The Dark Energy Survey : Detection of weak lensing magnification of supernovae and constraints on dark matter haloes (2406.05047v1)

Abstract: The residuals of the distance moduli of Type Ia supernovae (SN Ia) relative to a Hubble diagram fit contain information about the inhomogeneity of the universe, due to weak lensing magnification by foreground matter. By correlating the residuals of the Dark Energy Survey Year 5 SN Ia sample (DES-SN5YR) with extra-galactic foregrounds from the DES Y3 Gold catalog, we detect the presence of lensing at $6.0 \sigma$ significance. This is the first detection with a significance level above $5\sigma$. Constraints on the effective mass-to-light ratios and radial profiles of dark-matter haloes surrounding individual galaxies are also obtained. We show that the scatter of SNe Ia around the Hubble diagram is reduced by modifying the standardisation of the distance moduli to include an easily calculable de-lensing (i.e., environmental) term. We use the de-lensed distance moduli to recompute cosmological parameters derived from SN Ia, finding in Flat $w$CDM a difference of $\Delta \Omega_{\rm M} = +0.036$ and $\Delta w = -0.056$ compared to the unmodified distance moduli, a change of $\sim 0.3\sigma$. We argue that our modelling of SN Ia lensing will lower systematics on future surveys with higher statistical power. We use the observed dispersion of lensing in DES-SN5YR to constrain $\sigma_8$, but caution that the fit is sensitive to uncertainties at small scales. Nevertheless, our detection of SN Ia lensing opens a new pathway to study matter inhomogeneity that complements galaxy-galaxy lensing surveys and has unrelated systematics.

• The paper presents the first detection of weak lensing magnification in Type Ia supernovae with a high significance of 6.0σ using data from the Dark Energy Survey.
• By analyzing the correlation between supernova distance residuals and lensing, the study constrains dark matter halo properties and reduces Hubble diagram scatter using a new de-lensing term.
• This detection provides a new method to reduce systematic errors, study large-scale structure complementary to other techniques, and guides analysis for future high-precision cosmological surveys.

Detection of Weak Lensing Magnification in Supernovae from the Dark Energy Survey

This essay provides an overview of a paper conducted by the Dark Energy Survey (DES) collaboration, presented in the paper titled "Detection of weak lensing magnification of supernovae and constraints on dark matter haloes." The paper focuses on the detection of weak gravitational lensing effects in Type Ia supernovae (SNe Ia) and examines the implications for dark matter halo properties and cosmological parameters.

The primary achievement of the DES paper is the detection of weak lensing magnification effects in SNe Ia with a significance of 6.0σ, surpassing the conventional 5σ threshold for discovery claims in astronomical research. This is a notable accomplishment as it is the first detection of its kind to achieve such significance, offering a robust confirmation that gravitational lensing can be reliably detected in supernova observations.

Study Methodology and Results

The research utilizes data from the DES Year 5 supernova sample (DES-SN5YR) and cross-references these with extragalactic foregrounds from the DES Y3 Gold catalog. The central goal was to measure the correlation between supernova distance modulus residuals and lensing magnifications caused by intervening mass distributions. Using this correlation, the paper further constrains the mass-to-light ratios and radial profiles of dark matter halos enveloping galaxies.

The paper proposed an innovative modification to the standardization of distance moduli in SNe Ia by introducing a de-lensing term. This inclusion successfully reduced the scatter around the Hubble diagram. When recalculating cosmological parameters using these de-lensed distance moduli, the changes pointed to slightly higher matter density, Ω_M, and a more negative equation of state parameter, w, although the adjustments remain within the existing error margins (approximately 0.3σ shifts).

Implications

The detection of weak lensing magnification in SNe Ia opens new avenues for cosmology, particularly in studying matter inhomogeneities and their impacts on cosmological measurements. The enhanced understanding of how dark matter halos influence SNe Ia luminosities contributes valuable insights into the structure and mass distribution in the universe.

The implications of these findings are multifaceted:

1. Systematic Error Reduction: Incorporating weak lensing modeling in future surveys can significantly lower systematics, leading to more precise measurements of cosmological parameters.
2. Alternative Pathway for Cosmology: Weak lensing magnification offers a complementary method to galaxy-galaxy lensing surveys for studying the large-scale distribution of matter. It possesses different systematic influences, which could aid in resolving current tensions in cosmological measurements, such as the discrepancies in the derived S_8 parameter from cosmic microwave background (CMB) and weak lensing data.
3. Future Surveys: The methodology and findings provide a framework for incorporating and analyzing weak lensing in upcoming surveys with higher statistical power, such as those conducted by the Rubin Observatory.

Conclusion

The DES paper provides a significant step forward in astrophysics and cosmology by successfully detecting weak lensing effects in supernovae with high confidence. It offers a pioneering approach to accounting for these effects in cosmological analyses and sets the stage for improved precision in future cosmological parameter estimation. The continued paper of weak lensing in SNe Ia remains an exciting frontier for understanding the dark universe.