High-redshift Sources Research Articles

Characterizing gravitational wave detector networks: from A♯ to cosmic explorer

Abstract Gravitational-wave observations by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo have provided us a new tool to explore the Universe on all scales from nuclear physics to the cosmos and have the massive potential to further impact fundamental physics, astrophysics, and cosmology for decades to come. In this paper we have studied the science capabilities of a network of LIGO detectors when they reach their best possible sensitivity, called A#, given the infrastructure in which they exist and a new generation of observatories that are factor of 10 to 100 times more sensitive (depending on the frequency), in particular a pair of L-shaped Cosmic Explorer observatories (one 40 km and one 20 km arm length) in the US and the triangular Einstein Telescope with 10 km arms in Europe. We use science metrics derived from the top priorities of several funding agencies to characterize the science capabilities of different networks. The presence of one or two A# observatories in a network containing two or one next generation observatories, respectively, will provide good localization capabilities for facilitating multimessenger astronomy and precision measurement of the Hubble parameter. Two Cosmic Explorer observatories are indispensable for achieving precise localization of binary neutron stars, facilitating detection of electromagnetic counterparts and transforming multimessenger astronomy. Their combined operation is even more important in the detection and localization of high-redshift sources, such as binary neutron stars, beyond the star-formation peak, and primordial black hole mergers, which may occur roughly 100 million years after the Big Bang. The addition of the Einstein Telescope to a network of two Cosmic Explorer observatories is critical for accomplishing all the identified science metrics. For most metrics the triple network of next generation terrestrial observatories are a factor 100 better than what can be accomplished by a network of three A# observatories.

Lyα Profile Shape as an Escape-fraction Diagnostic at High Redshift

While the shape of the Lyα profile is viewed as one of the best tracers of ionizing-photon escape fraction (f esc) within low-redshift (z ∼ 0.3) surveys of the Lyman continuum, this connection remains untested at high redshift. Here, we combine deep, rest-UV Keck/LRIS spectra of 80 objects from the Keck Lyman Continuum Spectroscopic Survey with rest-optical Keck/MOSFIRE spectroscopy in order to examine potential correlations between Lyα profile shape and the escape of ionizing radiation within z ∼ 3 star-forming galaxies. We measure the velocity separation between double-peaked Lyα emission structure (v sep), between red-side Lyα emission peaks and systemic (v Lyα,red), and between red-side emission peaks and low-ionization interstellar absorption lines (v Lyα−LIS). We find that the IGM-corrected ratio of ionizing to nonionizing flux density is significantly higher in KLCS objects with lower v Lyα,red. We find no significant trend between measures of ionizing-photon escape and v Lyα−LIS. We compare our results to measurements of z ∼ 0.3 “Green Peas” from the literature and find that KLCS objects have larger v sep at fixed v Lyα,red, larger f esc at fixed v Lyα,red, and higher v Lyα,red overall than z ∼ 0.3 analogs. We conclude that the Lyα profile shapes of our high-redshift sources are fundamentally different, and that measurements of profile shape such as v Lyα,red map on to f esc in different ways. We caution against building reionization-era f esc diagnostics based purely on Lyα profiles of low-redshift dwarf galaxies. Tracing v sep, v Lyα,red, and f esc in a larger sample of z ∼ 3 galaxies will reveal how these variables may be connected for galaxies at the epoch of reionization.

