victor p. debattista - inaf · 2.7-m hjs telescope 1.7’ x 1.7’ fov. rebin data to s/n ~45...
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Victor P. Debattista R. Roškar, S. Loebman, P. Yoachim, D. Radburn-Smith, A. Clarke,
T. Quinn, J. Wadsley, Z. Ivezic, J. Dalcanton
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σ
B-V Dehnen & Binney 1998
ΔR ≈ √2 σR/κ ≈ 1.3 kpc
Rform Rfinal
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Negligible heating associated with the migration
Full Near circular ∆L
L
Radius
σR
ΔJR = (Ωp - Ω) ΔL/κ
ΔE = Ωp ΔL
Sellwood & Binney 2002
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60% truncated 10% pure expo.
Pohlen & Trujillo 2006
van der Kruit 1979
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Structural properties of break consistent with those observed
Gas+SF+feedback simulations
Disk (to break radius) grows from the inside out
10 kpc = 2.6 Rd
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Roškar et al. 2008a
Very few of the stars beyond the break actually born there
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Steady heating ~ t0.53 Ve
locity
Dispe
rsion
[km/s
]
Age [Gyr]
Data: Geneva-Copenhagen survey (Holmberg 2009)
Age [Gyr]Age [Gyr]
Simulation
Steady heating ~ t0.35
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Inward migrators ahead of the spiral while outward migrators are behind it
Roškar+ 12
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HST star count profiles
Rbr the same for all pops
Age
NGC 4244
Possible interpretations
Break just formed
Break has never changed
Radial migration forces stars to adopt a common break radius
de Jong+ 2007
simulation
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Outer Disk Stellar Pops Migration is basically a random walk, so older stars get to larger distance from formation
Expect the mean age of disk stars to increase beyond the break
The variation of outer disk scale-length for different age stellar bins constrain migration rates
Mea
n ag
e
Intermediate Young
Old
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NGC 7793
Radburn-Smith+ 12
Break radius
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NGC 7793
Radburn-Smith+ 12
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NGC 6155
Break at 34” (Pohlen & Trujillo 2006)
Data using VIRUS-P on 2.7-m HJS telescope 1.7’ x 1.7’ fov. Rebin data to S/N ~45 beyond break
Fit the spectra using GANDALF (Sarzi et al. 2006) assuming exponential SFH and varying metallicity
Yoachim+ 10
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Metallicity Gradients
Metallicity gradient of old stars does not reflect that of gas from which they formed
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SFH usually obtained by considering stars within an annulus or small region
Drastic difference between ‘observed’ and ‘real’ SFH due to radial migration
(NGC 300 mosaic from the ANGST HST survey, courtesy of Stephanie Gogarten)
Inferred
Roškar et al. 08b
Measured
Actual
Implications for Galactic Archaeology
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Rform
Roškar+ 08 Schoenrich & Binney 09ab
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Migration can give rise to a thick disc with density, kinematic, metallicity and abundance patterns not inconsistent with the observed
Loebman+ 11 Roškar+ 13
Ruchti+ 11
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Bland-Hawthorn+ 10
Disrupting Clusters
Fujii & Baba 12
See also poster by Martinez-Barbosa
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In 2 Gyr the cluster goes from 7.4 kpc to 10.6 kpc
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Other Migration Mechanism: Bar Driven
Final
Initial
Face-on azimuthally averaged profile
Initial disk
Inner exp Break radius
Outer exp
Edge-on profile
Debattista+ 06 (also Foyle+ 08, Minchev & Famaey 10)
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Rbr
Brunetti+ 11
Munoz-Mateo+S4G 13
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Ask the Star Clusters M
ean
age
Star clusters are an ideal probe of this age upturn in the Milky Way.
The upturn is predicted to occur at the break. This will hold for disc clusters but not for any clusters forming in the warp (migration does not lead to stars leaving the plane of the disc)
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Contrary to decades of assumption, a mechanism for mixing stars in Galactic radius without heating exists: scattering at corotation off transient spirals. This can substantially alter stellar populations in disks.
A large fraction of stars in outer disks probably formed at smaller radii and migrated outwards. There is a growing body of evidence that disks get increasingly old outwards of the break.
Migration may also be the explanation for at least part of the thick disk. Many of the properties and trends of the thick disk can be qualitatively matched by migration.
(Open) star clusters should experience migration in the same way as stars, but those moving inwards may be more prone to disruption while those moving outwards are more likely to survive. Clusters provide a very good way to trace the migration history of the outer disc.
Conclusions
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Nuclear Clusters in Galaxies and the Role of the Environment Lorentz Center June 30 – July 4, 2014