n-body simulations of double-barred (s2b) galaxies from cold...
TRANSCRIPT
Min Du (杜敏 )
Juntai Shen(沈俊太),V. P. Debattista (UClan, UK)
N-body Simulations of Double-barred (S2B) Galaxies from Cold Inner Disks
The 7th Korean Astrophysics Workshop
on Dynamics of Disk Galaxies
Erwin (2009): NGC 2950 2
Observational properties of
Double-barred galaxies
• An inner bar (secondary bar) embedded in an outer bar (primary bar)
• Common, exist in >25% early-type barred galaxies (S0-Sa) • Could be as large as 40% • Erwin & Sparke (2002); Laine et al. (2002)
• Appear long-lived • Stellar feature (NIR image)
• Not just dust and gas
• Random orientation between two bars • independent pattern rotation speeds • Buta & Crocker (1993); Corsini et al. (2003);
Emsellem et al. (2006); Fathi et al. (2007b, 2009)
• IFU observations: 𝝈 − 𝒉𝒐𝒍𝒍𝒐𝒘𝒔 • Lorenzo-Cáceres et al. (2008, 2009, 2011)
3
3
Simulations of Double-
barred galaxies
Gas Short-lived (less than 1Gyr) Gas dominated Friedli & Martinet (1993); Heller &
Shlosman (2001); Shlosman & Heller
(2002); Englmaier & Shlosman (2004)
Purely collisionless N-body simulations Ad hoc initial conditions Debattista & Shen (2007); Shen &
Debattista (2009)
Also Rautiainen & Salo (1999);
Rautiainen et al. (2002)
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Shen & Debattista (2009)
I. N-body simulation of S2Bs: initial condition
• Disk scale length 2.5kpc, time unit is 12.3Myr, 𝑴𝒅 =𝟑. 𝟒𝟓 × 𝟏𝟎𝟏𝟎𝑴⊙, 4 million particles
• An sufficiently massive exponential live disk, rigid halo
• No rotating pre-existing bulge
• Dynamical cold central region + hot outer disk
Cold inner disk
Du, Shen & Debattista, in preparation
Hot outer disk: delay
the formation of outer
bar
T=0 T=100 T=400 T=800
I. N-body simulation of S2Bs: formation stage
• The inner bar forms faster from independent bar instabilities.
• The outer bar forms later and slower.
• Inner bar can not extend to its co-rotation radius, “slow” bar.
Du, Shen & Debattista, in preparation
CR
CR of inner
bar
I. N-body simulation of S2Bs: oscillating properties
Different rotation speeds
𝑻𝒊𝒃𝒂𝒓 = 𝟏𝟐. 𝟖, 𝐓𝒐𝒃𝒂𝒓 = 𝟑𝟓. 𝟐 𝛀𝒊𝒃𝒂𝒓
𝛀𝒐𝒃𝒂𝒓=
𝑻𝒐𝒃𝒂𝒓
𝑻𝒊𝒃𝒂𝒓~𝟐. 𝟕𝟓
• Fathi et al. (2007b, 2009)
Oscillating
• Perpendicular ….
• Parallel ---- • Maciejewski & Athanassoula
(2007); Debattista & Shen
(2007)
Amplitude of inner bar
Amplitude of outer bar
Du, Shen & Debattista, in preparation
• The inner bar is
parallel to the
LON.
II. Velocity dispersion maps: 𝝈 − 𝒉𝒖𝒎𝒑𝒔
• The inner bar is
perpendicular
to the LON.
• Small 𝒊, • 𝝈 − 𝒉𝒖𝒎𝒑𝒔 are
beside the inner
bars.
• Large 𝒊, • 𝝈 − 𝒉𝒖𝒎𝒑𝒔 are
located along
the disk minor
axis.
II. Velocity dispersion maps: 𝝈 − 𝒉𝒖𝒎𝒑𝒔
• 𝝈 − 𝒉𝒐𝒍𝒍𝒐𝒘𝒔 of velocity dispersion from SAURON observations.
III. IFU observations: 𝝈 − 𝒉𝒐𝒍𝒍𝒐𝒘𝒔 at small 𝒊
Lorenzo-Cáceres et al. (2008)
𝒉𝒖𝒎𝒑
III. IFU observations: “dumb-bells” at large 𝒊
Falcon-Barroso et al. (2006)
An edge-on field galaxy
24 nearly edge-on galaxies
6 galaxies show clear “dumb-bells”, 25%
along the minor axes of disk
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IV. Kinematic properties in slices
Cutting slices:
• To compare with different models
• To figure out much more details
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IV. Kinematic properties: slices from S2B model
𝒙
𝒚
𝒛
y = 0 y = 0.1 y = 0.2 y = 0.3 y = 0.4
Slice
𝝈𝒙
𝝈𝒚
𝝈𝒛
4.0
2.0 The 𝝈 − 𝒉𝒖𝒎𝒑𝒔 are tightly
coupled with the inner bar.
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IV. Kinematic properties: slices from cold inner disk
model
𝒙
𝒚
𝒛
y = 0kpc y = 0.2kpc y = 0.5kpc y = 1.0kpc y = 1.7kpc
Slice
𝝈𝒙
𝝈𝒚
𝝈𝒛
4.0
2.0 Containing a cold inner disk in
the central region
Cole et al. in progress
The cold inner disk can evoke independent bar
instability to form the inner bar of double-barred
galaxies.
• No need for gas and pre-existing rotating bulge
The inner bar structures have distinct kinematic
properties: 𝝈 − 𝒉𝒖𝒎𝒑𝒔
• A possible mechanism to partially explain
𝝈 − 𝒉𝒐𝒍𝒍𝒐𝒘𝒔 and dumb-bells
Ongoing work:
• Comparing with Atlas3D data
• Comparing with cold disk model, single-
barred-model, nuclear-barred model
Thank you!
Comments and advice
are welcome.