The Hot Universe Baryon Surveyor (HUBS) is a satellite mission that is proposed to probe “hidden” baryons in the universe and thus to fill a void in observational astronomy that seriously affects our understand of galaxy formation and evolution. The HUBS payload is highly optimized for detecting diffuse X-ray emission from the baryons, with the combination of large field of view and high spectral resolution. To assess the scientific capabilities of HUBS, we created mock observations with data from a state-of-the-art cosmological hydrodynamical simulation (IllustrisTNG). The targets include systems that are representative of galaxies, galaxy groups, and galaxy clusters at various redshifts. We generated the X-ray spectra and images of the selected sources from the mock observations, taking into account galactic foreground emission, X-ray emission from cosmologically distant background sources, as well as emission from other sources along the lines of sight. The results from analyzing the mock observations show that the assumed design of HUBS is appropriate for achieving its primary scientific objectives. In this paper, we present the results and discuss issues related to observing strategies.
The Hot Universe Baryon Surveyor (HUBS) is a satellite concept proposed in China to address the so-called “missing baryon problem”, which has serious implications on the formation and evolution of galaxies. At the heart of HUBS there is a high-resolution soft X Ray spectrometer based on transition-edge sensors operating below 100 mK. A cooling system is needed to provide such a low-temperature environment. It necessarily consists of a precooling stage and a cold stage. The cold stage could be enabled by an adiabatic demagnetization refrigerator (ADR). Because an ADR could be operated without gravity’s assist and has no refrigerant consumption, it is a good candidate for satellite mission like HUBS. For HUBS, the ADR will be employed to cool the detector down to below 100 mK from the precooling stage (at about 4K), which is enabled by mechanical pulse tube refrigerators. ADR for HUBS is now under development in our lab. The key technologies of building an ADR including growth of paramagnetic salt pill crystals, gas-gap heat switch are under development. A preliminary design of the ADR is completed and the design parameters are optimized. In this paper, we report on the status of the development.
The Hot Universe Baryon Surveyor (HUBS) mission is proposed to study “missing” baryons in the universe. Unlike dark matter, baryonic matter is made of elements in the periodic table, and can be directly observed through the electromagnetic signals that it produces. Stars contain only a tiny fraction of the baryonic matter known to be present in the universe. Additional baryons are found to be in diffuse (gaseous) form, in or between galaxies, but a significant fraction has not yet been seen. The latter (“missing” baryons) are thought to be hiding in low-density warm-hot ionized medium (WHIM), based on results from theoretical studies and recent observations, and be distributed in the vicinity of galaxies (i.e., circumgalactic medium) and between galaxies (i.e., intergalactic medium). Such gas would radiate mainly in the soft X-ray band and the emission would be very weak, due to its very low density. HUBS is optimized to detect the X-ray emission from the hot baryons in the circumgalactic medium, and thus fill a void in observational astronomy. The goal is not only to detect the “missing” baryons, but to characterize their physical and chemical properties, as well as to measure their spatial distribution. The results would establish the boundary conditions for understanding galaxy evolution. Though highly challenging, detecting “missing” baryons in the intergalactic medium could be attempted, perhaps in the outskirts of galaxy clusters, and could shed significant light on the large-scale structures of the universe. The current design of HUBS will be presented, along with the status of technology development.
Hot Universe Baryon Surveyor (HUBS) is being conceptualized in China as a high throughput and high-resolution spectroscopic X-ray mission dedicated to studying cosmic "missing" baryons, which are thought to exist in the gas of very low density and temperature roughly one million degrees in the halo of galaxies or in large-scale structures. To detect weak emission from the "missing" baryons, HUBS will employ a TES-based X-ray microcalorimeter array that operates at very low temperatures. The key characteristics of the detector technology are excellent energy resolution and high quantum efficiency, which makes it an ideal choice for constructing a non-dispersive X-ray imaging spectrometer. We are developing X-ray microcalorimeters for HUBS, based on superconducting Mo/Cu bilayer films. In this work, we present results on the characterization of the Mo/Cu films and TES devices at temperatures below 100 mK, including their R-T curves, I-V characteristics, energy resolutions, etc. We have also studied correlations between the superconducting transition temperature and other properties of the films (including residual resistivity ratio, stress, crystalline structure, interface properties, and so on), and looked into factors that might affect the energy resolution of the detectors. Preliminary results will be presented.
Hot Universe Baryon Surveyor (HUBS)1 is being conceptualized in China as a high throughput and highresolution spectroscopic X-ray mission dedicated to studying cosmic “missing” baryons, which are thought to exist in the gas of very low density and temperature of roughly one million degrees in the halo of galaxies or in large-scale structures. To detect weak emission from the “missing” baryons, HUBS will employ an X-ray microcalorimeter based on transition-edge sensors (TES) array that operates at very low temperatures. The key characteristics of the detector technology are excellent energy resolution and high quantum efficiency, which makes it an ideal choice for constructing a non-dispersive X-ray imaging spectrometer. We are developing X-ray microcalorimeters for HUBS, based on superconducting Mo/Cu bilayer films. In this work, we present results on characterization of the Mo/Cu films and TES devices at temperatures below 200 mK, including their I − V characteristics, pulse signals and energy resolutions. We have also studied correlations between the superconductivity and other properties of the films (including residual resistivity ratio, stress, crystalline structure, interface properties, etc.). Preliminary results are presented in this work.
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