Tracking the Magellanic Stream s From Birthplace out to

Tracking the Magellanic Stream(s): From Birthplace out to 100° David L. Nidever University of Virginia Collaborators: Steven R. Majewski and W. Butler Burton (NRAO)

Previous Work

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

Background Early Models • Tidal models reproduce general 1982, features of Stream. (Lin & Lynden-Bell 1977, Murai & Fujimoto 1980) Lin & Lynden-Bell 1977 200 particles • Ram pressure models fit column density gradient better than tidal model (Meurer et al. 1985, Moore & Davis 1994) Moore & Davis 1994 Murai & Fujimoto 1980 600 particles

Background Recent Observations • HIPASS survey of Stream • Leading Arm discovered (Putman et al. 1998) • First high spatial resolution look at the Stream Putman et al. 1998 Putman et al. 2003 • 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) 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) Mastropietro et al. 2004 Observations Connors et al. 2005 Model

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. Kalberla et al. 2005 Velocity coverage: • Spatial resolution: 0. 5°, velocity resolution: 1. 3 km/s, rms TB = 0. 09 K – 450 < VLSR < +400 km/s.

Gaussian Decomposition of LAB Data GOAL: 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 • Stop adding Gaussians once RMS of residuals ≈ noise level Add the Gaussian that reduces the RMS of residuals the most

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 Brightness Temperature Average Decomposition Velocity

Latitude Longitude

Velocity Longitude

Latitude Longitude

High Velocity Clouds

Cleaning out the zero-velocity region • Putman et al. 2003 and • Can use the Gaussians to do the separation. Use continuity in: • space • velocity • Gaussian width • Gaussian height Velocity Brüns et al. 2005 had difficulty separating Stream from local gas at V≈0 km/s Galactic Longitude

Magellanic Stream Use a coordinate system that bisects the Stream

3 D Animation of Magellanic System HI

• 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 Latitude Plotting the Gaussian centers enhances the structures. Velocity Velocities Magellanic Longitude

Velocity LMC filament Bridge SMC/Bridge filament Magellanic Longitude

• 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 Latitude LMC filament originates in the 30 Dor Region after velocity mask Magellanic Longitude

Distinctive Sinusoidal Pattern LMC & SMC tumbling about each other? Velocity What’s causing it? Magellanic Longitude

Are the Filaments Wrapping Around Each Other? If the filaments are wrapping each other, LMC and SMC are bound to each other. • Could be used to Velocity • Could show that the trace the dynamical history of the LMC & SMC system. Magellanic Longitude

Filaments Are Not Wrapping! • LMC filament spiraling on its own • SMC/Bridge filament has a smaller scale spiral Velocity→ Filaments are NOT wrapping.

Distinctive Sinusoidal Pattern Possibly imprint of the LMC rotation curve. Can estimate drift rate: Velocity • 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 Magellanic Longitude

Distinctive Sinusoidal Pattern 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 Magellanic Latitude Possibly imprint of the LMC rotation curve. Magellanic Longitude

Sinusoidal pattern mysteriouslythe ends ~30° from the LMC edge sinusoids end • Something dramatic must happen there • Possibly crossing the LMC tidal linear • 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, Velocity radius sinusoid ends Magellanic Longitude

Stars Associated with the LMC Filament MC Clusters from Bica et al. 1999 Bluest stars from Irwin, Demers & Kunkel 1990

Leading Arm Staveley-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 Velocity LA 2 & 3 LA 1 Magellanic Longitude

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

Origin of the Leading Arm The Leading Arm complex closest to the LMC (LA 1) connects with the LMC in Where does it originate? Velocity SPACE and VELOCITY On the Sky Magellanic Latitude

Origin of the Leading Arm 250 < VLSR < 320 km/s Magellanic Longitude With a velocity cut, we can track LA to its origins Once again, Magellanic Latitude

The 30 Dor Region Filaments Kim et al. 2003 LMC filament & Leading Arm originate from the 30 Dor region. • Leading Arm also shows signs of periodic motion (spatially). 30 Dor Region 267 km/s • Both periodic motions probably have same cause • The Leading Arm is NOT coming from SMC! Leading Arm LMC Filament

The 30 Dor Region Filaments LMC filament & Leading Staveley-Smith et al. 2003 Arm originate from the 30 Dor region. 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! Leading Arm LMC Filament

Velocity Magellanic Longitude

Velocity Magellanic Longitude Magellanic Latitude

Leading Arm Velocity another filament? LMC filament Magellanic Stream Magellanic Latitude

Can Track both filaments all the way along Stream • Well separated either in velocity or spatially. LMC filament • Use space-velocity cuts for upper part of the Stream • Spatial cuts for the lower part of the Stream SMC/Bridge filament

Conclusions Gaussian 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 the Stream Can track both filaments all the way along 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!