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Medium-Band Photometric Redshifts

Medium-Band Photometric Redshifts. UCL Meeting 16 Sep 2008. Christian Wolf. flux / qef. 1000 nm. 400 nm. Redshift Errors & Resolution. Objects at different redshifts Filterset  's fixed. z = 0.843. G2 star vs. QSO z=3. z = 1.958. z = 2.828. E. colour. z=0.52. z=0.56. Sb.

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Medium-Band Photometric Redshifts

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  1. Medium-Band Photometric Redshifts UCL Meeting 16 Sep 2008 Christian Wolf

  2. flux / qef 1000 nm 400 nm Redshift Errors & Resolution • Objects at different redshifts • Filterset 's fixed z = 0.843 G2 star vs.QSO z=3 z = 1.958 z = 2.828

  3. E colour z=0.52 z=0.56 Sb colour Z-Bias & Calibration Offsets • N = number of filters, i.e. independent data points • Calibration offsets in N=3-D: • 1-D normalisation • 1-D z-bias • 1-D restframe SED bias • 1 out of N offset dimensions causes a photo-z bias z • More filters  smaller z (proj. component ~1/√N) • Narrow filters  small z (larger col/z on feature) • Spectroscopy with N~102..3: z without flux calibration • Few-filter photo-z’s limited by calibration accuracy • Many-filter photo-z’s limited by number and resolution of filters

  4. E colour z=0.52 z=0.56 Sb colour Redshift Error Regimes • Three regimes in photo-z quality • Saturation • Model-data calibration offsets in  test causes p(z)-biases • Transition • Locally linear colour(z) grid • Breakdown • Globally nonlinear colour(z) grid mag

  5. Galaxies: Saturation & Transition R=20 R=22 R=23.7 Galaxies at z~0.45

  6. R=21.5 R=22.9 R=23.8 QSOs: Saturation at R<24 rms 0.008 7%-20%outlier Calibrationoffsetsz biases Calibrationoffsetsline confusion QSOs at z~2.8

  7. 2-SED Classification, COMBO-17 Classification ~98% complete at R<23 Stars (~3,000) White Dwarfs (~30) Ultra-cool WD (1) Galaxies (~30,000) QSOs (~300)

  8. Old Red vs. Dusty Red Galaxies

  9. New Subject:Empirical 2 estimation? • 2 • PDF  Ambiguity warning • NN • No PDF, no warning • Template model • Can be extrapolated in z,mag • Calibration issues • Priors’ issues • Empirical model • Good priors • No calibration issues • Can not be extrapolated Code 2 NN Model Template  Empirical 

  10. Galaxies: No Ambiguities ANN 2 template 2 empirical Collister & Lahav 2004 ~0% outliersz/(1+z)>0.1 rmsz/(1+z) = 0.023 Bias ~0.00 ~4%outliersz/(1+z)>0.1 rmsz/(1+z) = 0.042 Bias -0.017 ~0% outliersz/(1+z)>0.1 rmsz/(1+z) = 0.020 Bias ~0.00

  11. QSOs: Strong Ambiguities ANN 2 template 2 empirical Filipe A. ~12% outliersz/(1+z)>0.3 rmsz/(1+z) = 0.113 Bias ~0.00 ~22%outliersz/(1+z)>0.3 rmsz/(1+z) = 0.056 Bias +0.015 ~1% outliersz/(1+z)>0.3 rmsz/(1+z) ~ 0.04 Bias ~0.000

  12. QSO Details

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