Diving into precision cosmology and the role of cosmic magnification

Transcription

1 Diving into precision cosmology and the role of cosmic magnification Jose Luis Bernal Institute of Cosmos Science - Barcelona University ICC Winter Meeting /02/2017 Jose Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

2 Outline 1 Introduction 2 Model Independent Approaches 3 New cosmological probes: cosmic magnification 4 Conclusions José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

3 Introduction State of the art The Landscape Almost two decades since the discovery of the acceleration of the expansion of the Universe. Huge observational and theoretical effort: large collaborations. ΛCDM (Λ - Cold Dark Matter) has survived the avalanche of data. Only 6 parameters to reproduce the observations. Distances measured at < 1% error (BAO) and equation of state of DE at w José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

4 Introduction State of the art The Landscape Almost two decades since the discovery of the acceleration of the expansion of the Universe. Huge observational and theoretical effort: large collaborations. ΛCDM (Λ - Cold Dark Matter) has survived the avalanche of data. Only 6 parameters to reproduce the observations. Distances measured at < 1% error (BAO) and equation of state of DE at w Any idea of what DE or DM are? José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

5 Introduction State of the art Precision cosmology Cosmology is a precise science, but precise is not the same that accurate! Constraining parameters Understanding the physics Cosmology tends to rely heavily in models. Now the challenge is not in getting the signal or enough numbers for statistics anymore Systematics! Systematics may appear in the observation, but also in the modelling and analysis of the data. Careful treatment and changes in the way of approaching the data have to come. José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

6 Model independent Back door of tensions Tensions in ΛCDM Tensions between early and late Universe? Systematics, wrong model, misunderstanding... σ 8 H 0 Long way from CMB until low-redshift Universe. (Although CMB can be analysed independently of late-time physics - Verde, Bellini et al. 2016) José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

7 Model independent Back door of tensions Tensions in ΛCDM Tensions between early and late Universe? Systematics, wrong model, misunderstanding... Photo-z problem? Problems in Planck? Something new? KIDS. Hildebrandt José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

8 Model independent Back door of tensions Tensions in ΛCDM Tensions between early and late Universe? Systematics, wrong model, misunderstanding... José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

9 Model independent Free modelling of expansion Reconstruction of H(z) Splines to parametrize H(z). Concept: Using standard objects to measure distances and constrain H(z). BAO measure D V /r s we need r s or H 0 to normalize it. BAO SNeIa Figure courtesy of A. Cuesta José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

10 Model independent Standard objects coincide with ΛCDM The shape is very well constrained JLB, Verde and Riess (2016) Whenever SNeIa are included, E(z) is very constrained to be ΛCDM-like! Changes in DE won t solve the problem. José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

11 Model independent Standard objects coincide with ΛCDM The low redshift standard ruler: r s h JLB, Verde, Riess (2016) / Verde, JLB et al. (2016) BAO normalization is H 0 r s. Contrained at 2% Only using BAO and SNeIa data. José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

12 New cosmological probes and approaches Exploit the cosmos to its fullest New information Traditional approaches usually focus in a limited part of the information that a certain observation may give: harder modelling, low S/N,... Example: large scale structure clustering can give more information than BAO or RSD (don t miss Alvise s talk). Look elsewhere to find new sources of information: Access to new epochs/redshifts: 21cm with SKA. Break degeneracies and cross-check: cosmic magnification. José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

13 Cosmic Magnification What is it? Side B of Gravitational Lensing Gravitational lensing: not only cosmic shear. Credit: LSST. José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

14 Cosmic Magnification What is it? Side B of Gravitational Lensing Gravitational lensing: not only shear, but also magnification. Credit: R. Scranton, B. Menard, R. Lupton, SDSS. José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

15 Cosmic Magnification What is it? Side B of Gravitational Lensing Gravitational lensing: not only shear, but also magnification. Affects background number density. Two compelling effects: Stretching of the sky solid angle behind. (n ) Fainter objects become detectable. (n ) Depends on the sample (slope of the differental magnitude number counts). Credit: R. Scranton, B. Menard, R. Lupton, SDSS. José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

16 Cosmic Magnification How to measure it? Detecting magnification n obs (> L) = 1/µ n 0 (> L/µ) Crosscorrelate sources and lenses distribution to observe magnification. wls total(θ) = w gg(θ) + w µg (θ) + w gµ (θ) + w µµ (θ) José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

17 Cosmic Magnification How to measure it? Detecting magnification n obs (> L) = 1/µ n 0 (> L/µ) Crosscorrelate sources and lenses distribution to observe magnification. wls total(θ) = w gg(θ) + w µg (θ) + w gµ (θ) + w µµ (θ) José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

18 Cosmic Magnification How to measure it? Detecting magnification Bins 1-1 Bins 1-2 Bins gg µµ gµ w(θ) 10-3 w(θ) 10-3 w(θ) θ θ θ dn/dz z José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

19 Cosmic Magnification How to measure it? Detecting magnification n obs (> L) = 1/µ n 0 (> L/µ) Crosscorrelate sources and lenses distribution to observe magnification. wls total(θ) = w gg(θ) + w µg (θ) + w gµ (θ) + w µµ (θ) Separated redhisft bins! The gµ term dominates. w total LS = 2.5b(s(m) 0.4) < δ L κ S > s(m): magnification bias logarithmic slope of differential magnitude number counts. José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

20 Cosmic Magnification Measurements Measurements Quasar-galaxy correlation in SDSS. Note the change of sign with the magnitude limit. Scranton José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

21 Cosmic Magnification Measurements Measurements Galaxy-galaxy correlation in DES. Different bands. SV data, very small area. García-Fernández José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

22 Cosmic Magnification Pros and cons Shear Vs. Magnification Why shear is much more used? S/N much higher ( 5 times for the same sources) However: much harder to model and more sensitive to systematics. Measures shapes: Intrinsic alignment, PSF,.. Photo-z errors may bias the measurement significantly What offers magnification? It only needs magnification and photo-z : comes for free! Simpler modelling and systematic. It may be affected by: Intrinsic clustering contamination z-bins separated. Much less sensitive to errors in photo-z. Spatial variations of s(m). José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

23 Cosmic Magnification What now? Shear AND Magnification Both probes are complementary Van Waerbeke (2010) José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

24 Cosmic Magnification What now? Brigh future Near future surveys (DESI, Euclid, SKA) will boost magnification signal to noise ratio. Larger redshift range. Target different types of galaxies (larger range of s(z)). Larger sky coverage. Enough to be used in cosmology at last! José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18

25 Conclusions Conclusions New era of cosmology: now the challenge is to deal with systematics. Understanding only constraining cosmological parameters. H 0 problem is a mismatch of anchors: there is no evidence of a strange expansion history. We need new probes to cross check current observations and break degeneracies of cosmological parameters. Magnification: easy to measure, to control the systematics and complementary to cosmic shear. José Luis Bernal (ICCUB) ICC Winter Meeting /02/ / 18