Warm dark matter as a solution to the small scale crisis: New constraints from high redshift Lyman-αforest data

Abstract

We present updated constraints on the free-streaming of warm dark matter (WDM) particles derived from an analysis of the Lyman-flux power spectrum measured from high-resolution spectra of 25 z > 4 quasars obtained with the Keck High Resolution Echelle Spectrometer and the Magellan Inamori Kyocera Echelle spectrograph. We utilize a new suite of high-resolution hydrodynamical simulations that explore WDM masses of 1, 2 and 4 keV (assuming the WDM consists of thermal relics), along with different physically motivated thermal histories. We carefully address different sources of systematic error that may affect our final results and perform an analysis of the Lyman-flux power with conservative error estimates. By using a method that samples the multidimensional astrophysical and cosmological parameter space, we obtain a lower limit m WDM * 3:3 keV (2) for warm dark matter particles in the form of early decoupled thermal relics. Adding the Sloan Digital Sky Survey Lyman-flux power spectrum does not improve this limit. Thermal relics of masses 1, 2 and 2.5 keV are disfavored by the data at about the 9, 4 and 3 C.L., respectively. Our analysis disfavors WDM models where there is a suppression in the linear matter power spectrum at (nonlinear) scales corresponding to k ¼ 10h=Mpc which deviates more than 10% from a Lambda cold dark matter model. Given this limit, the corresponding ''free-streaming mass'' below which the mass function may be suppressed is $2 Â 10 8 h À1 M . There is thus very little room for a contribution of the free-streaming of WDM to the solution of what has been termed the small scale crisis of cold dark matter.

Early-Universe constraints on dark matter-baryon scattering and their implications for a global 21 cm signal

“…Assuming ΔT b =T b < 0.1, which is around the current sensitivity of Lyman-α forest data [51,52], our calculated limit is shown in Fig. 13.…”

Structure formation with suppressed small-scale perturbations

“…The strongest constraints currently come from flux observations of the Lyman-α forest ruling out particle masses below mTH = 3.3 keV at the 2-σ confidence level (Viel et al 2013). Other limits are obtained from dwarf galaxy counts disfavouring particle masses below mTH = 2.3 keV (Polisensky & Ricotti 2011;Kennedy et al 2014).…”

“…Furthermore, WDM is generally assumed to reduce potential small-scale inconsistencies, such as the missing satellite or the too big to fail problem, occurring in a ΛCDM universe (see Weinberg et al 2013, for a review on these topics). Recent studies point out that both requirements -passing observational constraints and alleviating small scale inconsistencies -seem impossible to combine because constraints from Lyman-α are prohibitively strong in the case of WDM (Viel et al 2013;Schneider et al 2014). While some question the accuracy of the Lyman-α measurements, more and more people believe that the small-scale inconsistencies are a consequence of poorly understood baryonic processes of galaxy formation (Brooks & Zolotov 2014).…”

The galaxy population in cold and warm dark matter cosmologies

“…The masses of the WDM particles adopted in these studies vary from mx = 0.5kev to 3.3kev. These values were inferred from constraints provided by different observations: the numbers of Milky Way satellites (Polisensky & Ricotti 2010), X-ray observations of the Andromeda galaxy (Watson et al 2012), galaxy counts at high redshift (Pacucci et al 2013), high redshift long γ-ray bursts (de Souza et al 2013) and the high redshift Ly-α forest data (Viel et al 2013).…”