French-Chinese Days on Week Lensing

Cosmostat Day on Machine Learning in Astrophysics

Date: October 4-5, 2018

Organizer:  Jean-Luc Starck and Martin Kilbinger


Local information

CEA Saclay is around 23 km South of Paris. The astrophysics division (DAp) is located at the CEA site at Orme des Merisiers, which is around 1 km South of the main CEA campus. See for detailed information on how to arrive.

On January the 26th, 2017, we organize the third day on machine learning in astrophysics at DAp, CEA Saclay. 


All talks are taking place at DAp, Salle Galilée (Building 713)

Thursday, October 4

10:00 - 10:30h.   Hu Zhan,   Overview of CSS-OS

10:30 - 11:00h.   Martin Kilbinger, Overview of CFIS Weak Lensing

11:00 - 11:30h.  Jun Zhang, Fourier_Quad,  a shear measurement method in Fourier Space

11:30 - 12:00h. Morgan Schmitz,  PSF Modeling using a Graph Manifold

11:30 - 12:00h. Lunch

14:00 - 14:30h. Guoliang Li (or Chengliang Wei), A full sky WL simulation with semi-analytic galaxy formation 

14:30 - 15:00h. Jean-Luc Starck,  WL Mass Mapping,  

15:00 - 15:30h. Zuhui Fan,  WL peak statistics 

15:30 - 16:00h. Austin Peel,  Cosmology with Mass Maps

Friday, October 5

10:00 - 10:30h.   Sam Farrens,   The CFIS pipeline

10:30 - 11:00h.  Ran Li,  Lensing studies of sub-structures

11:00 - 11:30h.  Axel  Guinot,  Preliminary CFIS Results

11:30 - 12:00h.  Liping Fu, Shear measurement from VOICE deep survey

11:30 - 12:00h. Lunch

14:00 - 14:30h.  Huanyuan Shan: KiDS WL studies

14:30 - 15:00h.  Arnau Pujol,  Shear Calibration

15:00 - 15:30h.   Rebeca Araripe Furtado Cunha,  Optimal Transport and PSF Modeling

15:30 -  17:00h. Discussions


École Euclid de cosmologie 2018

Date: August 20 - September 1, 2018

Venue: Roscoff, Bretagne, France


Lecture ``Weak gravitational lensing'' (Le lentillage gravitationnel), Martin Kilbinger.

Find here links to the lecture notes, TD exercises, "tables rondes" topics, and other information.

  • Resources.
    • A great and detailed introduction to (weak) gravitational lensing are the 2005 Saas Fee lecture notes by Peter Schneider. Download Part I (Introduction to lensing) and Part III (Weak lensing) from my homepage.
    • Check out Sarah Bridle's video lectures on WL from 2014.
  • TD cycle 1+2, Data analysis.
    1.  We will work on a rather large (150 MB) weak-lensing catalogues from the public CFHTLenS web page. During the TD I will show instructions how to create and download this catalogue. These catalogues will also be available on the virtual machine for the school.
      If you like, you can however download the catalogue on your laptop at home. Please have a look at the instructions in the TD slides.
    2. If you want to do the TD on your laptop, you'll need to download and install athena (the newest version 1.7). Available on the VM.
    3.  For one of the bonus TD you'll need a new version of (v 1.8beta). Download it here. Available on the VM.
  • Lecture notes and exercise classes.  You can already download the slides in one file (40 - 60 MB), but be ware that the content will still change slightly until the classes.
    • Part I (Cycle 1):    [all | day 1 (1/6)  |   day 2 (2/6) |  day 3 (3/6)]
    • Part II (Cycle 2):  [all | day 1 (4/6)   |   day 2 (5/6)  | day 3 (6/6)]
    • TD:                             [1/2 and 2/2]
    • Table Ronde sujet
  • Slack channel:

CosmoSClub: 09-07-2018

Date: July 9th 2018

Speaker: Santiago Casas (CEA Saclay)

