J/A+A/693/A69 NGC 1261 and NGC 1904 potential members (Awad+, 2025)
S5: New insights from deep spectroscopic observations of the tidal tails
of the globular clusters NGC 1261 and NGC 1904.
Awad P., Li T.S., Erkal D., Peletier R.F., Bunte K., Koposov S.E.,
Li A., Balbinot E., Smith R., Canducci M., Tino P., Senkevich A.M.,
Cullinane L.R., Da Costa G.S., Ji A.P., Kuehn K., Lewis G.F.,
Pace A.B., Zucker D.B., Bland-Hawthorn J., Limberg G., Martell S.L.,
McKenzie M., Yang Y., Usman S.A.
<Astron. Astrophys. 693, A69 (2025)>
=2025A&A...693A..69A 2025A&A...693A..69A (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, globular ; Stars, halo ; Optical
Keywords: galaxy: halo - galaxy: globular clusters: individual -
stars: kinematics and dynamics
Abstract:
As globular clusters (GCs) orbit the Milky Way, their stars are
tidally stripped forming tidal tails that follow the orbit of the
cluster around the Galaxy. The morphology of these tails is complex
and shows correlations with the phase of orbit and the orbital angular
velocity, especially for GCs on eccentric orbits. Here, we focus on
two GCs, NGC 1261 and NGC 1904, that have potentially been accreted
alongside Gaia-Enceladus and that have shown signatures of having, in
addition to tidal tails, structures formed by distributions of
extra-tidal stars that are misaligned with the general direction of
the clusters' respective orbits. To provide an explanation for the
formation of these structures, we make use of spectroscopic
measurements from the Southern Stellar Stream Spectroscopic Survey
(S5) as well as proper motion measurements from Gaia's third data
release (DR3), and apply a Bayesian mixture modelling approach to
isolate high-probability member stars. We recover extra-tidal features
similar to those found in Shipp et al. (2018ApJ...862..114S 2018ApJ...862..114S)
surrounding each cluster. We conduct N-body simulations and compare
the expected spatial distribution and variation in the dynamical
parameters along the orbit with those of our potential member sample.
Furthermore, we use Dark Energy Camera (DECam) photometry to inspect
the distribution of the member stars in the color-magnitude diagram
(CMD). We find that potential members agree reasonably with the N-body
simulations and that the majority of them follow a simple stellar
population-like distribution in the CMD which is characteristic of
GCs. We link the extra-tidal features with their orbital properties
and find that the presence of the tails agrees well with the theory of
stellar stream formation through tidal disruption. In the case of NGC
1904, we clearly detect the tidal debris escaping the inner and outer
Lagrange points which are expected to be prominent when at or close to
the apocenter of its orbit. Our analysis allows for further
exploration of other GCs in the Milky Way that exhibit similar
extra-tidal features.
Description:
Observations of the GCs NGC 1261 and NGC were taken as part of S5
using the Two-degree Field (2dF) fiber positioner coupled with the
dual-arm AAOmega spectrograph on the 3.9-m Anglo-Australian Telescope
(AAT). Proper motions of each target are taken either from Gaia DR2
(for observations taken before Dec 2020) or Gaia DR3. Photometric
magnitudes are taken from the Dark Energy Survey (DES DR2). The
refinement and selection procedure to identify the clusters' potential
members are explained in the paper. as part of a Bayesian mixture
modelling approach which allows for the calculation of a membership
probability of each star in the sample. A threshold is then enforced
on the posterior membership probability to isolate the most probable
members of each cluster.
Objects:
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RA (2000) DE Designation(s)
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03 12 16.21 -55 12 58.4 NGC 1261, [KPS2012] MWSC 0263
05 24 10.59 -24 31 27.3 NGC 1904, [KPS2012] MWSC 0528
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
ngc1261.dat 108 115 Potential members of NGC 1261 (table B1)
ngc1904.dat 108 186 Potential members of NGC 1904 (table B2)
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
Byte-by-byte Description of file: ngc1261.dat ngc1904.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR3 Gaia star identifier
21- 26 F6.3 deg RAdeg Gaia right ascension (ICRS) at Ep=2016.0
28- 34 F7.3 deg DEdeg Gaia declination (ICRS) at Ep=2016.0
36- 40 F5.3 mas/yr pmRA Gaia proper motion in RA
42- 47 F6.3 mas/yr pmDE Gaia proper motion in DE
49- 53 F5.3 mag Bp-Rp Gaia color (GBP-GRP)
55- 60 F6.3 mag Gmag Gaia magnitude
62- 67 F6.3 mag gmag DECam g band magnitude
69- 74 F6.3 mag g-r DECam g-r color
76- 82 F7.3 km/s RV S5 radial velocity
84- 89 F6.3 km/s e_RV S5 error on radial velocity
91- 96 F6.3 [-] [Fe/H] S5 [Fe/H] metallicity
98-102 F5.3 [-] e_[Fe/H] S5 [Fe/H] error on the metallicity
104-108 F5.3 --- Pmemb Membership probability
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Acknowledgements:
Petra Awad, p.awad(at)rug.nl,
apteyn Astronomical Institute, The Netherlands
(End) Petra Awad [Kapteyn Astron. Inst.], Patricia Vannier [CDS] 20-Nov-2024