We have carried out semianalytic simulations to build redshifted 21-cm maps in the dark ages. An entropy-floor model is adopted for planting protogalaxies in simulated minihaloes. The model allocates gas quantities such as baryonic mass and temperature to every $N$-body particle and extensively exploits the particle nature of the data in the subsequent analysis. We have found that the number density of simulated minihaloes in the early universe is well described by the Sheth & Tormen function and consequently the signal powers of simulated minihaloes are far greater than the Press & Schechter prediction presented by Furlanetto (2006b). Even though the matter power spectrum measured in the halo particles at $z=15$ is about an order of magnitude smaller than the intergalactic medium (IGM), the 21-cm signal fluctuations of haloes are, to the contrary, one order of magnitude higher than the embedding adiabatic IGM on scales, $k\lesssim 10 h{\rm Mpc}^{-1}$. But their spectral shapes are almost same to each other. We have found that the adiabatic signal power on large scales lies between the linear predictions of the infinite spin-temperature model ($T_s\gg T_{\rm cmb}$) and the model with the uniform spin temperature equal to background value ($T_s = T_s^{bg}$). Higher preheating temperature (or higher background entropy) makes the power spectrum of signals more flattened because the hotter IGM signals are more thermally broadened and minihalo fluctuations dominating on small scales are more severely suppressed by the higher background entropy. Therefore, this model-dependent power spectrum slope measured on the scale of $100\le k \le 1000 ~h{\rm Mpc}^{-1}$ will enable us to easily determine a best-matching halo + IGM model in future observations.
Global signal in the redshifted hydrogen 21-cm line from the Dark Ages and Cosmic Dawn: Dependence on the nature of dark matter and modeling of first light
Sensitivity of the redshifted 21 cm signal from the Dark Ages to parameters of primordial magnetic fields
Ivan Franko National University of Lviv（利沃夫伊万·弗兰科大学）；Bogolyubov Institute for Theoretical Physics of the NAS of Ukraine（乌克兰国家科学院博戈留博夫理论物理研究所）；Dipartimento di Fisica e Astronomia, Universitá di Bologna（博洛尼亚大学物理与天文学系）
The Dark Ages, probed by the redshifted 21-cm signal, is the ideal epoch for a new rigorous test of the standard LCDM cosmological model. Divergences from that model would indicate new physics, such as dark matter decay (heating) or baryonic cooling beyond that expected from adiabatic expansion of the Universe. In the early Universe, most of the baryonic matter was in the form of neutral hydrogen (HI), detectable via its ground state's spin-flip transition. A measurement of the redshifted 21-cm spectrum maps the history of the HI gas through the Dark Ages and Cosmic Dawn and up to the Epoch of…
The emission in the hyperfine structure 21 cm line of atomic hydrogen arising in the halos with masses $\sim10^6-10^{10}$ M$_\odot$ from the Dark Ages in the models with Warm Dark Matter (WDM) is analysed. The halos are assumed to be formed from Gaussian density peaks of cosmological density perturbations at $10\lesssim z\lesssim50$. Semi-analytical modelling of the formation of individual spherical halos in multi-component models shows that gas in them has the kinetic temperature in the range of $60-800$ K under adiabatic compression of the collapsing halo, and the temperature of each halo de…
One of the next decade's most exciting prospects is to explore the cosmic "dark ages," during which the first stars in the Universe formed, with the 21 cm line of neutral hydrogen. At z>6, this light redshifts into the low-frequency radio regime and can be observed with new generations of wide-field arrays. These experiments have the potential to observe enormous volumes and to improve both cosmological and astrophysical constraints dramatically. In this white paper, we describe how the next decade will see the first steps toward unlocking this potential, allowing us to answer two key question…
Independent lines of evidence suggest that the first stars, which ended the cosmic dark ages, came in pairs, rather than singly. This could change the prevailing view that the early Universe had a Swiss-cheese-like appearance.
