Resonant scattering of the OVII X-ray emission line in the circumgalactic medium of TNG50 galaxies

We study the impact of resonantly scattered X-ray line emission on the observability of the hot circumgalactic medium (CGM) of galaxies. We apply a Monte Carlo radiative transfer post-processing analysis to the high-resolution TNG50 cosmological magnetohydrodynamical galaxy formation simulation. This allows us to model the resonant scattering of OVII(r) X-ray photons within the complex, multi-phase, multi-scale CGM. The resonant transition of the OVII He-like triplet is one of the brightest, and most promising, X-ray emission lines for detecting the hot CGM and measuring its physical properties. We focus on galaxies with stellar masses 10 < log(M*/Msun) < 11 at z ~ 0. After constructing a model for OVII(r) emission from the central galaxy as well as from CGM gas, we forward model these intrinsic photons to derive observable surface brightness maps. We find that scattering significantly boosts the observable OVII(r) surface brightness of the extended and diffuse CGM. This enhancement can be large -- an order of magnitude on average at a distance of 200 projected kpc for high-mass M* = 10^10.7 Msun galaxies. The enhancement is larger for lower mass galaxies, and can even reach a factor of 100, across the extended CGM. Galaxies with higher star formation rates, AGN luminosities, and central OVII(r) luminosities all have larger scattering enhancements, at fixed stellar mass. Our results suggest that next-generation X-ray spectroscopic missions including XRISM, LEM, ATHENA, and HUBS -- which aim to detect the hot CGM in emission -- could specifically target halos with significant enhancements due to resonant scattering.Comment: Published in MNRAS. See https://www.lem-observatory.org/ and https://www.tng-project.org/ for more details; 2023MNRAS.522.3665

Circumgalactic Medium on the Largest Scales: Detecting X-ray Absorption Lines with Large-Area Microcalorimeters

The circumgalactic medium (CGM) plays a crucial role in galaxy evolution as it fuels star formation, retains metals ejected from the galaxies, and hosts gas flows in and out of galaxies. For Milky Way-type and more massive galaxies, the bulk of the CGM is in hot phases best accessible at X-ray wavelengths. However, our understanding of the CGM remains largely unconstrained due to its tenuous nature. A promising way to probe the CGM is via X-ray absorption studies. Traditional absorption studies utilize bright background quasars, but this method probes the CGM in a pencil beam, and, due to the rarity of bright quasars, the galaxy population available for study is limited. Large-area, high spectral resolution X-ray microcalorimeters offer a new approach to exploring the CGM in emission and absorption. Here, we demonstrate that the cumulative X-ray emission from cosmic X-ray background sources can probe the CGM in absorption. We construct column density maps of major X-ray ions from the Magneticum simulation and build realistic mock images of nine galaxies to explore the detectability of X-ray absorption lines arising from the large-scale CGM. We conclude that the OVII absorption line is detectable around individual massive galaxies at the $3\sigma-6\sigma$ confidence level. For Milky Way-type galaxies, the OVII and OVIII absorption lines are detectable at the $\sim\,6\sigma$ and $\sim\,3\sigma$ levels even beyond the virial radius when co-adding data from multiple galaxies. This approach complements emission studies, does not require additional exposures, and will allow probing of the baryon budget and the CGM at the largest scales.Comment: 16 pages, 8 figures, accepted for publication in Ap

