First Year Results

1. SNLS - THE SUPERNOVA LEGACY SURVEY : first year results R. Pain (LPNHE, Univ Paris VI) for the SNLS Collaboration http:// www.cfht.hawaii.edu/SNLS Type Ia Supernovae for Cosmology Type Ia supernovae (SN Ia) peak luminosity dispersion can be reduced to better than 0.15 magnitude making use of empirical correlations observed between peak luminosity and decline rate. In 1988, the Supernova Cosmology Project and the High-Z Supernova team reported evidence for a non zero cosmological term using SN Ia as “calibrated” candles. The next challenge is to achieve precise measurement of the cosmological parameters WM and WL and to measure the equation of state of Dark Energy, pDE=w.rDE. Precise measurement of supernovae rates as a function of redshift can also be obtained using this technique and help constrain the Star Formation Rate. These goals can only be achieved by collecting samples of order of thousand well measured high redshift supernovae. A “Rolling Search” Survey mode Supernova surveys have usually been performed in three steps: i) detection by subtracting images of the same field taken two consecutive new moons apart, ii) spectroscopic identification from supernova spectroscopy at or nearmaximum light and redshift determination from host galaxy spectral features, and iii) light curve photometry by subtracting the underlying host galaxy light. Since August 2003, the SuperNova Legacy Survey project (SNLS) has engaged in a new high redshift supernova survey using the newly commissioned 1 square degree wide field imager MegaPrime, a joint project of CFHT and CEA/DAPNIA. SNLS relies in part on observations made within the CFHT Legacy Survey program, a large 5 year multi purpose imaging survey at CFHT, and on large allocations of spectroscopic time on 8-m class telescopes. 202 nights have been allocated on CFHT for the SN program. About 60h per semester have been allocated on VLT and Gemini for this program. Additional spectroscopic observations are done on Keck and Magellan telescopes. First Year Results The figure below shows the cumulative number of candidates, detected and identified after about 1 year of operation as well as the projected numbers at mid-survey time. As of November 2004, more than 120 SN Ia at redshifts 0.2<z<1.03 have been spectroscopically confirmed. Precise photometry and calibration of the g’, r’, i’ and z’ lightcurves is currently being performed. The figure above shows a Preliminary Hubble diagram based on 46 high-z SNe Ia from the 1st year of SNLS, and for which enough images without the SN (containing host galaxy light only) have already been collected. All these objects were measured in at least 2 bands and all distances are “color” corrected event by event, without any prior assumption on the extinction distribution. Discovery and photometric follow-up at CFHT Discovery and photometric follow-up of supernovæ is performed in a so called “Rolling Search” mode by continuous sampling of the same fields. Four square degrees are surveyed for 5 six months periods with 1h i’ filter exposure every 3-4 night. The fields are observed 5 times per lunation in g’, r’ and z’ as well. With this technique 8-12 SN Ia per pointing are detected and precisely followed-up within one lunation. Two pointing (2 square degrees) are surveyed at every lunation. To precisely measure the SN Ia luminosity at maximum, a S/N of about 10 is required during a time interval roughly 10 days before and after the peak luminosity. Measurement of the color excess E(B-V) of the supernovae is needed to address extinction. For redshifts up to z~0.8, this is achieved with i-filter exposures (r-filter exposures for redshifts up to z~0.6). For higher redshifts, up to z~0.9, measurements in z’-filter are used. Alternatively E(U-B) will be used if a good description of the SN Ia variability in u-filter can be obtained. Example of recent “ Real Time” Analysis of SN multicolor light curves. For clarity, only a fraction of observed events are shown. Note the excellent time sampling, including in the rising part, and color coverage achieved by the “rolling search” technique. Spectroscopic identification Identification of supernova types and redshift determination of the host galaxy rely on spectroscopy.Spectral identification of SN Ia can be achieved in about one hour on an 8-m class telescope up to redshifts z0.9.