Tracking the Magellanic Stream(s): From Birthplace out to100° David L. Nidever University of Virginia Collaborators: Steven R. Majewski and W. Butler Burton

Tracking the Magellanic Stream(s): From Birthplace

out to100°

David L. Nidever

University of VirginiaCollaborators: Steven R. Majewski and W. Butler Burton

(NRAO)

Previous WorkObservationsHI Magellanic Stream Putman et al. 1998, 2003 Stanimirović et al. 2002 Brüns et al. 2005HI LMC Staveley-Smith et al. 2003 Kim et al. 2003HI SMC & Bridge Staveley-Smith et al. 1995 Stanimirović et al. 1999, 2000, 2004COYamaguchi et a. 2001

Hα Weiner & Williams 1996 Putman et al. 2003

Simulations/TheoryTidal Models Lin & Lynden-Bell 1977, 1982 Murai & Fujimoto 1980 Gardiner et al. 1994, 1996, 1999 Connors et al. 2004, 2005 Yoshizawa & Noguchi 2003 Bekki et al. 2005 Ram Pressure Moore & Davis 1994 Mastropietro et al. 2004

Background

Discovery Papers

• A long stream of HI gas trailing the Magellanic Clouds. Large velocity gradient (Wannier & Wrixon 1972, Mathewson et al. 1974)

BackgroundEarly Models

• Tidal models reproduce general features of Stream. (Lin & Lynden-Bell 1977, 1982, Murai & Fujimoto 1980)

Murai & Fujimoto 1980600 particles

Lin & Lynden-Bell 1977200 particles

Moore & Davis 1994

• Ram pressure models fit column density gradient better than tidal model (Meurer et al. 1985, Moore & Davis 1994)

BackgroundRecent

Observations• HIPASS survey of Stream

• Leading Arm discovered

(Putman et al. 1998)

• First high spatial resolution look at the Stream

• Bifurcation in Stream

(Putman et al. 2003)

• One of the tidal arms coming from LMC connects to the Leading Arm (Staveley-Smith et al. 2003)

• First high velocity resolution look at the Stream (Brüns et al. 2005)

Putman et al. 1998Putman et al. 2003

Brüns et al. 2005

Background

Recent Models• Ram pressure models can reproduce most observations. But no Leading Arm (Mastropietro et

al. 2004)

• Tidal models reproduce correct Leading Arm shape & bifurcation, Stream bifurcation (LMC crashed through Stream) (Connors et al. 2005)

Connors et al. 2005

Observations Model

Mastropietro et al. 2004

Tidal ModelRam Pressure

ModelLeading

Arm XN(HI)

gradient XBifurcation ?No Stars X? ?

Leiden/Argentine/Bonn (LAB) all-sky HI survey

• Combination of Leiden/Dwingeloo Survey with the Instituto Argentino de Radioastronomia Survey (Kalberla et al. 2005)

• Stray radiation correction

• First HI all-sky survey. Velocity coverage: –450 < VLSR < +400 km/s.

•Spatial resolution: 0.5°, velocity resolution: 1.3 km/s, rms TB = 0.09 K

Kalberla et al. 2005

Gaussian Decomposition of LAB DataGOAL: Want to simplify datacube (e.g.

~260,000 HI spectra) and make it easier to following features that overlap in velocity.

Need an automated Gaussian decomposition program

Used an algorithm similar to the one presented in Haud 2000

• Add Gaussians one at a time

• Add the Gaussian that reduces the RMS of residuals the most

• Stop adding Gaussians once RMS of residuals ≈ noise level

Database of Gaussians

• Decomposed the whole LAB database

• Ran for several weeks on multiple computers

• Final Results:

Whole sky decomposed into

1,375,993 Gaussians

Average Decomposition

Velocity

Bri

gh

tness

Tem

pera

ture

Lati

tud

e

Longitude

Velo

city

Longitude

Lati

tud

e

Longitude

Velocity

Lati

tud

e

High Velocity Clouds

Cleaning out the zero-velocity region

• Putman et al. 2003 and Brüns et al. 2005 had difficulty separating Stream from local gas at V≈0 km/s

• Can use the Gaussians to do the separation. Use continuity in:

• space• velocity• Gaussian width• Gaussian height

Velo

city

Galactic Longitude

Magellanic Stream

Use a coordinate system that bisects the Stream

Magellanic Longitude

Mag

ella

nic

Lati

tud

e

QuickTime and aﾪGIF decompressor

are needed to see this picture.

3D Animation of Magellanic System HI

VelocitiesPlotting the Gaussian centers enhances the structures.

•Two filaments at the head of the Stream.

•One filament can be tracked to the LMC

•Other filament probably comes from the SMC/Bridge region Magellanic Longitude

V

elo

city

La

titu

de

SMC/Bridge filament

LMC filamentLMC

SMC

Bridge


Velo

city

after velocitymask

ATCA & Parkes Hires HIKim et al. 2003

267 km/sLMC filament originates in the 30

Dor Region• Can track the LMC filament back to its origin in the 30 Dor region using velocity cuts

• Birthplace of the Magellanic Stream

• Site of extreme star formation. Rich in HI, CO, Hα, GMCs and young stellar clusters Magellanic Longitude

Mag

ella

nic

Lati

tud

e

NANTEN CO Yamaguchi et al.