A concept for a new space-based cosmology mission called the Dark Ages Radio Explore (DARE) is presented in this paper. DARE's science objectives include (1) When did the first stars form? (2) When did the first accreting black holes form? (3) When did Reionization begin? (4) What surprises does the end of the Dark Ages hold (e.g., Dark Matter decay)? DARE will use the highly-redshifted hyperfine 21-cm transition from neutral hydrogen to track the formation of the first luminous objects by their impact on the intergalactic medium during the end of the Dark Ages and during Cosmic Dawn (redshift…
Observations of the frequency dependence of the global brightness temperature of the redshifted 21 cm line of neutral hydrogen may be possible with single dipole experiments. In this paper, we develop a Fisher matrix formalism for calculating the sensitivity of such instruments to the 21 cm signal from reionization and the dark ages. We show that rapid reionization histories with duration delta z< 2 can be constrained, provided that local foregrounds can be well modelled by low order polynomials. It is then shown that observations in the range nu = 50 - 100 MHz can feasibly constrain the Lyman…
The \hi 21 cm transition line is expected to be an important probe into the cosmic dark ages and epoch of reionization. Foreground source removal is one of the principal challenges for the detection of this signal. This paper investigates the extragalactic point source contamination and how accurately bright sources ($\gtrsim 1$ ~Jy) must be removed in order to detect 21 cm emission with upcoming radio telescopes such as the Murchison Widefield Array (MWA). We consider the residual contamination in 21 cm maps and power spectra due to position errors in the sky-model for bright sources, as well…
Constraints on dark matter annihilation or decay offer unique insights into the nature of dark matter. We illustrate how surveys dedicated to detect the highly redshifted 21 cm signal from the dark ages will offer a new window into properties of particle dark matter. The 21 cm intensity mapping signal and its fluctuations are sensitive to energy injection from annihilation or decay of long-lived particles in a way that is complementary to other probes. We present forecasted constraints from forthcoming and next-generation radio surveys. We show that, while SKA might be capable of a detection f…
The next generation 2 micron sky survey should target nascent galaxies in the epoch of reionization for spectroscopic followup on large telescopes. A 2.5 metre telescope at a site on the antarctic plateau has advantages for this purpose and for southern hemisphere infrared surveys generally.
Primordial molecules were formed during the Dark Ages, i.e. the time between recombination and reionization in the early Universe. The purpose of this article is to analyze the formation of primordial molecules based on heavy elements during the Dark Ages, with elemental abundances taken from different nucleosynthesis models. We present calculations of the full non-linear equation set governing the primordial chemistry. We consider the evolution of 45 chemical species and use an implicit multistep method of variable order of precision with an adaptive stepsize control. We find that the most ab…
The recent EDGES collaboration detection of an absorption signal at a central frequency of $ν= 78 \pm 1$ MHz points to the presence of a significant Lyman-$α$ background by a redshift of $z=18$. The timing of this signal constrains the dark matter particle mass ($m_χ$) in the warm dark matter (WDM) cosmological model. WDM delays the formation of small-scale structures, and therefore a stringent lower limit can be placed on $m_χ,$ based on the presence of a sufficiently strong Ly-$α$ background due to star formation at $z=18$. Our results show that the coupling the spin temperature to the gas t…
We demonstrate that elastic scattering between dark matter (DM) and baryons can affect the thermal evolution of the intergalactic medium at early epochs and discuss the observational consequences. We show that, due to the interaction between DM and baryons, the baryon temperature is cooled after decoupling from the CMB temperature. We illustrate our findings by calculating the 21 cm power spectrum in coexistence with a velocity-dependent DM elastic scattering cross section. For instance, for a DM mass of 10 GeV, the 21 cm brightness temperature angular power spectrum can be suppressed by a fac…
We explore the effects of elastic scattering between dark matter and baryons on the 21-cm signal during the dark ages. In particular, we consider a dark-matter---baryon interaction with a cross section of the form $σ= σ_0 v^{-4}$, in which case the effect of the drag force between the dark matter and baryon fluids grows with time. We show that, as opposed to what was previously thought, this effect heats up the baryons due to the relative velocity between dark matter and baryons. This creates an additional source of fluctuations, which can potentially make interactions easier to detect by 21-c…
We study the signature of primordial non-Gaussianity imprinted on the power spectrum of the 21-cm line differential brightness temperature during dark ages. Employing the perturbative treatment of gravitational clustering, we quantitatively estimate the effects of the non-Gaussian and one-loop corrections on the 21-cm power spectrum. The potential impact of the use of the 21-cm power spectrum for the constraint on local-type primordial non-Gaussianity is investigated based on the Fisher matrix analysis. Our results show that the 21-cm power spectrum for an array with a baseline of several tens…
Direct detection of regions of ionized hydrogen (HII) has been suggested as a promising probe of cosmic reionization. Observing the redshifted 21-cm signal of hydrogen from the epoch of reionization (EoR) is a key scientific driver behind new-generation, low-frequency radio interferometers. We investigate the feasibility of combining low-frequency observations with the Square Kilometre Array and near infra-red survey data of the Wide-Field Infrared Survey Telescope to detect cosmic reionization by imaging HII bubbles surrounding massive galaxies during the cosmic dawn. While individual bubbles…
The Cosmic Dark Ages represent the period in the early evolution of the Universe, starting immediately after the decoupling of CMB photons from matter, and ending with the formation of the first stars and galaxies. The HI signal from the neutral hydrogen atoms is the only mechanism for us to understand this crucial phase in the cosmological history of the Universe and answer fundamental questions about the validity of the standard cosmological model, dark matter physics, and inflation. Due to cosmological redshift, this signal is now only observable in the 3-30~MHz frequency band, which is blo…
Observations of redshifted 21-cm signal from neutral hydrogen (HI) appear to be the most promising probe of the cosmic dark ages. The signal carries information about the thermal state along with density distribution of the intergalactic medium (IGM). The cosmic microwave background radiation (CMBR), through its interaction with charged particles, plays a major role in determining the kinetic and spin temperature of HI gas in the IGM during dark ages. A Spatially fluctuating ionization fraction, which is caused by inhomogeneous recombinations, causes heat transfer from the CMBR to the IGM gas …
We present an update on the SCI-HI experiment, which is designed to measure the all-sky (global) 21 cm brightness temperature during the end of the Dark Ages. Results from preliminary observations in June 2013 are discussed, along with system improvements and planned future work.
