Giant molecular cloud formation through the Parker instability in a skewed magnetic field

The effect of the magnetic skew on the Parker instability is investigated bymeans of the linear stability analysis for a gravitationally stratified gaslayer permeated by a horizontal magnetic field. When the magnetic field isskewed (i.e., the field line direction is a function of the height), thewavelength of the most unstable mode is $ \lambda \; \sim \; 10 H $ where $ H $is the pressure scale height. The growth rate of the short wavelength modes isgreatly reduced when the gradient in the magnetic field direction exceeds 0.5radian per scale height. Our results indicate that the Parker instability in askewed magnetic field preferentially forms large scale structures like giantmolecular clouds.Comment: 12 page