astron. Astrophys. 645, A110 (2021)>
=2021A&A...645A.110Y 2021A&A...645A.110Y (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium; H II regions; Radio continuum
Keywords: HII regions - evolution - radio continuum: stars -
stars: massive - stars: formation
Abstract:
The derived physical parameters for young HII regions are normally
determined assuming the emission region to be optically-thin. However,
this is unlikely to hold for young HII regions such as Hyper-compact
HII(HCHII) and Ultra-compact HII(UCHII) regions and leads to the
underestimation of their properties. This can be overcome by fitting
the SEDs over a wide range of radio frequencies.
Two primary goals are (1) determining physical properties from radio
SEDs and finding potential HCHII regions; (2) using these physical
properties to investigate their evolution.
We used Karl G. Jansky Very Large Array (VLA) to make observations of
X-band and K-band with angular-resolutions of ∼1.7" and ∼0.7",
respectively, toward 114 HII regions with rising-spectra between
1-5GHz. We complement our observations with VLA archival data and
construct SEDs between 1-26GHz and model them assuming an
ionisation-bounded HII region with uniform density.
The sample has a mean electron density of ne=1.6*104cm-3, diameter
diam=0.14pc, and emission measure EM=1.9*107pc/cm6. We identify
16 HCHII region candidates and 8 intermediate objects between the
classes of HCHII and UCHII regions. The ne, diam, and EM change as
expected, however, 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.
Young HII regions are commonly located in dusty clumps; HCHII 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.
Description:
File table1.dat contains the sample of the 118 rising-spectra HII
regions that we have observed at X-band (8-12GHz) and K-band(18-26GHz)
by VLA, with resolution of 1.7" and 0.7" respectively.
File table3.dat contains the observational results of the sample of 112
HII regions that have good data at X-band (8-12GHz) and
K-band(18-26GHz).
File table5.dat contains the physical properties of 116 rising-spectra
HII regions and deconvolved, derived from the radio spectral energy
distribution (SED) between 1-26GHz, by including four sources with
data from archive and literature.
Fig. B1 contains the images of the SED fittings and the radio images
at C-band, X-band, and K-band for 116 HII regions, which are in the
subdirectory images.
These images can be shown in a link related to each source in
table5.dat.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 47 118 The sample of 118 rising-spectra HII regions
table3.dat 105 112 Observation results of 112 young HII regions at
X-band (8-12GHz) and K-band (18-26GHz)
table5.dat 206 116 Derived physical properties of 116 young
HII regions
images/* . 448 Individual pdf images
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See also:
J/AJ/131/2525 : MAGPIS 20cm survey (Helfand+, 2006)
J/MNRAS/435/400 : ATLASGAL compact HII regions (Urquhart+, 2013)
J/MNRAS/473/1059 : Complete sample of Galactic clumps (Urquhart+, 2018)
J/A+A/615/A103 : CORNISH project. III. UCHII region catalogue
(Kalcheva+, 2018)
J/A+A/579/A71 : Infrared emission of young HII regions (Cesaroni+, 2015)
J/ApJS/235/3 : Massive outflows associated with ATLASGAL clumps
(Yang+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 17 A17 --- Name Galactic name (GLLL.llll+BB.bbbb)
18 A1 --- n_Name [+*] Note on Name (1)
20- 26 F7.2 mJy S1.4GHz ?=- Integrated flux density at 1.4GHz
28- 35 F8.2 mJy S5GHz Integrated flux density at 5GHz
37- 40 F4.1 kpc Dist ?=- Heliocentric distance
43- 45 F3.1 [Lsun] logLb ?=- Log bolometric luminosity
47 I1 --- r_logLb References for luminosity and distance (2)
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Note (1): Note as follows:
+ = refers to the sources in our observation with bad images.
* = refers to the 4 sources with data from archive and literature.
Note (2): Reference as follows:
1 = Urquhart et al., 2013MNRAS.435..400U 2013MNRAS.435..400U, Cat. J/MNRAS/435/400
2 = Cesaroni et al., 2015A&A...579A..71C 2015A&A...579A..71C, Cat. J/A+A/579/A71
3 = Kalcheva et al., 2018A&A...615A.103K 2018A&A...615A.103K, Cat. J/A+A/615/A103
4 = Urquhart et al., 2018MNRAS.473.1059U 2018MNRAS.473.1059U, Cat. J/MNRAS/473/1059
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- Name Galactic name (GLLL.llll+BB.bbbb)
18 A1 --- n_Name [o+] Note on Name (1)
20- 25 F6.1 mJy/beam SpeakX ?=- Peak flux density at the central
frequency (10GHz) of X-band
27- 31 F5.2 mJy sigmaX rms of the the central frequency (10GHz)
of X-band
32- 38 F7.1 mJy S9GHz Integrated flux density at 9 GHz
40- 46 F7.1 mJy S10GHz Integrated flux density at 10 GHz
48- 54 F7.1 mJy S11GHz Integrated flux density at 11 GHz
56- 60 F5.2 arcsec thetaXa Deconvolved angular size (major axis)
at X band
61 A1 --- --- [x]
62- 65 F4.1 arcsec thetaXb Deconvolved angular size (minor axis)
at X band
67- 71 F5.1 mJy/beam SpeakK Peak flux density at the central frequency
(22GHz) of K-band
73- 77 F5.2 mJy sigmaK rms of the the central frequency (22GHz)
of K-band
78- 83 F6.1 mJy S20GHz ?=- Integrated flux density at 20 GHz
85- 90 F6.1 mJy S22GHz ?=- Integrated flux density at 22 GHz
92- 97 F6.1 mJy S24GHz ?=- Integrated flux density at 24 GHz
99-101 F3.1 arcsec thetaKa ?=- Deconvolved angular size at K band
(major axis)
102 A1 --- --- [x]
103-105 F3.1 arcsec thetaKb ?=- Deconvolved angular size at K band
(minor axis)
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Note (1): Notes as follows:
+ = refers to the added 5 UCHII regions in the observed fields with rising
spectra between C and X band, see Section 3.1.
o = indicates that the sources are extended and their K-band flux densities
should be considered to be lower limits.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- Name Galactic name (GLLL.llll+BB.bbbb)
19- 22 F4.2 cm-3 ne Electron number density
24- 28 F5.3 pc Diam physical linear diameter
30- 35 F6.2 pc/cm6 EM Emission measure
37- 41 F5.2 GHz nut Turnover frequency
43- 47 F5.2 [s-1] logNLy Lyman continuum photons
49- 52 A4 --- Sptype Spectral type derived from Lyman continuum flux
54- 57 F4.2 --- fd ?=- fraction of ionizing photons absorbed by
dust within HII regions (1)
59- 93 A35 --- Cband Name of the C-band image in subdirectory images
95-129 A35 --- Kband Name of the K-band image in subdirectory images
131-165 A35 --- Xband Name of the X-band image in subdirectory images
167-206 A40 --- Fit Name of the fitting image in subdirectory images
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Note (1): The fraction of Lyman continuum photons absorbed by dust within HII
regions fd should be taken as upper limits.
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Acknowledgements:
Aiyuan Yang, ayyang(at)mpifr-bonn.mpg.de
(End) Patricia Vannier [CDS] 19-Nov-2020