LEM All-Sky Survey: Soft X-ray Sky at Microcalorimeter Resolution

The Line Emission Mapper (LEM) is an X-ray Probe with with spectral resolution ~2 eV FWHM from 0.2 to 2.5 keV and effective area >2,500 cm$^2$ at 1 keV, covering a 33 arcmin diameter Field of View with 15 arcsec angular resolution, capable of performing efficient scanning observations of very large sky areas and enabling the first high spectral resolution survey of the full sky. The LEM-All-Sky Survey (LASS) is expected to follow the success of previous all sky surveys such as ROSAT and eROSITA, adding a third dimension provided by the high resolution microcalorimeter spectrometer, with each 15 arcsec pixel of the survey including a full 1-2 eV resolution energy spectrum that can be integrated over any area of the sky to provide statistical accuracy. Like its predecessors, LASS will provide both a long-lasting legacy and open the door to the unknown, enabling new discoveries and delivering the baseline for unique GO studies. No other current or planned mission has the combination of microcalorimeter energy resolution and large grasp to cover the whole sky while maintaining good angular resolution and imaging capabilities. LASS will be able to probe the physical conditions of the hot phases of the Milky Way at multiple scales, from emission in the Solar system due to Solar Wind Charge eXchange, to the interstellar and circumgalactic media, including the North Polar Spur and the Fermi/eROSITA bubbles. It will measure velocities of gas in the inner part of the Galaxy and extract the emissivity of the Local Hot Bubble. By maintaining the original angular resolution, LASS will also be able to study classes of point sources through stacking. For classes with ~$10^4$ objects, it will provide the equivalent of 1 Ms of high spectral resolution data. We describe the technical specifications of LASS and highlight the main scientific objectives that will be addressed. (Abridged)Comment: White Paper in support of a mission concept to be submitted for the 2023 NASA Astrophysics Probes opportunity. This White Paper will be updated when required. 30 pages, 25 figure

LEM All-Sky Survey: Soft X-ray Sky at Microcalorimeter Resolution

The Line Emission Mapper (LEM) is an X-ray Probe with with spectral resolution ~2 eV FWHM from 0.2 to 2.5 keV and effective area >2,500 cm$^2$ at 1 keV, covering a 33 arcmin diameter Field of View with 15 arcsec angular resolution, capable of performing efficient scanning observations of very large sky areas and enabling the first high spectral resolution survey of the full sky. The LEM-All-Sky Survey (LASS) is expected to follow the success of previous all sky surveys such as ROSAT and eROSITA, adding a third dimension provided by the high resolution microcalorimeter spectrometer, with each 15 arcsec pixel of the survey including a full 1-2 eV resolution energy spectrum that can be integrated over any area of the sky to provide statistical accuracy. Like its predecessors, LASS will provide both a long-lasting legacy and open the door to the unknown, enabling new discoveries and delivering the baseline for unique GO studies. No other current or planned mission has the combination of microcalorimeter energy resolution and large grasp to cover the whole sky while maintaining good angular resolution and imaging capabilities. LASS will be able to probe the physical conditions of the hot phases of the Milky Way at multiple scales, from emission in the Solar system due to Solar Wind Charge eXchange, to the interstellar and circumgalactic media, including the North Polar Spur and the Fermi/eROSITA bubbles. It will measure velocities of gas in the inner part of the Galaxy and extract the emissivity of the Local Hot Bubble. By maintaining the original angular resolution, LASS will also be able to study classes of point sources through stacking. For classes with ~$10^4$ objects, it will provide the equivalent of 1 Ms of high spectral resolution data. We describe the technical specifications of LASS and highlight the main scientific objectives that will be addressed. (Abridged

All-sky soft X-ray map with microcalorimeter resolution: prospects of the Line Emission Mapper probe mission

International audienceThe Line Emission Mapper (LEM) is a proposed NASA probe class mission which will combine ~ 1600 cm2 effective area at 0.5 keV (2600 cm2 at 1 keV) with microcalorimeter 2 eV spectral resolution and 15" spatial resolution over 30' by 30' field of view in the soft X-ray band (0.2-2 keV). Unprecedented grasp for a spectroscopic mission makes it possible to build sensitive maps for very large sky areas over short periods of time, opening a possibility of constructing a full-sky soft X-ray map of high sharpness and exquisite spectral detail. Such a map would allow us to probe physical conditions in the hot phase of the Milky Way's interstellar and circumgalactic medium, including such outstanding features as the North Polar Spur and Fermi/eROSITA bubbles, measure velocities of the gas motions in the inner part of the Galaxy, extract emissivity of the Local Hot Bubble and explore emission due to Solar Wind Charge exchange. Birth and death of the stars can be traced by tomography of bright and extended supernova remnants and star formation regions in our own and nearby galaxies, including Magellanic Clouds and M31. For a multitude of distant extra-galactic sources, mostly active galactic nuclei and galaxy clusters and groups, high resolution X-ray spectra will be obtained for the first time, as well as stacked spectra for their populations and intergalactic environments. A substantial number of transient sources, either Galactic (e.g. X-ray binaries), extragalactic (e.g. tidal disruption events) or Solar System (e.g. comets), might be discovered and studied in great detail. Finally, akin to the data of the ROSAT all-sky survey, the all-sky map by LEM will provide a high resolution X-ray background estimation for any position of the sky, so valuable for the in-depth analysis of extremely faint individual objects, as filaments of the warm-hot intergalactic medium or distant outskirts of massive galaxies, groups and clusters. We will present an outline of the survey parameters and design and highlight some scientific cases within the grasp of this mission

