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Back to the Galaxy II KITP – slide 1

Warps and Wiggles

Martin D. WeinbergUMass Astronomy

weinberg@astro.umass.edu

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