Dynamics and star formation histories of the LMC and the SMC. LMC Kenji Bekki (UNSW, Australia) SMC
Anniversary in Vienna 2006. • 250th anniversary of Mozart’s birth.
Anniversary in Vienna 2006. • 250th anniversary of Mozart’s birth. • 10th anniversary of the discovery of ultra-compact dwarfs (UCDs). • 40th anniversary of the publication of a paper by McGee & Milton (1966) on the LMC’s HI.
The Magellanic saga ~10 Gyr ago 3~4 Gyr ~0.2 Gyr 1. Dawn 3.Restoration 2.Hibernation 4.Inferno
The Magellanic saga Dawn Hibernation Restoration Inferno ~10 Gyr ago 3~4 Gyr ~0.2 Gyr
The Magellanic saga Dawn Hibernation Restoration Inferno ~10 Gyr ago 3~4 Gyr ~0.2 Gyr LMC’s History Old stellar halo & GC formation. Reactivation of GC Formation. Formation of 30 Doradus etc…
Can we really understand the origin of physical properties of the Clouds in the context of Galaxy-LMC-SMC interaction ?
A numerical study on the interplay between galaxy interaction and star formation
Today’s topics. • Formation of asymmetric HI and molecular gas distributions in the LMC and the origin of the Magellanic Bridge (MB). • The age gap problem in the LMC and the formation of the stellar ring in the SMC. • Formation of old stellar halos and GC. • Conclusions.
1. The Magellanic Inferno. 0.2 Gyr ago
1. The Magellanic Inferno: Triggered star formation in the last Magellanic collision. From the LMC Tidal force for the SMC From the Galaxy Past (Gardiner & Noguchi 1996)
Asymmetric distributions of field stars, HI, molecular gas, and young stars. Structure and kinematics of the Magellanic Bridge (MB). 1. The Magellanic Inferno. Observations to discuss. LMC SMC
Asymmetric HI structures in the LMC. (Column density image of the LMC HI) (Staveley-Smith et al. 2003)
The Asymmetric CO (molecular gas) distribution in the LMC. (Fukui et al. 2001, Mizuno et al. 2001; Kawamura et al. 2006)
Elliptic LMC disk (van der Marel 2001) 21kpc x 19 kpc Surface number distributions of RGB/AGB stars from 2MASS
Distributions of young stars. Spatial distribution of Cepheids (Grebel & Brandner 1998)
Were these asymmetric structures formed from the Last Magellanic Collision ?
A hint from numerical simulations. LMC • (b,l)=(-32.89,280.46) • Distance: 49 kpc • (U,V,W)=(-5,-225,194) km/s • Radial velocity: 80 km/s SMC • (b,l)=(-44.30,302.79) • Distance: 57 kpc • (U,V,W)=(40,-185,171) km/s • Radial velocity: 7 km/s
Numerical simulations of the LMC/SMC evolution:Two-hold model • Prediction of the LMC orbit for the last x Gyr (x=1 or 4 or 9) based on the ``backward integration scheme’’. • Grape-5/6 chemodynamical simulations for the predicted orbit(s).
The orbital evolution of the Clouds for the last ~ 0.8 Gyr. SMC-Galaxy LMC-Galaxy LMC-SMC
Dynamical evolution of the LMC disk (Bekki & Chiba 2006) SMC Gas (SPH) Old stars XZ XZ
Dynamical evolution of the LMC disk (Bekki & Chiba 2006) Gas (SPH) Old stars XZ XZ
Distributions of gas and new stars with ages < 20 Myr SMC Gas (SPH) New stars XZ XZ
B-band surface-brightness distributions of the LMC. Without SMC With SMC (Bekki & Chiba 2006)
The gas distribution of the LMC. East-West Asymmetric distribution. Connected to the MB.
Spatial distributions of young stars with ages less than 20 Myr. Young stars in the bar A possible formation Site of 30 Doradus ??
Is the formation of 30 Doradus closely associated with the last Magellanic collision ?
VUV observation Simulation (Young stars) Bar The location of the 30 Doradus can tell us anything about its formation ? 30 Doradus + R136
Hints from CO observations: Proto-GC cloud formation in the MC collision ? CO molecule observations by Mopra (Ott et al. 2006): [HI (blue), Ha(red), optical light (green)] Simulated gas density (BC06).
Structure and kinematics of the Magellanic Bridge (MB). DEC LMC SMC RA (Putman et al. 1998) (Muller et al. 2003)
Formation of stars and HI holes in the MB. HI shell OB associations (Muller et al. 2003)
Formation of the MB. Gas Gas LMC XY XZ
The MB as a tidal tail from the SMC Gas Gas LMC XY XZ
Distributions of gas and new stars in the SMC New stars Gas LMC XY XY
Inconsistency of the simulated MB with observations: No youngs star with ages < 10 Myr. New stars Gas Gas connected to MB. Is this due to the modelled threshold gas density, simulation resolution, etc……. ?
Velocity offset and bimodality inthe MB (Muller et al. 2003; 2005). DEC Velocity
Formation of ``the Great Magellanic Arc’’ in the last Magellanic collision. 30 Dor --- Asymmetric HI/CO --- MB --- Wing SF region in SMC
2. The Magellanic Restoration. ~ 3.7Gyr ago
2. The Magellanic Restoration. The age gap in the globular cluster system. The Magellanic Stream (MS). Stellar ring structures. Observations to discuss. LMC SMC
The Galactic GCs vs The LMC’s GCs Rc~1.5pc Re~10 pc 47Tuc NGC 1850 Significant differences between the two: More flattened shapes, a larger fraction of binary clusters, Rotational kinematics, disky distribution, a larger size for a given galactocentric radius, and age/metallicity gap.
Two mysteries in the LMC’s GCS. • A high fraction of binary GC candidates (e.g., Bhatia et al. 1991; Dieball & Grebel 1998; 15-56% in Dieball et al. 2002). • The age gap problem (e.g., Da Costa 1991) [NOTE: only one established case and possibly ~ 8% for open clusters in the Galaxy (e.g., Subramaniam et al. 1995)]
What is the age gap ? [Fe/H] Age (Gyr) (Da Costa 1991)
The essence of the age gap problem. • No cluster formation between 3-12 Gyrs ? (Why was GC formation reactivated 3-4 Gyr ago ?) • Selective destruction/stripping of clusters with ages of 3-12 Gyrs ? (What physical processes are responsible for this ?)