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Back to the Galaxy II KITP – slide 1
Warps and Wiggles
Martin D. WeinbergUMass Astronomy
September 30, 2008
Motivation
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 2
■ History of a galaxy is critical in determining its present state
◆ Satellite decay and disruption
◆ Bombardment by substructure
◆ “Cold-mode” streams, “hot-mode” infall, fountains . . .
■ Outer Galaxy sensitive to the transition between thebaryonic- and dark-matter-domination
◆ Properties of the dark matter halo
◆ MOND (?)
Motivation
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 2
■ History of a galaxy is critical in determining its present state
◆ Satellite decay and disruption
◆ Bombardment by substructure
◆ “Cold-mode” streams, “hot-mode” infall, fountains . . .
■ Outer Galaxy sensitive to the transition between thebaryonic- and dark-matter-domination
◆ Properties of the dark matter halo
◆ MOND (?)
Motivation
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 2
■ History of a galaxy is critical in determining its present state
◆ Satellite decay and disruption
◆ Bombardment by substructure
◆ “Cold-mode” streams, “hot-mode” infall, fountains . . .
■ Outer Galaxy sensitive to the transition between thebaryonic- and dark-matter-domination
◆ Properties of the dark matter halo
◆ MOND (?)
⇒ Connection to the neutral gas layer
Plan
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 3
■ Motivation . . . why study the Milky Way warp and otherasymmetric features?
■ Data & conundrums
◆ HI asymmetries
◆ Outer arms past the optical disk?
◆ Inner MW offsets, scale height?
■ Warping as an example
◆ How warps work
◆ LMC: bound or unbound?
◆ Gas response (New while at KITP)
■ Implications and next steps
Plan
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 3
■ Motivation . . . why study the Milky Way warp and otherasymmetric features?
■ Data & conundrums
◆ HI asymmetries
◆ Outer arms past the optical disk?
◆ Inner MW offsets, scale height?
■ Warping as an example
◆ How warps work
◆ LMC: bound or unbound?
◆ Gas response (New while at KITP)
■ Implications and next steps
Plan
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 3
■ Motivation . . . why study the Milky Way warp and otherasymmetric features?
■ Data & conundrums
◆ HI asymmetries
◆ Outer arms past the optical disk?
◆ Inner MW offsets, scale height?
■ Warping as an example
◆ How warps work
◆ LMC: bound or unbound?
◆ Gas response (New while at KITP)
■ Implications and next steps
Plan
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 3
■ Motivation . . . why study the Milky Way warp and otherasymmetric features?
■ Data & conundrums
◆ HI asymmetries
◆ Outer arms past the optical disk?
◆ Inner MW offsets, scale height?
■ Warping as an example
◆ How warps work
◆ LMC: bound or unbound?
◆ Gas response (New while at KITP)
■ Implications and next steps
The Milky Way Warp
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 4
Warp height (color coded), Levine et al. 2006
Outer Spiral arms
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 5
■ HI from Levine et al. 2006
Outer Spiral arms
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 5
■ Also by HI absorption from Strasser et al. 2007
Outer Spiral arms
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 5
■ Hα+[NII] continuum–subtracted image of NGC 628 fromFerguson, Wyse & Gallagher 1998
Outer Spiral arms
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 5
■ Hα+[NII] continuum–subtracted image of NGC 1058 fromFerguson, Wyse & Gallagher 1998
Outer Spiral arms
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 5
■ Hα+[NII] continuum–subtracted image of NGC 6946 fromFerguson, Wyse & Gallagher 1998
Inner gas
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 6
Gas at the Milky Way center,Blitz et al. 1993
Inner gas
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 6
Gas at the Milky Way center,Blitz et al. 1993
≈ 100 pc offset!
Warp excitation
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 7
Case study: warp. . . proposed theories:
1. Modes
2. Response to triaxial halo
3. Response to asymmetric disk accretion (cold streams)
4. Response to satellites & bombardment
Warp excitation
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 7
Case study: warp. . . proposed theories:
1. Modes
2. Response to triaxial halo
3. Response to asymmetric disk accretion (cold streams)
4. Response to satellites & bombardment
⋄ All of the above???
