X-rays and hard UV radiation From the First Galaxies: Ionization Bubbles and 21 cm Observations

Abstract

The first stars and quasars are known sources of hard ionizing radiation in the first billion years of the Universe. We examine the joint effects of X-rays and hard UV radiation from such first-light sources on the hydrogen and helium reionization of the intergalactic medium (IGM) at early times, and the associated heating. We study the growth and evolution of individual HII, HeII and HeIII regions around early galaxies with first stars and/or QSO populations. We find that in the presence of helium-ionizing radiation, X-rays may not dominate the ionization and thermal history of the IGM at redshifts, z, of 10-20, contributing relatively modest increases to IGM ionization, and heating up to about 10^3--10^5 K in IGM temperatures. We also calculate the 21 cm signal expected from a number of scenarios with metal-free starbursts and quasars at these redshifts. The peak values for the spin temperature reach about 10^4 to 10^5 K in such cases. The maximum values for the 21 cm brightness temperature are around 30-40 mK in emission, while the net values of the 21 cm absorption signal range from about a few to 60 mK on scales of 0.01-1 Mpc. We find that the 21 cm signature of X-ray versus UV ionization could be distinct, with the emission signal expected from X-rays alone occurring at smaller scales than that from UV radiation, resulting from the inherently different spatial scales at which X-ray and UV ionization/heating manifest. This difference is time-dependent, and becomes harder to distinguish with an increasing X-ray contribution to the total ionizing photon production. Such differing scale-dependent contributions from X-ray and UV photons may therefore "blur" the 21 cm signature of the percolation of ionized bubbles around early halos (depending on whether a cosmic X-ray or UV background built up first), and affect the interpretation of 21 cm data constraints on reionization.

Accepted for publication in MNRAS; 15 pages, 14 figures

References in corpus (14)

• Cosmology at Low Frequencies: The 21 cm Transition and the High-Redshift Universe
• Effect of Primordial Black Holes on the Cosmic Microwave Background and Cosmological Parameter Estimates
• 21 cm fluctuations from inhomogeneous X-ray heating before reionization
• HeII Reionization and its Effect on the IGM
• Precise Black Hole Masses From Megamaser Disks: Black Hole-Bulge Relations at Low Mass
• Resolving the Formation of Protogalaxies. II. Central Gravitational Collapse
• A Luminosity Function of Lyman Alpha Emitting Galaxies at Redshift 4.5
• Cosmic Reionization and the 21-cm signal: Comparison between an analytical model and a simulation
• The History and Morphology of Helium Reionization
• The Scattering of Lyman-series Photons in the Intergalactic Medium
• Time-evolution of ionization and heating around first stars and miniquasars
• Photo-heating and the fate of hard photons during the reionisation of HeII by quasars
• Inhomogeneous Helium Reionization and the Equation of State of the Intergalactic Medium
• Radiation from early black holes - I: effects on the neutral inter-galactic medium

Cited by in corpus (16)

• Cosmic Reionization On Computers I. Design and Calibration of Simulations
• Constraints on X-ray Emissions from the Reionization Era
• Cosmic Reionization On Computers II. Reionization History and Its Back Reaction on Early Galaxies
• Radiative Feedback from high mass X-ray binaries on the formation of the first galaxies and early reionization
• Decoding the X-ray Properties of Pre-Reionization Era Sources
• Recovery from population III supernova explosions and the onset of second generation star formation
• Heating of the Intergalactic Medium by Hydrogen Reionization
• Quasar Ionization Front Lyα Emission in an Inhomogeneous Intergalactic Medium
• Optimized Multi-Frequency Spectra for Applications in Radiative Feedback and Cosmological Reionization
• Interpreting the Global 21-cm Signal from High Redshifts. I. Model Independent Constraints
• Models of the Cosmological 21 cm Signal from the Epoch of Reionization Calibrated with Lyman-alpha and CMB Data
• Probing the thermal history during reionization using a semi-numerical photon-conserving code SCRIPT
• X-ray ionization of the intergalactic medium by quasars
• An Analytic Formulation of 21-cm Signal from Early Phase of Epoch of Reionization
• Growth and anisotropy of ionization fronts near high redshift quasars in the MassiveBlack simulation
• The long-lasting effect of X-ray preheating in the post-reionization intergalactic medium