Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published February 1, 2000 | Accepted Version + Published
Journal Article Open

Testing linear-theory predictions of galaxy formation


The angular momentum of galaxies is routinely ascribed to a process of tidal torques acting during the early stages of gravitational collapse, and is predicted from the initial mass distribution using second-order perturbation theory and the Zel'dovich approximation. We test this theory for a flat hierarchical cosmogony using a large N-body simulation with sufficient dynamic range to include tidal fields, allow resolution of individual galaxies, and thereby expand on previous studies. The predictions of linear collapse, linear tidal torque, and biased-peaks galaxy formation are applied to the initial conditions and compared with results for evolved bound objects. We find relatively good correlation between the predictions of linear theory and actual galaxy evolution. Collapse is well described by an ellipsoidal model within a shear field, which results primarily in triaxial objects that do not map directly to the initial density field. While structure formation from early times is a complex history of hierarchical merging, salient features are well described by the simple spherical-collapse model. Most notably, we test several methods for determining the turnaround epoch, and find that turnaround is successfully described by the spherical-collapse model. The angular momentum of collapsing structures grows linearly until turnaround, as predicted, and continues quasi-linearly until shell crossing. The predicted angular momentum for well-resolved galaxies at turnaround overestimates the true turnaround and final values by a factor of ∼3, with a scatter of ∼70 per cent, and only marginally yields the correct direction of the angular momentum vector. We recover the prediction that final angular momentum scales as mass to the 5/3 power. We find that mass and angular momentum also vary proportionally with peak height. In view of the fact that the observed galaxy collapse is a stochastic hierarchical and non-linear process, it is encouraging that the linear theory can serve as an effective predictive and analytic tool.

Additional Information

© 2000 RAS, MNRAS. Accepted 1999 September 10. Received 1999 July 30; in original form 1998 December 15. BS thanks Jim Applegate for numerous enlightening discussions on celestial dynamics and mechanics, and Gino Thomas for his Socratic cynicism. Additional thanks to Raul Jimenez, Alan Heavens, Paolo Catelan and Tom Theuns for their interest, discussions and ideas, and to our referee, Joshua Barnes. This work was supported by the U.S. Department of Energy Outstanding Junior Investigator Award under contract DE-FG02-92ER40699, NASA grant NAG5-3091, the Alfred P. Sloan Foundation, Columbia Astrophysics Lab and the Columbia Department of Astronomy. This is contribution No. 676 from the Columbia Astrophysics Laboratory, and CU-TP-927 from the Columbia Physics Department.

Attached Files

Published - 311-4-762.pdf

Accepted Version - 9909266.pdf


Files (2.0 MB)
Name Size Download all
996.1 kB Preview Download
1.0 MB Preview Download

Additional details

August 19, 2023
October 23, 2023