Bar-driven Evolution and Instability of Self-gravitating Disks

Chi Yuan

Institute of Astronomy and Astrophysics

Academia Sinica, Taipei, Taiwan, ROC

David C.C. Yen, Yi-Hsin Liu, Chao-Chin Yang

Three Observational Facts

• Starburst rings

• Dense circumnuclear molecular disks

• Gas depression central regions

Starburst Rings

NGC1512 NGC6782NGC4313

Circumnuclear Disk in ngc1068

Center of M51

The 3-kpc Arm

Gas Distribution in the Milky Way

CO and HCN in the Milky Way

Distribution of Gas in Galactic Disks

Diamond-shaped Ring in NGC6782

NGC 1068

9.5 arcmin

• Type : Sb / AGN

• Distance : 14.4 Mpc

( H0 = 75 km s-1 Mpc-1 )

1 arcsec = 74 pc

The Antares Code

• A high-performance CFD-MHD code for astrophysics

• It is a second-order Godunov code (or codes) equipped with exact Riemann solver and the balance law correction. (2-D)

• It is also featured with the fft Poisson solver, to include the self-gravitation of the disk, and with characteristics decomposition on the boundary, to guarantee the true radiation (non-reflecting) boundary conditions.

大火程序

Governing Equations

,0v

t

~,

,

,4

,Iv v v

2

02

bd0

d2

2

PaP

r

zG

at

Schematic Picture of a BarIn Numerical Simulations

Nearly Flat Rotation Curve

01.0,)( 2

1

0

r

rvv

OLROILR

Cases of Double Resonances: OLR-OILR

Double Ring Feature

Elmegreen Rotation Curve

1.0,01

0 , AB

AB rr

rvv

Cases for a Single OLR

Evolution of Self-gravitating Disks

Double Rings and Central Spirals

Double Rings and Central Spirals

Q-value for Self-gravitating Disk

Onset of Instability

G

aQ

Disk Instability

G

aQ

m

Conclusions• Starburst rings are the results of a gaseous

disk responding to a rotating bar potential. But, there are many possibilities.

• A fast nuclear bar like NGC1068 or the Milky Way (OLR and OILR)

• A fast nuclear bar like possibly NGC4313 (OLR).

Conclusions cont.

• A double ring due slow bar like NGC6278 (OLR-OILR).

• A fast bar in the center solves the starburst ring, dense circumnuclear molecular disk, and depletion of gas in between all together.• Self-gravitation plays an important role. It leads to instability, chaos, and star formation•Toomre’s criterion Q=1 works extremely well.