X-ray Emission Processes in Star-forming Galaxies
Summary
X-ray emission in star-forming galaxies arises from a combination of point sources and diffuse plasma heated by stellar feedback. Young massive stars end their lives in core-collapse supernovae, injecting energy into the interstellar medium and producing hot gas visible in the soft X-ray band (0.5–2 keV). Meanwhile, accreting compact objects—high-mass X-ray binaries (HMXBs) with short-lived, massive companions and low-mass X-ray binaries (LMXBs) with longer-lived, lower-mass donors—emit predominantly harder X-rays (2–10 keV). The relative contribution of these components scales with the star formation rate (SFR) and stellar mass, giving rise to empirically calibrated relations between X-ray luminosity, SFR and mass that serve as robust tracers of recent star formation and stellar population age.
Advances in high-resolution facilities have enabled the separation of point-source and diffuse emission, revealing how environmental factors such as metallicity and gas density modulate X-ray luminosity functions. Emission from hot tenuous gas often traces superbubbles and galactic winds, contributing to the enrichment of the circumgalactic medium and influencing galaxy evolution. At higher energies (>10 keV), ultraluminous X-ray sources (ULXs) and inverse Compton scattering may dominate in compact starburst regions. Understanding these processes is critical for interpreting observations of distant galaxies, calibrating the cosmic X-ray background and constraining models of feedback and reionisation in the early universe.
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X-ray Emission Processes in Star-forming Galaxies publication trend
The graph below shows the total number of articles in x-ray emission processes in star-forming galaxies across all publications each year (not limited to Nature Index journals).
Technical terms
High-mass X-ray binary (HMXB): A compact object accreting material from a massive stellar companion, emitting hard X-rays and tracing recent star formation.
Low-mass X-ray binary (LMXB): A system in which a neutron star or black hole accretes from an older, low-mass donor star, contributing to the X-ray output of older stellar populations.
Superbubble: A cavity of hot, X-ray–emitting gas formed by the combined action of stellar winds and supernovae in regions of intense star formation.
Spectral energy distribution (SED): The flux of electromagnetic radiation emitted by an astronomical object as a function of wavelength or energy.
Photoionisation: The process by which photons, including X-rays, ionise atoms or ions in the interstellar medium, driving nebular emission lines.
References
- The Chandra Source Catalog Release 2 Series. The Astrophysical Journal Supplement Series (2024).
- Decomposition of galactic X-ray emission with PHOX. Astronomy & Astrophysics (2023).
- Modeling the High-energy Ionizing Output from Simple Stellar and X-Ray Binary Populations. The Astrophysical Journal (2023).
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