New AGN diagnostic diagrams based on the [OIII]lambda4363 auroral line

The James Webb Space Telescope (JWST) is revolutionizing our understanding of black hole formation and growth in the early Universe. However, JWST has also revealed that some of the classical diagnostics, such as the Baldwin, Phillips Terlevich (BPT) diagrams and X-ray emission, often fail to identify active galactic nuclei (AGN) at high redshift and low metallicity. Here we present three new rest-frame optical diagnostic diagrams to identify narrow-line Type II AGN, leveraging the auroral line, which has been detected in several JWST spectra. Specifically, we show that high values of the ratio provide a sufficient (but not necessary) condition to identify the presence of an AGN, based on empirical calibrations (using local and high-redshift sources) and on a broad range of photoionization models. These diagnostics are able to separate much of the AGN population from star-forming galaxies (SFGs): the average energy of an AGN's ionizing photons is higher than that of young stars in SFGs, and hence AGN can more efficiently heat the gas, thus boosting the line. We also found independent indications of AGN activity in some high-redshift sources (z>4) that were not previously identified as AGN with the traditional diagnostics diagrams, but that are placed in the AGN region of the diagnostic presented in this work. We note, conversely, that low values of can be associated either with SFGs or AGN excitation. We note that the fact that strong auroral lines are often associated with AGN does not imply that they cannot be used for direct metallicity measurements (provided that proper ionization corrections are applied), but it does affect the calibration of strong line metallicity diagnostics.

Constraining the Clustering and 21 cm Signature of Radio Galaxies at Cosmic Dawn

The efficiency of radio emission is an important unknown parameter of early galaxies at cosmic dawn, as models with high efficiency have been shown to modify the cosmological 21 cm signal substantially, deepening the absorption trough and boosting the 21 cm power spectrum. Such models have been previously directly constrained by the overall extragalactic radio background, as observed by Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission 2 and Long Wavelength Array. In this work, we constrain the clustering of high-redshift radio sources by utilizing the observed upper limits on arcminute-scale anisotropy from the Very Large Array at 4.9 GHz and Australia Telescope Compact Array at 8.7 GHz. Using a seminumerical simulation of a plausible astrophysical model for illustration, we show that the clustering constraints on the radio efficiency are much stronger than those from the overall background intensity by a factor that varies between 18 and 55 in the redshift range of 7–22. As a result, the predicted maximum depth of the global 21 cm signal is lowered by a factor of 6 (to 1400 mK), and the maximum 21 cm power spectrum peak at cosmic dawn is lowered by a factor of 45 (to 1.3 × 105 mK2). We conclude that the observed clustering is the strongest current direct constraint on such models, but strong early radio emission from galaxies remains viable for producing a strongly enhanced 21 cm signal from cosmic dawn.

The radio properties of z>3.5 quasars: Are most high-redshift radio-loud active galactic nuclei obscured?

We explore the radio properties of powerful (rest-frame luminosity $ at 500 MHz) high-redshift ($z 3.5$) quasars. The aim of this study is to gain a better understanding of radio-loud sources at the epoch when they reach the highest space density. We selected 29 radio-loud quasars at low radio frequencies (76 MHz). Their radio spectra, covering the range from 76 MHz to 5 GHz, are generally well reproduced by a single power law. We created samples that were matched in radio luminosity at lower redshift (from $z to $z to investigate any spectral evolution. We find that the fraction of flat-spectrum radio quasars (FSRQs) strongly increases with redshift (from $ 8<!PCT!>$ at z=1.2 to $ 45<!PCT!>$ at z$>$3.5). This effect is also observed in quasars with lower luminosities (down to $ The increase in the fraction of FSRQs with redshift corresponds to a decrease in the steep- spectrum radio quasars. This result can be explained when we assume that the beaming factor and the slope of the luminosity function do not change with redshift and if high-redshift radio-loud sources can be recognized as quasars only when they are seen at a small viewing angle ($ but most of them, about 90<!PCT!> are obscured in the UV and optical bands. We also found a trend for the size of radio sources to decrease with increasing redshift. Because projection effects are insufficient to cause this trend, we suggest that the large amount of gas causing the nuclear obscuration also hampers the growth of the more distant sources.

