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)

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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.