J/ApJ/921/176 Galactic HII regions velocity gradients (Balser+, 2021)
Discovery of a new population of Galactic HII regions with ionized gas velocity
gradients.
Balser D.S., Wenger T.V., Anderson L.D., Armentrout W.P., Bania T.M.,
Dawson J.R., Dickey J.M.
<Astrophys. J., 921, 176 (2021)>
=2021ApJ...921..176B 2021ApJ...921..176B
ADC_Keywords: H II regions; Radio continuum; Interstellar medium; Interferometry
Keywords: Interstellar medium ; H II regions ; Radio astronomy ;
Radio spectroscopy
Abstract:
We investigate the kinematic properties of Galactic HII regions using
radio recombination line (RRL) emission detected by the Australia
Telescope Compact Array at 4-10GHz and the Jansky Very Large Array at
8-10GHz. Our HII region sample consists of 425 independent
observations of 374 nebulae that are relatively well isolated from
other, potentially confusing sources and have a single RRL component
with a high signal-to-noise ratio. We perform Gaussian fits to the RRL
emission in position-position-velocity data cubes and discover
velocity gradients in 178 (42%) of the nebulae with magnitudes between
5 and 200m/s/arcsec. About 15% of the sources also have an RRL width
spatial distribution that peaks toward the center of the nebula. The
velocity gradient position angles appear to be random on the sky with
no favored orientation with respect to the Galactic plane. We craft
HII region simulations that include bipolar outflows or solid body
rotational motions to explain the observed velocity gradients. The
simulations favor solid body rotation since, unlike the bipolar
outflow kinematic models, they are able to produce both the large,
>40m/s/arcsec, velocity gradients and also the RRL width structure
that we observe in some sources. The bipolar outflow model, however,
cannot be ruled out as a possible explanation for the observed
velocity gradients for many sources in our sample. We nevertheless
suggest that most HII region complexes are rotating and may have
inherited angular momentum from their parent molecular clouds.
Description:
Data are taken from two recent HII region radio recombination line
(RRL) surveys: the Southern HII Region Discovery Survey (SHRDS;
Wenger+ 2021, J/ApJS/254/36) using the Australia Telescope Compact
Array (ATCA) 4-10GHz, and the HII region Very Large Array (VLA)
8-10GHz RRL survey (Wenger+ 2019, J/ApJ/887/114).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 89 166 ATCA HII region sample (SHRDS;
Wenger+ 2021, J/ApJS/254/36)
table3.dat 89 12 VLA HII region sample (Wenger+ 2019, J/ApJ/887/114)
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See also:
J/ApJS/194/32 : The HII Region Discovery Survey (HRDS). II. (Anderson+, 2011)
J/ApJ/752/148 : κ-distributed electrons & OIII (Nicholls+, 2012)
J/ApJS/212/1 : The WISE catalog of Galactic HII regions (Anderson+, 2014)
J/ApJS/221/26 : Radio obs. of Galactic WISE HII regions (Anderson+, 2015)
J/A+A/587/A135 : Halpha images of NGC 6334 and NGC 6357 (Russeil+, 2016)
J/AJ/154/23 : Southern HII Region Discovery Survey: pilot (Brown+, 2017)
J/ApJS/234/33 : A GBT survey of large Galactic HII regions (Anderson+, 2018)
J/ApJ/887/114 : VLA ∼8-10GHz obs. of WISE Galactic HII regions (Wenger+, 2019)
J/ApJS/254/36 : Southern HII Region Discovery Survey. II. (Wenger+, 2021)
Byte-by-byte Description of file: table[23].dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- ID Source identifier (GLLL.lll+BB.bbb) (1)
17- 31 A15 --- Field Field identifier
33- 39 F7.2 km/s c0 [-129.13/116.85] Velocity offset
41- 44 F4.2 km/s e_c0 [0/0.51] Uncertainty in c0
46- 51 F6.2 m/s/arcsec Gradient [1.8/668] Velocity gradient magnitude
53- 57 F5.2 m/s/arcsec e_Gradient [0.05/46] Uncertainty in Gradient
59- 64 F6.2 deg PA [0.4/358] Position angle
66- 70 F5.2 deg e_PA [0.5/22.2] Uncertainty in PA
72 A1 --- QF Quality factor (A=highest); see text
74- 77 F4.1 --- Nbeam [1/11.2] Number of beams
79- 84 F6.2 --- PkSNR [16/551] Peak Signal-to-Noise
86- 89 F4.2 km/s RMS [0.13/9.2] Root mean square error
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Note (1): As in the WISE Catalog (Anderson+ 2014, J/ApJS/212/1) source name;
<[ABB2014] WISE GLLL.lll+BB.bbb> in Simbad
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 01-Mar-2023