We explore the galaxy formation physics governing the low-mass end of the H i mass function in the local Universe. Specifically, we predict the effects on the H i mass function of varying (i) the ...strength of photoionization feedback and the redshift of the end of the epoch of reionization, (ii) the cosmology, (iii) the supernovae feedback prescription and (iv) the efficiency of star formation. We find that the shape of the low-mass end of the H i mass function is most affected by the critical halo mass below which galaxy formation is suppressed by photoionization heating of the intergalactic medium. We model the redshift dependence of this critical dark matter halo mass by requiring a match to the low-mass end of the H i mass function. The best-fitting critical dark matter halo mass decreases as redshift increases in this model, corresponding to a circular velocity of ∼50 km s−1 at z = 0, ∼30 km s−1 at z ∼ 1 and ∼12 km s−1 at z = 6. We find that an evolving critical halo mass is required to explain both the shape and abundance of galaxies in the H i mass function below
$M_{\rm H\,\small {I}} \sim 10^{8} \,h^{-2}\,{\rm M_{{\odot }}}$
. The model makes specific predictions for the clustering strength of H i-selected galaxies with H i masses >106 and >107 h
−2 M⊙ and for the relation between the H i and stellar mass contents of galaxies which will be testable with upcoming surveys with the Square Kilometre Array and its pathfinders. We conclude that measurements of the H i mass function at z ≥ 0 will lead to an improvement in our understanding of the net effect of photoionization feedback on galaxy formation and evolution.
Abstract
We present a theoretical study of intergalactic metal absorption lines imprinted in the spectra of distant quasars during and after the Epoch of Reionization (EoR). We use high-resolution ...hydrodynamical simulations at high redshift (4 < z < 8), assuming a uniform UV background Haardt–Madau 12, post-processing with cloudy photoionization models and Voigt profile fitting to accurately calculate column densities of the ions C ii, C iv, Si ii, Si iv and O i in the intergalactic medium (IGM). In addition, we generate mock observations of neutral hydrogen (H i) at z < 6. Our simulations successfully reproduce the evolution of the cosmological mass density (Ω) of C ii and C iv, with
$\Omega _{\rm {C\,\small {II}}}$
exceeding
$\Omega _{\rm {C\,\small {IV}}}$
at z > 6, consistent with the current picture of the tail of the EoR. The simulated C ii exhibits a bimodal distribution with large absorptions in and around galaxies, and some traces in the lower density IGM. We find some discrepancies between the observed and simulated column density relationships among different ionic species at z = 6, probably due to uncertainties in the assumed UV background. Finally, our simulations are in good agreement with observations of the H i column density distribution function at z = 4 and the H i cosmological mass density
$\Omega _{\rm {H\,\small {I}}}$
at 4 < z < 6.
ABSTRACT
Before the end of the Epoch of Reionization, the Hydrogen in the Universe was predominantly neutral. This leads to a strong attenuation of Ly α lines of z ≳ 6 galaxies in the intergalactic ...medium. Nevertheless, Ly α has been detected up to very high redshifts (z ∼ 9) for several especially UV luminous galaxies. Here, we test to what extent the galaxy’s local environment might impact the Ly α transmission of such sources. We present an analysis of dedicated Hubble Space Telescope (HST) imaging in the CANDELS/EGS field to search for fainter neighbours around three of the most UV luminous and most distant spectroscopically confirmed Ly α emitters: EGS-zs8-1, EGS-zs8-2, and EGSY-z8p7 at zspec = 7.73, 7.48, and 8.68, respectively. We combine the multiwavelength HST imaging with Spitzer data to reliably select z ∼ 7–9 galaxies around the central, UV-luminous sources. In all cases, we find a clear enhancement of neighbouring galaxies compared to the expected number in a blank field (by a factor ∼3–9×). Our analysis thus reveals ubiquitous overdensities around luminous Ly α emitting sources in the heart of the cosmic reionization epoch. We show that our results are in excellent agreement with expectations from the Dragons simulation, confirming the theoretical prediction that the first ionized bubbles preferentially formed in overdense regions. While three UV luminous galaxies already have spectroscopic redshifts, the majority of the remaining fainter, surrounding sources are yet to be confirmed via spectroscopy. JWST follow-up observations of the neighbouring galaxies identified here will thus be needed to confirm their physical association and to map out the ionized regions produced by these sources.
We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 ...and 17.9 (113 and 75 MHz). 3 h of observations were conducted over two nights with significantly different levels of ionospheric activity. We use these data to assess the impact of systematic errors at low frequency, including the ionosphere and radio-frequency interference, on a power spectrum measurement. We find that after the 1–3 h of integration presented here, our measurements at the Murchison Radio Observatory are not limited by RFI, even within the FM band, and that the ionosphere does not appear to affect the level of power in the modes that we expect to be sensitive to cosmology. Power spectrum detections, inconsistent with noise, due to fine spectral structure imprinted on the foregrounds by reflections in the signal-chain, occupy the spatial Fourier modes where we would otherwise be most sensitive to the cosmological signal. We are able to reduce this contamination using calibration solutions derived from autocorrelations so that we achieve an sensitivity of 104 mK on comoving scales k ≲ 0.5 h Mpc−1. This represents the first upper limits on the 21 cm power spectrum fluctuations at redshifts 12 ≲ z ≲ 18 but is still limited by calibration systematics. While calibration improvements may allow us to further remove this contamination, our results emphasize that future experiments should consider carefully the existence of and their ability to calibrate out any spectral structure within the EoR window.
