On the fragmentation of cosmic gas clouds. I - The formation of galaxies and the first generation of stars

“Gas can come into the halo in two forms: hot, nearly spherical accretion (Rees & Ostriker 1977; Silk 1977), and cool, filamentary inflows along cosmic webs (e.g. Birnboim & Dekel 2003; Kereš et al. 2005).”

“Such hot (Tv & 106 K) virialized gas has a prohibitively long cooling time for making in situ cooling a plausible source of cold gas (Rees & Ostriker 1977; White & Rees 1978; Silk 1977).”

“In the standard paradigm of galaxy formation (e.g., Rees & Ostriker 1977; Silk 1977; White & Rees 1978), gas infalling into a dark matter halo suffers from virial shock-heating around the halo virial radius, which impedes the efficiency of gas cooling.”

“Although justifyable in numerical terms, this mass is also close to the one that results from the cooling criterion tcool < tcoll, where tcoll is the halo collapse time for the spherical collapse model (Rees & Ostriker 1977; Binney 1977; Silk 1977).”

“Hitherto, the detected free-floating planets have been giant worlds that could potentially represent the tail-end of the stellar mass distribution (Silk 1977).”

“In the last two decades this problem has been tackled intermittently (Silk 1977; Kashlinsky & Rees 1983; Palla, Salpeter & Stahler 1983; Carr, Bond & Arnett 1984; Carr 1994; Uehara et al. 1996; Omukai & Nishi 1998).”

“This departure from the faint-end power law can partly be ascribed to the inefficient cooling in massive galaxies (Rees & Ostriker 1977; Silk 1977).”

“…et al. 2009; van de Voort & E-mail: segers@strw.leidenuniv.nl Schaye 2012), which can extend far inside the halo virial radius, and through quasi-spherical infall from a diffuse hot halo, which contains gas that has been shock-heated to the halo virial temperature (Rees & Ostriker 1977; Silk 1977).”

“Traditional theory suggests that as gas enters a dark matter halo, it shock heats to the halo’s virial temperature before slowly cooling onto the galaxy (Rees & Ostriker 1977; Silk 1977; White & Rees 1978).”

“…heating during virialization will not provide sufficient pressure support for the infalling gas and gas could reach galaxies in near free-fall (Silk 1977; Rees & Ostriker 1977; Binney 1977; White & Rees 1978; for a more detailed spherical shock stability analysis with a modern ΛCDM cosmology,…”

“…to the gaseous cosmic web and that the evolution of galaxies is governed in large part by the dissipative response of baryonic gas due to the trade off of cooling and dynamical timescales as it accretes into dark matter halos (e.g., Binney 1977; Rees & Ostriker 1977; Silk 1977; White & Rees 1978).”

“The early theories, pioneered by Binney (1977); Rees & Ostriker (1977); Silk (1977), and White & Rees (1978), used a cooling rate argument to place an upper limit on the masses of galaxies.”

“The accretion is characterized according to two modes: radiatively efficient and radiatively inefficient (Binney 1977; Rees & Ostriker 1977; Silk 1977).”

“Such models have their roots in the analytic formulations of White & Frenk (1991) and Fall & Efstathiou (1980) which in turn have their roots in the works of Silk (1977) and Rees & Ostriker (1977).”

“The traditional view of galaxy formation stems from a number of early theoretical papers, Rees & Ostriker (1977), Silk (1977) and Fall & Efstathiou (1980).”

“Various physical mechanisms have been proposed to understand this process, such as the virial shock heating (e.g., Rees & Ostriker 1977; Silk 1977; White & Rees 1978; Birnboim & Dekel 2003; Kereš et al. 2005), stellar feedback (e.g., Dekel & Silk 1986; Murray et al. 2005), active galactic nucleus…”

“The existence of a characteristic mass-scale at high-mass (Mh ' 1012 M ) has been known since the late 1970s and early 1980s (e.g. Rees & Ostriker 1977; Silk 1977; White & Rees 1978).”

“The works of Rees & Ostriker (1977) and Silk (1977) proposed that C© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society nloaded from https://academ ic.oup.com /m nras/article-abstract/478/1/255/4963756 by C ardiff U niversity user on 10 M arch…”

“The assembly of dissipative baryons into galaxies in the presence of dark matter potential wells has been studied extensively based on general physical principles (see e.g. Binney 1977; Rees & Ostriker 1977; Silk 1977; White & Rees 1978).”

“Semianalytical arguments to this e†ect have existed for some time (Silk 1977), but many di†erent have beenAnsa tze invoked as the suppressing mechanism, including supernova energy that ejects gas (Dekel & Silk 1986), reheating of the intergalactic medium that suppresses gas infall (Blanchard,…”

“In this picture, as 2 gas falls into potential wells, it is shock heated and must radiate this energy away before forming stars (Rees & Ostriker 1977; Silk 1977).”