2001

Distinctive Sinusoidal Pattern

What’s causing it?

LMC & SMC tumbling about each other?

V

elo

city


Are the Filaments Wrapping Around Each Other?If the filaments are wrapping each other,

• Could show that the LMC and SMC are bound to each other.

• Could be used to trace the dynamical history of the LMC & SMC system.


Velo

city



Filaments Are Not Wrapping!

Filaments are NOT wrapping.

• LMC filament spiraling on its own

• SMC/Bridge filament has a smaller scale spiral

Velo

city

→


Possibly imprint of the LMC rotation curve.

Can estimate drift rate:

• Velocity Amplitude: 23 km/s

• Radius: 2.5°→2.2 kpc

• Period: 0.6 Gyr

• Drift Rate: ~30 km/s

• Age of Stream: ~3 Gyr

Velo

city



Mag

ella

nic

Lati

tud

e


Possibly imprint of the LMC rotation curve.

Can estimate drift rate:

• Velocity Amplitude: 23 km/s

• Radius: 2.5°→2.2 kpc

• Period: 0.6 Gyr

• Drift Rate: ~30 km/s

• Age of Stream: ~3 Gyr

Sinusoidal pattern

mysteriously ends

~30° from the LMC edge the sinusoids end

• Something dramatic must happen there

• Possibly crossing the LMC tidal radius

• Mũnoz et al. 2006 found LMC stars at 22° from LMC center

• Linear portion with smaller spirals/sinusoids

• Maybe interacting with MW halo gas, drag causing linear trend, damping the sinusoids

sinusoid ends

linear


Velo

city

Stars Associated with the LMC Filament

MC Clusters from Bica et al. 1999Bluest stars from Irwin,Demers & Kunkel 1990

Leading ArmStaveley-Smith et al. 2003 point out:

• Arm E points towards the Leading Arm

• Deep HIPASS shows Arm E is continuous with Leading Arm

• Most Leading Arm gas comes from SMC.

Staveley-Smith et al. 2003

Leading Arm


Velo

city

LA 1

LA 2 & 3

Leading ArmPutman et al. 1998 (discovery paper) showed that the first two concentrations of LA 1 are (nearly)

CONTINUOUS

Origin of the Leading ArmThe Leading Arm

complex closest to the LMC (LA 1) connects with the LMC in

SPACE and VELOCITY

Where does it originate?

Magellanic Latitude

Velo

city

On the Sky

Origin of the Leading Arm

With a velocity cut, we can track LA to its origins

Once again,

250 < VLSR < 320 km/s

The 30 Dor Region!! M

ag

ella

nic

Lon

git

ud

e

Magellanic Latitude

ATCA & Parkes hi-res HIKim et al. 2003

267 km/s

Leading ArmLMC Filament

30 Dor Region

Kim et al. 2003

LMC filament & Leading Arm originate from the 30 Dor region.

• Leading Arm also shows signs of periodic motion (spatially).

• Both periodic motions probably have same cause

• The Leading Arm is NOT coming from SMC!

The 30 Dor Region Filaments

267 km/s

Leading ArmLMC Filament

30 Dor Region

Staveley-Smith et al. 2003

LMC filament & Leading Arm originate from the 30 Dor region.

• Leading Arm also shows signs of periodic motion (spatially).

• Both periodic motions probably have same cause

• The Leading Arm is NOT coming from SMC!

The 30 Dor Region Filaments


Velo

city




Velo

city

Velo

city

Magellanic Latitude

Magellanic Latitude

Velo

city

another filament?

Magellanic Stream

Leading Arm

LMC filament

Can Track both filaments all the

way along Stream• Well separated either in

velocity or spatially.

• Use space-velocity cuts for upper part of the Stream

• Spatial cuts for the lower part of the Stream

LMC filament

SMC/Bridge filament

Tidal ModelRam Pressure

ModelLeading

Arm XN(HI)

gradient XBifurcation X?No Stars X? ?

LMC filament ?

SMC filament ?

ConclusionsGaussian decomposition of entire LAB survey.

First thorough analysis of the velocities of the Stream:

•Found the origins of the Stream

•Two filaments at head of Stream, one from LMC (30 Dor), other from SMC/Bridge region

•LMC filament has distinctive sinusoidal pattern that ends abruptly

•Filaments do not wrap around each other (at head of Stream)

•Leading Arm also originates in 30 Dor region

Conclusions• Can track both filaments all the way along the Stream

• Stars associated with the LMC filament

Thus the Magellanic Stream provides new and powerful constraints for models of the SMC-LMC-Milky Way interaction.

These findings will be submitted for publication soon

Thank You!

Documents

Tracking the Magellanic Stream(s): From Birthplace out to100° David L. Nidever University of Virginia Collaborators: Steven R. Majewski and W. Butler Burton