1 / 14

First Stars, QSO’s and Reionization in our Universe

First Stars, QSO’s and Reionization in our Universe. By Simon Strasser & Jon Vermedahl 22 April 2003. Outline. Ionization Halo formation First Stars Quasi-Stellar Objects Observational aspects of the first stars, QSO’s, and CMB. Conclusions Future Work.

edena
Download Presentation

First Stars, QSO’s and Reionization in our Universe

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. First Stars, QSO’s and Reionization in our Universe By Simon Strasser & Jon Vermedahl 22 April 2003

  2. Outline • Ionization • Halo formation • First Stars • Quasi-Stellar Objects • Observational aspects of the first stars, QSO’s, and CMB. • Conclusions • Future Work

  3. Reionization(End of the Dark Ages) • Period of time when the universe changes from atomic/molecular to ionized gas. • Benefit = Universe is transparent to light. • Mass fraction of baryons to ionize universe = ~10-5 • Hydrogen: Reionized at z ~10. • Helium: Reionized at z ~3. • Reionization heats up the universe and slows down star formation.

  4. Reionization • Oldest stars formed in halos at z ~ 20 - 30. - corresponds to 3-s peaks in density fields. • Reionization occurs when the photons emitted in one recombination time equal the number of H-atoms.

  5. Formation of Halos • Large-scale structure starts with collapse of low-mass halos, and grow via mergers. • Because of reionization, galaxies could only form in halos with velocity dispersion greater than 30 km/s. • Consequently, most of the gas is in diffuse form until z < 2. • Confirmed in numerical simulations.

  6. Physical Characteristics of First Stars • No metals. - ≥15M may build up some C nuclei prior to onset of MS burning. • Proton-Proton burning very inefficient. • Exhibit high effective temperatures and smaller radii. • Zero-Age MS on HR Diagram of a Pop III star and Pop I star. - diamonds reflect changes in metallicity.

  7. Physical Characteristics of First Stars (Pop III) • Lifetimes of zero-metallicity are similar in length to metal-enriched stars (Pop I). • Stars cool and become more luminous, similar to Pop I stars. • Ionizing radiation has ~50% more ionizing radiation in Pop III than Pop I. • Pop III stars can be identified via their spectra Teff = 36,000 K (Pop II) Teff = 63,000 K (Pop III)

  8. Unknowns of the first stars • Will the first stars be massive? -Jeans mass of clumps in halos ~103M • Will many stars be formed by rapid fragmentation? • What differences in the star formation process will be caused by the absence of heavy elements and magnetic fields? • If the first stars had the same IMF (Salpeter) as today, with a lower cutoff at about 0.1 M , one might expect stars smaller than 0.8 M to display arbitrarily low metallicity.

  9. Where are the first stars? • Between z = 20 and z = 9, only ~400 million years pass. • Current ages of oldest stars accurate to ~109 years! • Prediction that oldest stars will be metal poor will be difficult to test. • Strong bias of objects on small scale – oldest stars should be more abundant in central parts of galaxies and clusters. • Bulge of Milky Way should contain largest abundance of Pop III stars (assumes bulge formed first).

  10. Quasi-Stellar Objects • Farthest objects detected in our universe. • First detected via radio telescopes in 60’s. • Optical counter-parts appear as bright, starlike nuclei surrounded by faint halo. • ~105 more luminous than typical galaxies. • Z = 5.8

  11. Unified theory of AGN • QSOs are essentially Active Galactic Nuclei. • Host galaxies have a mass of ≥1012M • Luminosity is powered by a super massive black hole (~ 108M)

  12. Evolution of QSOs? • There were more brighter quasars at higher redshift.

  13. Evolution of QSOs • Number density (comoving) of QSOs has remained ~constant (z < 2). • 1000 times as many QSOs with MB≥ -25.9 at z = 2 than at z = 0. • Indicates an evolutionary effect of QSOs! • Above z = 2, events can not be explained by a constant number of QSOs with changing luminosity. - Comoving number density decreases by a factor of ~5 between z = 2 to z = 4. - Verdict is still out!

More Related