A possible origin of galactic magnetic fields

Large-scale galactic magnetic fields with strengths of several μG can result if galaxies typically undergo a brief but active phase during which magnetized plasma is channeled away from a central compact object through jets. When the jets are initially activated, they must tunnel through the ambient protogalactic medium, and, as they do so, material from the jets flows into the protogalactic medium. It is shown that if these jets possess magnetic fields with equipartition field strengths and large coherence lengths, then galactic fields with large coherence lengths and equipartition field strengths result, which suggests another possible origin of galactic magnetic fields. Observations of jets are consistent with the fields having large coherence lengths and equipartition field strengths, making the proposed model viable. The jet magnetic fields may be generated near the central compact object, and, subsequently, may be stretched and amplified by processes within the jets; this interpretation of the ultimate source of the field is not mandatory in this model, but it is discussed for completeness. Implications of the model are considered.