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

Photo-z Methods

Spectral Energy Distribution (SED) Template Fitting

Empirical Training Set (Neural Networks)

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

Flu

x

Wavelength

SED template fit

SED template fit

Redshift

Pro

babi

lity

prior: I = 26

without prior

with prior

with prior

Bayesian use of priors

Benítez00

Output:

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!

2 = 4.27

2 = 0.11

Wavelength

Flu

x

2mod = 0.03

2mod = 0.19

PHAT GOODS BPZ results (training set)Important to plot error bars and goodness-of-fit

PHAT GOODS BPZ results (training set)Single-peaked P(z) [ODDS 0.95]

no error bars plotted

Most GOODS objects have good photometry

ACSgroundIRAC

…but some are bad

ACSgroundIRAC

ACSgroundIRAC

…some are ugly

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?

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

UDF NICMOS fluxes too low

NICMOS flux recalibration

Objects w/ spec-z

Comprehensive Segmentation MapForced into SExtractor

Wish List(Goals for PHAT?)

Improve SED librarymore galaxy typesbroader wavelength coverageSED uncertainties derived from population synthesis models??

Improve Priors using UDF, surveys

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

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

Photo-z accuracy for ODDS ≥ 0.99 objectsBest is many non-overlapping (contiguous) filters

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

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

PAU Survey: BAO cosmological constraints

PAU Survey: relative w constraints