a couple of points/requests for Subsample_to_NoisySubsample.py

[eclake]

Hi Kevin,

I'm using your nice Subsample_to_NoisySubsample.py script to add noise to objects using different apertures (closer to total) and in reading through the script noticed a couple of things that thought might be easiest to document here.

1 - From what I can see when you're taking account of the amount of flux in an aperture, you're not taking account of the axis ratio, is that correct? But you're reading in the half-light radius of the semi-major axis? Might it be more appropriate to use the circularised half-light radius? This was just from reading it - sorry if you ran tests on this and decided that the major axis radius was more appropriate.

2 - It would be really great to add a few things to the output file: i - the aperture used ii - the fraction of total flux enclosed in that aperture

I'll send you my 'total' apertures to see whether you would also like to include them as an option when I've finished them.

Thanks! Emma

[kevinhainline]

Emma, Thanks for these comments! You're right, I am ignoring the axis ratio in my calculation. I can definitely change this to circularized effective radius:

(r_circ = r_hl * sqrt(b/a))

I hadn't looked at this, but I should probably see how this affects the final noise.

And I can modify the code to include both the aperture size and the value I define as ap_corr, the factor that I multiply by the flux to get the flux through the aperture. That's no problem.

A question though, how are you estimating total fluxes without some estimate of the sersic profile, which would require actual images?

[eclake]

Thanks Kevin,

As for the total fluxes, I was going to estimate Kron radii assuming you have perfect estimates of n, r_e and axis_ratio for now, and integrating the denominator and numerator to a fixed multiple of r_e. It's a first step to seeing how imperfect flux estimates can affect our stellar mass estimates, while still attempting to obtain an estimate of total fluxes. I realised just correcting back to total from the aperture fluxes you supplied was, in essence, assuming we would have perfect measurements of flux, which we will never have. I thought about applying PSF corrections give an aperture, but given that you didn't take account of PSF effects (right?) I didn't think that was helpful....

But using a Kron radius to define the aperture gives more realistic noise estimates on something approaching our best estimate of total fluxes, which we'll never get accurately anyway.