Science from Overlapping Lensing / Spec-Z Surveys

Science from overlapping lensing / spec-z surveys

Chris Blake (Swinburne) Probes of the cosmological model

How fast is the Universe How fast are structures expanding with time? growing within it? Redshift-space distortions • RSD allow spectroscopic galaxy surveys to measure the growth rate of structure coherent virialized ﬂows infalling motions galaxies

observer Why combination of lensing and RSD?

• Sensitive to theories of gravity in complementary ways • General perturbations to FRW metric:

• are metric gravitational potentials, identical in General Relativity but can differ in general theories • Relativistic particles (e.g. light rays for lensing) collect equal contributions and are sensitive to • Non-relativistic particles (e.g. galaxies infalling into clusters) experience the Newtonian potential Applications 12 F. Simpson et al.

0.9

arXiv:1212.3339Mon.0.8 Not. R. Astron. Soc. 000, 000–000 (0000) Printed 17 December 2012 (MN LATEX style ﬁle v2.2)

CFHTLenS:0.7 Testing the Laws of Gravity with Tomographic Weak Lensing and Redshift Space Distortions 0.6

1! 1 2 3 13 Fergus0.5 Simpson , Catherine Heymans , David Parkinson , Chris Blake , Martinφ Kilbinger4,5,6, Jonathan Benjamin7, Thomas Erben8, Hendrik Hildebrandt7,8, Henk Hoekstra9,10, Thomas D. Kitching1, Yannick Mellier11, Lance Miller12, Ludovic0.4 Van Waerbeke7, Jean Coupon13, Liping Fu14, Joachim Harnois-Deraps´ 15,16, Michael J. Hudson17,18, Konrad Kuijken9, Barnaby Rowe19,20, Tim Schrabback8,9,21, Elisabetta0.3 Semboloni9, Sanaz Vafaei7, Malin Velander12,9.

1Scottish Universities Physics Alliance, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK. 2School of Mathematics and Physics, University of Queensland, Brisbane, QLD 4072, Australia 3Centre0.2 for Astrophysics & Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, VIC 3122, Australia 4CEA Saclay, Service d’Astrophysique (SAp), Orme des Merisiers, Batˆ 709, F-91191 Gif-sur-Yvette, France. 5Excellence Cluster Universe, Boltzmannstr. 2, D-85748 Garching, Germany. 6Universit0.1 ats-Sternwarte,¨ Ludwig-Maximillians-Universitat¨ Munchen,¨ Scheinerstr. 1, 81679 Munchen,¨ Germany. 7Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, V6T 1Z1, BC, Canada. 8Argelander Institute for Astronomy, University of Bonn, Auf dem Hugel¨ 71, 53121 Bonn, Germany. 9Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands. 10Department0 of Physics and Astronomy, University of Victoria, Victoria, BC V8P 5C2, Canada. 11Institut0 d’Astrophysique de Paris,0.5 Universite´ Pierre et Marie1 Curie - Paris 6, 981.5 bis Boulevard Arago, F-750142 Paris, France. 2.5 12Department of Physics, Oxford University, Keble Road, Oxford OX1 3RH, UK. 13Institute of Astronomy and Astrophysics, Academia Sinica, P.O.Redshift Box 23-141, Taipei 10617, Taiwan. 14Key Lab1 for Astrophysics, Shanghai Normal University, 100 Guilin Road, 200234, Shanghai, China. 15Canadian Institute for Theoretical Astrophysics, University of Toronto, M5S 3H8, Ontario, Canada. 16Department of Physics, University of Toronto, M5S 1A7, Ontario, Canada. Figure 11. Here we explore fractional deviations in the two gravitational 17 arXiv:1003.2185 FigureDepartment 12. of PhysicsThe and Astronomy, redshift University sensitivity of Waterloo, Waterloo,of the ON, N2L modified 3G1, Canada. gravity parameter µ0. potentials, the Newtonian potential Ψ and the curvature potential Φ, from 18Perimeter Institute for Theoretical Physics, 31 Caroline Street N, Waterloo, ON, N2L 1Y5, Canada. The19Department weight of Physics function and Astronomy,φ University(z) is College defined London, Gower in Street, equation London WC1E (22) 6BT, UK.and evaluated with the GR value at z =0.5. The prescription for this is given by equation (21). 20California Institute of Technology, 1200 E California Boulevard, Pasadena CA 91125, USA. Confirmation of general relativity on large scales fromequation21Kavli Institute (23)for Particle. Astrophysics and Cosmology, Stanford University, 382 Via Pueblo Mall, Stanford, CA 94305-4060, USA. The contours represent the same combinations of data as those in the left 1 hand panelweak of Figure lensing 5. and galaxy velocities 17 December 2012 ples of theoretical models onto our parameter space, by evaluating 1 1 2-4 2 Reinabelle Reyes , Rachel Mandelbaum , Uros Seljak , Tobias Baldauf , Jamesequation E. (22). HoweverABSTRACT as stressed earlier, we do not aim to place 8 THEORETICAL MODELS Dark energy may be the first sign of new fundamental physics in the Universe, taking either a

