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and star formation. The delay of gas collapse until the minihalos have reached higher masses is evident in the bottom panel, which shows the fraction fSF of the minihalo gas that is dense and star-forming, defined as the gas that exceeds densities of 1 cm −3 . There is no star-forming gas in < 10 6 M⊙ halos for the highest streaming velocities. The gas fraction fgas, calculated as the gas mass in the halo over its total mass, is reduced by up to a factor of ∼ 1.2 for vs,i = 3 km s −1 , and a factor of ∼ 1.8 for vs,i = 10 km s −1 , even after the gas has reached high densities. However, once gas collapse has occured, the average H2 fraction fH2 is very similar in all cases, as is the subsequent thermal evolution (Fig. 5.3). 5.4 Summary and Discussion Our series of simulations show that Pop III star formation will be es- sentially the same in cosmologies with relative streaming motions between gas and DM, even in regions with streaming velocities much higher than average (vs,i > ∼ 3 km s −1 ). However, these regions of fast streaming will experience a modest delay in the collapse redshift at which Pop III stars will first form, while in regions of typical streaming the delay will be minimal (> ∼ 10 7 years), in good agreement with Maio et al. (2011). In their work they also find similar reductions in halo gas fractions of up to a factor of 2, even given their larger box size and lower resolution. This is furthermore consistent with other recent work such as that of Tseliakhovich et al. (2010). The effect on reionization should be similarly minimal. Though not yet known with certainty, recent work has suggested that the sources of reionization were dominated by early galaxies of virial temperatures above the hydrogen cooling threshold of 10 4 K (corresponding to masses > ∼ 10 8 M⊙), with 142
a much smaller contribution from < ∼ 10 6 M⊙ halos (e.g. Trac and Gnedin 2009; Trenti and Stiavelli 2009; Muñoz and Loeb 2011). The relative streaming motions will do little to alter the infall of gas into the larger potential wells of ionizing galaxies, and thus reionization should proceed virtually unaffected. The effect of streaming is mostly pronounced at the highest redshifts when the collapse fraction and the corresponding radiative effects of stars are ex- ceedingly small. In conclusion, we have directly simulated the delay in collapse, and the subsequent thermal evolution of the first baryonic structures under relative bulk velocities between gas and dark matter. Our results show that early star formation and subsequent evolution of reionization should quickly converge to the no-streaming case. Thus, results of previous and future cosmological studies concerning the formation of the first stars and galaxies will need only minimal modifications due to the relative streaming effect. 143
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Copyright by Athena Ranice Stacy 20
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New Insights into Primordial Star F
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Acknowledgments I first want to giv
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angular momentum to rotate at nearl
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2.4.2.5 Thermodynamics of accretion
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Chapter 7. Outlook 177 Bibliography
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List of Figures 2.1 Density project
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1.1 Motivation Chapter 1 Introducti
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leaving behind a neutron star or bl
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describe studies that have attempte
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CRs may therefore provide a pathway
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expected that some of the gas withi
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our numerical methodology in Chapte
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scattering is the major source of o
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portance. The reaction rates for an
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The size of the refinement levels h
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the sink a temperature and pressure
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same time, such as the fragments in
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Figure 2.2: Physical state of the c
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2.4.2 Protostellar accretion 2.4.2.
