SPIRAL SHOCK TRIGGERING OF STAR FORMATION
We present numerical simulations of the passage of clumpy gas through a galactic spiral shock and the subsequent formation of giant molecular clouds (GMCs) and the triggering of star formation. The spiral shock formsdense clouds while dissipating kinetic energy, producing regions that are locally gravitationally bound and collapse to form stars. In addition to triggering the star formation process, the clumpy gas passing through the shock naturally generates the observed velocity dispersion size relation ofmolecular clouds. In this scenario, the internal motions of GMCs need not be turbulent in nature. The coupling of the clouds’ internal kinematics totheir externally triggered formation removes the need for the clouds to beself-gravitating. Globally unbound molecular clouds provides a simple explanation of the low efficiency of star formation. While dense regions in the shock become bound and collapse to form stars, the majority of the gas disperses as it leaves the spiral arm.
KeywordsStar Formation Smooth Particle Hydrodynamic Velocity Dispersion Molecular Cloud Spiral Galaxy
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