Reconstructing the weak lensing magnification distribution of type Ia supernovae

Abstract

Weak lensing of Type Ia supernovae (SNe Ia) is a systematic uncertainty in the use of SNe Ia as standard candles, as well as an independent cosmological probe, if the corresponding magnification distribution can be extracted from data. We study the peak brightness distribution of SNe Ia in the Pantheon sample, and find that the high z sub-sample shows distinct weak lensing signatures compared to the low z subsample: a long tail at the bright end due to high magnifications and a shift of the peak brightness toward the faint end, consistent with findings from earlier work. We have developed a technique to reconstruct the weak lensing magnification distribution of SNe Ia, p(µ), from the measured SN Ia flux distribution, and applied it to the Pantheon sample. We find that p(µ) can be reconstructed at a significance better than 2σ for the subsample of SNe Ia at z > 0.7 (124 SNe Ia), and at a lower significance for the SNe Ia at z > 0.9 (49 SNe Ia), due to the small number of SNe Ia at high redshifts. The large number of z > 1 SNe Ia from future surveys will enable the use of p(µ) reconstructed from SNe Ia as an independent cosmological probe.

Forecasting cosmological constraints from the weak lensing magnification of type Ia supernovae measured by the Nancy Grace Roman Space Telescope

“…We follow the methodology from our previous analysis, [20], in reconstructing the weak lensing signal from the realistically simulated Roman data set of SNe Ia described in the previous section. We now summarize the methodology and present the analysis results.…”

“…The integral is from 0 to an upper limit L max int = f /µ min , due to the requirement µ = f /L int ≥ µ min , where µ min is the minimum value of the magnification due to lensing and can be computed for a given cosmological model. We adopt the same assumption as in [19,20] that g(L int ) is a Gaussian distribution with dispersion σ. The value of σ can be well estimated with a large sample of SNe Ia at low redshifts where the weak lensing effect is negligible.…”

“…Early investigation such as [19] reports a detection of this weak lensing magnification effect in a high-redshift SNe Ia sample. Recent analysis in [20] with the latest Pantheon sample reports a 2σ signal. These studies are based on the assumption that the weak lensing effect can be expressed in terms of a probability function of the magnification [21][22][23][24], and the resulting distribution of the observed SNe Ia brightness is a convolution of this magnification distribution and the intrinsic brightness distribution.…”

“…In our earlier work [20], we developed a method to extract the distribution function of the lensing magnification p(µ) from the latest SN Ia data compilation. We extend that earlier analysis by utilizing a realistically simulated SN Ia data set from Roman Space Telescope in this work.…”

“…We extend that earlier analysis by utilizing a realistically simulated SN Ia data set from Roman Space Telescope in this work. We adopt the method from [20] to model the underlying magnification distribution function p(µ) from observational data, and compress the results into physically intuitive quantities to enable a likelihood analysis to extract cosmological constraints. This enhances the cosmological constraints from SNe Ia beyond that of a geometrical probe only, and helps break the degeneracy between cosmological parameters.…”