Lunch & Learn: On the Formation of Massive Galaxies

Space probe All who listen to Jerry Ostriker, Professor of Astrophysical Sciences at Princeton University, come to know that we live in profoundly exciting times. We have learned only recently the age and composition of the universe, and for the first time, we are coming to understand how the galactic structures we observe throughout the sky came to be. Simply put, where do they come from, and how could they form if the early universe was relatively uniform? And how can we use them as standard objects unless we understand how and when they formed and how they evolved?

One of the key findings, said Ostriker at the September 29 Lunch ‘n Learn seminar, came from the WMAP satellite. Its observations of the Cosmic Background Radiation show the beginnings of structure in the aftermath of the Big Bang.

Armed with our best cosmological models, asks Ostriker, “Can we start with those initial conditions and our understanding of the standard model of cosmology, add standard physics, compute forward and end with galaxies like those we see about us?”

From 50 years of observations, he tells us, we know that giant elliptical galaxies, galaxies that involve on the order of 100 million stars, form early and grow in size and mass without much late star-formation. He adds that major mergers are uncommon at later times or else disk galaxies would have been destroyed.

Using high resolution simulations of massive galaxy formation, he has computed the formation of cosmic structures. He begins by putting down particles on a dense grid with slight perturbations of the positions consistent with the early large scale structure given by the CBR. He then gives the particles small velocities consistent with the density structure and the continuity equation. He then uses the supercomputers at Princeton to calculate the accelerations of all the particles using Newton’s laws.

The simulation updates again and again the positions and velocities and accelerations to find the new distribution of particles, all culminating with a video simulation of the evolution of cosmic structures.

Here are three videos from the presentation:

Jeremiah Ostriker

Says Ostriker, “Looking backwards we have been able to reconstruct from the detailed structure of our own Galaxy and from the fossil evidence derived from the study of nearby galaxies a plausible history of how galaxies formed over the last several billion years. In addition, now that we have a quite definite cosmological model, providing us with a quantitative picture of how perturbations grew from very low amplitude Gaussian fluctuations, we can perform the forward modeling of representative pieces of the universe using standard physical processes to see how well we match our local knowledge and the time-reversed modeling based on the fossil evidence. Finally, we can employ large ground and space based telescopes to use the universe as a time-machine – directly observing the past history of our light-cone. While none of these approaches can give us at the present time results accurate to more than roughly the 5% -> 10% level, a coherent and plausible picture is emerging.”

“Massive galaxies form in two phases. In the first phase, which peaks at redshift z = 6 and ends by redshift z = 2, cold gas streams in making stars in a small (<1kpc) region, but as the stellar mass approaches 10,11 Msolar, a hot bubble forms which suppresses further inflow of cold gas. But from redshift z = 3 to the present time, small stellar satellite systems are accreted at typically 10kpc from the center and the size of the total system grows by about a factor of three as the mass doubles. This added, accreted component is mainly comprised of old and low metallicity stars. Energy release from gravitational infall in various forms will terminate star-formation leaving the galaxies ‘red and dead’. Even in the absence of feedback from SN or MBHs. This physical picture seems naturally to lead to the mass, size scale and epoch of galaxy formation and, increasingly, to a first understanding of the detailed internal structure of these systems.”

A podcast and the speaker’s slides are available.

About the speaker:

Jeremiah P. Ostriker has been an influential researcher in one of the most exciting areas of modern science, theoretical astrophysics, with current primary work in the area of cosmology, particularly the aspects that can be approached best by large scale numerical calculations.

Ostriker has investigated many areas of research, including the structure and oscillations of rotating stars, the stability of galaxies, the evolution of globular clusters and other star systems, pulsars, X-ray binary stars, the dynamics of clusters of galaxies, gravitational lensing, astrophysical blast waves, active galactic nuclei, the cosmic web, and galaxy formation.

Most significantly, Ostriker’s research focused on the theories of:

  • Pulsars
  • Interstellar Medium
  • Dark Matter and Dark Energy
  • The Warm-Hot Intergalactic Medium (WHIM)
  • The First Stars and Reionization of the Universe
  • Galaxy Formation
  • Interaction between Quasars and their surroundings

Ostriker has supervised and collaborated with many young researchers and graduates students. He is the author or co-author of more than 300 scientific publications.

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