Astronomer at the Institut d'Astrophysique de Paris

Research

It's interesting to note that in French there is no "re" in research. It's about searching. But occasionally we like to actually find something. You can find partial summary of some of the work I've done in the last ten years in my HDR thesis. I am author or co-author of around many refereed scientific papers. Find a complete list here, at NASA ADS. Here is a list of my first author papers. This page is meant for specalists: for a non-technical introduction to this stuff, see my teaching page. These are some of the things I've worked on:

The universe at intermediate redshifts as seen by near-infrared selected surveys:

In a series of several papers (McCracken et al 2000,2010,2012) I have presented sucessively deeper views of the Universe at near-infrared wavelengths. Near-infrared data is vitally important: it provides accurate measurements of stellar masses, and the possibility to measure photometric redshifts in the all-important redshift range where the peak of the star-formation. The number of bright and faint passively-evolved systems measured in this paper are significantly different from the predictions of the model of semi-analytic model of galaxy formation, indicating the probable need to include additional physics in these models. In addition, very deep near-infrared data permits searching for very high-redshift galaxies, and I have participated in several papers which aim to do precisely this.

Clustering of galaxies in photometric surveys:

Using robust photometric redshifts for which systematic errors are well understood, the four CFHTLS deep fields provided one of the first opportunities to carry out a detailed study of the dependence of the clustering properties of the field galaxy population as a function of redshift, type and luminosity from z~0 to z~1, improving on previous surveys which used simpler selection criteria (McCracken et al. 2008). However, without a model to interpret these results, it was difficult to provide a physical interpretation for these measurements.

A phenomenological model for galaxy clustering:

In collaboration with J. Coupon and M. Kilbinger, I developed an analytic model of galaxy clustering, the ``halo model'' and applied it to the one million galaxies galaxies in the CFHTLS-wide (Coupon et al. 2012). This work provides the most accurate measurements to date of the dependence of galaxy clustering properties on type, luminosity and redshift out to z~1. By analysing our measurements in the framework of the halo model, we were are able to derive the halo mass where star-formation is most efficient and its dependence on redshift, a measurement which strongly discriminates between different galaxy formation theories.

Weak and strong gravitational lensing

I a co-author on the papers which made the first detection of weak gravitational lensing by large scale structure and the first three-dimensional mass maps of the Universe, primarily as a consequence of my experience with wide-field camera survey data.

Faint galaxy photometry, galaxy surveys:

I have been involved in the planning, execution and reduction of several large photometric surveys, in particular the CFHTLS survey using the Megacam camera on CFHT and now the UltraVISTA using the VIRCAM camera on VISTA. In addition I provided all the ultraviolet and much of the NIR data for the COSMOS survey. I have extensive experience in reducing and analysing wide-field mosaic camera data from both optical and near-infrared surveys.

Photometric redshifts:

Photometric redshifts have become a valuable technique to extract additional information from purely photometric surveys. Starting from precise photometric catalogues, I have worked on the test and development of photometric redshift techniques which have been applied to large ground-based catalogues, e.g., (Ilbert et al. 2006).

Future and on-going projects

EUCLID:

The ESA Euclid sattellite is a space telescope with a 1.2 metre mirror which will be launched in 2020. It is a highly precise "shape measuring machine" which will be survey more than 15,000 deg^2 of sky, providing the most precise measurements ever of the distribution of luminous and dark matter in the Universe and helping us to measure the geometry of the Universe. In Euclid I am leading the team which will process all the data from Euclid's visible camera.

UltraVISTA:

The UltraVISTA project is a public survey taking place on the VISTA telescope. The UltraVISTA project has produced a complete mass-selected sample of galaxies from redshift 0<z<5. The first UltraVISTA data release represents a significant improvement over previous NIR surveys in the COSMOS field, and is the subject of many on-going studies.

Other material

Our reflections about the future of the TERAPIX project can be found here.