The Signatures of Particle Decay in 21 cm Absorption from the First Minihalos
Abstract
The imprint of decaying dark matter (DM) particles on the characteristics of the "21 cm forest"—absorption at 21 cm from minihalos in the spectra of distant radio-loud sources—is considered within a one-dimensional, self-consistent hydrodynamic description of minihalos from their turnaround point to virialization. The most pronounced influence of decaying DM on the evolution of minihalos is found in the mass range M = 105-106 M ⊙, for which unstable DM with a current upper limit on its ionization rate of ξ L = 0.59 × 10-25 s-1 reduces the 21 cm optical depth by an order of magnitude compared with the standard recombination scenario. Even a rather modest ionization, ξ ~ 0.3ξ L , practically erases absorption features and results in a considerable decrease (by factor of more than 2.5) of the number of strong (W_\nu ^{obs} \gtrsim 0.3 kHz at z ~= 10) absorptions. In such circumstances, broadband observations are more suitable for inferring the physical conditions of the absorbing gas. X-ray photons from stellar activity of the initial episodes of star formation can compete with the contribution from decaying DM only at z < 10. Therefore, observing the 21 cm signal will allow us to follow the evolution of decaying DM particles in the redshift range z = 10-15. On the other hand, a non-detection of the 21 cm signal in the frequency range ν < 140 MHz can establish a lower limit on the ionization rate from decaying DM.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2013
- DOI:
- 10.1088/0004-637X/777/1/8
- arXiv:
- arXiv:1308.2169
- Bibcode:
- 2013ApJ...777....8V
- Keywords:
-
- cosmology: theory;
- dark matter;
- diffuse radiation;
- early universe;
- line: formation;
- radio lines: general;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 10 pages, 4 figures, accepted in ApJ. arXiv admin note: text overlap with arXiv:1205.1204