Gravitational Magnification of Population III Supernovae in Hierarchical Cosmological Models: Next Generation Space Telescope Perspectives

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Abstract
We study the gravitational lensing magnification produced by the intervening cosmological matter distribution, as deduced from three different hierarchical models (standard cold dark matter [SCDM], lambda cold dark matter [LCDM], and cold + hot dark matter [CHDM]) of very high redshift sources, particularly supernovae in protogalactic (Population III) objects. By means of ray-shooting numerical simulations, we find that caustics are more intense and concentrated in SCDM models. The magnification probability function presents a moderate degree of evolution up to z ≈ 5 (CHDM) and z ≈ 7 (SCDM/LCDM). All models predict that statistically large magnifications of μ 20 are achievable with a probability of on the order of a fraction of percent, the SCDM model being the most efficient magnifier. All cosmologies predict that above z ≈ 4 there is a 10% chance to get magnifications larger than 3. We have explored the observational perspectives for Population III supernovae (SNe) detection with the Next Generation Space Telescope (NGST) when gravitational magnification is taken into account. We find that NGST should be able to detect and confirm spectroscopically Type II SNe up to a redshift of z ≈ 4 in the J band (for TSN = 25,000 K); this limit could be increased up to z ≈ 9 in the K band, allowing for a relatively moderate magnification. Possibly promising strategies for discriminating among cosmological models using their GL magnification predictions and very high-z SNe are sketched. Finally, we outline and discuss the limitations of our study.

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