Browsing by Subject "First galaxies"
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Item Formation of the first galaxies under stellar feedback(2015-12) Jeon, Myoungwon; Bromm, Volker; Milosavljevic ́, Miloš; Pawlik, Andreas H; Gebhardt, Karl; Evans, Neal; Klessen, Ralf SThe stellar feedback is a crucial ingredient for modeling galaxy formation, especially for the first galaxies, which are susceptible to stellar feedback due to their shallow potential wells. In this thesis I have investigated the impact of stellar feedback from the first generation of metal-free massive stars on the process of the first galaxy formation. I present the results of self-consistent, cosmological radiation hydrodynamics zoomed-in simulations of the formation and the evolution of the first galaxies. In particular, we focus on the role of different stellar feedback from first stars, such as photoionization heating from individual stars, X-ray feed- back from a singly accreting black hole and from a high-mass X-ray black hole, and mechanical and chemical feedback from a core-collapse or pair-instability supernova explosion, in shaping the gas in the interstellar medium out of which first galaxies were assembled. We find that the severity of the stellar feedback from the first generation of stars formed during the first galaxy assembly strongly determines the properties of the first galaxies. More massive first stars are likely to alter their host system in which they reside and likely to suppress further star formation, thus resulting in a simpler star formation history during the assembly of the first galaxies. We show that the first galaxies at redshifts z ≈ 10 are already complex metal-enriched systems, capable of forming, long-lived, normal stars. Finally, we also predict the observability of such system with the upcoming James Webb Space Telescope (JWST).Item New insights into primordial star formation(2011-08) Stacy, Athena Ranice; Bromm, Volker; Milosavljevic, Milos; Wheeler, John C.; Evans, Neal J.; Dinerstein, Harriet; Loeb, AbrahamThe formation of the first stars, also known as Population III (Pop III), marked a pivotal point in the universe's evolution from relative smoothness and homogeneity to its current highly structured state. In this dissertation we study key aspects of Pop III star formation. We utilize three-dimensional cosmological simulations to follow the evolution of gas and DM from z ~100 until the first minihalo forms. Once the gas infalls toward the center of the minihalo and condenses, we implement the 'sink particle' method to represent regions that will form a star, and we follow the evolution of the metal-free, star-forming gas for many free-fall times. A disk forms around the initial Pop III star and fragments to form secondary stars with a range of masses (1 - 50 [solar mass]). This is markedly different from the previous paradigm of one single, massive star forming per minihalo. Using a ray-tracing technique, we also examine the effect of radiative feedback on protostellar growth and disk fragmentation. This feedback will not prevent the formation of secondary stars within the disk, but will reduce the final mass reached by the largest Pop III star. Measuring the angular momentum of the gas that falls onto the sink regions, we also find that the more massive Pop III stars accrete sufficient angular momentum to rotate at nearly break-up speeds, and can potentially end their lives as collapsar gamma-ray bursts or hypernovae. We furthermore numerically examine the recently discovered relative streaming motions between dark matter and baryons, originating from the era of recombination. Relative streaming will slightly delay the redshift at which Pop III stars first form, but will otherwise have little impact on Pop III star formation and the history of reionization. We finally evaluate the possible effect of a cosmic ray (CR) background generated by the supernova deaths of massive Pop III stars. A sufficiently large CR background could indirectly enhance the H₂ cooling within the affected minihalos. The resulting lower temperatures would lead to a reduced characteristic stellar mass (~ 10 [solar mass]), providing another possible pathway to form low-mass Pop III stars.Item Star formation in the assembly of the first galaxies(2009-05) Johnson, Jarrett Lawrence; Bromm, VolkerThe character of the first galaxies at redshifts z [greater-than or equal to] 10 strongly depends on the star formation which takes place during their assembly. Conducting cosmological hydrodynamics simulations, we study how the radiative output and chemical enrichment from the first stars impacts the properties of the first galaxies. We find that the radiative feedback from the first stars suppresses the star formation rate at redshifts z [greater-than or equal to] 15 by a factor of only a few. In turn, this suggests that a large fraction of the first galaxies may form from gas which has already been enriched with the first heavy elements ejected by primordial supernovae. In order to characterize the properties of primordial dwarf galaxies, we carry out radiation hydrodynamics simulations which allow to determine how the luminosities in hydrogen and helium emission lines depend on the initial mass function of the stars in the galaxy. As well, we show that the chemical abundance patterns observed in metal-poor Galactic halo stars contain the signature of the first supernovae, and we use this data to indirectly probe the properties of the first stars.Item Star formation in the first galaxies(2014-08) Safranek-Shrader, Chalence Timber; Bromm, Volker; Milosavljević, MilošThe ignition of the first sources of light marked the end of the cosmic dark ages, an era when the Universe transitioned from the relatively simple conditions following the Big Bang to the complex tapestry of dark matter, baryons, and pervasive cosmic radiation fields we see today. To better understand this uncharted cosmic epoch, we primarily utilize hydrodynamical, N-body simulations to model the assembly of the first galaxies at redshifts greater than ten and the stars that form within them. These simulations begin from cosmological initial conditions, employ a robust, non-equilibrium chemo-thermodynamic model, and take advantage of adaptive-grid-refinement to probe the multi-scale, complex process of star formation from ab initio principles. We explore the consequences that metal enrichment has on the process of star formation, confirming the presence of a critical metallicity for low-mass star formation. To assess the observational prospects of these primeval stellar populations with next-generation telescopes, like the James Webb Space Telescope, we constrain the star formation efficiency of both metal-enriched and metal-free star formation in a typical first galaxy. We also resolve the formation of individual metal-enriched stars in simulations that ultimately began from cosmological scales, allowing meaningful comparisons between our simulations and the recently discovered ultra-faint dwarf satellite galaxies, the suspected analogs of the first galaxies in the local Universe.