“As mentioned earlier, the dark matter halo mass influences the evolution of galaxies, driving processes of gas accretion and star formation rate (SFR; see, e.g., Rees & Ostriker 1977; Silk 1977; White & Rees 1978; Fall & Efstathiou 1980; Blumenthal et al. 1984).”

“Within these dark matter halos, baryons initially agglomerate onto the center of the potential well within the free-fall time of the halo and form stars (Rees & Ostriker 1977; Binney 1977; Silk 1977).”

“A large fraction of these missing baryons are likely embedded in the low density, warm-hot gas extended over 100 kpc in the circumgalactic medium (CGM) or galactic halo (Silk 1977; White & Rees 1978; Sommer-Larsen 2006).”

“The other characteristic scale is the upper limit for the MNRAS 000, 1–19 (2021) halo mass within which efficient cold inflow can supply gas for star formation (Rees & Ostriker 1977; Silk 1977; Binney 1977).”

“It is believed that below the critical mass ( M ∼ 10 12 M ⊙ ), the SNe feedback dominates the feedback whereas, the black hole feedback takes over at higher masses (Silk 1977; Dekel & Silk 1986; Silk & Mamon 2012).”

“In the basic picture of galaxy formation, baryons fall into dark matter potential wells located along the network of sheets and filaments formed by gravitational instability (Sunyaev & Zel’dovich 1972; Rees & Ostriker 1977; Silk 1977; White & Rees 1978).”

“In the widely accepted ΛCDM framework, dark matter halos are the building blocks of structure, with galaxies growing at their centers (Rees & Ostriker 1977; Silk 1977; White & Rees 1978).”

“To collapse and form stars, the gas must radiate this energy away, a process that takes longer in the largest, most gravitationally bound structures (e.g., Binney 1977; Rees & Ostriker 1977; Silk 1977).”

“These equations have beenthe basis for the standard paradigm of galaxy formation for over30 years now (Rees & Ostriker 1977; Silk 1977; White & Rees 1978; White & Frenk 1991).”

“General physical considerations suggest that in high-density regions the gas is cooling which creates favorable conditions for star formation (Rees & Ostriker (1977), Silk (1977)).”

“Earlier ideas (Hoyle, 1953, Binney 1977, Rees and Ostriker 1977, Silk 1977) seemed to suggest so.”

“This is presumably due to the inefficient cooling of the gas in massive systems because of the high temperature of the shock-heated gas (Rees & Ostriker 1977; Silk 1977; Blanton et al. 1999).”

“This is mostly the result of the gas virially shocking, in line with the classical analytical models of galaxy formation (Rees & Ostriker 1977; Silk 1977; White & Frenk 1991), whereby the cooling radius of the in-falling gas is much smaller than the virial radius, allowing for a quasihydrostatic…”

“Analytical as well as numerical studies have indicated the existence of a hot (T > 106 K) and diffuse circumgalactic medium (CGM), occupying the galactic halo (Rees & Ostriker 1977; Silk 1977; White & Frenk 1991; Maller & Bullock 2004; Kereš et al. 2005; Crain et al. 2010; Sharma et al. 2012).”

“…§ 1, in classic virial shock models (ignoring feedback, turbulence, magnetic fields, CRs, and assuming spherical symmetry), one expects something like 𝑡cool/𝑡ff ∼ (𝑀vir/1011 𝑀 )𝛼 with 𝛼 between 1/3 and 2/3 at 𝑟 ∼ 𝑅vir (Silk 1977; Rees & Ostriker 1977), so hot halos only form at high masses.”

“…near the mass of the Milky Way, fundamental galaxy formation theory suggests that gas accreting from the cosmic web passes through a virial shock as it falls onto a galaxy’s halo, filling the CGM with a hot (“virialized”) gas near T∼ 106–107 K (Rees & Ostriker 1977; Silk 1977; White & Rees 1978).”

“…strength, as well as the distribution of mass within the halos is used to estimate statistical properties of the density field (McClelland & Silk (1977); Scherrer & Bertschinger (1991); Seljak (2000); Peacock & Smith (2000); Scoccimarro et al. (2001); Cooray & Sheth (2002)) which readily…”

“The dominant idea of galaxy formation has changed recently: Decades ago it was though (Rees & Ostriker 1977; Silk 1977; White & Rees 1978) that galaxies collect their baryons through diffuse gas symmetrically falling into dark matter haloes and being shock-heated as it hits the gas residing in them…”

“Through ionization of H (Lin & Murray 1992) and dissociation of H2 (Silk 1977, Omukai & Nishi 1999), ultra violet (UV) radiation has negative feedback on further star formation in the host clouds.”

“A growing body of theoretical work has been devoted in the past few years to this subject (Rees 1976; Rees & Ostriker 1977; Silk 1977, 1983; Haiman, Thoul & Loeb 1996; Uehara et al. 1996).”