1 2 2 arXiv:1212.3339v1 [astro-ph.CO] 13 Dec 2012 rigorous parameterphysical constraints form or revealing on any a correction particular to Einsteinian family gravity. Weak of gravitational models. lensing and Gunn , Lucas Lombriser , Robert E. Smith galaxy peculiar velocities provide complementary probes of General Relativity, and in com- Below we briefly review some of the theoretical models which bination allow us to test modified theories of gravity in a unique way. We perform such an analysis by combining measurements of cosmic shear tomography from the Canada-France could generate1 a departure from µ0 = Σ0 =0, and interpret the Hawaii Telescope Lensing Survey (CFHTLenS) with the growth of structure from the Wig- Princeton University Observatory, Peyton Hall, Princeton, NJ 08544 USA f(R) gleZ Dark Energy Survey and the Six-degree-Field Galaxy Survey (6dFGS), producing the implications of our results. There is such a plethora of modified 8.1 strongest existing joint constraints on the metric potentials that describe general theories of 2Institute for Theoretical Physics, University of Zurich, Zurich, 8057, Switzerland gravity. For scale-independent modifications to the metric potentials which evolve linearly gravity models, that no single choice of parameterisation can ade- A more general formwith the of effective the dark Einstein-Hilbert energy density, we find present-day action cosmological replaces deviations the in the 3 Newtonian potential and curvature potential from the prediction of General Relativity to be Physics and Astronomy Department and Lawrence Berkeley National Laboratory, ∆Ψ/Ψ =0 .05 0.25 and ∆Φ/Φ = 0.05 0.3 respectively (68 per cent CL). quately encompass all of them. This is a situation reminiscent of the Ricci scalar R with an arbitrary± function −f(R±) such that Figure 2 | Comparison ofKey observational words: cosmology: observations constraints - gravitational lensing with predictions from dark energyUniversity equation of California of state,-Berkeley,w(z) ,CA except 94720 hereUSA we are faced with uncertainty4 not only in the functional form of the time-dependence, but alsoInstitute in its for scale-dependence. Early Universe, Ewha So University, how can Seoul, we S. relate KoreaGR a given and viable modified gravityS = theories.f(R)√ g d Estimates4x, of EG((24)R) are shown with ! − (µ, Σ) constraint to a specific model? The observed parameters µˆ0 [email protected] ! 19 c 0000 RAS 1! error bars! (s.d.) including the statistical error on the measurement of ! and Σˆ 0 may be interpreted as a weighted integral over the true func- where g is the determinant of the metric tensor. This defines the tional formEinstein’sµ(k, general z), such relativity that (GR) is the theory of gravity underpinning our broad class of f(R) models. One of the most difficult tasks for (filled circles).any The modified grey gravity shaded model region attempting indicates to replace the dark1! energyenvelope is of the mean understanding of the Universe, encapsulatedΩΛ in the standard cosmological model µˆ0 = φ(k, z) µ(k, z) dk dz. (22) to satisfy the stringent-1 Solar System constraints, and most natu- ΩΛ(z) E over scales R = 10 – 50h Mpc, where the systematic effects are least (!CDM). To explain!! observations showing that the UniverseG is undergoing ral choices of the function f(R) fail to do so. The subset of f(R) If we performaccelerated a expansion scale- and1,2, ! time-dependentCDM posits the existence principal of a component gravitationally repulsivemodels which have attracted interest are those which employ the analysis (see for example Zhao et al. 2009), then the weightimportant func- (see Supplementary Information). The