J/ApJ/806/199 RRL and continuum data of 21 Galactic H II regions (Balser+, 2015)
Azimuthal metallicity structure in the Milky Way disk.
Balser D.S., Wenger T.V., Anderson L.D., Bania T.M.
<Astrophys. J., 806, 199 (2015)>
=2015ApJ...806..199B 2015ApJ...806..199B (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; H II regions ; Radio lines ; Radio continuum
Keywords: Galaxy: abundances - H II regions - radio lines: ISM
Abstract:
Elemental abundance patterns in the Galactic disk constrain theories
of the formation and evolution of the Milky Way. H II region
abundances are the result of billions of years of chemical evolution.
We made radio recombination line and continuum measurements of 21
H II regions located between Galactic azimuth Az=90°-130°, a
previously unexplored region. We derive the plasma electron
temperatures using the line-to-continuum ratios and use them as
proxies for the nebular [O/H] abundances, because in thermal
equilibrium the abundance of the coolants (O, N, and other heavy
elements) in the ionized gas sets the electron temperature, with high
abundances producing low temperatures. Combining these data with our
previous work produces a sample of 90 H II regions with high-quality
electron temperature determinations. We derive kinematic distances in
a self-consistent way for the entire sample. The radial gradient in
[O/H] is -0.082±0.014 dex/kpc for Az=90°-130°, about a
factor of 2 higher than the average value between Az=0°-60°.
Monte Carlo simulations show that the azimuthal structure we reported
for Az=0°-60° is not significant because kinematic distance
uncertainties can be as high as 50% in this region. Nonetheless, the
flatter radial gradients between Az=0°-60° compared with
Az=90°-130° are significant within the uncertainty. We
suggest that this may be due to radial mixing from the Galactic Bar
whose major axis is aligned toward Az∼30°.
Description:
We select 21 of the best continuum sources based on the following
criteria. (1) Sources having a continuum intensity signal-to-noise
ratio greater than 10. (2) Since we are probing trans-Galactic paths,
source confusion can be a significant problem. We chose sources where
the H II region was either isolated or where any blending of
components could be well-fit by Gaussian profiles. (3) We select
sources with either flat radio recombination line (RRL) spectral
baselines or with baseline structure that could be well-fit by a low
order polynomial function. (4) Since we seek to explore metallicity
structure, we chose sources that span a wide range of Galactic radii
over the specified azimuth range.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 64 28 Radio Recombination Line Parameters of Galactic
H II Regions
table2.dat 86 21 Radio Continuum Parameters of Galactic H II
Regions
table3.dat 131 221 H II Region Properties
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See also:
J/ApJ/653/1226 : Physical properties of galactic HII regions (Quireza+, 2006)
J/ApJ/738/27 : Galactic HII regions RRL and continuum data (Balser+, 2011)
J/ApJS/194/32 : The HII Region Discovery Survey (HRDS). II. (Anderson+, 2011)
J/ApJ/754/62 : HRDS III. HII region kinematic distances (Anderson+, 2012)
J/ApJS/212/1 : The WISE catalog of Galactic HII regions (Anderson+, 2014)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Name Source name
16- 17 A2 --- El [H C He] Element name
19- 24 F6.2 mK TL H (or He) radio recombination line (RRL)
intensity
26- 29 F4.2 mK e_TL Uncertainty in TL
31- 35 F5.2 km/s DelV H (or He) RRL FWHM line width
37- 40 F4.2 km/s e_DelV Uncertainty in DelV
42- 47 F6.2 km/s VLSR Local Standard of Rest velocity
49- 52 F4.2 km/s e_VLSR Uncertainty in VLSR
54- 57 F4.1 h Tint ? Total integration time
59- 62 F4.2 mK rms ? rms spectral noise
64 A1 --- QF [BCD-] Quality factor (G1)
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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- 14 A14 --- Name Source name
16- 21 F6.1 mK TC-RA Continuum peak intensity along Right Ascension
23- 26 F4.2 mK e_TC-RA Uncertainty in TC-RA
28- 31 F4.2 arcmin Theta-RA FWHM angular width (Θ) along Right
Ascension
33- 37 F5.3 arcmin e_Theta-RA Uncertainty in Theta-RA
39- 44 F6.1 mK TC-DE Continuum peak intensity along Declination
46- 50 F5.2 mK e_TC-DE Uncertainty in TC-DE
52- 55 F4.2 arcmin Theta-DE FWHM angular width (Θ) along Declination
57- 61 F5.3 arcmin e_Theta-DE Uncertainty in Theta-DE
63- 68 F6.1 mK TC Average continuum peak intensity
70- 73 F4.2 mK e_TC Uncertainty in TC
75- 78 F4.2 arcmin Theta Average FWHM angular width (Θ)
80- 84 F5.3 arcmin e_Theta Uncertainty in Theta
86 A1 --- QF [ABC] Quality factor (G1)
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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- 14 A14 --- Name Source name
16 A1 --- n_Name [b] Note on Name (1)
18- 24 F7.3 deg GLON Galactic longitude
26- 32 F7.3 deg GLAT Galactic latitude
34- 37 F4.1 kpc Dsun1 ? Distance from the Sun (Kinematic-IAU) (3)
39- 43 F5.2 kpc e_Dsun1 ? Uncertainty in Dsun1 (Kinematic-IAU) (3)
45- 49 F5.1 deg Az1 ? Galactic azimuth (Kinematic-IAU) (3)
51- 54 F4.1 kpc Rgal1 ? Galactic radius (Kinematic-IAU) (3)
56- 59 F4.1 kpc Dsun2 ? Distance from the Sun (Kinematic-Reid) (4)
61- 65 F5.2 kpc e_Dsun2 ? Uncertainty in Dsun2 (Kinematic-Reid) (4)
67- 71 F5.1 deg Az2 ? Galactic azimuth (Kinematic-Reid) (4)
73- 76 F4.1 kpc Rgal2 ? Galactic radius (Kinematic-Reid) (4)
78- 81 F4.1 kpc Dsun3 ? Distance from the Sun (Best)
83- 87 F5.2 kpc e_Dsun3 ? Uncertainty in Dsun3 (Best)
89- 93 F5.1 deg Az3 ? Galactic azimuth (Best)
95- 98 F4.1 kpc Rgal3 ? Galactic radius (Best)
100-104 F5.3 --- y Helium abundance by number (2)
106-110 F5.3 --- e_y Uncertainty in y
112-116 I5 K Te Local thermodynamic equilibrium (LTE) electron
temperature
118-122 I5 K e_Te Uncertainty in Te
124-131 A8 --- Tel Telescope used for the RRL and continuum
observations (140 Foot, GBT)
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Note (1): Note as follows:
b = Distances for these sources are unrealistic because they are located
toward the Galactic Center. Our Galactic rotation curve model assumes a
maximum Rgal value of 25 kpc.
Note (2): For sources with no helium RRL detected, we assume y=0.080±0.000.
Note (3): IAU parameters :
Distance to the Galactic Center of Ro=8.5 kpc and a Solar circular
rotation speed of Θo=220 km/s.
Note (4): Reid et al. (2014, J/ApJ/783/130) where Ro=8.3 kpc and
Θo=240 km/s.
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Global notes:
Note (G1): The QF is a qualitative assessment of the line and continuum
measurement where "A" is excellent and "D" is poor.
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History:
From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 14-Sep-2017