Title: Dark Energy with Euclid

Euclid is an ESA medium-class mission expected to launch in 2020 that will map the geometry of the Universe by imaging 10^9 galaxies and measuring 10^7 galaxy redshifts in 15000 square degrees of the sky. This will provide us detailed information about the accelerated expansion, the evolution of large-scale structure and the matter-energy content of the Universe up to a redshift of about z≈2.
In this talk, I will review how the main probes of Euclid, namely galaxy clustering and weak lensing, will be able to constrain theories beyond the standard cosmological ΛCDM model and how we will be able to pin down the equation of state of dark energy with about 1% precision. Galaxy clustering measures mainly the movement of tracers along geodesics, while weak lensing is an almost direct mapping of the gravitational potentials at large scales. Using both of these observables, we can obtain valuable information about the growth of perturbations and the geometrical quantities of the Universe and therefore constrain the properties of General Relativity. Since the measurements of Euclid will also give insights on the properties of dark matter and neutrinos at cosmological scales, I will also show how we can measure non-standard couplings between matter species and dark energy and how we can give tight constraints on many alternative theories of gravity.

CosmoSClub: 25-06-2018

Date: June 25th 2018

Speaker: Viviana Niro (University of Heidelberg)

Title: Galaxy rotation curves in modified gravity models [slides]

I'll present the possibility that galaxy rotation curves can be explained in the framework of modified gravity models. A Yukawa term is considered in the gravitational potential and dark matter is included in the fit.
Using a set of 40 galaxy rotation curves data from the SPARC catalogue, I'll present constraints on the strength, β, and the range, λ, of the Yukawa fifth force. The global best-fit is found to be β=0.34±0.04 and λ=5.61±0.91 kpc and the dark matter content is on average 20% smaller than in the standard gravity parametrization. The Bayesian evidence for a NFW profile and a Yukawa term is higher than 8σ with respect to the case without the Yukawa term.

CosmoSClub: 03-05-2018

Date: May 3rd 2018

Speaker: Alessio Spurio Mancini

Title: Weak gravitational lensing as a (3D) probe of gravity


Cosmic shear, the weak gravitational lensing effect caused by the
large-scale structure, is one of the primary probes to test gravity on
cosmological scales with current and future surveys. In particular,
cosmic shear is sensitive to both standard GR cosmological parameters
and those that describe modified theories of gravity, such as those
belonging to the Horndeski class. These models include the majority of
universally coupled extensions to ΛCDM with one scalar degree of freedom
in addition to the metric, which are still in agreement with current
In this talk I will discuss some aspects concerning the constraining
power of current and future cosmic shear datasets on this broad class of
theories. I will compare in particular two main techniques to analyse a
cosmic shear survey: a tomographic method, where correlations between
the lensing signal in different redshift bins are used to recover
redshift information, and a 3D approach, where the full redshift
information is carried through the entire analysis. Due to its increased
amount of redshift information, a future 3D analysis can constrain both
standard gravity and Horndeski theories better than a tomographic one,
in particular with a decrease in the errors on the Horndeski parameters
of the order of 20%.

CosmoSClub: 13-04-2018

Date: April 13th 2018

Speaker: Benjamin Joachimi (University College London)

Title: Cosmic shear cosmology - where we stand


I will review the recent weak lensing cosmology results obtained by the ESO Kilo-Degree Survey, which display an intriguing, marginal discrepancy with the primary Planck CMB constraints on structure growth. Key analysis choices and challenges will be highlighted, and new approaches to validating the measurements presented. I will also briefly discuss the relation to the Dark Energy Survey Year 1 results and some lessons learnt for the forthcoming generation of cosmological galaxy surveys.

CosmoSClub: 05-04-2018

Date: April 5th 2018

Speaker: Elena Sellentin (University of Geneva)

Title: The skewed weak lensing likelihood: why biases arise, despite data and theory being sound


We derive the essentials of the skewed weak lensing likelihood via a simple Hierarchical Model. Our likelihood passes four objective and cosmology-independent tests which a standard Gaussian likelihood fails. We demonstrate that sound weak lensing analyses are naturally biased low, and this does not indicate any new physics such as deviations from ΛCDM. Mathematically, the biases arise because noisy two-point functions follow skewed distributions. This form of bias is already known from CMB analyses, where the low multipoles have asymmetric error bars. Weak lensing is more strongly affected by this asymmetry as galaxies form a discrete set of shear tracer particles, in contrast to a smooth shear field. We demonstrate that the biases can be up to 30 percent of the standard deviation per data point, dependent on the properties of the weak lensing survey. Our likelihood provides a versatile framework with which to address this bias in future weak lensing analyses.