INAF – Osservatorio Astronomico di Collurania-Teramo, V.M. Maggini, 64100 Teramo, Italy e-mail: firstname.lastname@example.org
2 Dipartimento di Scienze della Comunicazione, Universitá di Teramo, viale Crucioli 122, 64100 Teramo, Italy
3 Institute of Astronomy, Madingley Road, Cambridge, UK
4 INAF – Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
5 INAF – Osservatorio Astronomico di Bologna, V. Ranzani 1, 40127 Bologna, Italy
6 Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, Belfast BT 71NN, UK
7 European Southern Observatory, K. Schwarzschild Str. 2, 85748 Garching, Germany
8 Dipartimento di Fisica – Universitá di Ferrara, via del Paradiso 12, 44100 Ferrara, Italy
9 Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago, Chile
10 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 7, 85741 Garching bei München, Germany
Accepted: 16 October 2007
Aims.To measure the supernova (SN) rates at intermediate redshift we performed a search, the Southern inTermediate Redshift ESO Supernova Search (STRESS). Unlike most of the current high redshift SN searches, this survey was specifically designed to estimate the rate for both type Ia and core collapse (CC) SNe.
Methods.We counted the SNe discovered in a selected galaxy sample measuring SN rate per unit blue band luminosity. Our analysis is based on a sample of ~ galaxies and on 25 spectroscopically confirmed SNe plus 64 selected SN candidates. Our approach is aimed at obtaining a direct comparison of the high redshift and local rates and at investigating the dependence of the rates on specific galaxy properties, most notably their colour.
Results.The type Ia SN rate, at mean redshift , is 0.22 SNu, while the CC SN rate, at , is 0.82 SNu. The quoted errors are the statistical and systematic uncertainties.
Conclusions.With respect to the local value, the CC SN rate at is higher by a factor of ~2, whereas the type Ia SN rate remains almost constant. This implies that a significant fraction of SN Ia progenitors has a lifetime longer than Gyr. We also measured the SN rates in the red and blue galaxies and found that the SN Ia rate seems to be constant in galaxies of different colour, whereas the CC SN rate seems to peak in blue galaxies, as in the local Universe. SN rates per unit volume were found to be consistent with other measurements showing a steeper evolution with redshift for CC SNe than SNe Ia. We have exploited the link between SFH and SN rates to predict the evolutionary behaviour of the SN rates and compare it with the path indicated by observations. We conclude that in order to constrain the mass range of CC SN progenitors and SN Ia progenitor models it is necessary to reduce the uncertainties in the cosmic SFH. In addition it is important to apply a consistent dust extinction correction both to SF and to CC SN rate and to measure the SN Ia rate in star forming and in passively evolving galaxies over a wide redshift range.
Key words: supernovae: general / stars: formation / Galaxy: evolution / Galaxy: stellar content
Based on observations collected at the European Southern Observatory, using the 2.2 m telescope on the La Silla (ESO Programmes 62.H-0833, 63.H-0322, 64.H-0390, 67.D-0422, 68.D-0273, 69.D-0453, 72.D-0670, 72.D-0745, 73.D-0670, 74.A-9008, 75.D-0662) and using Very Large Telescope on the Cerro Paranal (ESO Programme 74.D-0714).
© ESO, 2008