Constraints on the origin of the radio synchrotron background via angular correlations

ABSTRACT The origin of the radio synchrotron background (RSB) is currently unknown. Its understanding might have profound implications in fundamental physics or might reveal a new class of radio emitters. In this work, we consider the scenario in which the RSB is due to extragalactic radio sources and measure the angular cross-correlation of Low-Frequency Array (LOFAR) images of the diffuse radio sky with matter tracers at different redshifts, provided by galaxy catalogues and cosmic microwave background lensing. We compare these measured cross-correlations to those expected for models of RSB sources. We find that low-redshift populations of discrete sources are excluded by the data, while higher redshift explanations are compatible with available observations. We also conclude that at least 20 per cent of the RSB surface brightness level must originate from populations tracing the large-scale distribution of matter in the Universe, indicating that at least this fraction of the RSB is of extragalactic origin. Future measurements of the correlation between the RSB and tracers of high-redshift sources will be crucial to constraining the source population of the RSB.

GA-NIFS: JWST/NIRSpec integral field unit observations of HFLS3 reveal a dense galaxy group at z ∼ 6.3

Massive, starbursting galaxies in the early Universe represent some of the most extreme objects in the study of galaxy evolution. One such source is HFLS3 (z ∼ 6.34), which was originally identified as an extreme starburst galaxy with mild gravitational magnification (μ ∼ 2.2). Here, we present new observations of HFLS3 with the JWST/NIRSpec integral field unit in both low (PRISM/CLEAR; R ∼ 100) and high spectral resolution (G395H/290LP; R ∼ 2700), with high spatial resolution (∼0.1″) and sensitivity. Using a combination of the NIRSpec data and a new lensing model with accurate spectroscopic redshifts, we find that the 3″ × 3″ field is crowded, with a lensed arc (C, z = 6.3425 ± 0.0002), two galaxies to the south (S1 and S2, z = 6.3592 ± 0.0001), two galaxies to the west (W1, z = 6.3550 ± 0.0001; W2, z = 6.3628 ± 0.0001), and two low-redshift interlopers (G1, z = 3.4806 ± 0.0001; G2, z = 2.00 ± 0.01). We present spectral fits and morpho-kinematic maps for each bright emission line (e.g. [OIII]λ5007, Hα, and [NII]λ6584) from the R2700 data for all sources except G2 (whose spectral lines fall outside the observed wavelengths of the R2700 data). From a line ratio analysis, we find that the galaxies in component C are likely powered by star formation, though we cannot rule out or confirm the presence of active galactic nuclei in the other high-redshift sources. We performed gravitational lens modelling, finding evidence for a two-source composition of the lensed central object and a magnification factor (μ = 2.1 − 2.4) comparable to findings of previous work. The projected distances and velocity offsets of each galaxy suggest that they will merge within the next ∼1 Gyr. Finally, we examined the dust extinction-corrected SFRHα of each z > 6 source, finding that the total star formation (510 ± 140 M⊙ yr−1, magnification-corrected) is distributed across the six z ∼ 6.34 − 6.36 objects over a region of diameter ∼11 kpc. Altogether, this suggests that HFLS3 is not a single starburst galaxy, but instead a merging system of star-forming galaxies in the epoch of reionisation.

A new derivation of the Hubble constant from γ-ray attenuation using improved optical depths for the Fermi and CTA era

ABSTRACT We present γ-ray optical-depth calculations from a recently published extragalactic background light (EBL) model built from multiwavelength galaxy data from the Hubble Space Telescope Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (HST/CANDELS). CANDELS gathers one of the deepest and most complete observations of stellar and dust emissions in galaxies. This model resulted in a robust derivation of the evolving EBL spectral energy distribution up to z ∼ 6, including the far-infrared peak. Therefore, the optical depths derived from this model will be useful for determining the attenuation of γ-ray photons coming from high-redshift sources, such as those detected by the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope, and for multi-TeV photons that will be detected from nearby sources by the future Cherenkov Telescope Array. From these newly calculated optical depths, we derive the cosmic γ-ray horizon and also measure the expansion rate and matter content of the Universe including an assessment of the impact of the EBL uncertainties. We find H0 = 62.4 $^{+4.1}_{-3.9}$ km s−1 Mpc−1 when fixing Ωm = 0.32, and H0 = 65.1 $^{+6.0}_{-4.9}$ km s−1 Mpc−1 and Ωm = 0.19 ± 0.08, when exploring these two parameters simultaneously.