horizontal line shows the mean fluid, called dark energy (in addition to ordinary matter and dark matter). so-called chameleon mechanism, where departures from GR are tion φ(k, z) may be expressed in terms of the principal componentsprediction ofstrongly the GR+ suppressed"CDM inmodel, regions E where= !R is/ large,f , for only the emerging effective redshift of the Alternatively, the breakdown of GR on cosmological length scales could also G m,0 ei(k, z) and the errors associated with their corresponding eigen- when R is sufficiently small. Our location within the potential well values σexplain(αj ) (Simpsonthe cosmic acceleration. & Bridle 2006), Indeed, such modifications that to GRmeasurement, have been proposedof the z = Sun 0.32. and theOn Milky the right Way haloside may of bethe sufficient panel,to labelled shield us vertical bars as alternatives to dark energy3,4, as well as to dark matter.5,6 These modifiedfrom this unusual gravitational behaviour. 2 ei(k, z) ei(k!,z!)dk! dz!/σ (αi) show the predictedFor aranges particular from subset three of f( Rdifferent) models whichgravity are theories: capable of (i) GR+"CDM φ(k,gravity z)= theoriesi are designed to explain the observed expansion. (23)history, so the only 2 2 satisfying Solar System tests, the departure from GR may be char- " j ej (k##!!,z!!)dk!! dz!! /σ (αj ) way to test them is to study cosmological perturbations (deviations( EG = of0.408 the matter±acterised0.029 ( as1! (Zhao)), (ii) et al.a 2012)class of cosmologically-interesting models The analysis of redshift" $## space distortions in% Blake et al. (2012) in- density from its mean value). This is a non-trivial task, compounded by our lack of 27 cludes information from the galaxy power spectrum up toin af max-(R) theory with Compton wavelength 1parameters B0 = 0.001! 0.1 a priori knowledge of relevant astrophysical1 parameters.7,8 Here, we successfully µ(k, a)= , (25) imum wavenumber kmax =0.2 hMpc− , corresponding to the 2 3 + 3(aM/k9) 9 regimemeasure over which the probe the densityof gravity and EG velocitythat is robust fields to these are sufficientlyuncertainties.( EG = 0.328 Under! 0.365 ), and (iii) a TeVeS model designed to match existing linear for our theoretical models to remain valid. Since the number where the scalaron mass M(a) = 1/ 3d2f/dR2. For any given GR+!CDM, EG should approximately equal 0.4. We find EG = 0.39±0.06 at of Fourier modes increases towards higher k, the scale-dependentcosmological redshift data andand wavenumber, to produce the a valuesignificant of µ lies enhancem in the rangeent0 of! the growth 1 & component of φ(k, z) peaks close to this value of kmax, and µ< 3 . This generically enhances growth, so we expect this 1 factor ( , shown with a nominal error bar of 10 per cent for clarity). φ(k, z)=0 Submittedfor kversion. > k maxAccepted. We version evaluate and thesupplementary redshift-dependence material are availableEG = at:family0.22 of models to lie vertically above the point (0, 0) in Fig- σ of the weighthttp://www.nature.com/nature/journal/v464/n7286/full/nature08857.html function φ(z) associated with the combined WiggleZ . ure 5. We parameterise M = M0a− and take as an example 1 and 6dFGS data of Figure 3, following the prescription of Simp- M0 =0.02 hMpc− and σ =3, corresponding to the type of son & Bridle (2006), and this is shown to peak at z 0.5 as il- model explored in Zhao et al. (2012). In f(R) models the lensing ∼ lustrated in Figure 12. In the following subsections we utilise the potential for a given mass distribution is unchanged from the case f(R) weight function φ(z) presented in Figure 12 to map specific exam- of GR, and so Σ0 =0. Our measure of µ is dominated by the

