Thursday, October 27, 2011

1110.5877 (N. Bouche et al.)

Physical properties of galactic winds using background quasars    [PDF]

N. Bouche, W. Hohensee, R. Vargas, G. G. Kacprzak, C. L. Martin, J. Cooke, C. W. Churchill
We investigate the spatial location of quasar lines-of-sight with strong MgII absorption (with EW>0.3 AA) passing near spectroscopically identified galaxies at z~0.1. Using a dozen quasar-galaxy pairs available from the literature, we find that the azimuthal orientation of the quasar sight-lines is bi-modal, with about half the MgII sight-lines aligned with the major axis and the other half within $\alpha=$30 degree of the minor axis. This dichotomy is also present in the instantaneous star-formation rates (SFRs) of the host. These results indicate that both gaseous disks and strong bipolar outflows contribute to MgII cross-section. In addition, a simple bi-conical wind model is able to reproduce the observed MgII kinematics for the sight-lines aligned with the minor axis, showing that bipolar outflows contribute significantly to the MgII cross-section. Finally, using our kinematic wind model, we can extract directly key wind properties such as the de-projected outflow speed $V_{out}$ of the material traced by MgII and the outflow rates. The outflow speed $V_{out}$ are found to be 150-300~km/s, i.e. of the order of the circular velocity, and smaller than the escape velocity by a factor of about ~2. The outflow rates are typically 2 to 3 times the SFRs. Our results provide a test bed for measuring wind properties with greater precision.
View original: http://arxiv.org/abs/1110.5877

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