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*Eric Huff, 05/03/2018 02:08 PM *

Back up: des_balrog_y3

# Balrog FAQ¶

What is Balrog?

Balrog is a set of software which: Adds artificial stars and galaxies to images and then reprocesses them, to come up with a input->output matrix of things such as detection efficiency vs magnitude, biases in magnitude,color, photo-z, shear vs. crowding, magnitude.

A paper on this is here:

http://adsabs.harvard.edu/abs/2016MNRAS.457..786S

What is DES Balrog Y3? DES Balrog for Y3 is specifically aimed at running balrog over the whole footprint (10000) tiles of DES Y3, using the same detection and measurement codes for magnitudes and shears and photo-zs that were used to generate the released Y3A2 dataset.

How is it different from Balrog Y1? Balrog for Y1 operated on coadd images, laying down objects in the coadd and recovering them. Balrog for Y3 lays down the objects in the single epoch exposures and then recombines the exposures into coadds (or MEDs files) the same way they were done for Y3 and redetects and measures there.

Where's the basic Balrog paper link? Here's the Y1 Balrog paper link: https://arxiv.org/abs/1507.08336

When are the meetings? Currently Thursdays at 3pm ET

When will Balrog be done? Hopefully shortly after the Y5A2 data are released to the collaboration the Y5 version of Balrog will be released to help scientists with their Y5 cosmology results. Before that we hope there will be a Y3 version of Balrog.

How is Balrog used by the DES collaboration? By weak lensing, photo-z, large scale structure and possibly other groups for refining their selection function and understanding biases.

When will Balrog start? It has already started!

Where are Balrog plots?

How can I get the Balrog outputs?

Where can I get the Balrog test data?

What is BFD? This is Bayesian Fourier D.

What are SOF, MOF, metacal/shear? These are the key measured quantities on galaxies. SOF = single object fit (no neighbor subtraction) CM_MAG (Composite Model magnitudes), where the composite model is a linear superposition of a DeVauc. spheroid and an elliptical disk. MOF (Multiobject fit) is like SOF but with neighbors subtracted. Both MOF and SOF mask neighbors, only MOF subtracts neighbors as part of the fit. Shear is also called metacal/ngmix and other things. This is how DES measures shapes of galaxies. In Y1 there was also im3shape.

Are there other balrog type things going on? Yes: HSC/LSST has this nice video: