agauss, zagauss: gaussian line profile in wavelength space

A simple gaussian line profile. If the width is $\leq 0$ then it is treated as a delta function. The zagauss variant computes a redshifted gaussian.

$$A(\lambda) = K {1\over{\sigma\sqrt{2\pi}}} \exp(-(\lambda-\lambda_l)^2/2\sigma^2)$$

where:

par1 = $\lambda_l$	line wavelength in Angstrom
par2 = $\sigma$	line width in Angstrom
Norm = K	total photons/cm$^2$/s in the line

For zagauss the corresponding formula is:

$$A(\lambda) = K {(1+z)\over{\sigma\sqrt{2\pi}}} \exp(-(\lambda/(1+z)-\lambda_l)^2/2\sigma^2)$$

and the parameters are:

par1 = $\lambda_l$	line wavelength in Angstrom
par2 = $\sigma$	line width in Angstrom
par3 = z	redshift
Norm = K	total photons/cm$^2$/s in the line

The line is truncated at the point that the integrated flux under the line is within a critical value of the total flux. This critical value can be changed using xset LINECRITLEVEL. The default critical value is $1.0\times10^{-6}$.