Small-scale clumping of dark matter and the mean free path of ionizing photons at $z=6$

Abstract

Recently, the mean free path of ionizing photons in the $z=6$ intergalactic medium (IGM) was measured to be very short, presenting a challenge to existing reionization models. At face value, the measurement can be interpreted as evidence that the IGM clumps on scales $M\lesssim 10^8$ M${}_{\odot }$, a key but largely untested prediction of the cold dark matter (CDM) paradigm. Motivated by this possibility, we study the role that the underlying dark matter cosmology plays in setting the $z>5$ mean free path. We use two classes of models to contrast against the standard CDM prediction: (1) thermal relic warm dark matter (WDM), representing models with suppressed small-scale power; (2) an ultralight axion exhibiting a white noise-like power enhancement. Differences in the mean free path between the WDM and CDM models are subdued by pressure smoothing and the possible contribution of neutral islands to the IGM opacity. For example, comparing late reionization scenarios with a fixed volume-weighted mean neutral fraction of $20\%$ at $z=6$, the mean free path is $19(45)\%$ longer in a WDM model with $m_x=3(1)$ keV. The enhanced power in the axion-like model produces better agreement with the short mean free path measured at $z=6$. However, drawing robust conclusions about cosmology is hampered by large uncertainties in the reionization process, extragalactic ionizing background, and thermal history of the Universe. This work highlights some key open questions about the IGM opacity during reionization.

arXiv comment23 pages, 11 figures

References in corpus (79)