Mapping the Decline with Redshift of Dusty Star-forming Galaxies Using JWST and SCUBA-2

We use JWST NIRCam observations of the massive lensing cluster field A2744 to develop a red galaxy selection of f F444W > 1 μJy and f F444W/f F150W > 3.5 that picks out all nine >4.5σ Atacama Large Millimeter/submillimeter Array 1.1 or 1.2 mm sources and 17 of the 19 >5σ SCUBA-2 850 μm sources in the covered areas. We show that by using the red galaxies as priors, we can probe deeper in the SCUBA-2 850 μm image. This gives a sample of 44 >3σ SCUBA-2 850 μm sources with accurate positions, photometric redshifts, and magnifications. To investigate why our red galaxy selection picks out the 850 μm sources, we next analyze an extended sample of 167 sources with f F444W > 0.05 μJy and f F444W/f F150W > 3.5. We find that the fainter f F444W sources in this sample are too faint to be detected in the SCUBA-2 850 μm image. We also show that there is a strong drop between z < 4 and z > 4 (a factor of around 5) in the ratio of the far-infrared luminosity estimated from the 850 μm flux to the ν (5000) at rest-frame 5000 Å. We argue that this result may be due to the high-redshift sources having less dust content than the lower-redshift sources.

Tensions with the flat ΛCDM model from high-redshift cosmography

ABSTRACT The longstanding search for the cosmological model that best describes the Universe has been made more intriguing since the recent discovery of the Hubble constant, H0, tension observed between the value of H0 from the Cosmic Microwave Background and from type Ia supernovae (SNe Ia). Hence, the commonly trusted flat Λ cold dark matter (ΛCDM) model is under investigation. In this scenario, cosmography is a very powerful technique to investigate the evolution of the Universe without any cosmological assumption, thus revealing tensions between observational data and predictions from cosmological models in a completely model-independent way. We here employ a robust cosmographic technique based on an orthogonal logarithmic polynomial expansion of the luminosity distance to fit quasars (QSOs) alone and QSOs combined with Gamma-Ray Bursts (GRBs), SNe Ia, and Baryon Acoustic Oscillations. To apply QSOs and GRBs as probes we use, respectively, the Risaliti–Lusso relation between ultraviolet and X-ray luminosities and the ‘Dainotti GRB 3D relation’ among the rest-frame end time of the X-ray plateau emission, its corresponding luminosity, and the peak prompt luminosity. We also correct QSOs and GRBs for selection biases and redshift evolution and we employ both the traditional Gaussian likelihood and the newly discovered best-fitting likelihoods for each probe investigated. This comprehensive analysis reveals a strong tension ($\gt 4 \, \sigma$) between our data sets and the flat ΛCDM model proving the power of both the cosmographic approach and high-redshift sources, such as QSOs and GRBs, which can probe the Universe at early epochs.

Multi-messenger study of merging massive black holes in the OBELISK simulation: Gravitational waves, electromagnetic counterparts, and their link to galaxy and black-hole populations

