Monday, October 18, 2010

Another idea...

Another idea I have about generating this random catalog. First I generate the random ra and random dec, then I use the function ang2pix_nest (converts angle to pixel) to figure out which pixel it occurs in. Once we have that, depending on the weight we can keep the random value or throw it away. However, this might take a really long time if most of our objects are outside of the mask.

I also am not sure how to use the weight value. Should it be a step function, if weight > 0.2 then keep, if not then throw away, or something more subtle like the weight represents the expectation value of the probability distribution of if the random is in the pixel or not. In terms of the redshifts, should I do what I did before and match the random redshift distribution to the data?

1 comment:

  1. I was thinking along similar lines, but on a pixel by pixel basis... Decide if the pixel's a keeper, then draw a square box around it within to generate random numbers. Each one you generate, decide if it lives in the pixel, and if so, keep it. Keep doing this until the number of randoms in the pixel is what you are after. I don't know a priori if this will be better or worse than the scheme you outline, it must depend to some extent on the patchiness and covering fraction.

    In answer to your second question, I think it depends on what the weight means. If it means the signal is lower in pixels with lower weight (such that a smaller fraction of total galaxies shows up) then you probably want to factor it in, but you should talk to somebody who can interpret what it means before deciding.

    Did you ever find out if these random catalogs exist? If not, you should figure out who to send them to once they've been made, they are usefol for everyone.