We describe a combined halo model to constrain the distribution of neutral hydrogen (H I) in the post-reionization universe. We combine constraints from the various probes of H I at different ...redshifts: the low-redshift 21-cm emission line surveys, intensity mapping experiments at intermediate redshifts, and the Damped Lyman-Alpha (DLA) observations at higher redshifts. We use a Markov Chain Monte Carlo approach to combine the observations and place constraints on the free parameters in the model. Our best-fitting model involves a relation between neutral hydrogen mass Math Processing ErrorMHI and halo mass M with a non-unit slope, and an upper and a lower cutoff. We find that the model fits all the observables but leads to an underprediction of the bias parameter of DLAs at z ~ 2.3. We also find indications of a possible tension between the H I column density distribution and the mass function of H I-selected galaxies at z ~ 0. We provide the central values of the parameters of the best-fitting model so derived. We also provide a fitting form for the derived evolution of the concentration parameter of H I in dark matter haloes, and discuss the implications for the redshift evolution of the H I-halo mass relation.
Abstract
The neutral hydrogen (H i) content of dark matter haloes forms an intermediate state in the baryon cycle that connects the hot shock-heated gas and cold star-forming gas in haloes. ...Measurement of the relationship between H i mass and halo mass therefore puts important constraints on galaxy formation models. We combine radio observations of H i in emission at low redshift (z ∼ 0) with optical/UV observations of H i in absorption at high redshift (1 < z < 4) to derive constraints on the evolution of the H i-mass–halo-mass (HIHM) relation from redshift z = 4 to 0. We find that one can model the HIHM relation similar to the stellar-mass–halo-mass (SHM) relation at z ∼ 0. At z = 0, haloes with mass 1011.7 M⊙ have the highest H i mass fraction (∼1 per cent), which is about four times smaller than their stellar-mass fraction. We model the evolution of the HIHM relation in a manner similar to that of the SHM relation. Combining this parametrization with a redshift- and mass-dependent modified Navarro–Frenk–White profile for the H i density within a halo, we draw constraints on the evolution of the HIHM relation from the observed H i column density, incidence rate and clustering bias at high redshift. We compare these findings with results from hydrodynamical simulations and other approaches in the literature and find the models to be consistent with each other at the 68 per cent confidence level.
A unique feature of gravity is its ability to control the information accessible to any specific observer. We quantify the notion of cosmic information (‘CosmIn’) for an eternal observer in the ...universe. Demanding the finiteness of CosmIn requires the universe to have a late-time accelerated expansion. Combining the introduction of CosmIn with generic features of the quantum structure of spacetime (e.g., the holographic principle), we present a holistic model for cosmology. We show that (i) the numerical value of the cosmological constant, as well as (ii) the amplitude of the primordial, scale invariant, perturbation spectrum can be determined in terms of a single free parameter, which specifies the energy scale at which the universe makes a transition from a pre-geometric phase to the classical phase. For a specific value of the parameter, we obtain the correct results for both (i) and (ii). This formalism also shows that the quantum gravitational information content of spacetime can be tested using precision cosmology.
We illustrate the observability of the end stages of the earliest (Population III) stars at high redshifts
z
≳
10
, using the recently observed transient, GN-z11-flash as an example. We find that the ...observed spectrum of this transient is consistent with its originating from a shock-breakout in a Population III supernova occurring in the GN-z11 galaxy at
z
∼
11
. The energetics of the explosion indicate a progenitor star of mass
∼
300
M
⊙
in that galaxy, with of order unity such events expected over an observing timescale of a few years. We forecast the expected number of such transients from
z
>
10
galaxies as a function of their host stellar mass and star formation rate. Our findings are important in the context of future searches to detect and identify the signatures of galaxies at Cosmic Dawn.
ABSTRACT
We combine the latest observationally motivated constraints on stellar properties in dark matter haloes, along with data-driven predictions for the atomic (H I) and molecular (H2) gas ...evolution in galaxies, to derive empirical relationships between the build-up of galactic components and their evolution over cosmic time. At high redshift (z ≳ 4), the frameworks imply that galaxies acquire their cold gas (both atomic and molecular) mostly by accretion, with the fraction of cold gas reaching about 20 per cent of the cosmic baryon fraction. We infer a strong dependence of the star formation rate on the H2 mass, suggesting a near-universal depletion time-scale of 0.1–1 Gyr in Milky Way-sized haloes (of masses 1012 M⊙ at z = 0). There is also evidence for a near-universality of the Kennicutt–Schmidt relation across redshifts, with very little dependence on stellar mass, if a constant conversion factor (αCO) of CO luminosity to molecular gas mass is assumed. Combining the atomic and molecular gas observations with the stellar build-up illustrates that galactic mass assembly in Milky Way-sized haloes proceeds from smooth accretion at high redshifts towards becoming merger-dominated at late times (z ≲ 0.6). Our results can be used to constrain numerical simulations of the dominant growth and accretion processes of galaxies over cosmic history.
Abstract
We predict the X-ray background (XRB) expected from the population of quasars detected by the James Webb Space Telescope spectroscopic surveys over the redshift range
z
∼ 4–7. We find that ...the measured UV emissivities imply a ∼10 times higher unresolved XRB than constrained by current experiments. We illustrate the difficulty of simultaneously matching the faint end of the quasar luminosity function and the XRB constraints. We discuss possible origins and consequences of this discrepancy.
We infer the evolution of the UV luminosities of galaxies in haloes of masses 10 ^10 –10 ^11 M _⊙ in the redshift range of z ∼ 9–16 from the recent JWST data. Within the standard ΛCDM cosmological ...model, it is found that the average luminosities in this halo mass range show an exponential evolution with redshift, in excess of that expected from astrophysical considerations including the evolution of UV luminosity from Population III galaxies. We find that an enhancement of power on scales k ∼ 1 Mpc ^−1 , as captured by a cosmological transfer function modified from the ΛCDM form, is able to alleviate this effect and allow for a nonevolving UV luminosity as a function of redshift at z > 10, consistently with the corresponding findings for lower redshifts. We discuss the possible astrophysical and cosmological reasons for such an enhancement.
Abstract
We use the measured scattering timescales of fast radio bursts (FRBs) from the CHIME catalog to derive an upper limit on the magnetic field on subkiloparsec scales in the intergalactic ...medium (IGM). A nonmagnetized, photoionized IGM is insufficient to explain the turbulent scattering at all redshifts, with a warm-hot component being marginally consistent with the data at
z
∼ 1. Accounting for the lower envelope of the temporal smearing distribution with a nonzero magnetic field leads to upper limits
B
< 10–30 nG on scales of 0.07–0.20 kpc in the IGM at
z
∼ 1–2. Our work introduces a novel technique to constrain small-scale magnetic fields in the IGM, in a regime unexplored by the rotation and dispersion measures of FRBs.
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