Plotting a Probability distribution with varying parameter

edit

Suppose I wish to plot the function

import numpy as np
var('a,y') 
A=np.linspace(-1,1,10)
for a in A:
    z=a+x-(e^(-y^2/2))/sqrt((2*pi))
    plot3d(z,(x,-1,1),(y,-1,1))

That is, I wish to plot the function z over a range of a. Actually the original function was z=a+x. But, in order to introduce randomization, I changed the variable x to x-y', where y' is the standard normal variable. I wish to obtain the plot of z as a kind of variable probability distribution over the grid of x and y with the variation of a (so kind of series of probability distributions overlapping each other). How do I do this? Any hints? Thanks beforehand.