J/AJ/162/42 Milky Way Age-Metallicity-orbital energy relation (Woody+, 2021)
The Age-Metallicity-Specific orbital energy relation for the Milky Way's
globular cluster system confirms the importance of accretion for its formation.
Woody T., Schlaufman K.C.
<Astron. J., 162, 42-42 (2021)>
=2021AJ....162...42W 2021AJ....162...42W (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular; Milky Way; Parallaxes, trigonometric;
Proper motions; Radial velocities; Abundances, [Fe/H]
Keywords: Galaxy formation; Globular star clusters; Milky Way dynamics
the Milky Way; Milky Way formation; Milky Way stellar halo
Abstract:
Globular clusters can form inside their host galaxies at high redshift
when gas densities are higher and gas-rich mergers are common. They
can also form inside lower-mass galaxies that have since been accreted
and tidally disrupted, leaving their globular cluster complement bound
to higher-mass halos. We argue that the age-metallicity-specific
orbital energy relation in a galaxy's globular cluster system can be
used to identify its origin. Gas-rich mergers should produce tightly
bound systems in which metal-rich clusters are younger than metal-poor
clusters. Globular clusters formed in massive disks and then scattered
into a halo should have no relationship between age and specific
orbital energy. Accreted globular clusters should produce weakly bound
systems in which age and metallicity are correlated with eachother but
inversely correlated with specific orbital energy. We use precise
relative ages, self-consistent metallicities, and space-based proper
motion-informed orbits to show that the Milky Way's metal-poor
globular cluster system lies in a plane in age-metallicity-specific
orbital energy space. We find that relatively young or metal-poor
globular clusters are weakly bound to the Milky Way, while relatively
old or metal-rich globular clusters are tightly bound to the Galaxy.
While metal-rich globular clusters may be formed either in situ or ex
situ, our results suggest that metal-poor clusters are formed outside
of the Milky Way in now-disrupted dwarf galaxies. We predict that this
relationship between age, metallicity, and specific orbital energy in
a L* galaxy's globular cluster system is a natural outcome of galaxy
formation in a ΛCDM universe.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 128 57 Input astrometric, distance, and radial
velocity data
table2.dat 89 57 Age, metallicity, and specific orbital energy
inferences
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See also:
VII/195 : Globular Clusters in the Milky Way (Harris, 1996)
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/A+AS/121/95 : Giant stars abundances in 24 clusters (Carretta+ 1997)
J/PASP/109/883 : Globular metallicity scale. I. (Rutledge+ 1997)
J/AJ/118/1671 : Fornax cluster 4 VI photometry (Buonanno+, 1999)
J/A+AS/141/371 : Low-mass stars evoluti. tracks & isochrones (Girardi+, 2000)
J/AJ/127/1545 : Abundance ratios of 4 stars in Pal 12 (Cohen+, 2004)
J/A+A/465/815 : Abundances of Sgr dSph stars (Sbordone+, 2007)
J/AJ/136/614 : Arp 2 and Ter 8 red giants equivalent widths (Mottini+, 2008)
J/A+A/520/A95 : Abundances of red giants in M54 and Sgr dSph (Carretta+, 2010)
J/ApJ/670/346 : Mgiant stars in the Sagittarius dwarf galaxy. V. (Chou+, 2007)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/A+A/561/A87 : FLAMES observations of Terzan 8 (Carretta+, 2014)
