The electron density is always calculated in Gaussian but you can make sure by adding the keyword Density=current. If you want to visualize it, then after the calculation is done you can produce a cube file. That can be done from the formated checkpoint file. For instance, see http://www.gaussian.com/g_tech/g_ur/u_cubegen.htm. There are many visualization programs that can handle cube files, like VMD, molgen, Gaussview, etc.
How to calculate electron density of nano iron atom and sulphate ion in gas phase using DFT method in Gaussian?
In a gas phase the electron eigenfunctions do not overlap. They behave as in free atom or ion. But DFT approach in a case of transition element (iron) suffers on self-interaction
(SIC), which could be cancelled. The simplest empirical way to improve the energy functional is DFT+U method.
The electron density is very easily seen on a QTAIM approach. To do that, use density=current and output=wfn keywords in your calculation and generate a wfn file, and after that integrate the wfn file with some program like AIMAll. Its standard version is free of charge.