2nd Regional Meeting of Extragalactic AstronomyCórdoba, Argentina, November 30th - December 5th 1987.

Counter-rotating Stellar Components in Simulated Disk Galaxies

Mario Abadi Observatorio Astronómico de Córdoba & CONICET

andDavid Algorry, Julio Navarro, Laura Sales, Matthias

Steinmetz, Franziska Piontek

Galaxies in the Dark WorkshopAugust 1st-4th 2011Cafayate, Argentina

OutlineObservational ResultsCosmological Numerical SimulationsAnalysis Preliminary Conclusions

Counter-rotating Car

Observational Results

There is observational evidence of counter-rotation in early type spiral galaxies

1) NGC 4550 an E7/S0 galaxy (Rix et al 1992)2) Counter-rotating stars in the disk of the SAB galaxy NGC 7217

(Merrifield & Kuijken 1994)3) Counter-rotating Stellar Disks in Early-Type (Sa) Spirals: NGC

3593 (Bertola et al 1996)

NGC 7217 NGC 3593

NGC 4550• Line of sight velocity distribution along the

major axis shows striking bimodality. This bimodality indicates the presence of two disk components, photometrically inseparable, but counterstreaming at projected velocities of -100km/s and +150km/s (Rix et al 1992)

NGC 5728

• NGC 5728 is an spiral barred Sb galaxy with a counter-rotating central component (Prada & Gutierrez 1999)

• Dynamical instabilities, retrograde accretion of gas (or satellites) are proposed to explain this component.

Line of Sight Velocity

NGC 7331Prada et al (1996) found that the line-of-sight velocity distribution has two distinct peaks and can be decomposed into a fast-rotating component with v/σ ~ 3, and a slower rotating, retrograde component with v/σ ~1–1.5. The radial surface brightness profile of the counter-rotating component follows that of the bulge, while the fast-rotating component follows the disk.

Numerical Simulations

• Zoom-in Cosmological Numerical Simulations in the λCDM model (Piontek & Steinmetz 2009)

• Gravitation, Hydrodynamics, Cooling, Star Formation, Feedback

• Temporal evolution from redshift z=50 to z=0• 7 different galactic halos • 1.5<Mvir/(1011 M⊙)<13.8

• Gas: mpar=4.9×105 M⊙ and ε=1.0 kpc

• Dark: mpar=2.3×106 M⊙ and ε=1.4 kpc

Simulated Galaxies

1011 M

60 kpc

1) Mvir=1.50 2) Mvir=2.89 3) Mvir=4.05 4) Mvir=5.49

5) Mvir=6.61 6) Mvir=7.93 7) Mvir=13.79 Piontek & Steinmetz 2009

Virial masses in 1011 M⊙

Line of Sight Velocity Distribution

2 kpc slit

d/kpc=-10,-6,-4,-2,+2,+4,+6,+10

d

Line of Sight Velocity

d=-10kpcd=- 6kpcd=- 4kpcd=- 2kpcd=+ 2kpcd=+ 4kpcd=+ 6kpcd=+10kpc

Circularity Distribution

Num

ber

C=Jz/Jcirc

C=-1 C=+1Counter-rotating star Co-rotating stars

Circularity: ratio between the z-component of the angular momentum Jz and the angular momentum of the circular orbit with the same binding energy Jcirc(E)

This distribution for all star particles inside a sphere of radius 30 kpc has 2 peaks: one at c=+1.0 and the other one at c=-0.5

Energy vs Circularity

Binding Energy(Increasing Radius )

Coun

ter-

rota

ting

Ci

rcul

arity

C

o-ro

tatin

g

Two well defined regions that help to define two different structures:

Co-rotating

Counter-rotating

Edge-On Face-On

Co and Counter Rotating Stars

X

YZ

Y

Velocity Field

Co-rotating Disk

X

YZ

Y

Counter-rotating Bar • (a,b,c)=(1.0,0.5,0.3)τ=0.74

X

YZ

Y

Mass Profile

Gas

Stars

Halo

Total

Star Formation Time Distribution

Old Young

Star Formation Time Distribution

Old Young

DiskBar

Stars in the bar are old stars in the disk are young

Star Formation Time Distribution

Old Young

DiskBar

Stars in the bar are old stars in the disk are young

z=0z=0

z=0z=0

Angular Momentum EvolutionDisk =Gas + Stars

Barra=Gas + Stars

Jx

Jy

Jz

Jtot

Time/Gyr

Line of Sight Velocity Distribution

2 kpc slit

d/kpc=-10,-6,-4,-2,+2,+4,+6,+10

d

Line of Sight Velocity

d=+10kpcd=+ 6kpcd=+ 4kpcd=+ 3kpcd=+ 2kpcd=- 2kpcd=- 3kpcd=- 4kpcd=- 6kpcd=-10kpc

Circularity Distribution

Num

ber

C=Jz/Jcirc

C=-1 C=+1Counter-rotating star Co-rotating stars

Circularity: ratio between the z-component of the angular momentum Jz and the angular momentum of the circular orbit with the same binding energy Jcirc(E)

This distribution for all star particles inside a sphere of radius 30 kpc has 2 peaks: one at c=+1.0 and the other one at c=-0.8

Energy vs Circularity

Binding Energy(Increasing Radius )

Circ

ular

ity

Two well defined regions that help to define two different structures:

Co-rotating

Counter-rotating

Edge-On Face-On

Co and Counter Rotating Stars

Co-rotating Disk

Counter-rotating Ring• (a,b,c)=(1.0,1.0,0.3) τ=0.04

Star Formation Time Distribution

Old Young

Star Formation Time Distribution

Old Young

Ring Disk

Stars in the ring are old stars in the disk are young

Numerical Simulations

• Each halo simulated with 3 different Feedback models: Standard, All in-Standard and All in-Low Kinetic

• All in=standard feedback model in combination with additional physical processes like a UV background, kinetic feedback, a delayed energy deposition as expected for type Ia supernovae, mass return

Circularity vs Feedback

Circularity C=Jz/Jcirc

Ring

Gal

axy

Bare

d G

alax

y

Standard

Circularity vs Feedback

Circularity C=Jz/Jcirc

Ring

Gal

axy

Bare

d G

alax

y

Standard All in-Standard

Circularity vs Feedback

Circularity C=Jz/Jcirc

Ring

Gal

axy

Bare

d G

alax

y

Standard All in-Low KineticAll in-Standard

Simulated Galaxies

1011 M

60 kpc

1) Mvir=1.50 2) Mvir=2.89 3) Mvir=4.05 4) Mvir=5.49

5) Mvir=6.61 6) Mvir=7.93 7) Mvir=13.79

λ=0.040 λ=0.029 λ=0.019

λ=0.016 λ=0.026 λ=0.058

λ=0.034

Piontek & Steinmetz 2009

Virial masses in 1011 M⊙

Preliminary Conclusions

• Simulated galaxies show counter-rotating stellar components

• Stars in the counter-rotating components seems to be old and could have bar/ring shape

• Seems to be related to low spin halos

Observational Results

• In the last 2 decades, or so, there has been increasing evidence of kinematic peculiarities in elliptical galaxies that may be explained by a counter-rotating nuclear disk. (e.g. Franx & Illingworth 1988, Bender et al 1994, Rix & White 1992)

IC 4889