所属:Osaka University, Graduate School of Science, Department of Earth and Space Science
概要:Star-forming galaxies (SFGs) have been established as an important source population in the extra-galactic gamma-ray background (EGB). Their intensive star-formation creates an abundance of environments able to accelerate particles, and these build-up a rich sea of cosmic rays (CRs). Above GeV energies, CR protons can undergo hadronic interactions with their environment to produce gamma-rays. SFGs can operate as CR proton "calorimeters", where a large fraction of the CR energy is converted to gamma-rays. However, CRs also deposit energy and momentum to modify the thermal and hydrodynamic conditions of the gas in SFGs, and can become a powerful driver of outflows. Such outflows are ubiquitous among some types of SFGs, and have the potential to severely degrade their CR proton calorimetry. This diminishes their contribution to the EGB. This work adopted a self-consistent treatment of particle transport in outflows from SFGs to assess their calorimetry. It used 1D numerical treatments of galactic outflows driven by CRs and thermal gas pressure, accounting for the dynamical effects and interactions of CRs, to show the impact CR-driven flows have on the relative contribution of SFG populations to the EGB, and found that star-forming galaxies can contribute a few 10s of percent of the gamma-ray background flux. Their contribution is dominated by highly star-bursting galaxies, with the emission originating just prior to the peak of star-formation in the Universe, around 11 billion years ago. Most of these galaxies are relatively low mass.
論文掲載,発表実績:
(国際会議会議録掲載論文)
- Owen, E. R.*, Kong, A. K. H., Pan, K.-C. (2023): Cosmic ray calorimetry in star-forming galaxy populations and implications for their contribution to the extra-galactic -ray background. In: Proceedings of Science, 38th International Cosmic Ray Conference, 26 July -3 August 2023 in Nagoya, Japan, id. 554.
Posted : 2024年03月31日