Speaker
Description
Context. Cosmological simulations indicate that half of the baryons in the nearby universe exist as warm-hot intergalactic medium (WHIM), and half of this WHIM gas resides in cosmic filaments that connect galaxy clusters. Accurate prescription of the filament gas is therefore essential for understanding the gravitational and baryonic processes that affect the assembly of the cosmic structures. Recent breakthroughs made by eROSITA with its all-sky imaging capabilities confirmed filament emission with stacking techniques and identified the largest catalog of X-ray-selected supercluster systems pointing to high-density regions of the cosmic web. Further diagnostics of WHIM properties with high-resolution spectroscopy, which will be necessary for revealing the thermal and chemical history of the cosmic filaments, can be expected in the foreseeable future with microcalorimetry missions, such as the Hot Universe Baryon Surveyor (HUBS), the Line Emission Mapper (LEM), and the Advanced Telescope for High-energy Astrophysics (Athena+).
Aims. By modeling filament emission in the eRASS1 superclusters (Liu et al., 2024), we aim to select appropriate targets for baryon census and characterization in the large-scale structure to be performed with the future HUBS mission, which is designed with superior energy resolution (2 eV) in the 0.1 - 2 keV band and a large field-of-view (1 square degree).
Methods. Based on the eRASS1 supercluster catalog, which identified 1338 supercluster systems encompassing 3948 member clusters, we constructed a sample of 2322 cluster pairs. We modeled the filament emission between each cluster pair with geometrical information drawn from the cluster catalog and CIE parameters determined based on published results from stacked observations and numerical simulations. We quantified the detection level of each filament using intensities of the redshifted oxygen lines.
Results. With 200 ks HUBS exposure, we can significantly detect (>5$\sigma$ OVIII line) the filament emission for 7 cluster pairs under a prudent assumption of 0.5 keV gas temperature. We generated and analyzed mocked spectra and images of these candidate targets. As an example, for the cluster pair [1eRASS J011004.5-360322, 1eRASS J010750.4-364317], we constrained the temperature, metallicity, and electron density with 1.2%, 7%, and 6.5% uncertainties, respectively. Even with a conservative gas temperature assumption of 0.1 keV, we can still detect the OVII triplet with >4$\sigma$ and recover the temperature and electron density with <10% uncertainty.
Conclusions. We identified 7 candidate filaments from the eRASS1 supercluster catalog as future HUBS targets, each of which can be robustly detected and precisely characterized with a single 200 ks pointed exposure. Our analysis demonstrates the line-resolving power of HUBS and the deep surveys obtained with eROSITA will be a powerful combination to substantially improve our understanding of the thermodynamical status and chemical enrichment of cosmic filaments.