“Molecules play an important role in the process of gravitational collapse through the mechanism of thermal instability (see Field 1965; Silk 1977; Fall & Rees 1985; Uehara et al. 1996; Puy & Signore 1996; Abel et al. 2000).”

“The pioneering work by Binney (1977), Rees & Ostriker (1977) and Silk (1977) assumed that the gas in a dark matter halo is heated by shocks as it collapses into dark matter halos.”

“In particular, it has been shown (Rees & Ostriker 1977; Silk 1977; Binney 1977; White & Frenk 1991) that a comparison between cooling times and ages of galactic halos can predict the transition from galaxies to groups and clusters.”

“…found that there is an upper mass threshold at which accreted gas is shocked to temperatures from which it can no longer cool within a Hubble time and file star formation, determining the mass at which galaxies must be red (Rees & Ostriker 1977; Silk 1977; Binney 1977; White and Rees 1978).”

“As haloes form and grow, they are assigned a cosmic abundance of diffuse primordial gas, which is assumed to be shock-heated to the virial temperature (Rees & Ostriker 1977; Silk 1977; White & Rees 1978).”

“Having this much HI inside a galaxy’s virial radius conflicts with the classic galaxy formation scenario (Binney 1977; Rees & Ostriker 1977; Silk 1977).”

“At a given redshift z, we shall now require that gas cooling occurs after virialization to allow for gas fragmentation and star formation & Ostriker(Silk 1977 ; Rees 1977).”

“…work (Kereš et al. 2005; Dekel & Birnboim 2006; Nelson et al. 2013) that suggests, to varying degrees, a two-mode gas accretion onto galaxies, in contrast to the classic description of gas cooling following virialization heating (Rees & Ostriker 1977; Silk 1977; Binney 1977; White & Rees 1978).”

“The current paradigm of hierarchical structure formation has been in place for decades (Rees & Ostriker 1977; Silk 1977; White & Rees 1978; White & Frenk 1991).”

“Baryons follow the DM into gravitationally bound structures, the halos, where they cool, which decreases their pressure and dissipates angular momentum (Binney 1977; Rees & Ostriker 1977; Silk 1977; White & Rees 1978).”

“The currently accepted paradigm suggests that present-day galaxies evolved from primordial inhomogeneities in the density distribution at very early times (e.g., Rees & Ostriker 1977; Silk 1977; White & Rees 1978; Blumenthal et al. 1984).”

“Otherwise, the gas within the cooling radius cools, sinks toward the halo center, and fuels both the formation of and the star formation within the central galaxy (Binney 1977; Rees & Ostriker 1977; Silk 1977; White & Rees 1978; White & Frenk 1991).”

“Gas entering the c© 2014 RAS potential well of a galaxy gets shocked to the virial temperature of the dark matter halo at an early epoch of infall, and then gradually cools and falls onto the central galaxy (Rees & Ostriker 1977; Silk 1977; Binney 1977, White &Rees 1978).”

“This changeover from the hydrogen cooling to heavy-element cooling occurs at Z/Z ∼ 10−4 (Silk 1977; Yoshii & Sabano 1980; Bromm et al. 2001).”

“This problem was already clear more than two decades ago, as pioneering works (Silk 1977 ; & Rees Salpeter, & StahlerKashlinsky 1983 ; Palla, 1983 ; Bond, & Arnett could not reach similar conclu-Carr, 1984) sions on the typical mass range of newly formed stars in the Ðrst protogalactic objects.”

“…simplified one-zone models to account for the dynamics of collapsing gas clouds in the presence of radiative cooling (Yoneyama 1972; Hutchins 1976; Silk 1977, 1983; Carlberg 1981; Kashlinsky & Rees 1983; Palla et al. 1983; Carr et al. 1984; Izotov & Kolesnik 1984; Couchman & Rees 1986; Susa et…”

“In massive halos, shock-heated gas may not cool to form stars (e.g. Silk 1977; Rees & Ostriker 1977; Binney 1977; Birnboim & Dekel 2003), and satellite galaxies can be quenched due to gas removal or consumption (e.g. Boselli & Gavazzi 2006); yet in order to match the observed fraction of quenched…”

“Rees & Ostriker (1977) and Silk (1977) laid the foundations of the modern theory of galaxy formation by discovering that the competition between the radiative cooling time tcool and the gravitational freefall time tff determines the characteristic mass of galaxies.”

“An extreme version of the cooling flow instability has been proposed to account for the masses of protogalaxies (Rees and Ostriker 1977; Silk 1977) and of globular clusters (Fall and Rees 1985).”

“For these massive objects, both Ly and H2 luminosities decline rapidly toward higher masses, because in the redshift range we are considering, such massive objects cannot cool within the merging timescale and then remain in the virialization state (Silk 1977; Rees &Ostriker 1977).”