Exploring a cosmic ray inverse-Compton origin to the SZ-to-X-ray pressure deficit in the cool core cluster ZwCl 3146
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| Format: | Preprint |
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2025
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| _version_ | 1866914096621813760 |
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| author | Silich, Emily M. Sayers, Jack Hopkins, Philip F. Romero, Charles Mason, Brian Orlowski-Scherer, John Sarazin, Craig L. |
| author_facet | Silich, Emily M. Sayers, Jack Hopkins, Philip F. Romero, Charles Mason, Brian Orlowski-Scherer, John Sarazin, Craig L. |
| contents | We explore the possibility that inverse-Compton (IC) scattering of cosmic microwave background photons by $\sim$GeV cosmic rays (CRs) injected by the central active galactic nucleus (AGN) in cool core (CC) clusters produces a non-negligible continuum-like X-ray signal that is easily misinterpreted as intracluster medium (ICM) thermal bremsstrahlung continuum. This is particularly relevant to the cooling flow problem--the lack of star formation relative to X-ray-inferred ICM cooling rates. Using ZwCl 3146, a relaxed CC system at $z = 0.291$, we compare pressure profiles derived via X-rays and the thermal Sunyaev-Zel'dovich (SZ) effect. While SZ measurements probe only thermal ICM electrons, additional CR-IC emission would appear to boost the X-ray-inferred pressure. Relative to unity, we measure a $\simeq30\%$ decrement in $P_{SZ}/P_X$ within 100 kpc of the ZwCl 3146 center at a statistical significance of $\simeq 3.3σ$, consistent with predicted deficits from CR-IC contamination in reasonable models of central AGN-driven CR injection. X-ray spectral fits of a two-component model with thermal ICM and CR-IC emission are consistent with CR-IC as the cause of this deficit. We test alternative explanations and systematics that could drive such a decrement, with the leading order systematics associated with halo triaxiality. Collectively, these systematics are unlikely to produce a $P_{SZ}/P_X$ decrement $\gtrsim10\%$. While our results establish that non-negligible CR-IC emission is plausible in ZwCl 3146, we stress that more detailed studies of larger cluster samples are required to robustly assess whether CR-IC is relevant to the cooling flow problem. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2510_14820 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Exploring a cosmic ray inverse-Compton origin to the SZ-to-X-ray pressure deficit in the cool core cluster ZwCl 3146 Silich, Emily M. Sayers, Jack Hopkins, Philip F. Romero, Charles Mason, Brian Orlowski-Scherer, John Sarazin, Craig L. High Energy Astrophysical Phenomena Cosmology and Nongalactic Astrophysics We explore the possibility that inverse-Compton (IC) scattering of cosmic microwave background photons by $\sim$GeV cosmic rays (CRs) injected by the central active galactic nucleus (AGN) in cool core (CC) clusters produces a non-negligible continuum-like X-ray signal that is easily misinterpreted as intracluster medium (ICM) thermal bremsstrahlung continuum. This is particularly relevant to the cooling flow problem--the lack of star formation relative to X-ray-inferred ICM cooling rates. Using ZwCl 3146, a relaxed CC system at $z = 0.291$, we compare pressure profiles derived via X-rays and the thermal Sunyaev-Zel'dovich (SZ) effect. While SZ measurements probe only thermal ICM electrons, additional CR-IC emission would appear to boost the X-ray-inferred pressure. Relative to unity, we measure a $\simeq30\%$ decrement in $P_{SZ}/P_X$ within 100 kpc of the ZwCl 3146 center at a statistical significance of $\simeq 3.3σ$, consistent with predicted deficits from CR-IC contamination in reasonable models of central AGN-driven CR injection. X-ray spectral fits of a two-component model with thermal ICM and CR-IC emission are consistent with CR-IC as the cause of this deficit. We test alternative explanations and systematics that could drive such a decrement, with the leading order systematics associated with halo triaxiality. Collectively, these systematics are unlikely to produce a $P_{SZ}/P_X$ decrement $\gtrsim10\%$. While our results establish that non-negligible CR-IC emission is plausible in ZwCl 3146, we stress that more detailed studies of larger cluster samples are required to robustly assess whether CR-IC is relevant to the cooling flow problem. |
| title | Exploring a cosmic ray inverse-Compton origin to the SZ-to-X-ray pressure deficit in the cool core cluster ZwCl 3146 |
| topic | High Energy Astrophysical Phenomena Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2510.14820 |