c 0000 RAS, MNRAS 000, 000–000 ! Overlaps of lensing and spec-z surveys

• Improvement of cosmological measurements through addition of galaxy-galaxy lensing • [e.g. determines bias of lens sample which improves RSD measurements of lenses, especially when using multiple-tracer techniques, e.g. Cai & Bernstein (2012)] • Spec-z survey allows deﬁnition of lens samples (e.g. groups, galaxy types) enabling a range of studies • Understanding, calibration and risk mitigation of systematic errors (photo-z errors including outliers, intrinsic alignments, cosmic shear) Overlaps of lensing and spec-z surveys • Mis-match between imaging and spectroscopic surveys! Mon. Not. R. Astron. Soc. 000, 1–21 (2009) Printed 31 July 2013 (MN LATEX style ﬁle v2.2)

Optimising Spectroscopic and Photometric Galaxy Surveys: Same-sky Beneﬁts for Dark Energy and Modiﬁed Gravity

Donnacha Kirk1, Ofer Lahav1, Sarah Bridle2, Stephanie Jouvel3, Overlaps of Filipelensing B. Abdalla 1and, Joshua A.spec-z Frieman4 surveys 1Department of Physics & Astronomy, University College London, Gower Street, London, WC1E 6BT, UK 2Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK 3Institut de Ci`encies de l’Espai (ICE, IEEC/CSIC), E-08193 Bellaterra (Barcelona), Spain 4Fermilab Center for Particle Astrophysics, Batavia, IL 60510 4Kavli Institute for Cosmological Physics, The University of Chicago, Chicago, IL 60637

• Many recent31 Julypapers 2013 considering impact for cosmology 10 Donnachaof same-sky Kirk, Ofer Lahav, vs. Sarah different-sky Bridle, StephanieABSTRACT lensing/spec-z Jouvel, Filipe B. Abdalla, surveys Joshua A. Frieman The combination of multiple cosmological probes can produce measurements of cosmological parameters much more stringent than those possible with any individual probe. Mon. Not. R. Astron. Soc. 000, 1–21 (2009) Printed 31 July 2013 (MN LATEX style file v2.2) 5 Weon examine deviations the combination from GR of and two highly thearXiv:1307.8062 final correlated joint probes constraint of late-t withime structure ee FoM = 1.6 growth: (i) weak gravitational lensing from a survey with photometric redshifts and (ii)cross-correlations galaxy clustering and is redshift over spacean order distortions of magnitude from a survey smaller with spectroscopic in 4 nn FoM = 0.9 ee + nn FoM = 7.2 redshifts.Optimisingterms We of MGchoose Spectroscopic FoM generic than survey when designsand RSDs Photometric so are that included. our results Galaxy are applicable to a ee + ne + nn FoM = 27.8 rangeSurveys: ofIn current the Same-sky followingand future Benefitsphotometric sub-sections for redshift we Dark perturb (e.g. Energy KiDS, in turn DES and, a HSC, range Modified Euclid) and 3 spectroscopic redshift (e.g. DESI, 4MOST, Sumire) surveys. Combining the surveys greatlyGravityof the improves assumptions their power we to have measure made both for dark our energy fiducial and mod forecast.ified gravity. An 2 independent,Some of non-overlapping the results are combination summarised sees a in dark table energy 4 for figu easere of of merit more thanDonnachacomparison. 4 times Kirk larger1, Ofer than Lahav that1 produced, Sarah Bridle by either2, Stephanie survey Jouvelalone.3 The, powerful syner- 1 giesFilipe between B. Abdalla the surveys1, Joshua are A. strongest Frieman4 for modified gravity, where their constraints are1Department orthogonal, of Physics producing & Astronomy, University a non-overlapping College London, Gower joint Street, figure London, WC1E of merit 6BT, UK nearly 2 orders of magnitude2Jodrell Bank Centre larger for Astrophysics, than either School ofalone. Physics andOurAstronomy, projected The University angular of Manchester, power Manchester, spectrum M13 formal-9PL, UK a 3Institut de Ciències de l’Espai (ICE, IEEC/CSIC), E-08193 Bellaterra (Barcelona), Spain

