Bayesian Photometric Redshifts (BPZ) Narciso Benítez 1,2 (2000) Narciso Benítez 1,2 et al. (2004)...
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Bayesian Photometric Redshifts (BPZ)
Narciso Benítez1,2 (2000) Narciso Benítez1,2 et al. (2004)Dan Coe1,2,3 et al. (2006)
Johns Hopkins University1 Instituto de Astrofísica de Andalucía2
JPL/Caltech3
ScienceTeamScienceTeam
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Photo-z Methods
Spectral Energy Distribution (SED) Template Fitting
Empirical Training Set (Neural Networks)
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Coleman, Wu, Weedman ‘80
Kinney ‘96
Bruzual & Charlot ‘03
Spectral Energy Distribution (SED) templates
BPZ v1.99bBPZ v1.99bBenítez ‘00,
‘04Benítez ‘00,
‘04Coe ‘06Coe ‘06
recalibrated with real photometry
http://adcam.pha.jhu.edu/~txitxo/
Normally interpolate 2 between adjacent templates
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Flu
x
Wavelength
SED template fit
SED template fit
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Redshift
Pro
babi
lity
prior: I = 26
without prior
with prior
with prior
Bayesian use of priors
Benítez00
Output:
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Benítez00
Redshift Inaccuracy (photo-z vs. spec-z)Redshift Inaccuracy (photo-z vs. spec-z)
Poo
rnes
s of
Fit
Poo
rnes
s of
Fit
Poorest fits yieldmost accurate redshifts!
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2 = 4.27
2 = 0.11
Wavelength
Flu
x
2mod = 0.03
2mod = 0.19
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PHAT GOODS BPZ results (training set)Important to plot error bars and goodness-of-fit
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PHAT GOODS BPZ results (training set)Single-peaked P(z) [ODDS 0.95]
no error bars plotted
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Most GOODS objects have good photometry
ACSgroundIRAC
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…but some are bad
ACSgroundIRAC
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ACSgroundIRAC
…some are ugly
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Robust photo-z’s require
Robust photometry
One of the best methods(even if Peter doesn’t like it ;)
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PSF-corrected aperture-matched photometry
What is the best method?
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PHOTEST
Photometry TestingPSF Degradation vs. Model FittingMagnitude UncertaintiesZeropoint CalibrationObject Detection & Deblending…
Sounds like a job for a new group Let’s meet in Greece 2009
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UDF NICMOS fluxes too low
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NICMOS flux recalibration
Objects w/ spec-z
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Comprehensive Segmentation MapForced into SExtractor
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Wish List(Goals for PHAT?)
Improve SED librarymore galaxy typesbroader wavelength coverageSED uncertainties derived from population synthesis models??
Improve Priors using UDF, surveys
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Optimal Filter Choice for a given amount of observing time
Benítez et al. (2008) A&A submitted
4 - 5 filters is sub-optimal ! addition of near-IR helps somewhat > 8 filters performs much better
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Filters tested
= const
contiguous overlapping
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Photo-z completenessBest is > 8 overlapping filters
Depth to which 80% of objects have ODDS ≥ 0.99
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Photo-z accuracy for ODDS ≥ 0.99 objectsBest is many non-overlapping (contiguous) filters
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lab
including CCD, atmosphere, mirror reflectivity
ALHAMBRA Survey (Moles08)
20 medium-band (310Å wide) filters3500 - 9700Å, supplemented by JHKs
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ALHAMBRA
Survey
1.5’ x 1.5’
14-filter color image
to cover4+ sq deg
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8,000 - 10,000 sq deg z < 0.9 - 1.0 4 - 5 years 6 sq deg camera new 2-3m telescope to be built in
Aragon, Spain
8,000 - 10,000 sq deg z < 0.9 - 1.0 4 - 5 years 6 sq deg camera new 2-3m telescope to be built in
Aragon, Spain
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PAU Survey: 40 100Å-wide filters (~4000-8000Å) + SDSS u & z
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PAU Survey: z/(1+z) < 0.0015 for z < 0.4, L > L*, I < 23 LRGs
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PAU Survey: BAO cosmological constraints
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PAU Survey: relative w constraints