J/A+A/696/A67 Parallax-based distances to Galactic HII regions (Shen+, 2025)
Parallax-based distances to Galactic HII regions: Nearby spiral structure.
Shen X.J., Hou L.G., Liu H.L., Gao X.Y.
<Astron. Astrophys. 696, A67 (2025)>
=2025A&A...696A..67S 2025A&A...696A..67S (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; H II regions ; Stars, distances
Keywords: Galaxy: general - Galaxy: kinematics and dynamics -
solar neighborhood - Galaxy: structure
Abstract:
The spiral structure of the Milky Way is not conclusive, even for the
disc regions in the solar neighbourhood. In particular, the arm-like
structures uncovered from the overdensity maps of evolved stars are
inconsistent with the commonly adopted spiral arm models based on
young objects.
We aim to reexamine the arm segments traced by young objects and
better understand the nearby spiral structure.
We identified the exciting stars of 459 HII regions and calculated
their parallax-based distances according to the Gaia DR3. Together
with other HII regions with spectrophotometric or parallax-based
distances in the literature, we used the largest ever sample of 572
HII regions with accurate distances to reveal the features shown in
their distributions projected onto the Galactic disc. We then compared
the results to the features traced by other young objects (high-mass
star-forming region masers, O-type stars, and young open clusters) and
evolved stars.
The structures outlined by different kinds of young objects do not
exhibit a significant deviation from each other. The distributions of
young objects are in agreement with three arm-like features emerging
in the overdensity map of evolved stars. In particular, the Local Arm
outlined by young objects follows an arm-like feature delineated by
evolved stars and probably spirals outwards towards the direction of
l∼240° in the third Galactic quadrant.
We conclude that the arm segments traced by young objects and evolved
stars are consistent with each other, at least in the solar
neighbourhood. In particular, the Local Arm delineated by young
objects is reinterpreted as an arm segment with a large pitch angle of
25.2°±2.0°, whose inner edge is in good agreement with the
recently discovered Radcliffe Wave.
Description:
We have produced the largest catalog of HII regions to date with
precise parallax-based distances based on Gaia DR3. Our results
provide critical insights into the nearby spiral structure and reveal
remarkable consistency in the spatial distribution between the young
and evolved objects. Table 2 listed parallax-based distances, velocity
measurements, and updated kinematic distances for the HII regions.
Table A1 listed the information of exciting stars which are used to
determine the distances of HII region. Our catalog is expected to
significantly advance the study of HII regions and their associated
molecular clouds by providing reliable distance estimates. Looking
ahead, we anticipate that future data releases, such as Gaia DR4 and
updated OB star catalogs, will further refine these distance
measurements and enhance our understanding of Galactic structure.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 141 459 HII regions with parallax distances based on
Gaia DR3
tablea1.dat 213 1382 Information of exciting stars
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- WISE HII region name given in Anderson et al.,
2014ApJS..212....1A 2014ApJS..212....1A, Cat. J/ApJS/212/1
(GLLL.lll+BB.bbb)
17 A1 --- Cl [CGKQ] Classification of HII region in Anderson
et al., 2014, Cat. J/ApJS/212/1 (1)
19- 22 I4 arcsec R Radius of HII region given by
Anderson et al., 2014, Cat. J/ApJS/212/1
24- 28 F5.2 kpc Dist Parallax-based distance of HII region
30- 33 F4.2 kpc e_Dist Lower uncertainty of parallax-based distance
35- 38 F4.2 kpc E_Dist Upper uncertainty of parallax-based distance
40- 45 F6.2 km/s VLSR ? LSR velocity of HII region (2)
46 A1 --- n_VLSR [;/]
47- 50 F4.1 km/s VLSR2 ? Second value of LSR velocity of HII region
52- 67 A16 --- Line ? Observed line to measure VLSR
69-110 A42 --- r_Line ? Reference for observed line
112-115 F4.2 kpc Dkin ? Updated kinematic distance
118-121 F4.2 kpc e_Dkin ? Lower uncertainty of kinematic distance
124-127 F4.2 kpc E_Dkin ? Upper uncertainty of kinematic distance
129-131 A3 --- Group Classification based on the robustness of the
estimated parallax distances (3)
133-141 A9 --- Remarks Note for the HII region with determined
parallax distances in literature (4)
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Note (1): Galactic HII region classification as follows:
K = Known
G = Group
C = Candidate
Q = radio Quiet
Note (2): The velocity information is primarily sourced from the latest catalog
by Anderson et al., 2014ApJS..212....1A 2014ApJS..212....1A and Hou et al., 2014A&A...569A.125H 2014A&A...569A.125H,
Cat. J/A+A/569/A125. A small portion of the data, particularly those with
updated RRL measurements, are obtained from Wenger et al.,
2021ApJS..254...36W 2021ApJS..254...36W, Cat. J/ApJS/254/36 (SHRDS) and Liu et al.,
2019ApJS..245...32L 2019ApJS..245...32L, Cat. J/ApJS/245/32 (SIGGMA).
