JWST Lensed quasar dark matter survey II: Strongest gravitational lensing limit on the dark matter free streaming length to date

Abstract: This is the second in a series of papers in which we use JWST MIRI multiband imaging to measure the warm dust emission in a sample of 31 multiply imaged quasars, to be used as a probe of the particle nature of dark matter. We present measurements of the relative magnifications of the strongly lensed warm dust emission in a sample of 9 systems. The warm dust region is compact and sensitive to perturbations by populations of halos down to masses $\sim 10^6$ M${\odot}$. Using these warm dust flux-ratio measurements in combination with 5 previous narrow-line flux-ratio measurements, we constrain the halo mass function. In our model, we allow for complex deflector macromodels with flexible third and fourth-order multipole deviations from ellipticity, and we introduce an improved model of the tidal evolution of subhalos. We constrain a WDM model and find an upper limit on the half-mode mass of $10^{7.6} M\odot$ at posterior odds of 10:1. This corresponds to a lower limit on a thermally produced dark matter particle mass of 6.1 keV. This is the strongest gravitational lensing constraint to date, and comparable to those from independent probes such as the Ly$\alpha$ forest and Milky Way satellite galaxies.

• The paper uses JWST observations of lensed quasars to set the strongest gravitational lensing limit on dark matter free streaming length.
• Researchers analyzed JWST MIRI data from 31 lensed quasars, probing dark matter substructure down to 10^6 Msol.
• This work constrains warm dark matter, setting a lower bound of approximately 6.1 keV on thermally produced dark matter particle mass, aligning with other methods.

A New Constraining Approach to Dark Matter Using JWST Observations

The paper "JWST Lensed quasar dark matter survey II: Strongest gravitational lensing limit on the dark matter free streaming length to date" by R. E. Keeley and collaborators presents a compelling observational study aimed at probing the nature of dark matter (DM) through gravitational lensing, leveraging data from the James Webb Space Telescope (JWST). This work highlights significant constraints on the properties of warm dark matter (WDM), specifically by measuring the free-streaming effects on dark matter halos based on the gravitational lensing of quasars.

Overview and Methodology

The research leverages the capability of JWST's Mid-Infrared Instrument (MIRI) to analyze a sample comprising 31 multiply imaged quasars through multiband imaging. The study specifically examines the magnifications of strongly lensed warm dust emissions, utilizing these measurements to probe DM via gravitational perturbations in halos. The observations focus on perturbations processed in quasars, revealing that the compact yet significant warm dust emission regions are sensitive to gravitational modulation caused by subhalos down to approximately $10^6$ M$_{\odot}$.

The significance of constraining these subhalo masses lies in better understanding the halo mass function, which delineates the distribution of dark matter halos across different mass scales. The analysis employs several previously collected narrow-line flux-ratio measurements and integrates these with new observations to provide a holistic model that considers complex deflector macromodeling and gravitational lensing effects. The research incorporates subhalo tidally influenced evolution characteristics, improving the modeling aspects related to gravitational lensing induced by DM.

Results and Implications

The researchers constrain a WDM model, achieving strong results with an upper limit on the half-mode mass of $10^{7.6} M_\odot$ at posterior odds of 10:1. Translating this constraint reflects a lower bound on thermally produced dark matter particle mass at approximately 6.1 keV.

This constraint represents a key milestone as the strongest gravitational lensing limit yet achieved for characterizing free streaming lengths, providing predictions that align closely with inferences derived from other independent methodologies such as Lyα forest measurements and studies of Milky Way satellite galaxies. By comparing these results, the understanding of the function and properties of sub-structural dark matter evolve, offering a robust method to explore potential granular effects in the dark matter-powered cosmic web.

Theoretical and Practical Implications

The implications of these findings expand both theoretical and practical domains. Theoretically, the constraints derived offer a refined lens on cosmological models of structure formation, providing evidence favoring dark matter models where higher mass particles exist, fitting within the observed halo distribution. Furthermore, these results underscore the utility of leveraging multiple, independent astronomical measures to triangulate on DM properties, aligning predictions across varying scales and epochs in cosmic history.

Practically, the work demonstrates the potentially transformative utility of high-resolution space telescopes like JWST in astrophysical research, especially for subjects traditionally bound by observational constraints such as DM studies. Given that the approach efficiently evaluates multiple potential dark matter models by directly exploring astrophysical discrepancies, future explorations could adapt similar mechanisms extended to survey larger cosmic volumes or alternate regions in differing cosmic environments.

This observably derived constraint directly contributes to the larger dialogue surrounding the characteristics of DM, advancing our understanding and paving the way for future surveys exploring alternative cosmic scales or environments using similar methodologies.

Conclusion

In conclusion, the research by Keeley et al. offers invaluable insights into DM properties through innovative methodologies combining gravitational lensing and mid-infrared observations. The stringent constraints on dark matter achieved highlight significant progress in understanding cosmic structure and the nature of the Universe, opening avenues for future research pursuits leveraging similar techniques.