On the Initial Mass Function of Population III Stars

By F. Nakamura, Masayuki Umemura. 2000

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The collapse and fragmentation of filamentary primordial gas clouds are explored using one- and two-dimensional hydrodynamical simulations coupled with the nonequilibrium processes of hydrogen molecule formation. The cloud evolution is computed from the initial central density nc = 10-106 cm-3. The simulations show that depending on the initial density, there are two occasions for the fragmentation of primordial filaments. If a filament has relatively low initial density such as nc ≲ 105 cm-3, the radial contraction is slow as a result of less effective H2 cooling and appreciably decelerates at densities higher than a critical density, where LTE populations are achieved for the rotational levels of H2 molecules and the cooling timescale becomes accordingly longer than the free-fall timescale. This filament tends to fragment into dense clumps before the central density reaches 108-109 cm-3, where H2 cooling by three-body reactions is effective and the fragment mass is more massive than some tens of M☉. In contrast, if a filament is initially as dense as nc ≳ 105 cm-3, the more effective H2 cooling with the help of three-body reactions allows the filament to contract up to n ~ 1012 cm-3. After the density reaches n ~ 1012 cm-3, the filament becomes optically thick to H2 lines and the radial contraction subsequently almost stops. At this final hydrostatic stage, the fragment mass is lowered down to ≈1 M☉ because of the high density of the filament. The dependence of the fragment mass upon the initial density could be translated into the dependence on the local amplitude of random Gaussian density fields or the epoch of the collapse of a parent cloud. Hence, it is predicted that the initial mass function of Population III stars is likely to be bimodal with peaks of ≈102 and ≈1 M☉, where the relative heights could be a function of the collapse epoch. Implications for the metal enrichment by Population III stars at high redshifts and baryonic dark matter are briefly discussed.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/d59cf9f7ea0f087eea6da01885acb2fdba8ef9a7

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Citations in the corpus

Quasars at z = 6: The Survival of the Fittest (2006, background): “If instead there is no gas readily available, the binary will be losing orbital energy to the stars, if the initial mass function of PopIII stars is bimodal and a large population of low mass stars is formed (Nakamura & Umemura 2001) or to dark matter background otherwise.”
HE 0107–5240, a Chemically Ancient Star. I. A Detailed Abundance Analysis (2003, background): “…that formed may have been quite massive objects, several hundred to perhaps 1000 M (Bromm et al. 2001; Schneider et al. 2002), while others have suggested that the first mass function may have included stars with masses as low as roughly the solar mass (Yoshii & Saio 1986; Nakamura & Umemura 2001).”
A New View of the Dwarf Spheroidal Satellites of the Milky Way from VLT FLAMES: Where Are the Very Metal-poor Stars? (2006, background): “For example, in the case of a bimodal IMF, low-mass stars can form even from zero metallicity gas (Nakamura & Umemura 2001).”
Early Reionization by Miniquasars (2003, background): “In minihalos a numerous population of low-mass stars may be present if the IMF were bimodal, with a second peak at 1-2 M⊙, as suggested by Nakamura & Umemura (2001).”
The First Stars (2003, background): “…22:8 AR AR222-AA42-03.tex AR222-AA42-03.sgm LaTeX2e(2002/01/18) P1: IKH FIRST STARS 81 and fragmentation of primordial gas clouds suggest that the first stars were predominantly very massive, with typical masses M∗ 100 M (Bromm et al. 1999, 2002; Nakamura & Umemura 2001; Abel et al. 2000, 2002).”
Intermediate - mass black holes (2003, unknown): “…1981; Lepp & Shull 1984; Palla, Salpeter, & Stahler 1983; Yoshii & Saio 1986; Shapiro & Kang 1987; Uehara et al. 1996; Haiman, Thoul, & Loeb 1996; Nishi et al. 1998; Abel et al. 1998; Omukai & Nishi 1988; Couchman & Rees 1986; Bromm et al. 1999; Abel et al. 2000; Nakamura & Umemura 1999, 2001).”
The aftermath of the first stars: massive black holes (2006, background): “How such vigorous accretion of matter could have taken place poses an important question, as it has been shown that the radiation from the first stars heats and evacuates the gas residing within the ∼ 106 M⊙ minihaloes in which they are born (Kitayama et al. 2004; Whalen, Abel & Norman 2004; Alvarez”
Evolution of the atomic and molecular gas content of galaxies (2013, background): “Hydrodynamic simulations containing detailed chemical networks and analytic calculations have shown that H2 can form through other channels in dark matter halos above a critical mass Mcrit ∼ 105M⊙ (e.g., Nakamura & Umemura 2001; Glover 2013).”
The Fragmentation of Pre-enriched Primordial Objects (2001, background): “Based on two-dimensional studies, Nakamura & Umemura (2001) have hypothesized a bimodal initial mass function (IMF) for the first stars, with one mode favouring very massive stars, and the other leading to ‘normal’ stars of mass , 1 M(.”
The physics of gamma-ray bursts & relativistic jets (2014, background): “Ten years ago it was thought that the typical mass of these stars might be more than 102M (e.g. Bromm et al., 1999; Abel et al., 2000; Nakamura and Umemura, 2001).”
The first galaxies : assembly, cooling and the onset of turbulence (2008, background): “…the first stars, termed Population III (Pop III), are predicted to have formed in dark matter (DM) ‘minihaloes’ with virial mass ∼ 106 M⊙ at z ∼ 20 (Bromm et al. 1999, 2002; Nakamura & Umemura 2001; Abel et al. 2000, 2002; Yoshida et al. 2003, 2006; Gao et al. 2007; O’Shea & Norman 2007).”
The transition from Population III to normal galaxies: Lyα and He II emission and the ionising properties of high redshift starburst galaxies (2002, background): “They should take into account all possible metallicities, and also probable systematic changes of the stellar initial mass function (IMF) at very low metallicity (Abel et al. 1998, Bromm et al. 1999, Nakamura & Umemura 2001, Hernandez & Ferrara 2001).”
Star formation in semi-analytic galaxy formation models with multiphase gas (2015, background): “Hydrodynamic simulations containing detailed chemical networks and analytic calculations have shown that H2 can form in metal-free gas in dark matter halos above a critical mass Mcrit ∼ 10 5 M⊙ (e.g., Nakamura & Umemura 2001; Glover 2013).”
Understanding the shape and diversity of dwarf galaxy rotation curves in ΛCDM (2016, background): “The gas was given a seed metallicity of Zgas = 10 −3 Z , representing Pop III enrichment (e.g. Nakamura & Umemura 2001; Boley et al. 2009; Karlsson et al. 2013).”
Formation of Massive Black Holes in Dense Star Clusters. I. Mass Segregation and Core Collapse (2003, background): “…possibility to keep in mind for future consideration, although the IMF of Pop III stars is essentially unknown (but see, e.g., Abia et al. 2001; Nakamura & Umemura 2001) and recent hydrodynamic simulations suggest that the first stars may actually form isolated rather than in clusters (Abel et…”