All-sky soft X-ray map with microcalorimeter resolution: prospects of the Line Emission Mapper probe mission

International audienceThe Line Emission Mapper (LEM) is a proposed NASA probe class mission which will combine ~ 1600 cm2 effective area at 0.5 keV (2600 cm2 at 1 keV) with microcalorimeter 2 eV spectral resolution and 15" spatial resolution over 30' by 30' field of view in the soft X-ray band (0.2-2 keV). Unprecedented grasp for a spectroscopic mission makes it possible to build sensitive maps for very large sky areas over short periods of time, opening a possibility of constructing a full-sky soft X-ray map of high sharpness and exquisite spectral detail. Such a map would allow us to probe physical conditions in the hot phase of the Milky Way's interstellar and circumgalactic medium, including such outstanding features as the North Polar Spur and Fermi/eROSITA bubbles, measure velocities of the gas motions in the inner part of the Galaxy, extract emissivity of the Local Hot Bubble and explore emission due to Solar Wind Charge exchange. Birth and death of the stars can be traced by tomography of bright and extended supernova remnants and star formation regions in our own and nearby galaxies, including Magellanic Clouds and M31. For a multitude of distant extra-galactic sources, mostly active galactic nuclei and galaxy clusters and groups, high resolution X-ray spectra will be obtained for the first time, as well as stacked spectra for their populations and intergalactic environments. A substantial number of transient sources, either Galactic (e.g. X-ray binaries), extragalactic (e.g. tidal disruption events) or Solar System (e.g. comets), might be discovered and studied in great detail. Finally, akin to the data of the ROSAT all-sky survey, the all-sky map by LEM will provide a high resolution X-ray background estimation for any position of the sky, so valuable for the in-depth analysis of extremely faint individual objects, as filaments of the warm-hot intergalactic medium or distant outskirts of massive galaxies, groups and clusters. We will present an outline of the survey parameters and design and highlight some scientific cases within the grasp of this mission

Line Emission Mapper (LEM): Probing the physics of cosmic ecosystems

The Line Emission Mapper (LEM) is an X-ray Probe for the 2030s that will answer the outstanding questions of the Universe's structure formation. It will also provide transformative new observing capabilities for every area of astrophysics, and to heliophysics and planetary physics as well. LEM's main goal is a comprehensive look at the physics of galaxy formation, including stellar and black-hole feedback and flows of baryonic matter into and out of galaxies. These processes are best studied in X-rays, and emission-line mapping is the pressing need in this area. LEM will use a large microcalorimeter array/IFU, covering a 30x30' field with 10" angular resolution, to map the soft X-ray line emission from objects that constitute galactic ecosystems. These include supernova remnants, star-forming regions, superbubbles, galactic outflows (such as the Fermi/eROSITA bubbles in the Milky Way and their analogs in other galaxies), the Circumgalactic Medium in the Milky Way and other galaxies, and the Intergalactic Medium at the outskirts and beyond the confines of galaxies and clusters. LEM's 1-2 eV spectral resolution in the 0.2-2 keV band will make it possible to disentangle the faintest emission lines in those objects from the bright Milky Way foreground, providing groundbreaking measurements of the physics of these plasmas, from temperatures, densities, chemical composition to gas dynamics. While LEM's main focus is on galaxy formation, it will provide transformative capability for all classes of astrophysical objects, from the Earth's magnetosphere, planets and comets to the interstellar medium and X-ray binaries in nearby galaxies, AGN, and cooling gas in galaxy clusters. In addition to pointed observations, LEM will perform a shallow all-sky survey that will dramatically expand the discovery space