Cosmology

Abstract:

Radio continuum emission provides a unique opportunity to study star-formation unbiased by dust obscuration. However, if radio observations are to be used to accurately trace star-formation to high redshifts, it is crucial that the physical processes which affect the radio emission from star-forming galaxies are well understood. While inverse Compton (IC) losses from the cosmic microwave background (CMB) are negligible in the local universe, the rapid increase in the strength of the CMB energy density with redshift [∼(1 + z)4] means that this effect becomes increasingly important at z ≳ 3. Using a sample of ∼200, 000 high-redshift (3 < z < 5) Lyman-break galaxies selected in the rest-frame ultraviolet (UV), we have stacked radio observations from the MIGHTEE survey to estimate their 1.4-GHz flux densities. We find that for a given rest-frame UV magnitude, the 1.4-GHz flux density and luminosity decrease with redshift. We compare these results to the theoretical predicted effect of energy losses due to inverse Compton scattering off the CMB, and find that the observed decrease is consistent with this explanation. We discuss other possible causes for the observed decrease in radio flux density with redshift at a given UV magnitude, such as a top-heavy initial mass function at high redshift or an evolution of the dust properties, but suggest that inverse Compton scattering is the most compelling explanation.

Abstract:

We measure the cross-correlation between cosmic shear from the third-year release of the Dark Energy Survey, thermal Sunyaev-Zel’dovich (tSZ) maps from , and x-ray maps from ROSAT. We investigate the possibility of developing a physical model able to jointly describe both measurements, simultaneously constraining the spatial distribution and thermodynamic properties of hot gas. We find that a relatively simple model is able to describe both sets of measurements and to make reasonably accurate predictions for other observables (the tSZ autocorrelation, its cross-correlation with x-rays, and tomographic measurements of the bias-weighted mean gas pressure). We show, however, that contamination from x-ray active galactic nuclei (AGN), as well as the impact of nonthermal pressure support, must be incorporated in order to fully resolve tensions in parameter space between different data combinations. Combining the tSZ and x-ray cross-correlations with cosmic shear we obtain simultaneous constraints on the mass scale at which half of the gas content has been expelled from the halo, ${\log }_{10}{M}_c=14.83_{-0.23}^{+0.16}$ , on the polytropic index of the gas, $\mathrm{\Gamma }=1.144_{-0.013}^{+0.016}$ , and on the ratio of the central gas temperature to the virial temperature ${\alpha }_T=1.30_{-0.28}^{+0.15}$ , marginalizing over AGN contributions to the signal.

Abstract:

Recent observations by James Webb Space Telescope reveal an unexpectedly abundant population of rapidly growing supermassive black holes (SMBHs) in the early Universe, underscoring the need for improved models for their origin and growth. Employing new full radiative transfer hydrodynamical simulations of galaxy formation, we investigate the local and intergalactic feedback of SMBH progenitors for the Population III.1 (Pop III.1) scenario, i.e. efficient formation of supermassive stars from pristine, undisturbed dark matter minihaloes. Our cosmological simulations capture the R-type expansion phase of these Pop III.1 stars, with their H-ionizing photon luminosities of generating H ii regions that extend deep into the intergalactic medium, reaching comoving radii of . We vary both the Pop III.1 ionization flux and cosmological formation environments, finding the former regulates their final , whereas the latter is more important in setting their formation redshift. We use the results from our radiation-hydrodynamics simulations to estimate the cosmic number density of SMBHs, , expected from Pop III.1 progenitors. We find , consistent with the results inferred from recent observations of the local and high-redshift universe. Overall, this establishes Pop III.1 progenitors as viable candidates for the formation of the first SMBH, and emphasizes the importance of exploring heavy mass seed scenarios.

Abstract:

Abstract In this work we study a robust, Ks-band complete, spectroscopically-confirmed sample of 104 unobscured (Type-1) quasars within the COSMOS and XMM-LSS fields of the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey, at 0.60 < zspec < 3.41. The quasars are selected via gJKs colour-space and, with 1.3-GHz flux-densities reaching rms ≈ 3.0 μ Jy beam−1, we find a radio-loudness fraction of 5percnt. Thanks to the deep, multiwavelength datasets that are available over these fields, the properties of radio-loud and radio-quiet quasars can be studied in a statistically-robust way, with the emphasis of this work being on the active-galactic-nuclei (AGN)-related and star-formation-related contributions to the total radio emission. We employ multiple star-formation-rate estimates for the analysis so that our results can be compared more-easily with others in the literature, and find that the fraction of sources that have their radio emission dominated by the AGN crucially depends on the SFR estimate that is derived from the radio luminosity. When redshift dependence is not taken into account, a larger fraction of sources is classed as having their radio emission dominated by the AGN. When redshift dependence is considered, a larger fraction of our sample is tentatively classed as ‘starbursts’. We also find that the fraction of (possible) starbursts increases with redshift, and provide multiple suggestions for this trend.

Abstract:

Early JWST photometric studies discovered a population of UV-faint ( 700 Å) exclude the most metal-poor efficient ionizers and favor (1) more chemically enriched systems with comparable extreme radiation fields and (2) older starbursting systems. In contrast, metallicity degeneracies are reduced in Hα space, enabling the identification of these metal-poor efficient ionizers by their specific star formation rate.