Rates and redshift distributions of high-z supernovae
Tomas Dahlén and
Received 5 February 1999 / Accepted 26 July 1999
Using observed star formation rates at redshifts up to 5, we calculate cosmic supernova rates for core collapse and Type Ia supernovae. Together with supernova statistics and detailed light curves, we estimate the number of supernovae, and their distribution in redshift, that should be detectable in different filters with various instruments, including both existing and future telescopes, in particular the NGST.
We find that the NGST should detect several tens of core collapse supernovae in a single frame. Most of these will be core collapse supernovae with 2, but about one third will have 2. Rates at 5 are highly uncertain. For ground based 8-10 m class telescopes we predict supernova per square arcmin to IAB = 27, with about twice as many core collapse SNe as Type Ia's. The typical redshift will be 1, with an extended tail up to 2. Detectability of high redshift supernovae from ground is highly sensitive to the rest frame UV flux of the supernova, where line blanketing may decrease the rates severely in filters below 1 µm.
In addition to the standard `Madau' star formation rate, we discuss alternative models with flat star formation rate at high redshifts. Especially for supernovae at 2 the rates of these models differ considerably, when seen as a function of redshift. An advantage of using SNe to study the instantaneous star formation rate is that the SN rest frame optical to NIR is less affected by dust extinction than the UV-light. However, if a large fraction of the star formation occurs in galaxies with a very large extinction the observed SN rate will be strongly affected. An additional advantage of using SNe is that these are not sensitive to selection effects caused by low surface brightness.
Different aspects of the search strategy is discussed, and it is especially pointed out that unless the time interval between the observations spans at least 100 days for ground based searches, and one year for NGST, a large fraction of the Type IIP supernovae will be lost. Because of the time delay between the formation of the progenitor star and the explosion, observations of 1 Type Ia supernovae may distinguish different progenitor scenarios.
A major problem is the determination of the redshift of these faint supernovae, and various alternatives are discussed, including photometric redshifts. In practice a reliable classification based on either spectroscopy or light curves requires the SNe to be 2 magnitudes above the detection limit. The uncertainties in the estimates are discussed extensively. We also discuss how the estimated rates depend on cosmology. Finally, some comments on effects of metallicity are included.
Key words: cosmology: observations stars: supernovae: general stars: formation nuclear reactions, nucleosynthesis, abundances
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© European Southern Observatory (ESO) 1999
Online publication: October 4, 1999