J/ApJ/587/714 H2CO and Hα observations of UC HII (Watson+, 2003)
Resolution of distance ambiguities of inner galaxy massive star formation
regions. I.
Watson C., Araya E., Sewilo M., Churchwell E., Hofner P., Kurtz S.
<Astrophys. J., 587, 714-726 (2003)>
=2003ApJ...587..714W 2003ApJ...587..714W
ADC_Keywords: H II regions ; Radio lines
Keywords: Galaxy: disk - radio lines: general - stars: formation
Abstract:
Fifty-four ultracompact (UC) HII regions in the GLIMPSE survey region
(|b|<1° and 30°<l<70°) were observed in H2CO and
H110α using the 305 m Arecibo telescope. By analyzing H2CO
absorption against the UC H II region continuum emission, we resolve
the distance ambiguity toward 44 sources. This determination is
critical to measure global physical properties of UC H II regions
(e.g., luminosity, size, mass) and properties of the Galaxy (e.g.,
spiral structure, abundance gradients). We find that the distribution
of UC H II regions in this survey is consistent with a ``local spur'',
the Perseus, Sagittarius, and Scutum arms as delineated by Taylor &
Cordes. However, departures from model velocities produce distance
uncertainties only slightly smaller than the proposed arm separations.
Description:
The observations were made between 2002 July 24 and 29 with the 305m
Arecibo Telescope. The 110-111 transition of interstellar
formaldehyde (H2CO, ν0=4829.6594MHz for F=2-2) was observed in
absorption against UC H II regions. Simultaneously, the H110α
(ν0=4874.1570MHz) radio recombination line was observed to establish
kinematic distances.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 50 54 Observed sources
table2.dat 65 54 H110α line (4874.16MHz)
and continuum parameters
table3.dat 76 138 Formaldehyde (H2CO, 4829.66MHz) line parameters
table4.dat 75 93 Kinematic parameters
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See also:
II/125 : IRAS catalogue of Point Sources, Version 2.0 (IPAC 1986)
J/A+AS/115/81 : A CS(2-1) survey of UC HII regions (Bronfman+, 1996)
J/A+AS/120/283 : Water maser features in UC HII regions (Hofner+ 1996)
J/A+A/336/339 : VLA observations of ultracompact HII regions (Molinari+ 1998)
J/MNRAS/301/640 : Ultracompact H II regions studies. II. (Walsh+, 1998)
J/ApJS/138/63 : H2CO and Halpha observations of UC HII (Araya+, 2002)
J/ApJS/155/123 : JHKs photometry of ultracompact HII regions (Alvarez+, 2004)
J/A+A/417/615 : Maser and outflows in UC HII region (Codella+, 2004)
J/A+A/453/1003 : SCUBA ultracompact HII regions (Thompson+, 2006)
J/ApJS/91/659 : Ultracompact HII regions radio images (Kurtz+ 1994)
J/MNRAS/420/1656 : RMS compact HII regions distances (Urquhart+, 2012)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Name Source name, GLL.ll+D.dd
13- 14 I2 h RAh Right ascension (B1950)
16- 17 I2 min RAm Right ascension (B1950)
19- 22 F4.1 s RAs Right ascension (B1950)
24 A1 --- DE- Declination sign (B1950)
25- 26 I2 deg DEd Declination (B1950)
28- 29 I2 arcmin DEm Declination (B1950)
31- 32 I2 arcsec DEs Declination (B1950)
34- 44 A11 --- IRAS IRAS name
46- 50 F5.1 hJy S100 IRAS 100µm flux density
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Name Source name
13 A1 --- f_Name [a] SNR (1)
15- 21 F7.1 mJy Sc Continuum flux density
23- 25 F3.1 mJy e_Sc The 1σ error in Sc
27- 31 F5.1 mJy SH110a ? H110α flux density
33- 35 F3.1 mJy e_SH110a ? The 1σ error in SH110a
37- 41 F5.1 km/s VLSR ? The Local Standard of Rest velocity
43- 45 F3.1 km/s e_VLSR ? The 1σ error in VLSR
47- 50 F4.1 km/s FWHM ? The Full-Width at Half-Maximum
52- 54 F3.1 km/s e_FWHM ? The 1σ error in FWHM
56- 60 I5 mJy.km/s Sint ? The integrated H110α line flux
62 A1 --- l_Sint Limit flag on Sint error (e_Sint)
63- 65 I3 mJy.km/s e_Sint ? The 1σ error on Sint
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Note (1): a = This source is a supernova remnant
(see Brogan & Troland, 2001ApJ...550..799B 2001ApJ...550..799B)
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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- 11 A11 --- Name Source name (1)
13-15 A3 --- CName Intervening cloud identification (1)
17- 25 F9.3 mJy Sc ? Continuum flux density
27- 31 F5.3 mJy e_Sc ? The 1σ error in Sc
33- 39 F7.1 mJy SH2CO ? H2CO flux density
41- 43 F3.1 mJy e_SH2CO ? The 1σ error in SH2CO
45- 49 F5.1 km/s VLSR ? The Local Standard of Rest velocity
51 A1 --- l_VLSR Limit flag on the VLSR error
52- 54 F3.1 km/s e_VLSR ? The 1σ error in VLSR
56- 59 F4.1 km/s FWHM ? The Full-Width at Half-Maximum
61 A1 --- l_FWHM Limit flag on the FWHM error
62- 64 F3.1 km/s e_FWHM ? The 1σ error in FWHM
66- 71 I6 mJy.km/s Sint ? The integrated H2CO line flux
73 A1 --- l_Sint Limit flag on the Sint error
74- 76 I3 mJy.km/s e_Sint ? The 1σ error on Sint
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Note (1): Indicates the direction of the H2CO cloud, but we do not imply
an association between the H2CO cloud and the UC HII region.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Name Source name
13 A1 --- f_Name [a] Note on near/far distance (1)
15- 17 A3 --- CName Intervening cloud identification
19- 23 F5.1 km/s VLSR The Local Standard of Rest velocity
25- 27 F3.1 km/s e_VLSR The 1σ error in VLSR
29- 32 F4.1 kpc DNear ? Inner Galaxy circular orbit near distance
34- 37 F4.1 kpc DFar ? Inner Galaxy circular orbit far distance
39- 42 F4.1 kpc VTP Distance derived to tangent point
44- 46 F3.1 kpc DTP Resolved Distance
48- 53 F6.3 kpc DLSR ? Distance derived from VLSR
55- 57 F3.1 kpc E_DLSR ? Upper 1σ error in DLSR
59- 61 F3.1 kpc e_DLSR ? Lower 1σ error in DLSR
63- 65 I3 pc z ? Galactic scale height
67- 70 F4.2 kpc DGC Distance from the Galactic center
72- 75 A4 --- Near/Far Comment on the source distance (2)
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Note (1): a = Araya et al. (2002ApJS..138...63A 2002ApJS..138...63A) report the near kinematic
distance to this source. The data presented here has a better signal to
noise than the Araya et al. spectra. Our observations revealed a weak H2CO
absorption not detected by Araya et al. which imply the FAR kinematic
distance.
Note (2): "Near" or "Far" distance estimation, or ambiguous:
b = This source has a velocity higher then the tangent velocity. We
locate this source at the tangent point, but this position should be
taken with caution since its velocity is not strictly predicted in
our rotation model.
c = This source has a velocity within 10km/s of the tangent velocity.
Because we are unable to strongly distinguish between the near and
far distance, we do not give a classification or distance.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 19-Feb-2014