The Dark Ages are the period between the last scattering of the cosmic microwave background and the appearance of the first luminous sources, spanning approximately 1100 < z < 30. The only known way to measure fluctuations in this era is through the 21-cm line of neutral hydrogen. Such observations have enormous potential for cosmology, because they span a large volume while the fluctuations remain linear even on small scales. Observations of 21-cm fluctuations during this era can therefore constrain fundamental aspects of our Universe, including inflation and any exotic physics of dark matter…
By means of a semi-analytic model of galaxy formation, we show how the local observed relation between age and galactic stellar mass is affected by assuming a DM power spectrum with a small-scale cutoff. We compare results obtained by means of both a Lambda-cold dark matter (LambdaCDM) and a Lambda-warm dark matter (LambdaWDM) power spectrum - suppressed with respect to the LambdaCDM at scales below ~ 1 Mpc. We show that, within a LWDM cosmology with a thermal relic particle mass of 0.75 keV, both the mass-weighted and the luminosity-weighted age-mass relations are steeper than those obtained …
In this work, we use a test based on the differential ages of galaxies for distinguishing the dark energy models. As proposed by Jimenez and Loeb, relative ages of galaxies can be used to put constraints on various cosmological parameters. In the same vein, we reconstruct $H_0dt/dz$ and its derivative ($H_0d^2t/dz^2$) using a model independent technique called non-parametric smoothing. Basically, $dt/dz$ is the change in the age of the object as a function of redshift which is directly link with the Hubble parameter. Hence for reconstruction of this quantity, we use the most recent $H(z)$ data…
Quasars show considerable promise as standard candles in a high-redshift window beyond Type Ia supernovae. Recently, Risaliti, Lusso \& collaborators \cite{Risaliti:2018reu, Lusso:2019akb, Lusso:2020pdb} have succeeded in producing a high redshift Hubble diagram ($ z \lesssim 7$) that supports "a trend whereby the Hubble diagram of quasars is well reproduced by the standard flat $Λ$CDM model up to $z \sim 1.5-2$, but strong deviations emerge at higher redshifts". This conclusion hinges upon a log polynomial expansion for the luminosity distance. In this note, we demonstrate that this expansion…
We study the formation and destruction of the first molecules at the epochs of the Dark Ages and Cosmic Dawn to evaluate the luminosity of the protogalaxy clumps (halos) in the molecular lines. The cosmological recombination is described using the model of an effective three-level atom, while the chemistry of the molecules is examined using the relevant basic kinetic equations. We then studied the effect of collisional and radiative excitation of molecules on the intensity of molecular emission in both warm and hot halos. Using the Planck data on the reionization of the intergalactic medium at…
Formation of halos in the Dark Ages from initial spherical perturbations is analyzed in a four component Universe (dark matter, dark energy, baryonic matter and radiation) in the approximation of relativistic hydrodynamics. Evolution of density and velocity perturbations of each component is obtained by integration of a system of nine differential equations from $z=10^8$ up to virialization, which is described phenomenologically. It is shown that the number density of dark matter halos with masses $M\sim10^8-10^9\,\mathrm{M_{\odot}}$ virialized at $z\sim10$ is close to the number density of ga…
We analyse the thermal emission and resonant scattering of CMB radiation from the dark ages halos in the rotational lines of the helium hydride ion (HeH$^{+}$), one of the first chemical compounds in the Universe. Evaluating the optical depth, thermal and resonant brightness temperatures and spectral fluxes of dark ages halos is based on computing the cross-sections and rate coefficients of excitation/de-excitation of the lowest five rotational states of HeH$^{+}$ by inelastic collisions with atomic hydrogen. It was shown that in the Dark Ages the collisional excitation/de-excitation by atoms …
One of the milestones in the cosmic history is the formation of the first luminous objects and Hydrogen reionization. The standard theory of cosmic structure formation predicts that the first generation of stars were born about a few hundred million years after the Big Bang. The dark Universe was then lit up once again, and eventually filled with ultraviolet photons emitted from stars, galaxies, and quasars. The exact epoch of the cosmic reionization and the details of the process, even the dominant sources, are not known except the fact that the universe was reionized early on. Signatures of …
