Formation and Signatures of the First Stars and Quasars

Details Formation and Signatures of the First Stars and Quasars Formation and Signatures of the First Stars and Quasars

Nov 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998phdt.........1h&link_type=abstract

Thesis (PHD). HARVARD UNIVERSITY , Source DAI-B 59/05, p. 2246, Nov 1998, 240 pages.

Mathematics

Logic

Intergalactic Medium, Cosmology, Stellar Formation, Cold Dark Matter, Hydrogen

Scientific paper

Although direct detection of the very first stars and quasars in the universe is beyond the capabilities of current instruments, there is substantial evidence for the existence of these objects. Observations of the intergalactic medium (IGM) reveal that it was highly ionized, and enriched with heavy elements, before redshift z~ 5. Standard cold dark matter (CDM) cosmological models predict that the first clouds indeed condensed prior to this redshift, around 10/ ~< z/ ~< 30. In this thesis, we study several questions related to the formation and observational signatures of the first generation of astrophysical objects in CDM cosmologies. Using one-dimensional simulations, we study the effects of gas pressure and H2 cooling on the sizes of the first collapsed systems. We find that the H2 abundance reaches high enough values to permit efficient cooling and collapse in the central, shock-heated regions of clouds with virial temperatures T vir/ ~> 100oK. Still smaller clouds (~103Msolar) are able to collapse by z~ 10, due to the gravitational potential of collisionless dark matter. We then examine the effect of ultraviolet (UV) photons on the H2 abundance in these clouds, and find that H2 is universally photodissociated by the low UV flux from the first few stars. This imposes a high minimum mass (~108Msolar) for typical halos that can cool and harbor astrophysical objects. Using phenomenologically calibrated semi-analytical methods, we calculate several indirect consequences of the first stars, including the reionization history of the IGM and the resulting suppression of the cosmic microwave background (CMB) anisotropies; or the optical depth of dust from high redshift Type I supernovae and the resulting spectral distortion of the CMB. Both of these effects will be observable with forthcoming satellites, such as MAP or Planck, while the Next Generation Space Telescope could directly image numerous z>10 star-clusters. Similarly, we extrapolate the observed quasar population to z ~> 5, and demonstrate that early quasars could have comparable effects. Finally, we show that data from the Hubble Deep Field already places useful constraints on these models.

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