Hot Halo Gas in Numerical Simulations of Galaxy Mergers

Open Access
Sinha, Manodeep
Graduate Program:
Astronomy and Astrophysics
Doctor of Philosophy
Document Type:
Date of Defense:
August 08, 2008
Committee Members:
  • Robin Bruce Ciardullo, Dissertation Advisor
  • Robin Bruce Ciardullo, Committee Chair
  • Pablo Laguna, Committee Member
  • George Chartas, Committee Member
  • Caryl Ann Gronwall, Committee Member
  • Richard Wallace Robinett, Committee Member
  • numerical simulations
  • galaxy evolution
  • galaxy formation
  • x-ray emission
Galaxy merger simulations have explored the behavior of gas within a galactic disk, yet the dynamics of hot gas within the galaxy halo has been neglected. We report on the results of high-resolution hydrodynamic simulations of colliding galaxies with hot halo gas. We explore a range of mass ratios, gas fractions and orbital configurations to constrain the shocks and the dynamics of the gas within the progenitor halos. We find that : (i) A strong shock is produced in the galaxy halos before the first passage, increasing the temperature of the gas by almost an order of magnitude to ~ 10^{6.3} K. (ii) The X-ray luminosity of the shock is strongly dependent on the gas fraction. It is >= 10^{39} erg/s for gas fractions larger than 10%. (iii) We find an analytic fit to the maximum X-ray luminosity of the shock as a function of merger parameters. This fit can be used in semi-analytic recipes for galaxy formation to estimate the total X-ray emission from shocks in merging galaxies. (iv) The hot diffuse gas in the simulation also produces X-ray luminosities as large as 10^{42} erg/s. This contributes to the total X-ray background in the Universe. (v) ~ 10-20% of the initial gas mass is unbound from the galaxies for equal-mass mergers, while 3-5% of the gas mass is released for the 3:1 and 10:1 mergers. This unbound gas ends up far from the galaxy and can be a feasible mechanism for metal enrichment of the IGM. We use an analytical halo merger tree to estimate the fraction of gas mass lost over the history of the Universe.