Focusing on Warm Dark Matter with Lensed High-redshift Galaxies

TL;DR

This paper uses high-redshift lensed galaxies to place new, astrophysics-independent constraints on warm dark matter particle mass, suggesting it must be heavier than about 1 keV based on observed galaxy counts.

Contribution

It introduces a novel method to constrain warm dark matter properties using small-volume high-redshift galaxy observations, independent of astrophysical modeling.

Findings

WDM particle mass > 1 keV at 84% confidence from current data

High-redshift galaxy counts can effectively constrain WDM models

Future observations will further tighten these constraints.

Abstract

We propose a novel use of high-redshift galaxies, discovered in deep Hubble Space Telescope (HST) fields around strong lensing clusters. These fields probe small comoving volumes (about 1000 cubic Mpc) at high magnification ({\mu} > 10), and can detect otherwise inaccessible ultra-faint galaxies. Even a few galaxies found in such small volumes require a very high number density of collapsed dark matter (DM) halos. This implies significant primordial power on small scales, allowing these observations to rule out popular alternatives to standard cold dark matter (CDM) models, such as warm dark matter (WDM). In this work, we analytically compute WDM halo mass functions at z = 10, including the effects of both particle free-streaming and residual velocity dispersion. The preliminary number density corresponding to the two galaxies at z about 10 already detected by the Cluster Lensing And Supernova survey with Hubble (CLASH) constrains the WDM particle mass to m_x > 1 (0.9) keV at 84% (99.9%) confidence limit (for a thermal relic relativistic at decoupling). This limit depends only on the WDM halo mass function and, unlike previous constraints on m_x, is independent of any astrophysical modeling. The forthcoming HST Frontier Fields can significantly tighten these constraints.