1. Discussion Session 5: Christian Wolf Should we invest more into photo-z or spectroscopic surveys?

2. Exposure Times Well established 8-m instrumentation (last ~5 years) –VLT 8m + VIMOS –Subaru 8m + SuprimeCam Methodz AccuracyExposure time Broad-band photo-z 0.03 1 Medium-band photo-z 0.01 5 Spectroscopy <0.001 50-100 More area / depth for less precision

3. Photo-Z Attractive For… Global galaxy evolution –1999+: optical HiFi photo-z, e.g. COMBO-17: 10 4.5 obj. –Now: Focus on environment needs  z /(1+z) ~ 0.001 –At z > 1 not at Poisson limit Flux-calibrated photometry –SED from constant physical footprint, while PSF = f( ) Large-scale structure –Photo-z: 2D in z slices Volume selection for spectroscopic surveys –Efficiency increase –Super-cluster environments –Try FMOS / FAST-SOUND at z = [1.3,1.7] without pre- selection (success <10%?) Weak gravitational lensing –Need accurate z distribution –2010+ lensing surveys want bias  z /(1+z)  ~ 0.001  Huge training effort (spec!) Stand-aloneCross-fertilization

4. Dis- / Advantage PropertyPhotometry Spectroscopy Area / depth + Z accuracy + SED accuracy + Z reliability ~ ~ Blended objects (+)

5. Combine SEDs + Spectra Improved SED analysis –Spectroscopic redshift prior –Rest-frame SED known: age and dust more reliable –Talk by Christian Wolf Improved composite stellar population analysis –Line indices & SED together break some degeneracy –Fix old population better and see young population as left-over SED difference –Talk by Daniel Thomas Age  Dust  Kinney et al. templates  25% z outliers Abell 901 z ~ 0.17