Absorption spectra of high-redshift quasars suggest that the reionization of cosmic hydrogen was complete near z∼ 6. The dominant sources of ionizing photons responsible for this reionization are ...generally thought to be stars and quasars. In this paper we make a quantitative estimate of the relative contributions made by these sources. Our approach is to compute the evolution of the post-overlap ionizing background radiation by combining semi-analytic descriptions of reionization in a clumpy medium with a model for the quasar luminosity function. Our overall model has two free parameters, the star formation efficiency and the minimum quasar luminosity. By adjusting these parameters, we constrain the relative contributions made by stars and quasars through comparison with reported observations. We find that the relative quasar contribution (at z= 5.7) to the ionizing background was between 1.4 and 14.5 per cent. The range of uncertainty is dominated by the unknown minimum quasar luminosity.
Several gravitationally lensed quasars are observed with anomalous magnifications in pairs of images that straddle a critical curve. Simple theoretical arguments suggest that the magnification of ...these images should be approximately equivalent, whereas one image is observed to be significantly demagnified. Microlensing provides a possible explanation for this discrepancy. There are two key parameters when modelling this effect. The first, the fraction of smooth matter in the lens at the image positions, has been explored by Schechter & Wambsganss. They have shown that the anomalous flux ratio observed in the lensed quasar MG 0414+0534 is a priori a factor of 5 more likely if the assumed smooth matter content in the lens model is increased from 0 to 93 per cent. The second parameter, the size of the emission region, is explored in this paper, and shown to be more significant. We find that the broadening of the magnification probability distributions due to smooth matter content is washed out for source sizes that are predicted by standard models for quasars. We apply our model to the anomalous lensed quasar MG 0414+0534, and find a 95 per cent upper limit of 2.62 × 1016 h−1/270 (M/M⊙)1/2 cm on the radius of the I‐band emission region. The smooth matter percentage in the lens is unconstrained.
ABSTRACT Detection of 21 cm emission of H i from the epoch of reionization, at redshifts , is limited primarily by foreground emission. We investigate the signatures of wide-field measurements and an ...all-sky foreground model using the delay spectrum technique that maps the measurements to foreground object locations through signal delays between antenna pairs. We demonstrate interferometric measurements are inherently sensitive to all scales, including the largest angular scales, owing to the nature of wide-field measurements. These wide-field effects are generic to all observations but antenna shapes impact their amplitudes substantially. A dish-shaped antenna yields the most desirable features from a foreground contamination viewpoint, relative to a dipole or a phased array. Comparing data from recent Murchison Widefield Array observations, we demonstrate that the foreground signatures that have the largest impact on the H i signal arise from power received far away from the primary field of view. We identify diffuse emission near the horizon as a significant contributing factor, even on wide antenna spacings that usually represent structures on small scales. For signals entering through the primary field of view, compact emission dominates the foreground contamination. These two mechanisms imprint a characteristic pitchfork signature on the "foreground wedge" in Fourier delay space. Based on these results, we propose that selective down-weighting of data based on antenna spacing and time can mitigate foreground contamination substantially by a factor of ∼100 with negligible loss of sensitivity.
ABSTRACT We present the 21 cm power spectrum analysis approach of the Murchison Widefield Array Epoch of Reionization project. In this paper, we compare the outputs of multiple pipelines for the ...purpose of validating statistical limits cosmological hydrogen at redshifts between 6 and 12. Multiple independent data calibration and reduction pipelines are used to make power spectrum limits on a fiducial night of data. Comparing the outputs of imaging and power spectrum stages highlights differences in calibration, foreground subtraction, and power spectrum calculation. The power spectra found using these different methods span a space defined by the various tradeoffs between speed, accuracy, and systematic control. Lessons learned from comparing the pipelines range from the algorithmic to the prosaically mundane; all demonstrate the many pitfalls of neglecting reproducibility. We briefly discuss the way these different methods attempt to handle the question of evaluating a significant detection in the presence of foregrounds.
Abstract
We present a theoretical model to predict the properties of an observed z = 5.72 Lyman α emitter galaxy–C iv absorption pair separated by 1384 comoving kpc h
−1. We use the separation of the ...pair and an outflow velocity/time travelling argument to demonstrate that the observed galaxy cannot be the source of metals for the C iv absorber. We find a plausible explanation for the metal enrichment in the context of our simulations: a dwarf galaxy with M
⋆ = 1.87 × 109 M⊙ located 119 comoving kpc h
−1 away with a wind velocity of ∼100 km s−1 launched at z ∼ 7. Such a dwarf (M
UV = −20.5) is fainter than the detection limit of the observed example. In a general analysis of galaxy–C iv absorbers, we find galaxies with − 20.5 <M
UV < −18.8 are responsible for the observed metal signatures. In addition, we find no correlation between the mass of the closest galaxy to the absorber and the distance between them, but a weak anti-correlation between the strength of the absorption and the separation of galaxy–absorber pairs.
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