The Conditional CMB Visibility of High-Redshift X-Ray Cavities in Galaxy clusters
Abstract
At high redshift, the cosmic microwave background (CMB) both cools relativistic leptons and provides seed photons for inverse-Compton (IC) X-ray emission. These two effects link the particle content of a bubble directly to the soft X-ray depression used to identify a cavity. We derive a physical criterion connecting lepton cooling, bubble volume, enthalpy evolution, and 0.5--2 keV X-ray visibility, while separating intrinsic filling of the X-ray depression from detector-dependent cavity recovery. For uncooled electron populations described by a power law with spectral index s=2.5, minimum Lorentz factor 100≤γmin≤1000, and maximum Lorentz factor γmax=105, the measured atmosphere of the testbed high-redshift cluster SPT-CL J2215−3537 requires 0.6--1.2\% of the pressure in radiating leptons to fill the soft-band deficit. Across the full tested ranges of s, γmin, and atmospheric properties, the required fraction is 0.2--3.7\%. Complete loss of this component reduces the enthalpy by less than 3\% relative to an otherwise identical adiabatic bubble at the same pressure. A low-cutoff control with γmin=10 and s=3 instead requires 18.9\%, identifying the poorly constrained low-energy spectrum as the main physical uncertainty. For a fixed atmosphere and spectrum, the required fraction scales as (1+z)−4. The declining-pressure tracks show that the X-ray deficit can cross the adopted detection threshold while the enthalpy deficit remains below 0.4\%; the time of this transition depends on the assumed pressure history. Thus, high-redshift cavity visibility depends on both the surrounding atmosphere and the pressure-carrying particle spectrum. This criterion provides the physical basis for an instrument-specific recovery analysis.
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BibTeX
@misc{santra2026conditional,
title = {{The Conditional CMB Visibility of High-Redshift X-Ray Cavities in Galaxy clusters}},
author = {Ramananda Santra and Samik Mitra},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.40610},
eprint = {2610.40610},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.40610},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Conditional CMB Visibility of High-Redshift X-Ray Cavities in Galaxy clusters
AU - Ramananda Santra
AU - Samik Mitra
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.40610
UR - https://arxiv.org/abs/2610.40610
AB - At high redshift, the cosmic microwave background (CMB) both cools relativistic leptons and provides seed photons for inverse-Compton (IC) X-ray emission. These two effects link the particle content of a bubble directly to the soft X-ray depression used to identify a cavity. We derive a physical criterion connecting lepton cooling, bubble volume, enthalpy evolution, and 0.5--2 keV X-ray visibility, while separating intrinsic filling of the X-ray depression from detector-dependent cavity recovery. For uncooled electron populations described by a power law with spectral index s=2.5, minimum Lorentz factor 100≤γ_min≤1000, and maximum Lorentz factor γ_max=10^5, the measured atmosphere of the testbed high-redshift cluster SPT-CL J2215−3537 requires 0.6--1.2\% of the pressure in radiating leptons to fill the soft-band deficit. Across the full tested ranges of s, γ_min, and atmospheric properties, the required fraction is 0.2--3.7\%. Complete loss of this component reduces the enthalpy by less than 3\% relative to an otherwise identical adiabatic bubble at the same pressure. A low-cutoff control with γ_min=10 and s=3 instead requires 18.9\%, identifying the poorly constrained low-energy spectrum as the main physical uncertainty. For a fixed atmosphere and spectrum, the required fraction scales as (1+z)^−4. The declining-pressure tracks show that the X-ray deficit can cross the adopted detection threshold while the enthalpy deficit remains below 0.4\%; the time of this transition depends on the assumed pressure history. Thus, high-redshift cavity visibility depends on both the surrounding atmosphere and the pressure-carrying particle spectrum. This criterion provides the physical basis for an instrument-specific recovery analysis.
ER -