THE 21 cm FOREST AS A PROBE OF THE REIONIZATION AND THE TEMPERATURE OF THE INTERGALACTIC MEDIUM

Journal Article · Tue Oct 20 04:00:00 EDT 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/704/2/1396· OSTI ID:21367336

Yidong, Xu; Zuhui, Fan ^[1]; Xuelei, Chen ^[2]; Trac, Hy ^[3]; Cen, Renyue ^[4]

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1. Department of Astronomy, School of Physics, Peking University, Beijing 100871 (China)
2. National Astronomical Observatory of China, CAS, Beijing 100012 (China)
3. Harvard-Smithsonian Center for Astrophysics, Harvard University, 60 Garden Street, Cambridge MA 02138 (United States)
4. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

Using high-redshift radio sources as background, the 21 cm forest observations probe the neutral hydrogen absorption signatures of early structures along the lines of sight. Directly sensitive to the spin temperature of the hydrogen atoms, it complements the 21 cm tomography observations, and provides information on the temperature as well as the ionization state of the intergalactic medium (IGM). We use a radiative transfer simulation to investigate the 21 cm forest signals during the epoch of reionization. We first confirmed that the optical depth and equivalent width (EW) are good representations of the ionization and thermal state of the IGM. The features selected by their relative optical depth are excellent tracers of ionization fields, and the features selected by their absolute optical depth are very sensitive to the IGM temperature, so the IGM temperature information could potentially be extracted from 21 cm forest observation, thus breaking a degeneracy in 21 cm tomographic observation. With the EW statistics, we predict some observational consequences for 21 cm forest. From the distributions of EWs and the number evolution of absorbers and leakers with different EWs, we see clearly the cosmological evolution of ionization state of the IGM. The number density of potentially observable features decreases rapidly with increasing gas temperature. The sensitivity of the proposed EW statistic to the IGM temperature makes it a unique and potentially powerful probe of reionization. Missing small-scale structures, such as small filaments and minihalos that are unresolved in our current simulation, and lack of an accurate calculation of the IGM temperature, however, likely have rendered the presented signals quantitatively inaccurate. Finally, we discuss the requirements of the background radio sources for such observations, and find that signals with equivalent widths larger than 1 kHz are hopeful to be detected.

• OSTI ID: 21367336
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 704; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
ANGULAR MOMENTUM
COSMIC RADIO SOURCES
COSMOLOGY
DIAGNOSTIC TECHNIQUES
ELEMENTS
ENERGY TRANSFER
EVOLUTION
GALACTIC EVOLUTION
HEAT TRANSFER
HYDROGEN
IONIZATION
MATHEMATICS
NONMETALS
PARTICLE PROPERTIES
QUASARS
RADIANT HEAT TRANSFER
RED SHIFT
SIGNALS
SIMULATION
SORPTION
SPIN
STATISTICS
TOMOGRAPHY