We study the fluctuations in the brightness temperature of 21-cm signal $δT_{21}$ at the dark ages ($z\sim100$) with a dark matter candidate in Inter Doublet Model (IDM). We then explore the effects of different fractions of IDM dark matter on $δT_{21}$ signal. The IDM dark matter masses are chosen in few tens of GeV region as well as in the high mass region beyond 500 GeV. It has been observed that the $δT_{21}$ signal is more sensitive in the dark matter mass range of $70 - 80$ GeV. A lower bound on annihilation cross-section for this dark matter is also obtained analyzing the $δT_{21}$ sign…
The second-order vector mode is inevitably induced from the coupling of first-order scalar modes in cosmological perturbation theory and might hinder a possible detection of primordial gravitational waves from inflation through 21cm lensing observations. Here, we investigate the weak lensing signal in 21cm photons emitted by neutral hydrogen atoms in the dark ages induced by the second-order vector mode by decomposing the deflection angle of the 21cm lensing signal into the gradient and curl modes. The curl mode is a good tracer of the cosmological vector and tensor modes since the scalar mode…
The observed power spectrum of redshifted 21cm fluctuations is known to be sensitive to the astrophysical properties of the galaxies that drove reionization. Thus, detailed measurements of the 21cm power spectrum and its evolution could lead to measurements of the properties of early galaxies that are otherwise inaccessible. In this paper, we study the effect of mass and redshift dependent escape fractions of ionizing radiation on the ability of forthcoming experiments to constrain galaxy formation via the redshifted 21cm power spectrum. We use a model for reionization which combines the hiera…
After recalling some puzzles in cosmology and briefly reviewing the Friedmann-Lemaître cosmos a simple unified model of the ``Dark Sector'' is described. This model involves a scalar field and a pseudo-scalar axion field that give rise to Dark Energy in the form of ``quintessence'' and to ``fuzzy'' Dark Matter, respectively. Predictions of the model concerning the late-time evolution of the Universe and possible implications for the problem of the observed Matter-Antimatter Asymmetry in the Universe are sketched.
The initial conditions for the density perturbations in the early Universe, which dictate the large scale structure and distribution of galaxies we see today, are set during inflation. Measurements of primordial non-Gaussianity are crucial for distinguishing between different inflationary models. Current measurements of the matter power spectrum from the CMB only constrain this on scales up to $k\sim 0.1$ Mpc$^{-1}$. Reaching smaller angular scales (higher values of $k$) can provide new constraints on non-Gaussianity. A powerful way to do this is by measuring the $\textrm{H}\textrm{I}$ matter …
In the absence of complex astrophysical processes that characterize the reionization era, the 21-cm emission from neutral hydrogen (HI) in the post-reionization epoch is believed to be an excellent tracer of the underlying dark matter distribution. Assuming a background cosmology, it is modelled through (i) a bias function b(k,z), which relates HI to the dark matter distribution and (ii) a mean neutral fraction (x_{HI}) which sets its amplitude. In this paper, we investigate the nature of large scale HI bias. The post-reionization HI is modelled using gravity only N-Body simulations and a suit…
Cold dark matter as the sum of different mass Primordial Black Holes (PBH) can explain a number of unsolved astrophysical mysteries. Here I assume a broad PBH mass distribution providing the bulk of the dark matter, consistent with all constraints and estimate the baryon accretion onto PBH contributing to cosmic background radiations, mainly the correlation signal between the Cosmic X-ray and the Cosmic infrared background fluctuations in deep Chandra and Spitzer surveys. I assume Bondi capture and advection dominated disk accretion with reasonable baryon densities and effective relative veloc…
This work presents an analytical approach for studying the cosmological 21cm background signal from the Dark Ages (DA) and subsequent Epoch of Reionization (EoR). We simulate differential observations of a galaxy cluster to demonstrate how these epochs can be studied with a specific form of the Sunyaev-Zel'dovich Effect called the SZE-21cm. This work produces simulated maps of the SZE-21cm and shows that the SZE-21cm can be extracted from future observations with low-frequency radio interferometers such as the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array (SKA). In…
