A Tentative Size-Luminosity Relation for the Iron Emission-Line Region   in Quasars
  New reverberation mapping measurements of the size of the optical iron emission-line region in quasars are provided, and a tentative size-luminosity relation for this component is reported. Combined with lag measurements in low-luminosity sources, the results imply an emission-region size that is comparable to and at most twice that of the H$\beta$ line, and is characterized by a similar luminosity dependence. This suggests that the physics underlying the formation of the optical iron blends in quasars may be similar to that of other broad emission lines. 
Doron Chelouche, Stephen E. Rafter, Gabriel I. Cotlier, Shai Kaspi,   Aaron J. Barth
astro-ph.GA