Cosmic Ray Mediated Thermal Fronts in the Warm-hot Circumgalactic Medium
We investigate the 1D plane-parallel front connecting the warm (10 ^4 K) and hot (10 ^6 K) phases of the circumgalactic medium (CGM), focusing on the influence of cosmic rays (CRs) in shaping these transition layers. We find that cosmic rays dictate the thermal balance while other fluxes (thermal co...
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/add333 |
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| author | Hanjue Zhu Ellen G. Zweibel Nickolay Y. Gnedin |
| author_facet | Hanjue Zhu Ellen G. Zweibel Nickolay Y. Gnedin |
| author_sort | Hanjue Zhu |
| collection | DOAJ |
| description | We investigate the 1D plane-parallel front connecting the warm (10 ^4 K) and hot (10 ^6 K) phases of the circumgalactic medium (CGM), focusing on the influence of cosmic rays (CRs) in shaping these transition layers. We find that cosmic rays dictate the thermal balance while other fluxes (thermal conduction, radiative cooling, and gas flow) adjust to compensate. We compute column densities and ratios for the transition-temperature ions Si iv , C iv , O vi , and N v , and compare them with observational data. While most models struggle to simultaneously reproduce the observed Si iv /C iv and C iv /O vi ratios, a subset with intermediate magnetic field strength (e.g., B = 20 μ G) shows overlap with the data, although we make no claims for their uniqueness. These discrepancies suggest that the models perform better at reproducing higher-temperature ions but underestimate the contribution from cooler, photoionized regions. Compared to models without CRs, CR-mediated fronts in sufficiently strong magnetic fields produce broader transition layers and higher ion ratios, indicating that CRs can significantly alter the thermal and ionization structure of the CGM. Our results suggest that CR heating may help explain some observed ion columns under specific conditions, though additional physics may be needed for full agreement with observations. |
| format | Article |
| id | doaj-art-c3d1f91dc20f42b6a349fa4ffc2716e4 |
| institution | DOAJ |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj-art-c3d1f91dc20f42b6a349fa4ffc2716e42025-08-20T02:42:16ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01987213210.3847/1538-4357/add333Cosmic Ray Mediated Thermal Fronts in the Warm-hot Circumgalactic MediumHanjue Zhu0https://orcid.org/0000-0003-0861-0922Ellen G. Zweibel1https://orcid.org/0000-0003-4821-713XNickolay Y. Gnedin2https://orcid.org/0000-0001-5925-4580Department of Astronomy & Astrophysics, The University of Chicago , Chicago, IL 60637, USA ; hanjuezhu@uchicago.eduDepartment of Astronomy, University of Wisconsin-Madison , 475 N. Charter Street, Madison, WI 53706, USA; Department of Physics, University of Wisconsin-Madison , 150 University Avenue, Madison, WI 53706, USADepartment of Astronomy & Astrophysics, The University of Chicago , Chicago, IL 60637, USA ; hanjuezhu@uchicago.edu; Particle Astrophysics Center , Fermi National Accelerator Laboratory, Batavia, IL 60510, USA; Kavli Institute for Cosmological Physics, The University of Chicago , Chicago, IL 60637, USAWe investigate the 1D plane-parallel front connecting the warm (10 ^4 K) and hot (10 ^6 K) phases of the circumgalactic medium (CGM), focusing on the influence of cosmic rays (CRs) in shaping these transition layers. We find that cosmic rays dictate the thermal balance while other fluxes (thermal conduction, radiative cooling, and gas flow) adjust to compensate. We compute column densities and ratios for the transition-temperature ions Si iv , C iv , O vi , and N v , and compare them with observational data. While most models struggle to simultaneously reproduce the observed Si iv /C iv and C iv /O vi ratios, a subset with intermediate magnetic field strength (e.g., B = 20 μ G) shows overlap with the data, although we make no claims for their uniqueness. These discrepancies suggest that the models perform better at reproducing higher-temperature ions but underestimate the contribution from cooler, photoionized regions. Compared to models without CRs, CR-mediated fronts in sufficiently strong magnetic fields produce broader transition layers and higher ion ratios, indicating that CRs can significantly alter the thermal and ionization structure of the CGM. Our results suggest that CR heating may help explain some observed ion columns under specific conditions, though additional physics may be needed for full agreement with observations.https://doi.org/10.3847/1538-4357/add333Cosmic raysCircumgalactic medium |
| spellingShingle | Hanjue Zhu Ellen G. Zweibel Nickolay Y. Gnedin Cosmic Ray Mediated Thermal Fronts in the Warm-hot Circumgalactic Medium The Astrophysical Journal Cosmic rays Circumgalactic medium |
| title | Cosmic Ray Mediated Thermal Fronts in the Warm-hot Circumgalactic Medium |
| title_full | Cosmic Ray Mediated Thermal Fronts in the Warm-hot Circumgalactic Medium |
| title_fullStr | Cosmic Ray Mediated Thermal Fronts in the Warm-hot Circumgalactic Medium |
| title_full_unstemmed | Cosmic Ray Mediated Thermal Fronts in the Warm-hot Circumgalactic Medium |
| title_short | Cosmic Ray Mediated Thermal Fronts in the Warm-hot Circumgalactic Medium |
| title_sort | cosmic ray mediated thermal fronts in the warm hot circumgalactic medium |
| topic | Cosmic rays Circumgalactic medium |
| url | https://doi.org/10.3847/1538-4357/add333 |
| work_keys_str_mv | AT hanjuezhu cosmicraymediatedthermalfrontsinthewarmhotcircumgalacticmedium AT ellengzweibel cosmicraymediatedthermalfrontsinthewarmhotcircumgalacticmedium AT nickolayygnedin cosmicraymediatedthermalfrontsinthewarmhotcircumgalacticmedium |