Warp excitation
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 7
Case study: warp. . . proposed theories:
1. Modes
2. Response to triaxial halo
3. Response to asymmetric disk accretion (cold streams)
4. Response to satellites & bombardment ⇐this talk
⋄ All of the above???
If you hit a bell it rings, it doesn’t
matter how you hit it . . .
Dynamics of warps
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 8
■ Any large-scale feature is a collective effect
■ Collective response has discrete and continuous parts
◆ Discrete parts are self-similar and may damp (modes)
◆ Continuous parts mix (like wave packets)
Dynamics of warps
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 8
■ Any large-scale feature is a collective effect
■ Collective response has discrete and continuous parts
◆ Discrete parts are self-similar and may damp (modes)
◆ Continuous parts mix (like wave packets)
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8 10 12 14 16 18
Pow
er
Ω
orbital freq
Dynamics of warps
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 8
■ Any large-scale feature is a collective effect
■ Collective response has discrete and continuous parts
◆ Discrete parts are self-similar and may damp (modes)
◆ Continuous parts mix (like wave packets)
orbital decay
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8 10 12 14 16 18
Pow
er
Ω
orbital freq
Dynamics of warps
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 8
■ Any large-scale feature is a collective effect
■ Collective response has discrete and continuous parts
◆ Discrete parts are self-similar and may damp (modes)
◆ Continuous parts mix (like wave packets)
continuousorbital decay
0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8 10 12 14 16 18
Pow
er
Ω
orbital freq
Dynamics of warps
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 8
■ Any large-scale feature is a collective effect
■ Collective response has discrete and continuous parts
◆ Discrete parts are self-similar and may damp (modes)
◆ Continuous parts mix (like wave packets)
■ We need to think about natural structure (e.g. modes)!
◆ Important for ALL warp theories
◆ More generally: all time-dependent interactions
Dynamics of warps
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 9
Example: m = 1 bending mode, thin disk
Halo-embedded disk Tipping mode with halo mass
Satellites and substructure
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 10
■ Satellite (Magellanic Clouds) distort
◆ the halo by exciting wakes
◆ the disk directly by the tidal force
■ The halo wake distorts the disk
■ Halo wake close to disk ⇒ large effect!
■ Perturbation theory (struggle for simulations)
◆ “Matrix mechanics” (e.g. Weinberg 1990s)
◆ Hunter-Toomre 2-d bending (1969)
Movies
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 11
Total (left) and m = 0 (right)
wake0x.aviMedia File (video/avi)
Movies
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 11
Total (left) and m = 1 (right)
wake1x.aviMedia File (video/avi)
Movies
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 11
Total (left) and m = 2 (right)
wake2x.aviMedia File (video/avi)
Movies
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 11
Total (left) and m = 3 (right)
wake3x.aviMedia File (video/avi)
Halo wake
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 12
-0.035-0.03-0.025-0.02-0.015-0.01-0.005 0 0.005 0.01 0.015 0.02
kpc
kpc
-30 -20 -10 0 10 20 30-30
-20
-10
0
10
20
30
-0.05-0.04-0.03-0.02-0.01 0 0.01 0.02 0.03 0.04 0.05
kpc
kpc
-30 -20 -10 0 10 20 30-30
-20
-10
0
10
20
30
m = 0 vertical force from halowake at disk plane
m = 1 vertical force from halowake at disk plane
■ Warp is shifted by π/m from force symmetry axis (m > 0)
■ Will/can slosh inner and outer galaxy in opposite directions
Halo wake
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 12
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
kpc
kpc
-30 -20 -10 0 10 20 30-30
-20
-10
0
10
20
30
-0.02-0.015-0.01-0.005 0 0.005 0.01 0.015 0.02
kpc
kpc
-30 -20 -10 0 10 20 30-30
-20
-10
0
10
20
30
m = 2 vertical force from halowake at disk plane
m = 3 vertical force from halowake at disk plane
■ Warp is shifted by π/m from force symmetry axis (m > 0)
■ Will/can slosh inner and outer galaxy in opposite directions
Halo wake
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 12
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
NFW halo split log
-60 -40 -20 0 20 40 60
kpc
-80
-60
-40
-20
0
20
40
60
80
kpc
0.001
0.01
0.1
1
10
100
1000
NFW halo split log
-60 -40 -20 0 20 40 60
kpc
-80
-60
-40
-20
0
20
40
60
80
kpc
m = 1 potential from halo wakein disk plane
m = 2 potential from halo wakein disk plane
■ Warp is shifted by π/m from force symmetry axis (m > 0)
■ Will/can slosh inner and outer galaxy in opposite directions
An LMC first passage?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 13
■ Lower overall mass implied by ΛCDM dark halo model
■ Large space velocity confirmed from recent proper motionmeasurements (Kallivayalil et al. 2006)
■ =⇒ LMC may not be orbiting but on first approach!
