C IV and He II line emission of Lyman α blobs: powered by shock-heated gas

Utilizing ab initio ultrahigh resolution hydrodynamical simulations, we investigate the properties of the interstellar and circumgalactic medium of Ly alpha blobs (LABs) at z = 3, focusing on three important emission lines: Ly alpha 1216 angstrom, He II 1640 angstrom and C IV 1549 angstrom. Their relative strengths provide a powerful probe of the thermodynamic properties of the gas when confronted with observations. By adjusting the dust attenuation effect using one parameter and matching the observed size-luminosity relation of LABs using another parameter, we show that our simulations can reproduce the observed C IV/Ly alpha and He II/Ly alpha ratios adequately. This analysis provides the first successful physical model to account for simultaneously the LAB luminosity function, luminosity-size relation and the C IV/Ly alpha and He II/Ly alpha ratios, with only two parameters. The physical underpinning for this model is that, in addition to the stellar component for the Ly alpha emission, the Ly alpha and C IV emission lines due to shock-heated gas are primarily collisional excitation driven and the He II emission line collisional ionization driven. We find that the density, temperature and metallicity of the gas responsible for each emission line is significantly distinct, in a multiphase interstellar and circumgalactic medium that is shock heated primarily by supernovae and secondarily by gravitational accretion of gas.