A&A 423, 881–894 (2004) Astronomy DOI: 10.1051/0004-6361:20035948 & c ESO 2004 Astrophysics Type Ia supernova rate at a redshift of ∼0.1 G. Blanc1,12,22,C.Afonso1,4,8,23,C.Alard24,J.N.Albert2, G. Aldering15,,A.Amadon1, J. Andersen6,R.Ansari2, É. Aubourg1,C.Balland13,21,P.Bareyre1,4,J.P.Beaulieu5, X. Charlot1, A. Conley15,, C. Coutures1,T.Dahlén19, F. Derue13,X.Fan16, R. Ferlet5, G. Folatelli11, P. Fouqué9,10,G.Garavini11, J. F. Glicenstein1, B. Goldman1,4,8,23, A. Goobar11, A. Gould1,7,D.Graff7,M.Gros1, J. Haissinski2, C. Hamadache1,D.Hardin13,I.M.Hook25, J. de Kat1,S.Kent18,A.Kim15, T. Lasserre1, L. Le Guillou1,É.Lesquoy1,5, C. Loup5, C. Magneville1, J. B. Marquette5,É.Maurice3,A.Maury9, A. Milsztajn1, M. Moniez2, M. Mouchet20,22,H.Newberg17,S.Nobili11, N. Palanque-Delabrouille1 , O. Perdereau2,L.Prévot3,Y.R.Rahal2, N. Regnault2,14,15,J.Rich1, P. Ruiz-Lapuente27, M. Spiro1, P. Tisserand1, A. Vidal-Madjar5, L. Vigroux1,N.A.Walton26, and S. Zylberajch1 1 DSM/DAPNIA, CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France 2 Laboratoire de l’Accélérateur Linéaire, IN2P3 CNRS, Université Paris-Sud, 91405 Orsay Cedex, France 3 Observatoire de Marseille, 2 pl. Le Verrier, 13248 Marseille Cedex 04, France 4 Collège de France, Physique Corpusculaire et Cosmologie, IN2P3 CNRS, 11 pl. M. Berthelot, 75231 Paris Cedex, France 5 Institut d’Astrophysique de Paris, INSU CNRS, 98 bis boulevard Arago, 75014 Paris, France 6 Astronomical Observatory, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen, Denmark 7 Departments of Astronomy and Physics, Ohio State University, Columbus, OH 43210, USA 8 Department of Astronomy, New Mexico State University, Las Cruces, NM 88003-8001, USA 9 European Southern Observatory (ESO), Casilla 19001, Santiago 19, Chile 10 Observatoire Midi-Pyrénées, 14 avenue Edouard Belin, 31400 Toulouse, France 11 Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden 12 Osservatorio Astronomico di Padova, INAF, vicolo dell’Osservatorio 5, 35122 Padova, Italy e-mail: [email protected] 13 Laboratoire de Physique Nucléaire et de Hautes Énergies, IN2P3 - CNRS - Universités Paris 6 et Paris 7, 4 place Jussieu, 75252 Paris Cedex 05, France 14 Laboratoire Leprince-Ringuet, LLR/École Polytechnique, Route de Saclay, 91128 Palaiseau Cedex, France 15 Lawrence Berkeley National Lab, 1 Cyclotron Road, Berkeley, CA 94720, USA 16 Steward Observatory, The University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721-0065, USA 17 Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180, USA 18 Fermilab Wilson and Kirk Roads, Batavia, IL 60510-0500, USA 19 Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA 20 LUTH, Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon Cedex, France 21 Institut d’Astrophysique Spatiale, Bâtiment 121, Université Paris 11, 91405 Orsay Cedex, France 22 Université Paris 7 - Denis Diderot, 2 place Jussieu, 75005 Paris, France 23 NASA/Ames Research Center, Mail Stop 244, Moffet Field, CA 94035, USA 24 GEPI, Observatoire de Paris, 77 avenue de l’Observatoire, 75014 Paris, France 25 Department of Physics, University of Oxford, Nuclear and Astrophysics laboratory, Keble Road, Oxford OX1 3RH, UK 26 Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK 27 Department of Astronomy, University of Barcelona, Barcelona, Spain Received 24 December 2003 / Accepted 28 April 2004 Abstract. We present the type Ia rate measurement based on two EROS supernova search campaigns (in 1999 and 2000). Sixteen supernovae identified as type Ia were discovered. The measurement of the detection efficiency, using a Monte Carlo ∼ . +0.044+0.028 2 simulation, provides the type Ia supernova explosion rate at a redshift 0.13. The result is 0 125−0.034−0.028 h70 SNu where 10 B 1SNu= 1SN/ 10 L / century. This value is compatible with the previous EROS measurement (Hardin et al. 2000), done with a much smaller sample, at a similar redshift. Comparison with other values at different redshifts suggests an evolution of the type Ia supernova rate. Key words. stars: supernovae: general – galaxies: evolution – cosmology: miscellaneous – methods: observational Visiting astronomer, Cerro Tololo Inter-American Observatory, Association of Universities for Research in Astronomy, under contract National Optical Astronomy Observatories, which are operated by the with the National Science Foundation. Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20035948 882 G. Blanc et al.: Type Ia supernova rate at a redshift of ∼0.1 1. Introduction weeks to one month apart to detect transient events and catch only supernovae near maximum light (a typical type Ia su- Type Ia supernovae are believed to be caused by thermonu- pernova reaches its maximum light in the optical wavelength clear explosions of a white dwarf reaching the Chandrasekhar roughly 15 to 20 days after the explosion). Both observations mass after accreting matter in a binary system (see e.g. Livio are done around new moon to limit the sky background. The 2001). They are the main mechanism to enrich the interstel- two sets of images are then automatically subtracted after a lar medium (ISM) with iron-peak elements (with ∼0.6 M of spatial alignment, a flux alignment and a seeing convolution. nickel released per event on average). The knowledge of the Cuts are applied to eliminate known classes of variable ob- number of such events per galaxy and per unit of time is crucial jects such as asteroids, variable stars and cosmic rays. The most to understand the matter cycle and the ISM chemistry. From important cut is the requirement that the transient object be near a cosmological point of view the measurement of the evolu- an identified galaxy. More precisely, it is required to be within tion of the explosion rate will put strong constraints on galaxy an ellipse centered on any galaxy with semi-major and minor evolution. Measuring the evolution of the core-collapse super- axes of length 8 times the rms radius of the galaxy’s flux distri- novae (type II and Ib/c) explosion rate would give a new unbi- bution along each axis. This ellipse should contain essentially ased view on the star formation rate (SFR) history, independent all supernovae associated with a galaxy since ∼99% of galactic of any peculiar tracer, because gravitational supernovae are di- light is contained within an ellipse of size 3 times the rms ra- rectly linked to massive star formation. Up to now, the type II dius. To eliminate cosmic rays, each exposure consists of two supernova rate has been measured only in the local Universe subexposures: SExtractor (Bertin & Arnouts 1996) software is (Cappellaro et al. 1999). On the other hand, the measurement run on both images to make a cosmic-ray catalog before adding of the evolution of the explosion rate of type Ia supernova the two images. would give strong constraints on the SFR history and on many In spite of these cuts, a human eye is still needed to check other parameters such as the progenitor evolution (birth rate the remaining candidates and discard obvious artefacts (resid- of binaries, time delay between the white dwarf formation and ual cosmic rays, bad subtractions, asteroids, variable stars...). the thermonuclear explosion...) or the nature of the progenitor Ten to fifteen search fields are observed every night and the itself. human scanner has to deal with about 100 candidates the fol- This paper is organized as follows: first the EROS search lowing day. The serious candidates are observed again on the for supernovae is reviewed in Sect. 2. The two supernova search following night for confirmation. Then a spectrum is taken to campaigns at the origin of this work are presented in Sect. 3. obtain the supernova type, phase and redshift. Sections 4 to 7 deal with the rate computation. Our results are EROS supernova search fields lie near the celestial equa- presented in Sect. 8 and discussed in Sect. 9. ◦ ◦ tor (declination between −4.5 and −12 ) to be reached from both hemispheres and between 10h and 14.5h in right ascen- 2. The EROS search for supernovae sion. They overlap some of the Las Campanas Redshift Survey (LCRS) (Shectman et al. 1996) fields which will facilitate the The EROS experiment used a 1-meter telescope based at galaxy sample calibration. La Silla observatory, Chile, designed for a baryonic dark mat- ter search using the microlensing effect (see e.g. Lasserre et al. 2000; Afonso et al. 2003b,a). The telescope beam light was 3. The 1999 and 2000 campaigns split by a dichroic cube into two wide field cameras (1 deg2). At the beginning of 1999, the Supernova Cosmology Project The cube sets the passband of both cameras, a “blue” one over- (SCP) undertook a large nearby supernova search involving lapping the V and R standard bands, a “red” one matching eight supernova search groups, including EROS. The goal was roughly the I standard band1. Each camera was a mosaic of to gather a large set of well sampled, CCD discovered, nearby eight 2048×2048 pixels CCDs with a pixel size of 0.60 on the (z ∼< 0.15) type Ia supernovae to calibrate the distant events sky (Bauer & de Kat 1997; Palanque-Delabrouille et al. 1998). used to measure the cosmological parameters. The whole col- In the following, we will use only the blue camera. One “im- laboration obtained 37 SNe out of which 19 were type Ia SNe age” stands for one CCD, and one “field” is for the entire cam- near or before maximum light and were followed both spec- era with its eight CCDs, i.e.