Amélie Saintonge, Postdoc

amelie

Education:
2002 B.Sc. in Mathematics and Physics, U. de Montréal
2005 M.Sc. in Astronomy, Cornell U.
2007 Ph.D. in Astronomy, Cornell U.

Research History:
2000-2002 Research assistant, National Research Council of Canada
2002-2007 Research assistant, Cornell University
2007-present Postdoctoral researcher, University of Zurich

Awards/Recognition:
2006 Cranson W. and Edna B. Shelley award for outstanding graduate research
2002-2007 Postgraduate research fellowships, National Science and Engineering Research Council of Canada (NSERC) and Fond québécois de la recherche sur la nature et les technologies (NATEQ)
2000-2002 Women in Engineering and Science (WES) Fellowship of the National Research Council of Canada

Teaching:
Fall 2007 Guest lecturer, Overview of Modern Astrophysics
Spring 2008 Guest lecturer, Introduction to Modern Astrophysics

Projects:

The Arecibo Legacy Fast ALFA Survey (ALFALFA)

ALFALFA is a major ongoing project at the Arecibo Observatory. When completed, it will have covered 7000 square degrees of sky and detected an expected 30,000 galaxies. It is by far the largest and most sensitive blind HI survey ever conducted: ALFALFA can detect galaxies up to distances of ~250 Mpc (z~0.06) and is sensitive to systems with log(HI mass) = 8.0 up to distances of about 25 Mpc, a considerable improvement over previous HI surveys, considering the significant sky area covered. Fig.1 shows cone diagrams for an early sample of ~3200 ALFALFA galaxies (data in Giovanelli et al. 2007 and Saintonge et al. 2007). 

cone
Distribution of ALFALFA detections in two different sky areas. The red filled circles are galaxies which had a previously measured HI redshift, while the open blue circles are new HI detections made by ALFALFA.

The blue symbols mark galaxies for which ALFALFA provides a first HI measurement. Over 60% of the galaxies had never been observed in HI before, indicating how optically targeted surveys fail to select the majority of HI-rich objects. A sensitive blind HI survey such as ALFALFA will therefore significantly contribute to our understanding of the distribution of HI in the local Universe. Because of its great sensitivity, one of the main goals of the survey is to determine the faint end slope of the HI mass function, and characterize its dependency on cosmic environment. Significant multi-wavelength follow-up observation efforts are also underway, from synthesis HI observations, to optical imaging and spectroscopy, to GALEX UV observations. For a full description of all the science goals and current projects, an update on the status of the survey, and access to the data releases, see the ALFALFA website: http://egg.astro.cornell.edu/alfalfa/

Properties of the low mass dwarf galaxies discovered in the ALFALFA survey

Because of the sensitivity of the ALFALFA survey and the complementary observations being conducted, it is possible to study in detail the properties of some of the lowest mass dwarf galaxies in the nearby Universe. These galaxies, which are detected by ALFALFA based on their significant gas component, have very low optical surface brightnesses and are extremely metal-poor, indicating that star formation doesn't proceed in these systems as in more massive objects.  Fig.2 shows SDSS images for a sample of 15 such dwarf galaxies. 

sdss>> click for high resolution image
Sloan Digital Sky Survey images of 15 low surface brightness dwarf galaxies detected in HI by ALFALFA for which oxygen abundances were measured. These objects tend to be extremely metal-poor.

Using a combination of broad-band and narrow-band optical images, optical spectra and HI synthesis maps, we are investigating the conditions that lead to star formation in these systems.  Since ALFALFA has been designed to cover a broad range of environments, from clusters and groups to nearby voids, we are looking into the dependency of environment on star formation, and the distribution of the low-HI mass systems in the cosmic density field (Saintonge 2007, PhD thesis). To achieve all these goals we are obtaining and using in addition to the ALFALFA data HI maps from radio synthesis telescope (VLA, GMRT), optical images from public surveys (DSS, SDSS) and our own targeted campaigns, and optical spectra from the Palomar 5m telescope.

 

Geometrical tests of cosmological models based on the kinematics of high-redshift galaxies

In collaboration with colleagues in Marseille and members of the VVDS survey, we have recently presented a series of papers where we have demonstrated the potential of a new method to perform geometrical cosmological tests. These tests (in our case the angular diameter test and the Hubble diagram) can be used to constrain cosmological parameters by defining a set of standard rods and candles and tracing through redshift their apparent magnitudes, angular sizes or number density. The novel element of our study is the objects used as standard rods and candles: disc galaxies from large redshift surveys, selected by their rotation velocities on the grounds of the known scaling relations between the kinematics of a disc, its size and its luminosity (e.g. the Tully-Fisher relation).  Without a priori knowing the shape of the evolution function for luminosity and size over redshift, cosmology-evolution diagrams can be built, which enable us to constrain cosmological models based on the amount of galaxy size/luminosity evolution expected at a given redshift, or vice versa to determine the amount of evolution given a set of cosmological parameters. Fig.3 shows an example of such a cosmology-evolution diagram.

cosmo
Cosmology-evolution diagram from Marinoni et al. (2007a) for simulated data   evolved to be smaller and brighter at higher redshift. For a given set of cosmological parameters, the amount of disc evolution can be determined, and vice versa.

After the successful proof of concept presented in Marinoni et al. (2007a), Saintonge et al. (2007) and Marinoni et al. (2007b), larger data sets from surveys such as VVDS and COSMOS will be used to put stronger constraints on cosmological parameters and galaxy evolution. Because of the need to calibrate the cosmological tests with data unaffected by evolution, we have also derived disc scaling relations for the large and homogeneous SFI++ sample of galaxies. The size-rotation velocity relation presented in Saintonge et al. (2007) is by far the best derived to date, with scatter around the relation smaller by a factor of at least 2 or 3 compared with previous studies. This new relation (see Fig.4), which now rivals in tightness with the well-known Tully-Fisher relation, will now be used to put constraints on models for disc galaxy formation, for example the range of spin parameters allowed by the tight scatter.

vrot
Size-rotation velocity relation for a sample of ~4200 galaxies from the SFI++ sample of galaxies (Springob et al. 2007). The size is the radius corresponding to the 23.5 surface brightness isophote, after correections for inclination, foreground extinction and cosmological stretch. Figure from Saintonge et al. (2007).

Publications

CV

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