Magnetically Driven Outflows in a Starburst Environment

We here investigate the possibility that the observed collimated outflows inluminous infrared galaxies (LIGs) and some Seyfert galaxies can be produced ina starburst (SB) environment. A nuclear disk can be quickly produced by gasinfall during star formation in a rotating, stellar cluster. We find thatmassive nuclear SBs with core disk masses M_d \sim 10^8 - 10^9 M_{\odot}, andsupernova rates \nu_{SN} \simeq 5 \times 10^{-3} - 2 yr^{-1} (which areconsistent with the \nu_{SN} values inferred from the observed non-thermalradio power in source candidates) may inject kinetic energies which are highenough to blow out directed flows from the accreting disk surface, within theSB lifetimes. In our models, the acceleration and collimation of the nuclearoutflow are provided by magnetic fields anchored into the rotating SB-disk. Theemerging outflow carries a kinetic power that is only a small fraction (a fewpercent) of the supernovae energy rate produced in the SB. Based on conditionsdetermined from observed outflows and disks, we find that moderate diskmagnetic fields (\gtrsim 8 \times 10^{-4} G) are able to accelerate theoutflows up to the observed terminal velocities (\lesssim few 100 km s^{-1} inthe case of the Seyfert galaxies, and \sim 400 - 950 km s^{-1} in the case ofthe LIGs). The outflow is produced within a wind zone in the disk of radius\lesssim 100 pc in the LIGs, and \lesssim 10 pc in the Seyferts, with wind massloss to disk accretion rate ratios \dot M_w /\dot M_d \gtrsim 0.1 (where \dotM_d \sim 100 M_{\odot} yr^{-1}). The observation of rotating nuclear disks ofgas within few 100 pc scales in source candidates like the LIG Arp 220, andmagnetized outflows provide observational support for the picture drawn here.Comment: 31 pages, Latex file, 1 Figure, accepted for publication in the Astrophys. Journa