1,721,017 research outputs found
The role of Pop III stars and early black holes in the 21-cm signal from Cosmic Dawn
No full textModeling the 21-cm global signal from the Cosmic Dawn is challenging due to the many poorly constrained physical processes that come into play. We address this problem using the semi-analytical code 'Cosmic Archaeology Tool' (CAT). CAT follows the evolution of dark matter haloes tracking their merger history and provides an ab initio description of their baryonic evolution, starting from the formation of the first (Pop III) stars and black holes (BHs) in mini-haloes at z > 20. The model is anchored to observations of galaxies and AGN at z < 6 and predicts a reionization history consistent with constraints. In this work, we compute the evolution of the mean global 21-cm signal between 4 ≤ z ≤ 40 based on the rate of formation and emission properties of stars and accreting BHs. We obtain an absorption profile with a maximum depth δTb = -95 mK at z ~ 26.5 (54 MHz). This feature is quickly suppressed turning into an emission signal at z = 20 due to the contribution of accreting BHs that efficiently heat the intergalactic medium (IGM) at z < 27. The high-z absorption feature is caused by the early coupling between the spin and kinetic temperature of the IGM induced by Pop III star formation episodes in mini-haloes. Once we account for an additional radio background from early BHs, we are able to reproduce the timing and the depth of the EDGES signal only if we consider a smaller X-ray background from accreting BHs, but not the shape
Dark-ages reionization and galaxy formation simulation – XVI. The thermal memory of reionization
No full textIntergalactic medium temperature is a powerful probe of the epoch of reionization, as information is retained long after reionization itself. However, mean temperatures are highly degenerate with the timing of reionization, with the amount heat injected during the epoch, and with the subsequent cooling rates. We post-process a suite of semi-analytic galaxy formation models to characterize how different thermal statistics of the intergalactic medium can be used to constrain reionization. Temperature is highly correlated with redshift of reionization for a period of time after the gas is heated. However as the gas cools, thermal memory of reionization is lost, and a power-law temperature–density relation is formed, T = T0(1 + δ)1 − γ with γ ≈ 1.5. Constraining our model against observations of electron optical depth and temperature at mean density, we find that reionization likely finished at
with a soft spectral slope of
. By restricting spectral slope to the range [0.5, 2.5] motivated by population II synthesis models, reionization timing is further constrained to
. We find that, in the future, the degeneracies between reionization timing and background spectrum can be broken using the scatter in temperatures and integrated thermal history
Dark-ages Reionization and Galaxy Formation Simulation – XIV. Gas accretion, cooling, and star formation in dwarf galaxies at high redshift
Full text linkDark-ages reionization and galaxy formation simulation – IV. UV luminosity functions of high-redshift galaxies
Full text linkDark-ages reionization and galaxy-formation simulation – VII. The sizes of high-redshift galaxies
No full textDark-ages reionization and galaxy formation simulation - XII. Bubbles at dawn
Full text linkThe direct detection of regions of ionized hydrogen (H II) 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 will be too small to be detected, we find that by stacking redshifted 21-cm spectra centred on known galaxies, it will be possible to directly detect the EoR at z ~ 9-12, and to place qualitative constraints on the evolution of the spin temperature of the intergalactic medium (IGM) at z ≳ 9. In particular, given a detection of ionized bubbles using this technique, it is possible to determine if the IGM surrounding them is typically in absorption or emission. Determining the globally averaged neutral fraction of the IGM using this method will prove more difficult due to degeneracy with the average size of HII regions
Dark-ages reionization and galaxy formation simulation - XIII. AGN quenching of high-redshift star formation in ZF-COSMOS-20115
Full text linkMassive quiescent galaxies (MQGs) are thought to have formed stars rapidly at early times followed by a long period of quiescence. The recent discovery of aMQG, ZF-COSMOS-20115 at z ~ 4, only 1.5 Gyr after the big bang, places new constraints on galaxy growth and the role of feedback in early star formation. Spectroscopic follow-up confirmed ZF-COSMOS- 20115 as a MQG at z = 3.717 with an estimated stellar mass of ~1011 M⊙, showing no evidence of recent star formation. We use the MERAXES semi-analytic model to investigate how ZF-COSMOS-20115 analogues build stellar mass, and why they become quiescent. We identify three analogue galaxies with similar properties to ZF-COSMOS-20115. We find that ZF-COSMOS-20115 is likely hosted by a massive halo with virial mass of ~1013M⊙, having been through significant mergers at early times. These merger events drove intense growth of the nucleus, which later prevented cooling and quenched star formation. Therefore, ZFCOSMOS- 20115 is unlikely to have experienced strong or extended star formation events at z < 3.7.We find that the analogues host the most massive black holes in our simulation and were luminous quasars at z ~ 5, indicating that ZF-COSMOS-20115 and other MQGs may be the descendants of high-redshift quasars. In addition, themodel suggests that ZF-COSMOS-20115 formed in a region of intergalactic medium that was reionized early
Dark-ages reionization and galaxy formation simulation V: morphology and statistical signatures of reionization
Full text linkDark-ages Reionization & Galaxy Formation Simulation VIII. Suppressed growth of dark matter halos during the Epoch of Reionization
Full text linkWe investigate how the hydrostatic suppression of baryonic accretion affects the growth rate of dark matter haloes 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 ∼6 and ∼11), haloes that host dwarf galaxies (≲109 M⊙) can be reduced by up to a factor of 2 in mass due to the hydrostatic pressure of baryons. Consequently, the inclusion of baryonic effects reduces the amplitude of the low-mass tail of the halo mass function by factors of 2–4. In addition, we find that the fraction of baryons in dark matter haloes hosting dwarf galaxies at high redshift never exceeds ∼90 per cent of the cosmic baryon fraction. When implementing baryonic processes, including cooling, star formation, supernova feedback and reionization, the suppression effects become more significant with further reductions of 30–60 per cent. Although convergence tests suggest that the suppression may become weaker in higher resolution simulations, this suppressed growth will be important for semi-analytic models of galaxy formation, in which the halo mass inherited from an underlying N-body simulation directly determines galaxy properties. Based on the adiabatic simulation, we provide tables to account for these effects in N-body simulations and present a modification of the halo mass function along with explanatory analytic calculations
Dark-ages reionization and galaxy formation simulation – III. Modelling galaxy formation and the epoch of reionization
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