Photometric redshift for clusters through A1689 and simulation studies

Photometric redshift for clusters through A1689 andsimulation studies

Stephanie Jouvel, Ofer Lahav, Ole Host

Outline

- Presentation of Le Phare code

- A1689 photoz results : BPZ (Dan Coe) & Le Phare

- Massimo Neghetti’s simulation : photoz results

Le Phare photoz code

Stephane Arnouts & Olivier Ilbert :

http://www.cfht.hawaii.edu/~arnouts/LEPHARE/cfht_lephare/lephare.html

Interesting features and new developments include :

- A prior on the redshift distribution using the VVDS spectroscopic redshift survey

- Emission lines fluxes included in the library of templates. This is calculated using the relation between UV absolute magnitude – OII fluxes (Kennicutt et al. 1998). Other lines are derived from emission line ratios.

- Possibility of including several extinction laws and E(B-V) values.

- FIR scaling


COSMOS photoz : Ilbert et al. 2009

A1689 photometric bands

A1689 : photoz BPZ & Le PhareCOSMOS : 31 templates – Bruzual & Charlot 03 (Ext,NoEm) + Nz priori (VVDS)

Photoz results for A1689

Adding prior on the redshift distribution

Error budget for HST filters probably underestimated : Filter calibration , source extraction Sextractor, photometry accuracy

=> High constraints on the fitting procedure We release it in adding +0.02 in quadrature to r,i,z HST filters photometric errors

Photoz results for A1689 : BPZ and Le Phare

A1689 photoz distribution

Need to carefully select the filters to calculate photoz

Massimo's simulations : LePhare & BPZ

Massimo's simulations : lenses

Contamination by galaxy cluster members :Photometry extraction problems

Between Le Phare and BPZ we will probablyBe able to remove catastrophic redshit

Conclusion

- Validate the 0.02*(1+z) photoz accuracy- Remove catastrophic redshift using pdz information of several photoz codes- Need careful work on the photometry extraction- Do a proper analysis of the photometry error budget to improve the photoz accuracy- Optimize the observation strategy to get good photometry in the key filters- Do a pre-selection of cluster members from background galaxies following Umetsu et al. 2010 paper

A1689 : 85 zpsec

Le Phare parameters

Photoz results for A1689 : dz

Massimo's simulations : LePhare vs BPZ


Jouvel et al. 2009

Why in one sentence

Improve photoz fit through error budget

+0.02

Error budget for HST filters probably underestimated : Filter calibration , source extraction Sextractor, photometry accuracy

=> High constraints on the fitting procedure We release it in adding +0.02 in quadrature to r,i,z HST filters photometric errors

Photometric redshift for clusters through A1689 and simulation studies

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