Main Research Projects

(1) Lenses Structure & Dynamics (LSD) Survey

In collaboration with Tommaso Treu (UCSB), I initiated an observational program with Keck - the Lens Lenses Structure & Dynamics (LSD) Survey - with the aim to combine stellar kinematics and strong gravitational lensing and constrain the internal structure of luminous and dark-matter in early-type galaxies to z=1, as well as their evolution.

(2) The Sloan Lens ACS (SLACS) Survey

In collabroration with Tommaso Treu (UCSB), Adam Bolton and Scott Burles (MIT) and Lexi Moustakas (STScI), we are targeting lens candidates with HST that were spectroscopically selected from the SDSS (167 targets in Cycle 13/14; PI Koopmans/Bolton). The targets were selected to have a low-redshift (z<0.5) luminous red (early-type) galaxy as a lens and a blue emission-line galaxy as a source. This makes these systems particularly suitable for detailed lensing and stellar kinematic follow-up. Deep follow-up with HST (cycle-14) of 15 systems is planned and 2D IFU spectroscopy with VLT (PI: Koopmans).

(3) The ANGLES RTN Network

On april 1st 2004, the new EU-funded ANGLES RTN network has started. The network aims to study the properties of high-z galaxies through galaxy-scale strong gravitational lensing. I am a member of the network and part of its steering committee.

(4) Flux-ratio Anomalies in Lensed Radio Sources.

I am currently studying the physical processes, in particular scattering, micro and milli-lensing, that can cause the flux-ratio "anomalies" observed in many strongly lensed radio sources, i.e. deviations of the relative brightnesses of merging lensed images from those predicted from smooth gravitational-potential models.

Small-scale perturbations of the gravitational-lens potential, caused by Cold-Dark-Matter substructures as predicted from cosmological N-body simulations, have been proposed as the cause of these anomalies, even though no other observational evidence of these structures is known. In addition, both monitoring programs with the VLA, MERLIN and the WSRT, and high-resolution VLBI observations indicate that scattering by the ionized medium in the lens galaxy and microlensing might also play important roles.

The ultimate goal is to study these different processes both through existing and new (especially wide-field VLBI) radio observations and compare the results with detailed numerical simulations, in order to (i) disentangle these competing effects and (ii) place realistic limits on the properties of CDM substructure in lens galaxies.

With my graduate student drs. A. Bercian-Alba I'm further studying these anomalies.

(5) Non-parametric Lens Modelling

I am developing non-parametric lensing and modeling codes to analyze the imaging and stellar kinematic data. Additional collaborators on parts of this program are Tommaso Treu (UCSB) Chris Fassnacht (UC Davis) and Roger Blandford (KIPAC/Stanford). My graduate student drs. M. Barnabe is developing a joint lensing & stellar dynamical code.

(6) The Hubble Constant

Together with Chris Fassnacht, Tommaso Treu and Roger Blandford and others, I am studying a number of lens systems with measured time-delays, to pin down the global value of the Hubble Constant. We do this through a detailed analysis of their stellar kinematics, the structure of their Einstein rings and arcs (if present), and through a detailed study of the field around these systems (e.g. the effects of nearby groups and/or clusters).

We have recently (Cycle-13) been awarded 24 orbits of HST-ACS time to target the system B1608+656 and quantify, in exquisite detail, its Einstein ring and use the information contained in the ring structure to make a non-parametric non-linear correction to the lens potential between the four lensed images (all three time-delays are known in this system).

(7) Reionisation with LOFAR

I am member of the theory/simulation working group of the Reionization Key-Project, planned with the Low-Frequency Array (LOFAR). Our group aims to simulate the "Sky-to-ApJ pipeline" and develop parallelized codes to extract and analyze the HI signal (e.g. power-spectra) from the EoR. I am in charge of the signal extraction and analysis part of the program. I'm member of the Astronomy Research Committe (ARC) of LOFAR overseeing strategic issues.

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