Probing for Cosmic Dawn Mon. Not. R. astr. Soc. (1986) 220, 259-269 .259L 6MNRAS.220. Cooling of Population III objects in a pressure supported 198 collapse Ofer Lahav* Physics Department, Ben-Gurion University, Beer-Sheva, Israel Accepted 1985 December 17. Received 1985 November 25 ; in original form 1985 August 29 Summary. The cooling and collapse of Population III objects is investigated in the framework of ‘flat’ standard cosmological model. We haveRichard assumed that the Ellis (UCL) significant component of fluctuations was isothermal and that the cooling of the collapsing cloud was due to the H2 molecule. We have taken into account the pressure inside the cloud. The only parameter in our models is the cloud’s mass. Our numerical solutions show that the first bound systems were of about a million solar masses. In the range of 105-107M© there are four different modes of the behaviour of the cloud’s radius, depending on the mass: expansion, expansion followed by collapse because of the cooling, collapse after oscillations due to the pressure, and a direct contraction. It is suggested that the different ways to collapse gave rise to different fragmentation processes and hence to different star systems with a similar mass. We find that the collapse was delayed by the pressure, and the first clouds completed their contraction at redshift 100-140. 1 Introduction In this paper we reconsiderOfer@60 the problem of the masses that first collapsed to form bound systems, April 9th 2019 the so-called Population III objects. The formation of structures in the post-recombination gaseous medium is commonly explained by gravitational instabilities experienced by primordial density fluctuations. In a self-gravitating collapsing cloud the temperature tends to increase with contraction. A cooling mechanism is required to lower the pressure opposing gravity (Jeans criterion). The condition for efficient cooling is that the cooling time-scale be shorter than the free-fall time-scale (Yoneyama 1972). The difficulty in cooling the post-recombination clouds is due to the simplicity of the chemical composition of the cold medium. The main cooling agent is the hydrogen molecule that is formed during the collapse (Takayanagy & Nishimura 1960). According to Peebles & Dicke (1968) the first objects to form were the globular clusters. Recent works on that subject are by Hutchins (1976); Silk (1977, 1983); Carlberg (1981); Palla, Salpeter & Stabler (1983) and Lepp & Shull * Present address: Institute of Astronomy, Madingley Road, Cambridge CB30HA. © Royal Astronomical Society • Provided by the NASA Astrophysics Data System The Holy Grail: Locating the First Galaxies? Neutron star mergers & A commonly promoted idea for isolating first generation systems has been to search for chemically pristene examples Rapid (<60 Myr) SN Enrichment in Early Mini-Halos Identifying rare pristene (Pop III) galaxies will be very hard Smith et al (2015) (also Richardson et al 2013, Wise et al 2012, c.f. Cen & Riquelme 2008) Planck Indicates Late and Fast Reionisation CMB polarisation probes foreground Thomson scattering from the start of reionisation to the present epoch. Optical depth of scattering τ constrains the mean redshift <z> and (model dependent) duration of reionisation Parametric models Reionisation begins consistent with PlanckPlanck Collaboration: τ Planck constraints on reionization history PlanckPlanck Collaboration: Collaboration: Planck Planck constraintsToday constraints on on reionization reionization history history δδδzzz===000...5),.5),5), for for for the the the various various various data data data combinations combinations combinations are: are: +++000..014..014014 lollipoplollipop55 ⌧⌧⌧===000...053.053053 000..016..016016,,, lollipoplollipop ;; (4) (4) IONISED −−− +++000..012..012012 lollipop ⌧⌧⌧===000...058.058058 000..012..012012,,, lollipoplollipop++PlanckTTPlanckTT ; ; (5) (5) −−− ⌧ = . +++000..011..011011, lollipoplollipop+ + ⌧⌧==000..058.058058 000..012..012012,, lollipoplollipop++PlanckTTPlanckTT++lensinglensing ; ; (6) (6) −−− ⌧⌧ = .. +++000..012..012012,, lollipoplollipop+ + .. ⌧⌧==000.054.054054 000..013..013013,, lollipoplollipop++PlanckTTPlanckTT++VHLVHL.. 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