At what cosmic time was/is star formation density at its peak?

Question

-At present time.
-Within the first billion years after the Big Bang.
-At about few billion years after the Big Bang.
-About few billion years ago.

Answer 1

http://www.nature.com/nature/journal/v469/n7331/fig_tab/nature09717_F4.html

I am not certain you meant star formation density, however, here is indicates a maximum about 3billion years ago.

Answer 2

Qwerty, remember the honor code in Coursera.