Comments • Tried to be complementary to other lectures – Please ask ques<ons (some<mes controversial on purpose!) • Only talks about cosmological surveys – Galaxy evolu<on, planetary searches, galaxy archeology are not covered • Personal views – Many surveys will be missed (sorry) – Op<cal astronomy (radio/CMB surveys are poorly represented)
Advice • Wise • Old • ForgoKen • Sartre "Youre free, choose, that is, invent.” • Nichol “I told you so! I’m always right”
Measuring ξ(r) or P(k) Simple es<mator: Data ξ(r) = DD(r)/RR(r) -‐ 1 Advanced es<mator: ξ(r) = (DD-‐RR)2/RR-‐1 r The la,er does a be,er job with edge eﬀects, which cause a bias to the Random mean density of points Usually 10x as many random points over SAME area / volume Same techniques for P(k) -‐ take Fourier transform of density ﬁeld rela<ve to a random catalog over same volume. Several techniques for this -‐ see Tegmark et al. and Pope et al. Also “weighted” and mark correla<ons
Measuring ξ(r) II Essential the random catalog looks like the real data!
Errors on ξ(r) Hardest part of esLmaLng these staLsLcs On small scales, the errors are Poisson On large scales, errors correlated and typically larger than Poisson • Use mocks catalogs • PROS: True measure of cosmic variance • CONS: Hard to include all observa<onal eﬀects and model clustering • Use jack-‐knifes (JK) • PROS: Uses the data directly • CONS: Noisy and unstable matrices
Jack-‐knife Errors Real Data • Split data into N equal subregions 1 3 • Remove each subregion in turn and compute ξ(r ) 4 5 6 • Measure variance between regions as func<on of scale N=6 2 3 N (N −1) σ = 2 N i=1 ∑ (ξi − ξ ) 2 4 5 6 Note the (N-‐1) factor because there are N-‐1 es<mates of mean
SDSS & WMAP • Now the most successful astronomical facili<es in the world • 4187 papers with 162913 cita<ons (Jan 17th at 4pm) • At least a paper a day!
The DETF ﬁgure-‐of-‐merit is the reciprocal of the area of the error ellipse enclosing the 95% conﬁdence limit in the w0–wa plane. Stage II – today (ish) Stage III – factor of 3 Stage IV – factor of 10
Dark Energy is bad for Astronomy (ArXiv:0704.2291)1. Cultural differences: HEPs are fundamentalists (“specialists”) and astronomers are generalists. Respect each others cultures2. Don’t over optimize your surveys - plan for the unexpected3. Don’t over prioritize DE surveys to the expense of others4. Be inclusive and publish your data5. Nurture young talent and give recognition where due The SDSS is the last of its kind!
Don’t over-optimize• Dark energy is now systematics limited - young scientists should do PhD’s in dust and biasing. • DETF proposed diversity in experiments• All the new surveys are building this in, e.g., DES will get less SNe but (hopefully) understand them better• These will greatly beneﬁt astrophysics and I would argue would not be done without the driving force of DE (unfocused science is also a risk and can be expensive)• DE experiments will deliver more numbers and area. Excellent for cosmic variance, environment studies and high-dimensional parameter searches. • Larger ﬁeld of views are driven by technology, so we would do large area surveys anyway.
