The hydrodynamic collapse of protogalaxies to Ly-alpha disks

Abstract

view Abstract Citations (7) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Hydrodynamic Collapse of Protogalaxies to LY alpha Disks Schiano, A. V. R. ; Wolfe, A. M. ; Chang, C. A. Abstract A series of two-dimensional, Eulerian hydrodynamic simulations of the formation of disk galaxies is presented. These simulations are used to test the hypothesis that high-redshift damped Lyα absorption systems detected in QSO spectra (Wolfe and coworkers) originate in large (R > 3 R_H_0__), massive disks of gas which are the progenitors of present-day galactic disks. We assume that the disks form out of collapsing gas in extended halos of nondissipative matter. The gas starts out with the same density distribution as the halo, i.e., as a gaseous corona, but collapses as a result of radiative cooling. Assuming axisymmetry about the spin axis, we numerically integrate the hydrodynamical and gravitational field equations in one quadrant of the meridional plane. In the first stage of the calculations the time evolution of the flow is followed until the gaseous disk which forms is centrifugally supported. Our results reveal hydrodynamic phenomena such as pancaking, accretion shocks, and contact discontinuities. For a wide range of input parameters a dislike structure approached centrifugal equilibrium in less than ~ 2 Gyr after the start of collapse. In agreement with earlier studies, the final size of the disk depends on the spin parameter. For a fixed spin parameter, the size also depends on the core radius of the halo; the disk radius increases with core radius. The model disks were subject to ring-forming gravitational instabilities unless the disk gas was prevented from cooling below 10^5^ K. We also find that gaseous halos with metallicities substantially below 10% solar abundance cannot cool rapidly enough to form disks by z > 2. In the second stage of the calculation we considered a specific mechanism for contraction of the centrifugally supported disk: we were motivated by evidence that damped Lyα absorption systems evolve into current disks with R ~ R_H_0__. We show how mass shed by an assumed population of halo stars reaches the plane ~ 1 Gyr after formation of the initial disk, and how this causes the disk to contract by a factor of more than 2 after another 1 Gyr, i.e., the contraction is completed in ~ 3 Gyr after the start of collapse. Publication: The Astrophysical Journal Pub Date: December 1990 DOI: 10.1086/169498 Bibcode: 1990ApJ...365..439S Keywords: Disk Galaxies; Galactic Structure; Gravitational Collapse; Hydrodynamic Equations; Lyman Alpha Radiation; Quasars; Computational Astrophysics; Gas Flow; Gravitational Fields; Red Shift; Astrophysics; GALAXIES: FORMATION; GALAXIES: STRUCTURE; HYDRODYNAMICS; QUASARS full text sources ADS |