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Despite some amount of rotational s
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Figure 2.6: Velocity field of the c
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Figure 2.7: Disk mass vs. time sinc
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Figure 2.8: Angular momentum struct
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sink tform [yr] Mfinal [M⊙] rinit
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sink (∼ 4 M⊙) that merged with
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actual final mass of the star is li
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the average temperature of all part
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disk accretion onto a primordial pr
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Figure 2.12: Impact of feedback on
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Figure 2.13: Comparison of specific
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the central core, eventually compri
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extending our simulation to later t
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that such a non-primordial origin t
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impose an upper mass limit to Pop I
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we use a ray-tracing scheme to foll
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3.2.3 Sink Particle Method When an
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convenient way to directly measure
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where the sum now extends from the
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Figure 3.1: Evolution of various pr
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ased on the prescription of Omukai
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ate found at late times in our ‘n
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Figure 3.2: Evolution of various di
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Figure 3.3: Evolution of disk mass
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Figure 3.4: Temperature versus numb
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disk mass is able to level off in d
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Figure 3.6: Projected density and t
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onto the disk. The numerical experi
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that the I-front expands as an hour
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Figure 3.8: Evolution of various H
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˙ M∗ = 3πΣν, (3.18) where ν
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the discrete nature of the gas part
Page 105 and 106: stars. We also note that, despite t
Page 107 and 108: current computational limits. If ra
Page 109 and 110: the deaths of massive stars (see Wo
Page 111 and 112: It is apparent that the angular mom
Page 113 and 114: h = 0.7. To accelerate structure fo
Page 115 and 116: acc = Lres 50 AU, where: Lres 0.5
Page 117 and 118: years, up to several dynamical time
Page 119 and 120: sp = GM∗ c2 , (4.1) s where cs is
Page 121 and 122: Figure 4.2: Left: Angular momentum
Page 123 and 124: through the disk, and the disk is e
Page 125 and 126: steadily grows for the rest of the
Page 127 and 128: Fig. 4.5 shows these timescales for
Page 129 and 130: sink B. Once on the MS, the sink A
Page 131 and 132: Figure 4.6: Evolution of stellar ro
Page 133 and 134: sink M∗(5000 yr) [M⊙] M∗(10 5
Page 135 and 136: present here, particularly if the s
Page 137 and 138: the stars grow to larger masses (se
Page 139 and 140: Here, Σ is the disk surface densit
Page 141 and 142: which has already detected GRBs at
Page 143 and 144: M⊙. They find that the specific a
Page 145 and 146: are initialized at high z with smal
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Page 149 and 150: Figure 5.1: Top panels: Effective v
Page 151 and 152: Figure 5.2: Effect of relative stre
Page 153 and 154: Using cs ∝ T 1/2 results in ρ
Page 155: Figure 5.4: Evolution of gas proper
Page 159 and 160: abundances of HD, which also acts a
Page 161 and 162: first stars had very short lifetime
Page 163 and 164: of star-forming material. Here we t
Page 165 and 166: star formation, they found CR energ
Page 167 and 168: The GZK cutoff applies only to thos
Page 169 and 170: and virialization redshift zvir = 2
Page 171 and 172: and undergoes free-fall collapse. I
Page 173 and 174: β = 1 − −2 1/2 ɛ + 1 mHc2
Page 175 and 176: and where ΓCR(D) = 5 × 10 −29 e
Page 177 and 178: Figure 6.2: Thermal evolution of pr
Page 179 and 180: Figure 6.3: Minimum temperature rea
Page 181 and 182: Figure 6.4: Thermal evolution of pr
Page 183 and 184: The CR energy density can now be es
Page 185 and 186: 2007). When considering realistic c
Page 187 and 188: 6.3.5 Fragmentation scale As is evi
Page 189 and 190: 2006). This decrease in fragmentati
Page 191 and 192: Chapter 7 Outlook Our understanding
Page 193 and 194: that Pop III stars likely experienc
Page 195 and 196: to be part of an area of scientific
Page 197 and 198: Barkana, R. and Loeb, A. (2001). In
Page 199 and 200: Bromm, V., Kudritzki, R. P., and Lo
Page 201 and 202: Daigne, F., Olive, K. A., Silk, J.,
Page 203 and 204: Gao, L., White, S. D. M., Jenkins,
Page 205 and 206: Heger, A., Woosley, S. E., and Spru
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Kratter, K. M. and Murray-Clay, R.
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Machida, M. N., Omukai, K., Matsumo
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Navarro, J. F. and White, S. D. M.
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Rollinde, E., Vangioni, E., and Oli
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Simon, M., Ghez, A. M., Leinert, C.
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Tanvir, N. R., Fox, D. B., Levan, A
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Rays, volume 576 of Lecture Notes i
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Zatsepin, G. T. and Kuz’min, V. A
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