J/A+A/689/A232 Galactic globular clusters shapes (Cruz Reyes+, 2024)
Relation between the geometric shape and rotation of Galactic globular clusters.
Cruz Reyes M., Anderson R.I.
<Astron. Astrophys. 689, A232 (2024)>
=2024A&A...689A.232C 2024A&A...689A.232C (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, globular ; Morphology ; Optical
Keywords: galaxies: star clusters: general -
galaxies: star clusters: individual: NGC 104 -
galaxies: star clusters: individual: NGC 5139 -
galaxies: star clusters: individual: NGC 6341
Abstract:
We homogeneously measured the elliptical shapes of 163 Globular
Clusters (GCs) using the on-sky distribution of their cluster members
and the third data release of the ESA mission Gaia (DR3). The
astrometry enables the differentiation of stars within clusters from
those in the field. This feature is particularly valuable for clusters
located in densely populated areas of the sky, where the conventional
methods for measuring the geometry of the GCs are not applicable. The
median axial ratio of our full sample is <b/a≥0.935+0.033-0.090,
and 0.986+0.009-0.004 for the subset of 11 GCs previously studied
based on HST imaging. We investigated whether the minor axis of the
ellipses can be interpreted as a pseudo-rotation axis by comparing it
to measurements of cluster rotation. Using the radial velocities from
Gaia, we detected rotation for three clusters, NGC 5139, NGC 104, and
NGC 6341, and observed alignment between the pseudo-rotation axis and
the 2D projection of the real rotation axis. To expand the set of
clusters for which rotation has been detected, we analyzed multiple
literature references. Depending on the reference used for comparison,
we observed alignment in between 76% to 100% of the clusters. The lack
of alignment observed in some clusters may be linked to the fact that
some studies analyze different scales, since multiple studies have
demonstrated that the orientation of rotation varies with the distance
from the center. We estimate that the next Gaia release will increase
the number of stars with radial velocities in GCs from ∼10000 in Gaia
DR3 to ∼55000 in Gaia DR4. This will enable the measurement of
rotation and ellipticities at identical angular scales for additional
clusters, which will help to clarify whether the previously mentioned
alignment occurs across all clusters.
Description:
The sample of clusters and their members used in this study for our
analysis is exactly the same as was used in Paper I (Cruz Reyes et al.
2024A&A...684A.173C 2024A&A...684A.173C, Cat. J/A+A/684/A173) to measure the ellipticity
of GCs and to identify their population of RR Lyrae stars.
We compile the cluster parameters discussed in this paper, covering
ellipticities in Table A.1 and position angles in Table A.3.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 92 163 Ellipticity of globular clusters
tablea3.dat 76 163 Position angles
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See also:
J/A+A/671/A106 : Galactic globular cluster stars RVs (Martens+, 2023)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- Cluster Cluster name
17- 21 F5.3 --- e Ellipticity determined in this study
23- 27 F5.3 --- e_e Uncertainty in the ellipticity
29- 32 F4.2 --- eC10 ? Ellipticity determined by
Chen & Chen, 2010ApJ...721.1790C 2010ApJ...721.1790C
34- 37 F4.2 --- e_eC10 ? Uncertainty in the Chen & Chen,
2010ApJ...721.1790C 2010ApJ...721.1790C ellipticity
39- 42 F4.2 --- eH10 ? Ellipticity determined by
Belokurov et al., 2024MNRAS.528.3198B 2024MNRAS.528.3198B
44- 48 F5.3 --- eF14 ? Ellipticity determined by
Fabricius et al. 2014ApJ...787L..26F 2014ApJ...787L..26F
50- 54 F5.3 --- e_eF14 ? Uncertainty in the Fabricius et al.
2014ApJ...787L..26F 2014ApJ...787L..26F ellipticity
56- 60 F5.3 deg theta Angular scale used to determine the
PCA parameters
62- 67 I6 --- NPCA Number of stars used to determine the
PCA parameters
69- 73 I5 --- NM23 ? Number of stars used by Martens et al.,
2023A&A...671A.106M 2023A&A...671A.106M, Cat. J/A+A/671/A106
75- 79 F5.3 deg thetaM23 ? Angular scale used by Martens et al.,
2023A&A...671A.106M 2023A&A...671A.106M, Cat. J/A+A/671/A106 to
measure rotation
81- 86 I6 --- NF14 ? Number of stars used by
Fabricius et al. 2014ApJ...787L..26F 2014ApJ...787L..26F
88- 92 F5.3 deg thetaF14 ? Angular scale used by Fabricius et al.
2014ApJ...787L..26F 2014ApJ...787L..26F to determine the
ellipticities
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Byte-by-byte Description of file: tablea3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- Cluster Cluster name
17- 21 F5.1 deg PA Position angle of the PCA ellipse
23- 26 F4.1 deg e_PA Uncertainty in the position angle
28- 32 F5.1 deg PAkF14 ? Kinematic position angle of
Fabricius et al. 2014ApJ...787L..26F 2014ApJ...787L..26F
34- 37 F4.1 deg e_PAkF14 ? Uncertainty in the kinematic position angle
of Fabricius et al. 2014ApJ...787L..26F 2014ApJ...787L..26F
39- 43 F5.1 deg PAphF14 ? Photometric position angle of
Fabricius et al. 2014ApJ...787L..26F 2014ApJ...787L..26F
45- 49 F5.1 deg e_PAphF14 ? Uncertainty in the photometric position
angle of Fabricius et al. 2014ApJ...787L..26F 2014ApJ...787L..26F
51- 55 F5.1 deg PAS19 ? Position angle of
Sollima et al., 2019MNRAS.485.1460S 2019MNRAS.485.1460S
57- 60 F4.1 deg e_PAS19 ? Uncertainty in the position angle of
Sollima et al., 2019MNRAS.485.1460S 2019MNRAS.485.1460S
62- 66 F5.1 deg PAM23 ? Position angle of Martens et al.,
2023A&A...671A.106M 2023A&A...671A.106M, Cat. J/A+A/671/A106
68- 71 F4.1 deg E_PAM23 ? Upper value of the uncertainty in the
position angle of Martens et al.,
2023A&A...671A.106M 2023A&A...671A.106M, Cat. J/A+A/671/A106
73- 76 F4.1 deg e_PAM23 ? Lower value of the uncertainty in the
position angle of Martens et al.,
2023A&A...671A.106M 2023A&A...671A.106M, Cat. J/A+A/671/A106
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Acknowledgements:
Mauricio Cruz Reyes, mauricio.cruz(at)correo.nucleares.unam.mx
(End) Patricia Vannier [CDS] 01-Aug-2024