New constraints on the free-streaming of warm dark matter from intermediate and small scale Lyman- α forest data

Abstract

We present new measurements of the free-streaming of warm dark matter (WDM) from Lyman-α flux-power spectra. We use data from the medium resolution, intermediate redshift XQ-100 sample observed with the X-shooter spectrograph (z = 3−4.2) and the high-resolution, high-redshift sample used in obtained with the HIRES/MIKE spectrographs (z = 4.2 − 5.4). Based on further improved modelling of the dependence of the Lyman-α flux-power spectrum on the freestreaming of dark matter, cosmological parameters, as well as the thermal history of the intergalactic medium (IGM) with hydrodynamical simulations, we obtain the following limits, expressed as the equivalent mass of thermal relic WDM particles. The XQ-100 flux power spectrum alone gives a lower limit of 1.4 keV, the re-analysis of the HIRES/MIKE sample gives 4.1 keV while the combined analysis gives our best and significantly strengthened lower limit of 5.3 keV (all 2σ C.L.). The further improvement in the joint analysis is partly due to the fact that the two data sets have different degeneracies between astrophysical and cosmological parameters that are broken when the data sets are combined, and more importantly on chosen priors on the thermal evolution. These results all assume that the temperature evolution of the IGM can be modelled as a power law in redshift. Allowing for a non-smooth evolution of the temperature of the IGM with sudden temperature changes of up to 5000K reduces the lower limit for the combined analysis to 3.5 keV. A WDM with smaller thermal relic masses would require, however, a sudden temperature jump of 5000 K or more in the narrow redshift interval z = 4.6 − 4.8, in disagreement with observations of the thermal history based on high-resolution resolution Lyman-α forest data and expectations for photo-heating and cooling in the low density IGM at these redshifts.

QCD Axion Dark Matter with a Small Decay Constant

“…Axions are colder for a larger Γ Ã since they receive more redshifting after production. Given the recent constraint on the warmness of dark matter (see, e.g., [38,39]), we require that the axion velocity is smaller than 10 −3 at a temperature of 1 eV,…”

Degenerate Sub-keV fermion dark matter from a solution to the Hubble tension

“…We also comment ample, dark radiation [5,16], dark energy at early time [17][18][19][20], etc. about the constraint from the Lyman-α forest [39,40] and showed that our model is not inconsistent with its mass bound.…”

Colder freeze-in axinos decaying into photons

“…If M Ã ∼ 10 16 GeV, y 0 ∼ 0.1, and v PQ ∼ 10 10 GeV, one finds μ ∼ 500 GeV. This is a well-known solution to μ-term generation by the Kim-Nilles mechanism [11].…”

“…All the 7 keV DM models proposed to explain the 3.5 keV excess need to be revisited to examine whether their structure formation is compatible with the up-to-date constraint from the Lyman-α forest data, m WDM > 5.3 keV [16]. Weaker constraints are also worth mentioning since the uncertainty in the reported constraint from the baryon complexity like the temperature evolution of intergalactic medium is in debate: m WDM > 2.0 [17], 3.3 [18], and 4.09 keV [19].…”