On a somewhat related note to scale factor, is the value of little_h a constant 0.704 across all redshifts and in every Illustris run, or does it vary and need to be adjusted for each redshift? Thanks
Little h is always constant with redshift.
It can vary with run, but all the currently released Illustris runs (all 6) have the same little_h, so you can just hard-code it. Future runs will have different little_h, so you may want to keep this easily changeable in your scripts.
Thank you very much Dr. Nelson, this is good to know!