Metal-absorption Column Densities in Fast Radiative Shocks

In this paper we present computations of the integrated metal-ion column densities produced in the post-shock cooling layers behind fast, radiative shock-waves. For this purpose, we have constructed a new shock code that calculates the non-equilibrium ionization and cooling; follows the radiative transfer of the shock self-radiation through the post-shock cooling layers; takes into account the resulting photoionization and heating rates; follows the dynamics of the cooling gas; and self-consistently computes the initial photoionization state of the precursor gas. We discuss the shock structure and emitted radiation, and study the dependence on the shock velocity, magnetic field, and gas metallicity. We present a complete set of integrated post-shock and precursor metal-ion column densities of all ionization stages of the elements H, He, C, N, O, Ne, Mg, Si, S, and Fe, for shocks with velocities of 600 and ∼ 2000 km s, corresponding to initial post-shock temperatures of 5× 10 and 5 × 10 K, cooling down to 1000 K. We consider shocks in which the magnetic field is negligible (B = 0) so that the cooling occurs at approximately constant pressure (“isobaric”), and shocks in which the magnetic pressure dominates everywhere such that the cooling occurs at constant density (isochoric). We present results for gas metallicities Z ranging from 10 to twice the solar abundance of heavy elements, and we study how the observational signatures of fast radiative shocks depend on Z. We present our numerical results in convenient online figures and tables. Subject headings: ISM:general – atomic processes – plasmas – absorption lines – intergalactic medium – shock waves