We have developed a general model for determining density-dependent effective dielectronic recombination ( DR ) rate coefficients in order to explore finite-density effects on the ionization balance of plasmas .
Our model consists of multiplying by a suppression factor those highly-accurate total zero-density DR rate coefficients which have been produced from state-of-the-art theoretical calculations and which have been benchmarked by experiment .
The suppression factor is based-upon earlier detailed collision-radiative calculations which were made for a wide range of ions at various densities and temperatures , but used a simplified treatment of DR. A general suppression formula is then developed as a function of isoelectronic sequence , charge , density , and temperature .
These density-dependent effective DR rate coefficients are then used in the plasma simulation code Cloudy to compute ionization balance curves for both collisionally ionized and photoionized plasmas at very low ( n _ { e } = 1 ~ { } cm ^ { -3 } ) and finite ( n _ { e } = 10 ^ { 10 } ~ { } cm ^ { -3 } ) densities .
We find that the denser case is significantly more ionized due to suppression of DR , warranting further studies of density effects on DR by detailed collisional-radiative calculations which utilize state-of-the-art partial DR rate coefficients .
This is expected to impact the predictions of the ionization balance in denser cosmic gases such as those found in nova and supernova shells , accretion disks , and the broad emission line regions in active galactic nuclei .