J/A+A/666/A31 Sgr B2 UCHII regions in 6, 22.4 and 96GHz (Meng+, 2022)
The physical and chemical structure of Sagittarius B2.
VI. UCHII regions in Sgr B2.
Meng F., Sanchez-Monge A., Schilke P., Ginsburg A., DePree C., Budaiev N.,
Jeff D., Schmiedeke A., Schwoerer A., Veena V.S., Moeller T.
<Astron. Astrophys. 666, A31 (2022)>
=2022A&A...666A..31M 2022A&A...666A..31M (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; H II regions ; Radio sources
Keywords: stars: formation - stars: massive - radio continuum: ISM -
radio lines: ISM - ISM: individual objects: Sgr B2 - ISM: clouds
Abstract:
The giant molecular cloud Sagittarius B2 (hereafter SgrB2) is the most
massive region with ongoing high-mass star formation in the Galaxy.
Two ultra-compact HII (UCHII) regions were identified in SgrB2's
central hot cores, SgrB2(M) and SgrB2(N). Our aim is to characterize
the properties of the HII regions in the entire SgrB2 cloud. Comparing
the HII regions and the dust cores, we aim to depict the evolutionary
stages of different parts of SgrB2. We use the Very Large Array in its
A, CnB, and D configurations, and in the frequency band C (∼6GHz) to
observe the whole SgrB2 complex. Using ancillary VLA data at 22.4GHz
and ALMA data at 96GHz, we calculated the physical parameters of the
UCHII regions and their dense gas environment. We identify 54 UCHII
regions in the 6GHz image, 39 of which are also detected at 22.4GHz.
Eight of the 54 UCHII regions are newly discovered. The UCHII regions
have radii between 0.006pc and 0.04pc, and have emission measure
between 106pc/cm6 and 109pc/cm6. The UCHII regions are ionized
by stars of types from B0.5 to O6. We found a typical gas density of
∼106-109cm-3 around the UCHII regions. The pressure of the UCHII
regions and the dense gas surrounding them are comparable. The
expansion timescale of these UCHII regions is determined to be
∼104-105yr. The percentage of the dust cores that are associated
with HII regions are 33%, 73%, 4%, and 1% for SgrB2(N), SgrB2(M),
SgrB2(S), and SgrB2(DS), respectively. Two-thirds of the dust cores in
SgrB2(DS) are associated with outflows. The electron densities of the
UCHII regions we identified are in agreement with that of typical
UCHII regions, while the radii are smaller than those of the typical
UCHII regions. The dust cores in SgrB2(N) are more evolved than in
SgrB2(DS) but younger than in SgrB2(M).
Description:
VLA D+CnB+A array feathered image of whole SgrB2 in 4-8GHz, with
synthesized beam of 0.62"x0.28", having a position angle (PA) of
7.27°. The observed and derived properties of UCHII regions in
SgrB2 are based on this image and the 22.4GHz data used in
Gaume et al., (1995ApJ...449..663G 1995ApJ...449..663G) and (Ginsburg et al.,
2018ApJ...853..171G 2018ApJ...853..171G, Cat. J/ApJ/853/171)
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 88 54 Photometry of UCHII regions in 6, 22.4 and 96GHz
tableb2.dat 45 54 Derived physical parameters of UCHII regions
list.dat 123 1 Infornation on fits image
fits/* . 1 fits image
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See also:
J/ApJS/155/421 : Survey of Galactic Center region at 20cm (Yusef-Zadeh+, 2004)
J/ApJS/181/110 : Galactic center X-ray sources (Muno+, 2009)
J/ApJS/184/18 : Spitzer survey of young stellar clusters (Gutermuth+, 2009)
J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)
J/A+A/595/A94 : Galactic center clouds temperature structures (Immer+, 2016)
J/A+A/586/A50 : Central Molecular Zone H2CO temperature maps (Ginsburg+, 2016)
J/A+A/604/A6 : SgrB2 ALMA continuum and spectral index (Sanchez-Monge+, 2017)
J/ApJ/853/171 : 3mm point sources in extended Sgr B2 cloud (Ginsburg+, 2018)
Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- ID [1/54] Identifier
4- 5 A2 --- n_ID [ab* ] Note on ID (1)
7- 8 I2 h RAh Right ascension (J2000)
10- 11 I2 min RAm Right ascension (J2000)
13- 18 F6.3 s RAs Right ascension (J2000)
20 A1 --- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination sign (J2000)
24- 25 I2 arcmin DEm Declination sign (J2000)
27- 31 F5.2 arcsec DEs Declination sign (J2000)
33- 36 F4.2 arcsec r6GHz Observed radius in 6GHz
38- 42 F5.1 mJy S66GHz Observed flux in 6GHz
44- 46 F3.1 mJy e_S66GHz Error of observed flux in 6GHz
48- 51 F4.2 arcsec r22GHz ?=- Observed radius in 22.4GHz (2)
53- 57 F5.1 mJy S22GHz ?=- Observed flux in 22.4GHz (2)
59- 61 F3.1 mJy e_S22GHz ?=- Error of observed flux in 22.4GHz (2)
63- 66 F4.2 arcsec r96GHz Observed radius in 96GHz
68- 73 F6.1 mJy S96GHz Observed flux in 96GHz
75- 77 F3.1 mJy e_S96GHz Error of observed flux in 96GHz
79- 83 F5.2 --- alpha ?=- Spectral index between 6 and 22.4GHz (2)
85- 88 F4.2 --- e_alpha ?=- Error of spectral index (2)
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Note (1): Note as follows:
a = Assoc. w/ HII regions in (Benson et al., 1984ApJ...277..181B 1984ApJ...277..181B)
b = Assoc. w/ HII regions in (Gaume et al., 1995ApJ...449..663G 1995ApJ...449..663G)
* = Newly identified in this study
Note (2): Non-detection is denoted as "---"
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- ID [1/54] Identifier
4- 8 F5.2 10-3pc rcalc Calculated Radius of UCHII regions
10- 15 F6.2 10+7pc/cm^6 EM Emission measure
17- 21 F5.2 [s-1] log(N'Ly) Log of Lyman continuum flux
23- 27 F5.2 10+4cm-3 ne Electron number density
29- 34 F6.2 10+6cm-3 nH2 ?=- Neutral gas number density in H2
36- 40 F5.3 10-3pc ri Initial radius of HII regions
42- 45 F4.1 10+4yr T Expansion-time of HII regions
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 55 A26 "datime" Obs.date Observation date
57- 62 I6 Kibyte size Size of FITS file
64- 74 A11 --- FileName Name of FITS file, in subdirectory fits
76-123 A48 --- Title Title of the FITS file
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Acknowledgements:
Fanyi Meng, meng(at)ph1.uni-koeln.de
References:
Schmiedeke et al., Paper I 2016A&A...588A.143S 2016A&A...588A.143S
Sanchez-Monge et al., Paper II 2017A&A...604A...6S 2017A&A...604A...6S, Cat. J/A+A/604/A6
Pols et al., Paper III 2018A&A...614A.123P 2018A&A...614A.123P
Schworer et al., Paper IV 2019A&A...628A...6S 2019A&A...628A...6S
Meng et al., Paper V 2019A&A...630A..73M 2019A&A...630A..73M
(End) Patricia Vannier [CDS] 26-Aug-2022