RESEARCH
The center of our Galaxy is 100 times closer than the nearest spiral galaxy’s core. Therefore, it offers a unique opportunity to study the processes allowing the central supermassive black hole to access the reservoir of material that can potentially enhance its activity.
INTERSTELLAR MEDIUM IN THE GALACTIC CENTER
I studied the structure and dynamics of the interstellar medium in the central parsec of the Galaxy, using spectro-imaging data (gathered by the VLT) and a new method: a regularized 3D fit (CubeFit). This method injects as much prior information as possible into the spatial gradients of flux, velocity and linewidth of emission lines, and allows to recover low signal-to-noise emission lines and well-characterizes the interstellar medium’s extended emission. In the central parsec, where the strong UV field is supposed to dissociate the molecular phase of the interstellar medium, molecular hydrogen (H2) is detected everywhere. These molecules might have formed in the winds of evolved mass-losing stars in the region, and produce the observed emission shortly before being dissociated by the strong UV radiation.
ENVIRONMENT OF THE CENTRAL BLACK HOLE
The inner few tens of arcseconds of the Galactic center have been observed at high resolution with Keck telescopes for 20 years, with the primary goal of monitoring stars orbiting around the central supermassive black hole. This unique dataset also allows to closely examine gas features and their dynamics. In particular, I highlighted several compact emission sources in Brγ emission line (near-infrared hydrogen recombination line) which are in orbit around the central supermassive black hole. These objects appear to have many of the same characteristics as the tidally-interaction G2. The debate on the stellar or purely gaseous nature of G2 (and G1) is still open. The discovery and characterization of the new sources (G3, G4, G5 and G6) demonstrates the existence of a population of these "G objects," which helps to constrain assumptions about their origin. The G-objects could be the product of a fusion of binary star systems, in the form of a stellar core masked by a gas and dust envelope. These results represent an important step in understanding the nature of these objects as well as the environmental conditions of the Galactic Center.
PSF-RECONSTRUCTION
The knowledge of the PSF (Point Spread Function) is central for extracting science information from observations made with adaptive optics systems. However, it is often challenging to have a good PSF estimate, for instance in very crowded fields (e.g. the Galactic Center) or extended sources (e.g. galaxies). This happens for the Keck’s integral field, OSIRIS, which small field of view prevents from obtaining any good empirical PSF estimate. OSIRIS is equipped with a parallel imager, but its distance of 20 arcseconds from the spectrograph makes it impossible to apply its PSF directly to spectroscopic data. The Galactic Center Group at UCLA has developed algorithms to predict PSF variability (Off-axis PSF reconstruction): AIROPA. Its approach consists in predicting a PSF at a given position starting from an empirical on-axis PSF and taking into account instrumental aberrations and atmospheric perturbations. AIROPA allows to use the parallel imager to predict a PSF on the spectrograph. This semi-empirical approach to off-axis PSF reconstruction, applied to an integral field spectrograph, represents an example for future instruments of extremely large telescopes.