w 0 ism4Fermilab5.1 makes Center Survey it for easy Particle to Astrophysics, model Specific the Batavia, cross-correlation Target IL 60510 Selection observable when the surveys overlap on4Kavli the Institute sky, for producing Cosmological Physics, a joint The data University vector of Chicago, and Chicago, full IL covariance 60637 matrix. We calculate a !1 same-skyWe have improvement assumed factor, a generic from the survey inclusion strategy of these for cross- ourcorrelations, spec-z relative to31 non-overlapping July 2013 surveys. We find nearly a factor of 4 for dark energy and more than survey in order that our results might be as widely applicable !2 a factor of 2 for modified gravity. The exact forecast figures of merit and same-sky benefitsas possible. can be radically AnotherABSTRACT affected benefit by a range of assuming of forecasts a assumpt constantion, galaxy which we explore methodically in a sensitivityThe combination analysis. of multiple We cosmological show that probes that can ourproduce fiducial measurements assumptions of cosmo- !3 density out to zlogical=1 parameters.7 is that much more our stringent results than those are possible not with hostage any individual probe. arXiv:1307.8062v1 [astro-ph.CO] 30 Jul 2013 produceto the robust particularities resultsWe which examine giveof the a acombination certain good average of target two highly picture selection correlated of the probessc strateience of late-tgy returnime structure from combining photometricgrowth: and spectroscopic (i) weak gravitational surveys. lensing from a survey with photometric redshifts and !4 which could interact(ii) galaxy in clustering a peculiar and redshift way space distortions with, from for a example, survey with spectroscopic Key words: cosmology:redshifts. observations We choose generic– gravitational survey designs lensing so that – our dark results energy are applicable – modified to a range of current and future photometric redshift (e.g. KiDS, DES, HSC, Euclid) and gravityredshift – cosmological coverage, parameters photo-z – error large-scale or k/z-dependence structure of Univ oferse galaxy !5 spectroscopic redshift (e.g. DESI, 4MOST, Sumire) surveys. Combining the surveys !2 !1.5 !1 !0.5 0 bias. greatly improves their power to measure both dark energy and modified gravity. An w independent, non-overlapping combination sees a dark energy figure of merit more 0 We recognisethan that 4 times no larger individual than that produced survey by either as survey carried alone. The outpowerful syner- gies between the surveys are strongest for modified gravity, where their constraints 2 will look exactlyare like orthogonal, the producing toy survey a non-overlapping we assume joint figure here. of merit nTheearly 2 orders of ee MGFoM1 INTRODUCTION = 0.3 impact of specificmagnitude surveyColless larger and than 2003)either target chronicle alone. selection Our the projected growth strategies angular of cosmic power spectrum ar structuree formal- and nn MGFoM = 0.6 ism makesWeak it easy toGravitational model the cross-correlation Lensing (WGL) observable (Hoekstra when the surveys & Jain overlap 2008; 1.8 considered in ouron the companion sky, producing a jointpaper data vector Jouvel and full (2013). covariance matrInix. this We calculate a For me a keyee +The nn MGFoM eraissue of “precision= 50.1 is cosmology” systematic is now a reality. Different same-skyerror improvementHeymans 2012) factor,control from gives the us, inclusion through of these the cross- bendingcorrelations, of light, relative ac- • section we reproduceto non-overlappingcess the to constraints surveys. dark matter, We find nearly the of aonedominant factor representative of 4 for matter dark energy species, and more invisible than ee +cosmological ne + nn MGFoM probes = 112.7 are able to measure some of the most 1.6 a factor ofto 2 for direct modified observation. gravity. The exact forecast figures of merit and same-sky fundamental properties of our Universesurvey from drawn the Cosmic frombenefits that can be radically paper affected to illustrate by a range of forecasts the assumpt differencesion, which we explore Microwave Background (CMB) (Planck Collaboration et al.methodically inThe a sensitivity next decadeanalysis. We will show bring that an that even our fiducial greater assumptions wave of 1.4 arXiv:1307.8062v1 [astro-ph.CO] 30 Jul 2013 with respect to theproduce survey robust results model which we give assume a good average here. picture We of the choose science return from 2013; Carlstrom 2011; Sievers 2013) to the type2 Ia su-combiningdata photometric as many and spectroscopic of these surveys. cosmic probes are scaled up to pernovae (SNe) (Riess 1998; Perlmuttera 5000 1999) deg whichsurvey chart withcover an more exposure area on the time sky, greater of 20 volumes minutes and more ob- Key words: cosmology: observations – gravitational2 lensing – dark energy – modified 1.2 the accelerating expansion of the Universe.using a Large 4000 volume fibregravity spectrograph – cosmologicaljects. We parameters detail with a number– large-scalea 3 deg of structure thesefield surveys of Univ oferse view. in tables 1 and

