Time-evolution of ionization and heating around first stars and miniquasars

TL;DR

This paper develops a radiative transfer model to study ionization and heating patterns around the first stars and miniquasars, revealing differences in heating, ionized bubble evolution, and implications for future radio observations.

Contribution

It introduces a one-dimensional radiative transfer code that accurately models ionization and heating around first stars and miniquasars, highlighting differences from analytical approximations.

Findings

Massive miniquasars produce large ionized bubbles detectable by future radio telescopes.

Ionized bubbles persist and expand after source turn-off due to secondary collisions.

Varying spectral shapes significantly affect ionization and temperature profiles.

Abstract

A one dimensional radiative transfer code is developed to track the ionization and heating pattern around the first miniquasars and Population III stars. The code follows the evolution of the ionization of the species of hydrogen and helium and the intergalactic medium temperature profiles as a function of redshift. The radiative transfer calculations show that the ionization signature of the first miniquasars and stars is very similar yet the heating pattern around the two is very different. Furthermore, the first massive miniquasars (~>10^5 M_{sun}) do produce large ionized bubbles around them, which can potentially be imaged directly using future radio telescopes. It is also shown that the ionized bubbles not only stay ionized for considerable time after the switching off of the source, but continue to expand for a short while due to secondary collisions prompted by the X-ray part of their spectra. Varying spectral shapes also produced sizable variations in ionized fraction and temperature profile. We also compare the radiative transfer results with the analytical approximation usually adopted for heating by miniquasars and find that, because of the inadequate treatment of the He species, the analytical approach leads to an underestimation of the temperature in the outer radii by a factor ~5. Population III stars - with masses in the range of 10 - 1000 M_{sun} and modelled as blackbodies at a temperature of 50000 K - are found to be efficient in ionizing their surroundings. Observational effects on the 21 cm brightness temperature, the thermal and kinetic Sunyaev-Ze'ldovich effects, are also studied in the context of the upcoming radio and microwave telescopes like LOFAR and SPT.