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Newcomers in the Physics of galaxies and cosmology team

» Monday 13 February 2012

In Fall 2011, two PhD students and a post-doc cam and join the “Physics of galaxies and cosmology” team. Karen Disseau (on the left in the picture) works in the Meudon site, whereas Francesco Shankar et Rossella Licitra (respectively in the middle and on the right) work in the Paris site. Each of them presents his/her career.

Karen Disseau

I have started a PhD thesis under the supervision of François Hammer and Mathieu Puech, who I met during my Master 2 internship in GEPI in 2010. This internship validated my study at the University of Toulouse. After graduating, I completed my training by attending in the Observatoire de Paris the Master 2 Astronomical and Space-based Systems Engineering. With this double training, I wanted to acquire knowledge and skills both in observational astrophysics and ground based instrumentation and engineering. Science and Instrumentation feed each other, and I aim to follow a way that brings me to the interface between engineering and research.

The main topic of my thesis focuses on an instrumental project of multi-object spectrometer (MOS) for the E-ELT. None of the two spectrometers EAGLE and OPTIMOS-EVE, in which GEPI was deeply involved, were selected as first light instruments for the ELT by ESO, who chose HARMONI and MICADO. Therefore a such ELT/MOS is still under study. It requires the redefinition of the scientific needs and instrumental constraints, adaptative optics needs and also the optimization of data reduction methods such as sky subtraction procedures.

In parallel with this instrumental topic, a purely scientific part of my PhD consists in studying the Low Surface Brightness Galaxies (LSBG) in the distant universe. These galaxies have been extensively studied in the local universe thanks to the SDSS survey, and their peculiar properties (especially low stellar formation rates, low metallicity and large amount of neutral hydrogen gas) suggest that they are not evolved systems expected to be found in the universe at earlier times. Searching for them in deeper fields such as GOODS and the Ultra Deep Field, observed by the HST, is totally new and promising, particularly thanks to the deep survey CANDELS carried out recently with the WFC3 camera. These multi-wavelength data should lead to a representative sample of the LSBG population with redshifts up to z=1, allowing a study of their evolution, in terms of number density and physicochemical properties.

Rossella Licitra

I discussed my master thesis in July 2011 at the University of Naples,
where I did all my studies. In particular, in my thesis I focused my attention on the evolution of high-redshift galaxies: starting on the determination of
photometric redshifts through the spectral energy distribution (SED) fitting
method, I studied the evolution of the stellar mass and star-formation rate
as a function of the cosmic time from redshift z∼3 up to the present.

I then started my PhD in October at the GEPI under the supervision of
Simona Mei and I am currently trying to develop a method for the galaxy
cluster detection: the main idea relies on the observational evidence that
rich clusters show a red-sequence in the color-magnitude diagram, due to
the typical concentration of early-type galaxies in the cluster cores. Recognizing
this sequence, it is hence possibile to look for some overdensities
and to individuate the cluster members checking their spatial and redshift
distribution: in particular, I will use photometric redshifts to assign cluster
membership. Once detected, I will be able to study cluster and cluster
galaxy properties.

Francesco Shankar

I graduated (Laurea Thesis) at the University of Rome ‘Tor Vergata‘, and then got the PhD in the Institute for Advanced Studies (ISAS/SISSA) in Trieste. I then moved to the US for a research fellowship at the Ohio State University. After that I moved back to Europe, in Munich, Germany as a senior postdoc at the Max Planck Institute for Astrophysics. After a few months I was awarded an Alexander von Humboldt Fellowship there. Currently I am a Marie Curie Fellow at the Observatoire de Paris-GEPI.

My research has been focused on key aspects of the evolution undergone by the population of super-massive Black Holes (BHs), to understand the origin of the clear link they have with their host galaxies and dark matter haloes. My preferred approach is to work with a variety of independent data sets to derive, in ways independent of specific models, firm constraints on how BHs and galaxies must have evolved, or co-evolved, within their dark matter haloes. Therefore my current research is also carried out in close interaction with several observers. More specifically, I have been interested in the Halo Occupation/semi-analytic modelling of BHs and galaxy evolution, of Active Galactic Nuclei (AGNs) and galaxy clustering, of the X-ray background, of the high-redshift universe, of the mass-metallicity relation and galaxy winds, in studying the structure and statistics of black hole massive hosts in the Sloan Digital Sky Survey, and in constraining general properties of the radio/Broad Absorption Line Quasars.

In the current and future 5 to 10 years a large number of data are and will be available to the Observatoire de Paris, and in particular to the GEPI laboratory. My direct collaborators, prof. Simona Mei and Dr. Marc Huertas-Company, for example, are involved in major surveys of massive galaxies in the local Universe, intermediate (The Next Generation Virgo Cluster survey, NGVS), and high redshift (ACS GTO, the HAWKI high redshift survey). My work and proven experience with halo occupation distribution (HOD) and semi-analytic models (SAMs) of BHs and galaxy formation along the years will allow the Observatoire de Paris to cultivate and develop the art of semi-analytic modelling, an invaluable tool to exploit the large available incoming data sets, setting them in the proper theoretical context and make predictions for future surveys.

On other grounds, I am now acting as an asset between the GEPI and the LUTH for the programme ‘Action Synergie Structuration de l’Univers’, an extensive collaboration between observers and numerical scientists. I am then developing new HOD/SAMs to study galaxy evolution, also in collaboration with Marseille, IAP, and CEA, to follow the mapping between galaxies and haloes through time, and probe the links between high-z clumpy disks with bulges and AGNs. I am also leading the organization of regular meetings between the GEPI and the LERMA laboratories in Paris, and of the ‘Astrocoffee’ that allows all the participants to keep updated with the increasing scientific literature.

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