• Efficient Computation of CMB anisotropies in closed FRW models
• Toward a halo mass function for precision cosmology: the limits of universality
• An analytic model for the spatial clustering of dark matter haloes
• Did LIGO detect dark matter?
• Halo Formation in Warm Dark Matter Models
• Constraining Warm Dark Matter candidates including sterile neutrinos and light gravitinos with WMAP and the Lyman-alpha forest
• Warm Dark Matter as a solution to the small scale crisis: new constraints from high redshift Lyman-alpha forest data
• Dark Energy Survey Year 1 Results: Cosmological Constraints from Cosmic Shear
• The clustering of massive Primordial Black Holes as Dark Matter: measuring their mass distribution with Advanced LIGO
• Massloss of galaxies due to a UV-background
• New Constraints on the free-streaming of warm dark matter from intermediate and small scale Lyman-$\alpha$ forest data
• On the evolution of the HI column density distribution in cosmological simulations
• Cosmological Constraints from the Clustering of the Sloan Digital Sky Survey DR7 Luminous Red Galaxies
• First constraints on fuzzy dark matter from Lyman-$\alpha$ forest data and hydrodynamical simulations
• Hydrodynamic Simulations of Galaxy Formation. II. Photoionization and the Formation of Low Mass Galaxies
• Efficient Simulations of Early Structure Formation and Reionization
• The Birth of a Galaxy - III. Propelling reionisation with the faintest galaxies
• The morphology of HII regions during reionization
• The population of galaxy-galaxy strong lenses in forthcoming optical imaging surveys
• Conditions for Reionizing the Universe with A Low Galaxy Ionizing Photon Escape Fraction
• Disruption of Dark Matter Substructure: Fact or Fiction?
• Photoevaporation of Cosmological Minihalos during Reionization
• Dwarf galaxies in voids: Suppressing star formation with photo-heating
• The halo mass function through the cosmic ages
• Large Lyman-alpha opacity fluctuations and low CMB tau in models of late reionization with large islands of neutral hydrogen extending to z<5.5
• Primordial Black Holes as Dark Matter: The Power Spectrum and Evaporation of Early Structures
• The Small-Scale Power Spectrum of Cold Dark Matter
• Primordial Black Holes as All Dark Matter
• What mass are the smallest protohalos?
• The one-dimensional Ly-alpha forest power spectrum from BOSS
• Effects of cold dark matter decoupling and pair annihilation on cosmological perturbations
• Signatures of primordial black hole dark matter
• The Giant Gemini GMOS survey of z>4.4 quasars - I. Measuring the mean free path across cosmic time
• Long troughs in the Lyman-$\alpha$ forest below redshift 6 due to islands of neutral hydrogen
• The mean free path of ionizing photons at 5 < z < 6: evidence for rapid evolution near reionization
• Constraints from Ly-$\alpha$ forests on non-thermal dark matter including resonantly-produced sterile neutrinos
• Minihalo photoevaporation during cosmic reionization: evaporation times and photon consumption rates
• Early supersymmetric cold dark matter substructure
• A Direct Measurement of the IGM Opacity to HI Ionizing Photons
• Large Fluctuations in the High-Redshift Metagalactic Ionizing Background
• Large fluctuations in the hydrogen-ionizing background and mean free path following the epoch of reionization
• Probing dark matter structure down to $10^7$ solar masses: flux ratio statistics in gravitational lenses with line of sight halos
• The THESAN project: properties of the intergalactic medium and its connection to Reionization-era galaxies
• Was reionization complete by z ~ 5-6?
• Observing the tail of reionization: neutral islands in the $z=5.5$ Lyman-$\alpha$ Forest
• Matter power spectrum: from Ly$\alpha$ forest to CMB scales
• Radiative Feedback from high mass X-ray binaries on the formation of the first galaxies and early reionization
• The Impact of Small-Scale Structure on Cosmological Ionization Fronts and Reionization
• On the intergalactic temperature-density relation
• Novel constraints on non-cold (non-thermal) Dark Matter from Lyman-$\alpha$ forest data
• Gravitational Lensing Signatures of Axion Dark Matter Minihalos in Highly Magnified Stars
• A physical understanding of how reionization suppresses accretion onto dwarf halos
• The depletion of gas in high-redshift dwarf galaxies from an inhomogeneous reionization
• Implementing the DC Mode in Cosmological Simulations with Supercomoving Variables
• Simulations of Axion Minihalos
• A Moving Frame Algorithm for High Mach Number Hydrodynamics
• Heating of the Intergalactic Medium by Hydrogen Reionization
• Constraints on the Primordial Power Spectrum from High Resolution Lyman-alpha Forest Spectra and WMAP
• Hydrodynamic Response of the Intergalactic Medium to Reionization
• A short mean free path at $z=6$ favors late and rapid reionization by faint galaxies
• Optimal identification of HII regions during reionization in 21-cm observations
• The short ionizing photon mean free path at z=6 in Cosmic Dawn III, a new fully-coupled radiation-hydrodynamical simulation of the Epoch of Reionization
• Early Structure Formation Constraints on the Ultra-Light Axion in the Post-Inflation Scenario
• New Roads to the Small-Scale Universe: Measurements of the Clustering of Matter with the High-Redshift UV Galaxy Luminosity Function
• The Hydrodynamic Feedback of Cosmic Reionization on Small-Scale Structures and Its Impact on Photon Consumption during the Epoch of Reionization
• Position-dependent power spectra of the 21-cm signal from the epoch of reionization
• The Opacity of the Intergalactic Medium During Reionization: Resolving Small-Scale Structure
• The primordial matter power spectrum on sub-galactic scales
• The Predicament of Absorption-Dominated Reionization: Increased Demands on Ionizing Sources
• Nonlinear Bias of Cosmological Halo Formation in the Early Universe
• Self-shielding of hydrogen in the IGM during the epoch of reionization
• Warm Dark Matter and Cosmic Reionization
• Hydrodynamic Response of the Intergalactic Medium to Reionization II: Physical Characteristics and Dynamics of Ionizing Photon Sinks
• Radiation from early black holes - I: effects on the neutral inter-galactic medium
• Cosmic Reionization History and Dark Matter Scenarios
• Non-equilibrium temperature evolution of ionization fronts during the Epoch of Reionization
• Fully Coupled Simulation of Cosmic Reionization. III. Stochastic Early Reionization by the Smallest Galaxies
• Effects of Small-Scale Absorption Systems on Neutral Islands during the Late Epoch of Reionization
• The Epoch of Reionization in Warm Dark Matter Scenarios

Cited by in corpus (1)

• Kiloparsec-scale turbulence driven by reionization may grow intergalactic magnetic fields