Note (3): Classification as follows:
I = Group I: the HII region has more than one associated star and all the
stars present consistent distances
II = Group II: the HII region originally has two or more associated stars,
but only one is left after selection procedure
III = Group III: the HII region has only one associated star
Note (4): Remarks as follows:
M22 = the distance was given by Mendez-Delgado et al., 2022MNRAS.510.4436M 2022MNRAS.510.4436M,
based on Gaia DR3
maser = the distance is determined from the associated HMSFR maser
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- WISE HII region name given in in Anderson et al.,
2014ApJS..212....1A 2014ApJS..212....1A, Cat. J/ApJS/212/1
(GLLL.lll+BB.bbb)
17- 47 A31 --- Stars Exciting star name
49- 72 A24 --- SpType Spectral type of exciting star
74- 85 F12.8 deg GLON Coordinate of Galactic longitude
87- 98 F12.8 deg GLAT Coordinate of Galactic latitude
100-120 A21 --- Ref Reference for exciting star (1)
122-129 A8 --- --- [Gaia DR3]
131-149 I19 --- GaiaDR3 Gaia DR3 ID of matched source
151-157 F7.4 mas Plx Parallax of Gaia DR3
159-164 F6.4 mas e_Plx Standard error of parallax
166-171 F6.3 mas/yr pmRA Proper motion in right ascension direction
173-177 F5.3 mas/yr e_pmRA Standard error of proper motion in
right ascension direction
179-185 F7.3 mas/yr pmDE Proper motion in declination direction
187-191 F5.3 mas/yr e_pmDE Standard error of proper motion in
declination direction
193-197 F5.2 kpc Dist Adopted parallax distance (2)
200-203 F4.2 kpc e_Dist Lower uncertainty of distance (3)
205-208 F4.2 kpc E_Dist Upper uncertainty of distance (4)
210-213 A4 --- Remarks [rgeo ] Note on whether to use the median of
the geometric distance posterior (rgeo)
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Note (1): For references to the exciting stars, the Bibcode is from
Skiff et al., 2014, Cat. B/mk, while others are directly from Chen et al.,
2019MNRAS.487.1400C 2019MNRAS.487.1400C, Cat. J/MNRAS/487/1400, or SIMBAD.
Note (2): If 'rgeo' is marked in column Remarks, the median of the geometric
distance posterior (rmedgeo) given by Bailer-Jones et al.,
2021AJ....161..147B 2021AJ....161..147B, Cat. I/352, is adopted, otherwise, the median of the
photogeometric distance posterior (rimedpgotogeo) is adopted.
Note (3): Calculated by using the 16th percentile (r_lo) of the
geometric/photogeometric distance posterior: r_lo - r_med.
Note (4): Calculated by using the 84th percentile (r_hi) of the
geometric/photogeometric distance posterior: r_hi - r_med.
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Acknowledgements:
Xianjin Shen, shenxj(at)mail.ynu.edu.cn
(End) Patricia Vannier [CDS] 17-Mar-2025