Massive black-hole (BH) mergers are predicted to be powerful sources of low-frequency gravitational waves (GWs). Coupling the detection of GWs with an electromagnetic (EM) detection can provide key information about merging BHs and their environments as well as cosmology. We study the high-resolution cosmological radiation-hydrodynamics simulation OBELISK, run to redshift z = 3.5, to assess the GW and EM detectability of high-redshift BH mergers, modelling spectral energy distribution and obscuration. For EM detectability, we further consider sub-grid dynamical delays in postprocessing. We find that most of the merger events can be detected by LISA, except for high-mass mergers with very unequal mass ratios. Intrinsic binary parameters are accurately measured, but the sky localisation is poor generally. Only ∼40% of these high-redshift sources have a sky localisation better than 10 deg2. Merging BHs are hard to detect in the restframe UV since they are fainter than the host galaxies, which at high redshift are star-forming. A significant fraction, 15–35%, of BH mergers instead outshine the galaxy in X-rays, and about 5 − 15% are sufficiently bright to be detected with sensitive X-ray instruments. If mergers induce an Eddington-limited brightening, up to 30% of sources can become observable. The transient flux change originating from such a brightening is often large, allowing 4 − 20% of mergers to be detected as EM counterparts. A fraction, 1 − 30%, of mergers are also detectable at radio frequencies. Transients are found to be weaker for radio-observable mergers. Observable merging BHs tend to have higher accretion rates and masses and are overmassive at a fixed galaxy mass with respect to the full population. Most EM-observable mergers can also be GW-detected with LISA, but their sky localisation is generally poorer. This has to be considered when using EM counterparts to obtain information about the properties of merging BHs and their environment.

Quasars: Standard Candles up to z = 7.5 with the Precision of Supernovae Ia

Currently, the Λ cold dark matter model, which relies on the existence of cold dark matter and a cosmological constant Λ, best describes the universe. However, we lack information in the high-redshift (z) region between Type Ia supernovae (SNe Ia; up to z = 2.26) and the cosmic microwave background (z = 1100), an interval crucial to test cosmological models and their possible evolution. We have defined a sample of 983 quasars up to z = 7.54 with a reduced intrinsic dispersion δ = 0.007, which determines the matter density parameter Ω M with the same precision of SNe Ia. Although previous analysis have used quasars as cosmological tools, this is the first time that high-redshift sources, in this case quasars, as standalone cosmological probes yield such tight constraints on Ω M . Our results show the importance of correcting cosmological relationships for selection biases and redshift evolution and how the choice of a golden sample reduces considerably the intrinsic scatter. This proves the reliability of quasars as standard cosmological candles.

Inferring, not just detecting: Metrics for high-redshift sources observed with third-generation gravitational-wave detectors

The detection of black-hole binaries at high redshifts is a cornerstone of the science case of third-generation gravitational-wave interferometers. The star-formation rate peaks at $z\ensuremath{\sim}2$ and decreases by orders of magnitude by $z\ensuremath{\sim}10$. Any confident detection of gravitational waves from such high redshifts would imply either the presence of stars formed from pristine material originating from cosmological nucleosynthesis (the so-called population III stars), or black holes that are the direct relics of quantum fluctuations in the early Universe (the so-called primordial black holes). Crucially, detecting sources at cosmological distances does not imply inferring that sources are located there, with the latter posing more stringent requirements. To this end, we present two figures of merit, which we refer to as ``$z\text{\ensuremath{-}}z$ plot'' and ``inference horizon,'' that quantify the largest redshift one can possibly claim a source to be beyond. We argue that such inference requirements, in addition to detection requirements, should be investigated when quantifying the scientific payoff of future gravitational-wave facilities.

Formation of proto-globular cluster candidates in cosmological simulations of dwarf galaxies at z &amp;gt; 4