BOSS in a nutshell 8,000 deg2 footprint in Spring (Eisenstein et al. 2011) 3,000 deg2 footprint in Fall• Upgraded spectrographs (with better throughput) • 1000x 2-arcsec fibers in cartridges • Increase wavelength range to 3600-10,000A (R=1500-2600)• Finished ~3,000 deg2 southern imaging in Fall 2008. • Released as part of DR8, published in ApJS (2011).• Currently doing only spectroscopy • 1.5 million galaxies, i<19.9, z<0.8, over 10,000 deg2 • 150,000 QSOs, g<22, 2.3<z<3, over 8,000 deg2
Data so far et al. 2011, Ho et al. 2012, Seo et al. 2012 Ross Current status Done by 2014
BOSS • BOSS is designed as a “stage III” project to constrain DE using the baryon acous<c oscilla<on (BAO) method – Galaxies z~0.1-‐0.7 1% dA, 2% H(z), z~0.35 & 0.6 – QSOs (LyAF) z~2-‐3 1.5% dA,H at z~2.5
AS3: e-‐BOSS • gri selection conducted on a single plate based on DR8 photometry (targeting the CFHT-LS W3 ﬁeld) • 78% redshift success efﬁciency - ~68% in 0.6<z<1 DES overlap BOSS e-BOSS MaNGA Start 2014? J.P. Kneib 28
The Dark Energy Survey Blanco 4-‐meter at CTIO • Survey project using 4 complementary techniques: I. Cluster Counts II. Weak Lensing III. Large-scale Structure IV. Supernovae• Two multiband surveys: 5000 deg2 grizY to 24th mag 30 deg2 repeat (SNe)• Build new 3 deg2 FOV camera and Data management system Survey 2012-2017 (525 nights) Facility instrument for Blanco29
DECam C4 in its cell (UCL) New ﬂat-‐ﬁeld Screen (CTIO) Completed Imager (FNAL)
DES Science Summary Forecast Constraints on DE Equa<on of State Four Probes of Dark Energy• Galaxy Clusters DES • ~100,000 clusters to z>1 • Synergy with SPT, VHS • Sensitive to growth of structure and geometry• Weak Lensing • Shape measurements of 300 million galaxies • Sensitive to growth of structure and geometry• Large-scale Structure • 300 million galaxies to z = 1 and beyond Planck prior assumed • Sensitive to geometry• Supernovae • 30 sq deg time-domain survey • ~4000 well-sampled SNe Ia to z ~1 Factor 3-‐5 improvement over • Sensitive to geometry Stage II DETF Figure of Merit 31
DES Science Summary II Planck prior assumed 32
BigBOSS • 5000-‐ﬁber instrument on 4m telescope • Stage IV BAO on the “cheap”
The Euclid machine Space-based Vis and NIR observations of galaxies VIS Imaging NIR Spectroscopy NIR Photometry NIR Imaging Tomographic shear Redshib machine machine Dark MaRer and Galaxy PowerSpectra-‐meters Astronomical data base for Explorer of gravity and expansion Legacy science
Area requirements • FoM increases with increasing area/volume and galaxy number density. • This ignores that any survey is limited by cost: <me is ﬁnite • weak-‐lensing, intrinsic alignments become increasingly important for shallower surveys • This changes the trade-‐oﬀ between area and depth • 6-‐year dura<on, WL+GC gives op<mal survey area of 15,000 deg2
Euclid clustering measurements 20% of the Euclid data, assuming the slitless baseline at z~1 Distance-‐redshib rela<on moves P(k)
Measuring Modiﬁed Gravity • The growth factor [or its deriva<ve, the growth rate f(z)] quan<ﬁes the eﬃciency with which cosmological structure is built. • The growth rate well described by f(z)=Ωm(z)γ. • A detec<on of γ≠0.55 would indicate a devia<on from General Rela<vity, and thus a completely diﬀerent origin of cosmic accelera<on, rather than dark energy. • Euclid can constrain this parameter to 0.01 (where ΛCDM corresponds to γ=0.55). • the γ-‐parameterisa<on is merely an example. In general, Euclid will provide <ght constraints on the cosmological growth rate.
Most people look at about 20 galaxies. All galaxies looked at by at least 20 people (median 38).
Karen Masters: The Enigma of Red Spirals. Wednesday 9th December 2009 49
Summary • Era of surveys is here – More to come (DR9, DES, Euclid). – By end of decade, billions of galaxies in public domain – Only held back by your imagina<on! – Wonderful technologies to share and collaborate with such data • Era of maximal ignorance – We know “nothing”, but not what caused it or what it could be – Progress will only be made through observa<on! – Don’t let anyone tell you it’s a “crazy idea”