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EAZY: A FAST, PUBLIC PHOTOMETRIC REDSHIFT CODE

EAZY: A FAST, PUBLIC PHOTOMETRIC REDSHIFT CODE. Author: Brammer et al. 2008 Speaker: Guang Yang 2013.04.10. Introduction. Methods of measuring Z 1. Spectroscopic  Accurate  Time-consuming 2. Photometric

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EAZY: A FAST, PUBLIC PHOTOMETRIC REDSHIFT CODE

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  1. EAZY: A FAST, PUBLIC PHOTOMETRIC REDSHIFT CODE Author: Brammer et al. 2008 Speaker: Guang Yang 2013.04.10

  2. Introduction • Methods of measuring Z • 1. Spectroscopic •  Accurate •  Time-consuming • 2. Photometric • : Measure many objects at same time • : Unreliable • Heavly rely on method !

  3. So, We Need PowerfulCodeto Get Reliable Z-photo

  4. Main Procedure of Most Codes

  5. Features of EAZY • 1. Template produced by semi-analytical model (, all done by authors) • 2. Allow linear combination of templates • 3. Bayesian analysis • 4. New parameter to evaluate reliability

  6. Specific Procedure

  7. Develop Template • Traditonal spectroscopic template •  Strong selection effect e.g. low z, bright objects • ❤ stellar population synthetic model

  8. 10k Objecs Synthetic catalog from Blaizot et al. 2005 (B05)

  9. Specific Process • 3000 objects from PEGASE model library • NMF algorithm + B05 (for calibration) • 5 templates • + 1 (dusty) ( quite arbitrary) • Only Six !

  10. The dusty one, just fill the ‘blank” !

  11. Estimate template error I strongly recommend iterative procedure !

  12. Fit data • (j: the index of filters) where (i: index of templates) &

  13. Results before Bayesian analysis 1. Calculate best to minimize for each Z in grid 2. Z with minimum PS:  only consider one point neglect other possible Z

  14. Apply Bayesian Analysis • Get the prior: (Benitez 2000) p(z|), for a specific band, e.g. R, K in a given bin

  15. Calculate Posterior Z Distribution Bayesian Theorem , should be p(C|z)

  16. Yield Final Results • Z with highest •  Make use of the whole distribution

  17. Addenda • Confidence level: (traditional way) • Fresh Reliability Parameter:

  18. Test of the effect of  both simulated & spec samples

  19. Application • Apply EAZY to following catalog:

  20. to descirbe diffusion (disregard the effect of terrible outliers and system offset ) Catastrophic outliers

  21. Changing Default Parameter

  22. (  

  23. Z-spec Test: Is That Reliable? no spec data selection effect?

  24. Similar Test

  25. Reference • Brammer et al. The Astrophysical Journal, 686:1503 Y 1513, 2008 October 20 • EAZY manual: Brammer et al, 2008 EAZY Website http://www.astro.yale.edu/eazy/

  26. Thanks !

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