An LMC first passage?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 13
■ Lower overall mass implied by ΛCDM dark halo model
■ Large space velocity confirmed from recent proper motionmeasurements (Kallivayalil et al. 2006)
■ =⇒ LMC may not be orbiting but on first approach!
“Highly unlikely that LMC excites a warp”Besla et al. 2007
An LMC first passage?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 13
■ Lower overall mass implied by ΛCDM dark halo model
■ Large space velocity confirmed from recent proper motionmeasurements (Kallivayalil et al. 2006)
■ =⇒ LMC may not be orbiting but on first approach!
An LMC first passage?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 13
■ Lower overall mass implied by ΛCDM dark halo model
■ Large space velocity confirmed from recent proper motionmeasurements (Kallivayalil et al. 2006)
■ =⇒ LMC may not be orbiting but on first approach!
m = 1 (right)
movie11.aviMedia File (video/avi)
An LMC first passage?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 13
■ Lower overall mass implied by ΛCDM dark halo model
■ Large space velocity confirmed from recent proper motionmeasurements (Kallivayalil et al. 2006)
■ =⇒ LMC may not be orbiting but on first approach!
m = 1 (right)
movie11.aviMedia File (video/avi)
An LMC first passage?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 13
■ Lower overall mass implied by ΛCDM dark halo model
■ Large space velocity confirmed from recent proper motionmeasurements (Kallivayalil et al. 2006)
■ =⇒ LMC may not be orbiting but on first approach!
m = 1 (right)
movie11.aviMedia File (video/avi)
An LMC first passage?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 13
■ Lower overall mass implied by ΛCDM dark halo model
■ Large space velocity confirmed from recent proper motionmeasurements (Kallivayalil et al. 2006)
■ =⇒ LMC may not be orbiting but on first approach!
“Highly unlikely that LMC excites a warp”Besla et al. 2007
■ Could predict LMC orbit and mass based on warp givenexact Milky Way parameters
What does the gas *really* do?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 14
■ Halo wake extends through to disk
■ Amplitude scales as η ≡ Msat/Mgal
■ Pattern speed is supersonic, so . . .
■ Gas shocks, angular momentum removed ⇒ gas inflow
■ Although coherent wake yields large η, background fromsubstructure and dwarfs may keep a low level of shockstructure promoting inward gas flux
◆ Detailed calc in progress
What does the gas *really* do?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 14
■ Halo wake extends through to disk
■ Amplitude scales as η ≡ Msat/Mgal
■ Pattern speed is supersonic, so . . .
■ Gas shocks, angular momentum removed ⇒ gas inflow
■ Although coherent wake yields large η, background fromsubstructure and dwarfs may keep a low level of shockstructure promoting inward gas flux
◆ Detailed calc in progress
What does the gas *really* do?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 14
■ Halo wake extends through to disk
■ Amplitude scales as η ≡ Msat/Mgal
■ Pattern speed is supersonic, so . . .
■ Gas shocks, angular momentum removed ⇒ gas inflow
■ Although coherent wake yields large η, background fromsubstructure and dwarfs may keep a low level of shockstructure promoting inward gas flux
◆ Detailed calc in progress
What does the gas *really* do?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 14
■ Halo wake extends through to disk
■ Amplitude scales as η ≡ Msat/Mgal
■ Pattern speed is supersonic, so . . .
■ Gas shocks, angular momentum removed ⇒ gas inflow
■ Although coherent wake yields large η, background fromsubstructure and dwarfs may keep a low level of shockstructure promoting inward gas flux
◆ Detailed calc in progress
What does the gas *really* do?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 14
■ Halo wake extends through to disk
■ Amplitude scales as η ≡ Msat/Mgal
■ Pattern speed is supersonic, so . . .
■ Gas shocks, angular momentum removed ⇒ gas inflow
■ Although coherent wake yields large η, background fromsubstructure and dwarfs may keep a low level of shockstructure promoting inward gas flux
◆ Detailed calc in progress
What does the gas *really* do?
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 14
■ Halo wake extends through to disk
■ Amplitude scales as η ≡ Msat/Mgal
■ Pattern speed is supersonic, so . . .
■ Gas shocks, angular momentum removed ⇒ gas inflow
■ Although coherent wake yields large η, background fromsubstructure and dwarfs may keep a low level of shockstructure promoting inward gas flux
◆ Detailed calc in progress
Perhaps the halo “noise” is the major driver ofdisk structures (bars, spiral arms, etc.) not self-excitation??
Gas forcing by a satellite
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 15
■ Parallel DSMC code (Direct Simulation Monte Carlo,100% shock capturing)
■ Live halo, live stellar disk, 3-d gas but no self gravity
Gas forcing by a satellite
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 15
■ Parallel DSMC code (Direct Simulation Monte Carlo,100% shock capturing)
■ Live halo, live stellar disk, 3-d gas but no self gravity
Gas forcing by a satellite
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 15
■ Parallel DSMC code (Direct Simulation Monte Carlo,100% shock capturing)
■ Live halo, live stellar disk, 3-d gas but no self gravity
NGC 2403, HI (in M81 group, SAB)
Gas forcing by a satellite
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 15
■ Parallel DSMC code (Direct Simulation Monte Carlo,100% shock capturing)
■ Live halo, live stellar disk, 3-d gas but no self gravity
Gas forcing by a satellite
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 15
■ Parallel DSMC code (Direct Simulation Monte Carlo,100% shock capturing)
■ Live halo, live stellar disk, 3-d gas but no self gravity
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0.0014
0.0001 0.001 0.01 0.1 1 10
Mas
s
R
T=0T=1 Gyr
Implications
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 16
■ N-body simulations
◆ Bending modes and multiscale interactions difficult
◆ N-body bending predictions agree(e.g. Tsuchiya 2003, Bailin & Steinmetz 2005)
■ Other warping theories [Occam’s Razor]
◆ Cosmic infall(e.g. Ostriker, E. & Binney 1989, Ing-Guey & Binney 1999, Shen & Sellwood 2006)
◆ Triaxiality (e.g. Binney 1990)
■ MOND
◆ No halo, increase the force of gravity at large distances
◆ ⇒ Different disk modes! Outer disk!!!
Implications
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 16
■ Substructure detection/other galactic systems
◆ Coherent warping dominated by the largestsubhalo/dwarf
◆ Excitation of outer disk by the cumulative subhalopopulation
◆ Heating of the disk by bending modes (homogenizescale height?)
◆ HI structure survey!!
■ Does halo structure cause spiral arms?
■ Does noise drive cold gas accretion?
■ Lots more work!
Motivation
Plan
The Milky Way Warp
Outer Spiral arms
Inner gas
Warp excitation
Dynamics of warps
Satellites andsubstructure
Movies
Halo wake
1st passage?
Neutral gas
DSMC simulation
Implications
————
Back to the Galaxy II KITP – slide 17
The End
MotivationPlanThe Milky Way WarpOuter Spiral armsInner gasWarp excitationDynamics of warpsDynamics of warpsSatellites and substructureMoviesHalo wakeAn LMC first passage?What does the gas *really* do?Gas forcing by a satelliteImplications