Formation Of First Galaxies Research Articles

Redshift-dependent galaxy formation efficiency at z = 5 − 13 in the FirstLight Simulations

Context. Some models of the formation of first galaxies predict low masses and faint objects at extremely high redshifts, z ≃ 9 − 15. However, the first observations of this epoch indicate a higher-than-expected number of bright (sometimes massive) galaxies. Aims. Numerical simulations can help to elucidate the mild evolution of the bright end of the UV luminosity function and they can provide the link between the evolution of bright galaxies and variations of the galaxy formation efficiency across different redshifts. Methods. We use the FirstLight database of 377 zoom-in cosmological simulations of a volume- and mass-complete sample of galaxies. Mock luminosities are estimated by a dust model constrained by observations of the β–MUV relation at z = 6 − 9. Results. FirstLight contains a high number of bright galaxies, MUV ≤ −20, consistent with current data at z = 6 − 13. The evolution of the UV cosmic density is driven by the evolution of the galaxy efficiency and the relation between MUV and halo mass. The efficiency of galaxy formation increases significantly with mass and redshift. At a fixed mass, galactic halos at extremely high redshifts convert gas into stars at a higher rate than at lower redshifts. The high gas densities in these galaxies enable high efficiencies. Our simulations predict higher number densities of massive galaxies, M* ≃ 109 M⊙, than other models with constant efficiency. Conclusions. Cosmological simulations of galaxy formation with detailed models of star formation and feedback can reproduce the different regimes of galaxy formation across cosmic history.

How Population III Supernovae Determined the Properties of the First Galaxies

Massive Population III stars can die as energetic supernovae that enrich the early Universe with metals and determine the properties of the first galaxies. With masses of about 109 M ⊙ at z ≳ 10, these galaxies are believed to be the ancestors of the Milky Way. This paper investigates the impact of Population III supernova remnants (SNRs) from both Salpeter-like and top-heavy initial mass functions (IMFs) on the formation of first galaxies with high-resolution radiation-hydrodynamical simulations with the ENZO code. Our findings indicate that SNRs from a top-heavy Population III IMF produce more metals, leading to more efficient gas cooling and earlier Population II star formation in the first galaxies. From a few hundred to a few thousand Population II stars can form in the central regions of these galaxies. These stars have metallicities of 10−3–10−2, Z ⊙, greater than those of extremely metal-poor (EMP) stars. Their mass function follows a power-law distribution with dN(M*)/dM*∝M*α , where M * is stellar mass, and α = 2.66–5.83 and is steeper for a top-heavy IMF. We thus find that EMP stars were not typical of most primitive galaxies.

Warm Dark Matter and the Formation of First Galaxies

By numerical integration of hydro-dynamical equations, we study the formation of elliptical and spiral galaxies starting from primordial linear density-velocity-gravitational perturbations. Both dark matter and baryons are included. Warm dark matter perturbations acquire two low mass cut-offs: the free-streaming cut-off due to the power spectrum free-streaming cut-off factor τ2(k), and the velocity dispersion cut-off. The Press-Schechter mass distribution does not include velocity dispersion, and should not be used below the velocity dispersion cut-off mass. From the formation of first galaxies and reionization, we estimate limits on the non-relativistic warm dark matter velocity dispersion at expansion parameter , with .

Measurement of the Dark Matter Velocity Dispersion with Dwarf Galaxy Rotation Curves

Warm dark matter has, by definition, a velocity dispersion. Let vhms(a)=vhms(1)/a be the root-mean-square velocity of non-relativistic warm dark matter particles in the early universe at expansion parameter a. vhms(1) is an adiabatic invariant. We obtain vhms(1) in the core of 11 dwarf galaxies dominated by dark matter, from their observed rotation curves, up to a rotation and relaxation correction. We obtain a mean 0.490 km/s and standard deviation 0.160 km/s, with a distribution peaked at the lower end. We apply a mild, data driven, rotation and relaxation correction that obtains the adiabatic invariant in the core of the galaxies: vhms(1)=0.406 ± 0.069 km/s. These two small relative standard deviations justify the prediction that the adiabatic invariant vhms(1) in the core of the galaxies is of cosmological origin if dark matter is warm. This result is in agreement with measurements of vhms(1) based on spiral galaxy rotation curves, galaxy ultra-violet luminosity distributions, galaxy stellar mass distributions, the formation of first galaxies, reionization, and the velocity dispersion cut-off mass.

Measurement of the Dark Matter Velocity Dispersion with Galaxy Stellar Masses, UV Luminosities, and Reionization

The root-mean-square of non-relativistic warm dark matter particle velocities scales as vhrms(a)=vhrms(1)/a , where a is the expansion parameter of the universe. This velocity dispersion results in a cut-off of the power spectrum of density fluctuations due to dark matter free-streaming. Let kfs (teq) be the free-streaming comoving cut-off wavenumber at the time of equal densities of radiation and matter. We obtain , and , at 68% confidence, from the observed distributions of galaxy stellar masses and rest frame ultra-violet luminosities. This result is consistent with reionization. From the velocity dispersion cut-off mass we obtain the limits vhrms(1)kfs (teq) >1.5 Mpc-1. These results are in agreement with previous measurements based on spiral galaxy rotation curves, and on the formation of first galaxies and reionization. These measured parameters determine the temperature-to-mass ratio of warm dark matter. This ratio happens to be in agreement with the no freeze-in and no freeze-out warm dark matter scenario of spin 0 dark matter particles decoupling early on from the standard model sector. Spin 1/2 and spin 1 dark matter are disfavored if nature has chosen the no freeze-in and no freeze-out scenario. An extension of the standard model of quarks and leptons, with scalar dark matter that couples to the Higgs boson that is in agreement with all current measurements, is briefly reviewed. Discrepancies with limits on dark matter particle mass that can be found in the literature are addressed.