J/A+A/616/A12 : Gaia DR2 sources in GC and dSph (Gaia Collaboration+, 2018)
J/MNRAS/482/5138 : Galactic GC mean pm & velocities (Baumgardt+, 2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- NGC NGC identifier
9- 17 A9 --- Name Common name
19- 28 F10.6 deg RAdeg [6/327] Right Ascension (J2000) (1)
30- 39 F10.6 deg DEdeg [-73/44] Declination (J2000) (1)
41- 48 F8.4 mas/yr pmRA [-13/10] Proper motion along RA (1)
50- 55 F6.4 mas/yr e_pmRA [0.001/0.08] Uncertainty in pmRA (1)
57- 64 F8.4 mas/yr pmDE [-19/2] Proper motion along DE (1)
66- 71 F6.4 mas/yr e_pmDE [0.001/0.06] Uncertainty in pmDE (1)
73- 78 F6.4 mas plx [0.006/0.51]? Parallax (1)
80- 85 F6.4 mas e_plx [0.0002/0.007]? Uncertainty in plx (1)
87- 91 F5.2 --- sigma1 [-0.32/0.3]? Covariance between pmRA & pmDE
93- 97 F5.2 --- sigma2 [-0.38/0.15]? Covariance between pmRA & plx
99-103 F5.2 --- sigma3 [-0.27/0.18]? Covariance between pmDE & plx
105-108 F4.1 kpc Dist [2.2/27.6] Distance (2)
110-112 F3.1 kpc E_Dist [0.1/0.6] Upper uncertainty in D (2)
114-116 F3.1 kpc e_Dist [0.1/0.6] Lower uncertainty in D (2)
118-123 F6.1 km/s RVel [-412/494] Radial velocity (2)
125-128 F4.1 km/s e_RVel [0.1/15] Uncertainty in RVel (2)
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Note (1): While most cluster astrometric data come from
Gaia Collaboration+, 2018, J/A+A/616/A12, the data for NGC6584 and
NGC6723 come from Baumgardt+, 2019, J/MNRAS/482/5138 while the data
for NGC1261, NGC4147, NGC6101, Terzan7, Arp2, Terzan8, NGC6934, and
Pal12 come from Sohn+, 2018ApJ...862...52S 2018ApJ...862...52S.
Note (2): Distance and radial velocity data come from the December 2010
revision of the Harris, 1996, VII/195 compilation.
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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- 7 A7 --- NGC NGC identifier
9- 17 A9 --- Name Common name
19- 22 F4.2 --- Age [0.57/1.09] Normalized age (1)
24- 27 F4.2 --- e_Age [0.02/0.2] Uncertainty in tau
29- 33 F5.2 [Sun] [M/H] [-1.98/-0.42] Metallicity (2)
35- 38 F4.2 [Sun] e_[M/H] [0.05] Uncertainty in [M/H]
40- 45 F6.2 [10+4km2/s2] SOE [-11.4/-3.1] MWPotential2014 specific
orbital energy
47- 50 F4.2 [10+4km2/s2] E_SOE [0.02/0.9] Upper uncertainty in SOE
52- 55 F4.2 [10+4km2/s2] e_SOE [0.01/0.8] Lower uncertainty in SOE
57- 62 F6.2 [10+4km2/s2] SOEscl [-16.2/-7.21] Scaled MWPotential2014
specific orbital energy (3)
64- 67 F4.2 [10+4km2/s2] E_SOEscl [0.02/0.97] Upper uncertainty in SOEscl
69- 72 F4.2 [10+4km2/s2] e_SOEscl [0.01/0.73] Lower uncertainty in SOEscl
74- 79 F6.2 [10+4km2/s2] SOEMc17 [-24.6/-8.3] Mc17 specific orbital energy
(4)
81- 84 F4.2 [10+4km2/s2] E_SOEMc17 [0.04/0.92] Upper uncertainty in SOMc17
86- 89 F4.2 [10+4km2/s2] e_SOEMc17 [0.04/0.91] Lower uncertainty in SOMc17
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Note (1): Normalized age=age/12.8Gyr from Marin-Franch+, 2009ApJ...694.1498M 2009ApJ...694.1498M
calculated using the Dartmouth Stellar Evolution Program assuming
the metallicities presented in Rutledge+, 1997PASP..109..907R 1997PASP..109..907R, and
1997, J/PASP/109/883 on the Carretta & Gratton, 1997, J/A+AS/121/95
scale.
Note (2): From Rutledge+, 1997PASP..109..907R 1997PASP..109..907R, and 1997, J/PASP/109/883 on the
Carretta & Gratton, 1997, J/A+AS/121/95 scale.
Note (3): From Bovy+, 2015ApJ...216...29B 2015ApJ...216...29B.
Note (4): From McMillan+, 2017MNRAS.465...76M 2017MNRAS.465...76M.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 15-Nov-2021