Neron models and Compactified Picard schemes over the moduli stack of   stable curves
  We prove that there exist some stacks, representable over the stack of stable curves, having the following universal property with respect to N\'eron models of Jacobians. For every one-parameter family of stable curves, with regular total space, the N\'eron model of the Jacobian of its generic fibre is isomorphic to the base change of the above stacks via the moduli map of the given family. We also obtain a stack compactification of the universal Picard scheme and hence a geometrically meaningful completion of the N\'eron model of the Jacobian for every family as above. 
Lucia Caporaso