Browsing by Subject "chemical enrichment"

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Effect of Streaming Motion of Baryons Relative to Dark Matter on the Formation of the First Stars
(2011-03) Stacy, Athena; Bromm, Volker; Loeb, Abraham; Stacy, Athena; Bromm, Volker
We evaluate the effect of a supersonic relative velocity between the baryons and dark matter on the thermal and density evolution of the first gas clouds at z less than or similar to 50. Through a series of cosmological simulations, initialized at z(i) = 100 with a range of relative streaming velocities and minihalo Formation redshifts, we find that the typical streaming velocities will have little effect on the gas evolution. Once the collapse begins, the subsequent evolution of the gas will be nearly indistinguishable from the case of no streaming, and star Formation will still proceed in the same way, with no change in the characteristic Pop III stellar masses. Reionization is expected to be dominated by halo masses of greater than or similar to 10(8)M(circle dot), for which the effect of streaming should be negligible.
Gravitational Fragmentation In Turbulent Primordial Gas And The Initial Mass Function Of Population III Stars
(2011-02) Clark, Paul C.; Glover, Simon C. O.; Klessen, Ralf S.; Bromm, Volker; Bromm, Volker
We report results from numerical simulations of star formation in the early universe that focus on the dynamical behavior of metal-free gas under different initial and environmental conditions. In particular we investigate the role of turbulence, which is thought to ubiquitously accompany the collapse of high-redshift halos. We distinguish between two main cases: the birth of Population III. 1 stars-those which form in the pristine halos unaffected by prior star formation-and the formation of Population III. 2 stars-those forming in halos where the gas has an increased ionization fraction. We find that turbulent primordial gas is highly susceptible to fragmentation in both cases, even for turbulence in the subsonic regime, i.e., for rms velocity dispersions as low as 20% of the sound speed. Fragmentation is more vigorous and more widespread in pristine halos compared to pre-ionized ones. If such levels of turbulent motions were indeed present in star-forming minihalos, Population III. 1 stars would be on average of somewhat lower mass, and form in larger groups, than Population III. 2 stars. We find that fragment masses cover over two orders of magnitude, suggesting that the Population III initial mass function may have been much broader than previously thought. This prompts the need for a large, high-resolution study of the formation of dark matter minihalos that is capable of resolving the turbulent flows in the gas at the moment when the baryons become self-gravitating. This would help to determine the applicability of our results to primordial star formation.
The Source Density And Observability Of Pair-Instability Supernovae From The First Stars
(2012-08) Hummel, Jacob A.; Pawlik, Andreas H.; Milosavljevic, Milos; Bromm, Volker; Hummel, Jacob A.; Pawlik, Andreas H.; Milosavljevic, Milos; Bromm, Volker
Theoretical models predict that some of the first stars ended their lives as extremely energetic pair-instability supernovae (PISNe). With energies approaching 10(53) erg, these supernovae are expected to be within the detection limits of the upcoming James Webb Space Telescope (JWST), allowing observational constraints to be placed on the properties of the first stars. We estimate the source density of PISNe using a semi-analytic halo mass function based approach, accounting for the effects of feedback from star formation on the PISN rate using cosmological simulations. We estimate an upper limit of similar to 0.2 PISNe per JWST field of view at any given time. Feedback can reduce this rate significantly, e. g., lowering it to as little as one PISN per 4000 JWST fields of view for the most pessimistic explosion models. We also find that the main obstacle to observing PISNe from the first stars is their scarcity, not their faintness; exposures longer than a few times 10(4) s will do little to increase the number of PISNe found. Given this, we suggest a mosaic style search strategy for detecting PISNe from the first stars. Even rather high-redshift PISNe are unlikely to be missed by moderate exposures, and a large number of pointings will be required to ensure a detection.