Dark matter annihilation or de-excitation, decay of metastable species, or other new physics may inject energetic electrons and photons into the photon-baryon fluid during and after recombination. As such particles cool, they partition their energy into a large number of efficiently ionizing electrons and photons, which in turn modify the ionization history. Recent work has provided a simple method for constraining arbitrary energy deposition histories using the cosmic microwave background (CMB); in this note, we present results describing the energy deposition histories for photons and electr…
A measurement of primordial non-gaussianity will be of paramount importance to distinguish between different models of inflation. Cosmic microwave background (CMB) anisotropy observations have set unprecedented bounds on the non-gaussianity parameter f_NL but the interesting regime f_NL <~ 1 is beyond their reach. Brightness-temperature fluctuations in the 21-cm line during the dark ages (z ~ 30-100) are a promising successor to CMB studies, giving access to a much larger number of modes. They are, however, intrinsically non-linear, which results in secondary non-gaussianities orders of magnit…
We investigate the impact of radiation from primordial black holes (PBHs), in the mass range of $10^{15} \lesssim M_{\rm PBH} \lesssim 10^{17}~\rm g$ and $10^{2} \lesssim M_{\rm PBH} \lesssim 10^{4}~M_{\odot}$, on the 21-cm angular-power spectrum in the dark ages. PBHs in the former mass range effect the 21-cm angular-power spectrum through the evaporation known as Hawking radiation, while the radiation from the accretion process in the latter mass range. In the dark ages, radiation from PBHs can increase the ionization fraction and temperature of the intergalactic medium, change the global 21…
Exact solutions of the perturbations equations in the magnetized LambdaCDM scenario are presented. They apply during the dark ages and, more specifically, after the baryons are freed from the drag of the photons. The magnetized growth rate of matter perturbations is compared with the growth index obtained in the concordance paradigm and under the assumption that dark energy does not cluster for a redshift window ranging from the epoch of reionization to the stage of dark-energy dominance. The constraints derived from this analysis are shown to be qualitatively complementary and quantitatively …
During the last century many observations have been made to peep into the dark matter in the universe and many astonishing behaviors of Galaxy clusters have been found which do not fit to any theories formulated before. However, Optical Spectroscopic observation has been initially used to measure the rotational velocity of the Andromeda Galaxy as a function of distance found in contrast to the Law of Gravitation.Due to the expansion of space, electromagnetic radiation emitted in the distant Universe is redshifted on its path towards us which can be used to determine the distances of astronomic…
We investigate tomography of 21-cm brightness temperature fluctuations during the Dark Ages as a probe for constraining primordial non-Gaussianity. We expand the 21- cm brightness temperature up to cubic order in perturbation theory and improve previous models of the signal by including the effect of the free electron fraction. Using modified standard perturbation theory methods that include baryonic pressure effects we derive an improved secondary bispectrum and for the first time derive the secondary trispectrum of 21-cm brightness temperature fluctuations. We then forecast the amount of inf…
Recent measurements of the cosmic microwave background (CMB) anisotropies by Planck provide a sensitive probe of dark matter annihilation during the cosmic dark ages, and specifically constrain the annihilation parameter $f_\mathrm{eff} \langle σv \rangle/m_χ$. Using new results (Paper II) for the ionization produced by particles injected at arbitrary energies, we calculate and provide $f_\mathrm{eff}$ values for photons and $e^+e^-$ pairs injected at keV-TeV energies; the $f_\mathrm{eff}$ value for any dark matter model can be obtained straightforwardly by weighting these results by the spect…
We investigate how the hydrostatic suppression of baryonic accretion affects the growth rate of dark matter halos during the Epoch of Reionization. By comparing halo properties in a simplistic hydrodynamic simulation in which gas only cools adiabatically, with its collisionless equivalent, we find that halo growth is slowed as hydrostatic forces prevent gas from collapsing. In our simulations, at the high redshifts relevant for reionization (between ${\sim}6$ and ${\sim}11$), halos that host dwarf galaxies ($\lesssim 10^{9} \mathrm{M_\odot}$) can be reduced by up to a factor of 2 in mass due t…
