X線天文衛星XMMニュートン、「宇宙のクローバー」に新たな光を見る(X-ray Satellite XMM-Newton Sees ’Space Clover’ in a New Light)

2024-05-02 NASA

＜関連情報＞

• https://www.nasa.gov/missions/xmm-newton/x-ray-satellite-xmm-newton-sees-space-clover-in-a-new-light/
• https://www.aanda.org/articles/aa/full_html/2024/05/aa49900-24/aa49900-24.html

クローバーリーフ奇電波円系の銀河群合体起源 The galaxy group merger origin of the Cloverleaf odd radio circle system

E. Bulbul, X. Zhang, M. Kluge, M. Brüggen, B. Koribalski, A. Liu, E. Artis, Y. E. Bahar, F. Balzer, C. Garrel, V. Ghirardini, N. Malavasi, A. Merloni, K. Nandra, M. E. Ramos-Ceja, J. S. Sanders and S. Zelmer,＋
Astronomy & Astrophysics  Published:30 April 2024
DOI:https://doi.org/10.1051/0004-6361/202449900

Abstract

Odd radio circles (ORCs) are a newly discovered class of extended faint radio sources of unknown origin. We report the first detection of diffuse X-ray gas at the location of a low-redshift ORC (z = 0.046) known as Cloverleaf ORC. This observation was performed with the XMM-Newton X-ray telescope. The physical extent of the diffuse X-ray emission corresponds to a region of approximately 230 kpc by 160 kpc, lying perpendicular to the radio emission detected by ASKAP. The X-ray spectrum shows characteristics of thermal multiphase gas with temperatures of 1.10 ± 0.08 keV and 0.22 ± 0.01 keV and a central density of (4.9 ± 0.6)×10⁻⁴ cm⁻³, indicating that the Cloverleaf ORC resides in a low-mass galaxy group. Using X-ray observations, with hydrostatic equilibrium and isothermal assumptions, we measure the galaxy group to have a gas mass and a total mass of (7.7 ± 0.8)×10¹¹ M_⊙ and 2.6 ± 0.3 × 10¹³ M_⊙ within the overdensity radius R₅₀₀. The presence of a high-velocity subgroup identified in optical data, the orientation of the brightest cluster galaxy, the disturbed morphologies of galaxies toward the east of the Cloverleaf ORC, and the irregular morphology of the X-ray emission suggest that this system is undergoing a galaxy group merger. The radio power of the ORC could be explained by the shock reacceleration of fossil cosmic rays generated by a previous episode of black hole activity in the central active galactic nucleus.