)/2 surveys of galaxies and galaxy clusters (Eisenstein 2005; 2 (Soares-Santos & DES Collaboration 2012; Amiaux 2012; 0 We assume two galaxy populations, LRGs and ELGs are 1 !c 2009 RAS separately targeted in a ratio of 30/70. Assuming 8 hours (1+R 1 INTRODUCTION Colless 2003) chronicle the growth of cosmic structure and 0 observing per night and a 10% overheadWeak Gravitational in survey Lensing (WGL) time, (Hoekstra we & Jain 2008; Q 0.8 Heymans 2012) gives us, through the bending of light, ac- Theestimate era of “precision that cosmology” it is would now a reality. take Different about 139 observing nights to cosmological probes are able to measure some of the most cess to dark matter, the dominant matter species, invisible fundamentalsaturate properties the of available our Universe from target the Cosmic list. to direct observation. 0.6 Microwave Background (CMB) (Planck Collaboration et al. The next decade will bring an even greater wave of 2013; CarlstromDespite 2011; Sievers the 2013) diff toerences the type Ia in su- surveydata as strategy many of these between cosmic probes our are scaled up to pernovae (SNe) (Riess 1998; Perlmutter 1999) which chart cover more area on the sky, greater volumes and more ob- 0.4 thetoy accelerating model expansion and of the this Universe. more Large specific volume jects. example, We detail a the number basic of these trendssurveys in tables 1 and surveysin DEof galaxies & MG and galaxy constraints clusters (Eisenstein from 2005; spec-z/photo-z2 (Soares-Santos & DES combinations Collaboration 2012; Amiaux 2012; 0.2 !c 2009are RAS relatively robust. While the nn survey alone is less con- straining due to a more uneven z-distribution and slightly 0 !4 !2 0 2 4 6 smaller z-range, the independent !!+nn combination contin- Q 0 ues to improve on the WGL-alone constraint by more than a factor of three in the case of DE and nearly two orders of magnitude in the case of MG. The same-sky benefit from

Figure 2. Upper panel: Marginalised 95% errors on w0, wa for including the n! correlations is more pronounced with these !! from our photo-z survey [green contours], nn from our spec-z specific survey assumptions. In fact the joint DE constrain- survey [black contours], their independent combination, !! + nn, ing power is better than for our fiducial scenario while the [red contours] & their combination including cross-correlations, joint MG result is lower but roughly similar. What is clear !! + n! + nn, [blue contours]. Our fiducial survey strategies are is that none of the simplifying assumptions we have made assumed. 5 tomographic bins are used for the photo-z survey, 40 in our fiducial scenario badly bias the trends we are inter- tomographic bins for the spec-z survey. We marginalise over our ested in exploring when our spec-z and photo-z surveys are standard cosmological parameters, assuming GR. We marginalise over galaxy bias, assuming one overall amplitude term and a 2×2 combined. Nevertheless we will continue to use the simple fiducial spec-z survey scenario so that the other assumptions grid of bg(k, z) nodes, while fixing rg(k, z) = 1. We marginalise over a single global photo-z error term. Any observable contain- we explore below can be quantified without a complicated ing galaxy clustering is assumed to be cut at large ell. RSDs are interplay with the irregular n(z) that is the result of some included for the spec-z survey. Lower panel: Marginalised 95% specific target selection assumptions. errors on Q0, Q0(1 + R0)/2 for !! from our photo-z survey [green contours], nn from our spec-z survey [black contours], their independent combination, !!+nn, [red contours] & their combination 5.2 CMB Prior including cross-correlations, !! + n! + nn, [blue contours]. We marginalise over w0 and wa, all other assumptions are the same This paper is primarily concerned with the details of the as for the upper panel. combination of a spec-z galaxy clustering/RSD survey with a photo-z WGL survey. It is from this sort of joint probes analysis that all the most stringent constraints on cosmology will be derived. Of course there are cosmological probes

"c 2009 RAS, MNRAS 000, 1–21 Photometric redshift calibration

• Photometric redshift errors are one of the leading systematics for weak lensing tomography • Mean and width of redshift distributions in each photo-z bin must be known to accuracy ~ 10-3 • Method (1) : spectroscopic training set [issues : sample variance, incompleteness of training set, outliers] • Method (2) : photo-z/spec-z cross-correlations [issues : degeneracies with galaxy bias, cosmic magniﬁcation] • Can OzDES currently help with either method? Photometric redshift calibration

• Training set method : suppressing sample variance systematic for DES weak lensing requires 100 AAOmega pointings or 5 VIPERS surveys !

• Phot-z/spec-z cross-correlation method : need ~50,000 spec-z’s per unit redshift -- can use 2dFGRS, SDSS, BOSS at z < 0.6 and VIPERS at z > 0.6?

• OzDES is not currently transformational for this science, but photo-zs are still useful for other large- scale structure topics with less stringent requirements Future AAT proposals?

• OzDES-wide proposed in March 2013 (150 nights, 3000 deg2 coverage) - not approved • Issue (1) : time now allocated to other projects (SAMI, OzDES-deep) - only 10-15 nights/semester remain? • Issue (2) : can only observe DES ﬁelds in B semesters • Issue (3) : need to map > 1000 deg2 to be competitive (e.g. existing RCS2, future HSC projects) • Current status : musing on competitiveness of 2014B proposal targetting KiDS, later widening to DES?