Conclusion

This work constitutes the analysis complete of the remote supernovæ discovered by our group and followed by the space telescope Hubble from research to the measurement of the cosmological parameters.

One of the first work carried out at the time of this thesis was the optimization and the control of the tools for detection used at the time of the research campaigns carried out within our group. These tools allowed us, at the time of the countryside led to the CFHT in spring 2001, registered within the framework of follow-up a campaign to very redshifts ($z\simeq 1$), of the Supernova Cosmology Project, to detect 4 supernovæ of the Ia type with redshifts included/understood enters $1.12$.

The three supernovæ most remote discovered at the time of this countryside, associated with 2 supernovæ discovered with the CTIO during the same period and a supernova discovered at the time of spring 2000 with the CFHT were followed during 2 month old meadows by instrument WFPC2 of the space telescope Hubble. They constituted the batch of analysis of this work.

The half of these supernovæ being polluted by the light of their galaxy host, it was necessary to take images of reference without supernova to consider the bottom galactic. These observations were carried out with the new camera of the HST: ACS. The study of the photometry of our supernovæ thus implied the construction of tools for analysis of differential photometry adapted and specific to the two instruments which made it possible to build the lightcurves of our supernovæ.

The determination of the parameters of the lightcurves was carried out by means of tools for synthesis of lightcurves using a simulation of the instruments of observation; the adjustment of the parameters was carried out directly in the photometric system as of the instruments. In particular, the various corrections (correction of filter, absorption by dust of the Milky Way or K-correction) were directly integrated in the adjustment of the model.

The observation in filter I of both supernovæ most remote (with a shift towards the red around 1), filter which corresponds to the filter U in the reference frame of the supernova, required the study of a new estimator of distance corresponding to this filter. The study of a batch of 15 close supernovæ out of U made it possible to show that the luminosity to the maximum of the supernovæ of the Ia type presented after correction for the factor of stretching and the color ($U-b$) a dispersion equivalent to the dispersion observed in the filter B used for the standard analysis.

Finally, the use of this new estimator of distance for our supernovæ observed in the filters corresponding to the filter U and of the estimator of distance out of B allowed two estimates independent of the cosmological parameters $\Omega _ \Lambda$.

By considering a flat universe, we find:

$${\rm En} ~ {\rm B} : \Omega_{\rm M}= 0.35^{+0.2}_{-0.15}$$ (10.11)

$${\rm En} ~ {\rm U} : \Omega_{\rm M}= 0.22^{+0.3}_{-0.25} \nonumber$$

in agreement with the results of SCP and High-Z TEAM (riess1998, perlmutter1999, tonry2003, knop2003).