Cosmic variance of z > 7 galaxies: prediction from bluetides

ABSTRACT In the coming decade, a new generation of telescopes, including JWST and WFIRST, will probe the period of the formation of first galaxies and quasars, and open up the last frontier for structure formation. Recent simulations and observations have suggested that these galaxies are strongly clustered (with large-scale bias ≳6), and therefore have significant cosmic variance. In this work, we use bluetides, the largest volume cosmological simulation of galaxy formation, to directly estimate the cosmic variance for current and upcoming surveys. Given its resolution and volume, bluetides can probe the bias and cosmic variance of z > 7 galaxies between magnitude MUV ∼ −16 and MUV ∼ −22 over survey areas ∼0.1 arcmin2 to ∼10 deg2. Within this regime, the cosmic variance decreases with survey area/ volume as a power law with exponents between ∼−0.25 and ∼−0.45. For the planned 10 deg2 field of WFIRST, the cosmic variance is between $3{{\ \rm per\ cent}}$ and $10{{\ \rm per\ cent}}$. Upcoming JWST medium/ deep surveys with areas up to A ∼ 100 arcmin2 will have cosmic variance ranging from ${\sim}20\,\mathrm{ to}\,50{{\ \rm per\ cent}}$. Lensed surveys have the highest cosmic variance ${\gtrsim}40{{\ \rm per\ cent}}$; the cosmic variance of MUV ≲ −16 galaxies is ${\lesssim}100{{\ \rm per\ cent}}$ up to z ∼ 11. At higher redshifts such as z ∼ 12 (14), effective volumes of ≳ (8 Mpc h−1)3 (≳(12 Mpc h−1)3) are required to limit the cosmic variance to within $100{{\ \rm per\ cent}}$. Finally, we find that cosmic variance is larger than Poisson variance and forms the dominant component of the overall uncertainty in all current and upcoming surveys. We present our calculations in the form of simple fitting functions and an online cosmic variance calculator (CV_AT_COSMIC_DAWN) that we publicly release.

Galaxy formation with BECDM – II. Cosmic filaments and first galaxies

ABSTRACT Bose–Einstein condensate dark matter (BECDM, also known as fuzzy dark matter) is motivated by fundamental physics and has recently received significant attention as a serious alternative to the established cold dark matter (CDM) model. We perform cosmological simulations of BECDM gravitationally coupled to baryons and investigate structure formation at high redshifts (z ≳ 5) for a boson mass m = 2.5 × 10−22 eV, exploring the dynamical effects of its wavelike nature on the cosmic web and the formation of first galaxies. Our BECDM simulations are directly compared to CDM as well as to simulations where the dynamical quantum potential is ignored and only the initial suppression of the power spectrum is considered – a warm dark matter-like (‘WDM’) model often used as a proxy for BECDM. Our simulations confirm that ‘WDM’ is a good approximation to BECDM on large cosmological scales even in the presence of the baryonic feedback. Similarities also exist on small scales, with primordial star formation happening both in isolated haloes and continuously along cosmic filaments; the latter effect is not present in CDM. Global star formation and metal enrichment in these first galaxies are delayed in BECDM/‘WDM’ compared to the CDM case: in BECDM/‘WDM’ first stars form at z ∼ 13/13.5, while in CDM star formation starts at z ∼ 35. The signature of BECDM interference, not present in ‘WDM’, is seen in the evolved dark matter power spectrum: although the small-scale structure is initially suppressed, power on kpc scales is added at lower redshifts. Our simulations lay the groundwork for realistic simulations of galaxy formation in BECDM.

Formation of First Galaxies inside Density Peaks and Voids under the Influence of Dark Matter–Baryon Streaming Velocity. I. Initial Condition and Simulation Scheme

Abstract We present a systematic study of the cosmic variance that existed in the formation of the first stars and galaxies. We focus on the cosmic variance induced by the large-scale density and velocity environment engraved at the epoch of recombination. The density environment is predominantly determined by the dark-matter overdensity, and the velocity environment by the dark matter–baryon streaming velocity. Toward this end, we introduce a new cosmological initial condition generator, BCCOMICS, which solves the quasi-linear evolution of small-scale perturbations in the large-scale density and streaming-velocity environment and generates the initial condition for dark matter and baryons, as either particles or grid data at a specific redshift. We also describe a scheme to simulate the formation of the first galaxies inside density peaks and voids, where a local environment is treated as a separate universe. The resulting cosmic variance in the number density of minihalos and the amount of cooling mass are presented as an application. Density peaks become a site for enhanced formation of the first galaxies, which compete with the negative effect from the dark matter–baryon streaming velocity on structure formation.

The Formation of the First Galaxies

The primary concern of this thesis is to understand the formation and properties of the first galaxies, as well as the influence of the first stars in terms of radiative, mechanical and chemical feedback. In particular, we elucidate the role of turbulence, ionizing radiation by massive Population III stars, mechanical feedback by highly energetic supernovae, and chemical enrichment. In light of the next generation of ground- and space based telescopes, we derive their observational signature in terms of recombination radiation, bremsstrahlung and 21 cm emission. We find that the cumulative 21 cm signal of the first H II regions will likely be observable by the planned SKA, while the recombination radiation from the first starbursts might be observable by JWST. These probes are essential to test the theoretical framework of the first stars and galaxies and shed some light on this elusive period of cosmic history.