ABSTRACT We perform cosmological hydrodynamical simulations to study the formation of proto-globular cluster candidates in progenitors of present-day dwarf galaxies $(M_{\rm vir} \approx 10^{10}\, {\rm M}_\odot$ at z = 0) as part of the ‘Feedback in Realistic Environment’ (FIRE) project. Compact (r1/2 &amp;lt; 30 pc), relatively massive (0.5 × 105 ≲ M⋆/M⊙ ≲ 5 × 105), self-bound stellar clusters form at 11 ≳ z ≳ 5 in progenitors with $M_{\rm vir} \approx 10^9\, \mathrm{M}_{\odot }$. Cluster formation is triggered when at least $10^7\, \mathrm{M}_{\odot }$ of dense, turbulent gas reaches $\Sigma _{\rm gas} \approx 10^4\, {\rm M}_\odot \, {\rm pc}^{-2}$ as a result of the compressive effects of supernova feedback or from cloud–cloud collisions. The clusters can survive for $2-3\, {\rm Gyr}$; absent numerical effects, they could possibly survive substantially longer, perhaps to z = 0. The longest lived clusters are those that form at significant distance – several hundreds of pc – from their host galaxy. We therefore predict that globular clusters forming in progenitors of present-day dwarf galaxies will be offset from any pre-existing stars within their host dark matter haloes as opposed to deeply embedded within a well-defined galaxy. Properties of the nascent clusters are consistent with observations of some of the faintest and most compact high-redshift sources in Hubble Space Telescope lensing fields and are at the edge of what will be detectable as point sources in deep imaging of non-lensed fields with JWST. By contrast, the star clusters’ host galaxies will remain undetectable.

Shortcut in codimension-2 brane cosmology in light of GW170817

In this paper, our universe is regarded as a codimension-2 brane embedded in a noncompact six-dimensional Anti-de Sitter (AdS) spacetime. We derive the gravitational horizon radius on the brane under the low-energy approximation, which reflects how the extra dimensions cause the shortcut effect of gravitational waves (GWs). We also study the time delay between a GW signal and an electromagnetic (EM) wave signal in the low-redshift limit by combining with the joint observations of GW170817 and GRB 170817A, which gives an upper limit to the text {AdS}_{6} radius as ell ^{2}_{~} lesssim 3.84,text {Mpc}^{2}_{~}. For a high-redshift source, the time delay is converted into the discrepancy between the source redshift derived from the GW signal and the one derived from the EM counterpart. It is found that if one expects to detect the EM counterpart of a high-redshift GW event within a reasonable observation time, it requires a stronger constraint on the text {AdS}_{6} radius. Our research shows that the text {AdS}_{6} radius should satisfy ell ^{2}_{~}lesssim 0.02,text {Mpc}^{2}_{~} for the DECIGO and BBO.

High-redshift quasars along the main sequence

Context. The 4D Eigenvector 1 empirical formalism (4DE1) and its main sequence (MS) for quasars has emerged as a powerful tool for organising the diversity among quasar populations, as several key observational measures and physical parameters are systematically changing along it. Aims. Trends revealed by 4DE1 are very well established to explain all the diverse characteristics seen in low-redshift quasar samples. Nevertheless, the situation is far less clear when dealing with high-luminosity and high-redshift sources. Here, we aim to evaluate the behaviour of our sample of 22 quasars at high redshift (2.2 ≤ z ≤ 3.7) and high luminosity (47.39 ≤ Lbol ≤ 48.36) in the context of the 4DE1. Methods. Our approach involves studying quasar physics through a spectroscopic exploration of UV and optical emission line diagnostics. We used new observations from the ISAAC instrument at ESO-VLT and primarily from the SDSS to cover the optical and the UV rest-frames, respectively. The emission lines were characterised both via a quantitative parametrisation of the line profiles and a decomposition of the emission line profiles using multicomponent fitting routines. Results. We provide spectrophotometric properties and line profile measurements for Hβ+[O III]λλ4959,5007, as well as Si IVλ1397+O IV]λ1402, C IVλ1549+He IIλ1640, and the 1900 Å blend (including Al IIIλ1860, Si III]λ1892, and C III]λ1909). For six out of the 22 objects, a significantly blueshifted component on the Hβ profile is present. In 14 out of 22 cases, an Hβ outflowing component associated with [O III] is detected. The majority of [O III]λλ4959,5007 emission line profiles show blueshifted velocities higher than 250 km s−1. We find extremely broad [O III]λλ4959,5007 emission that is comparable to the width of Hβ broad profile in some highly accreting quasars. The [O III]λλ4959,5007 and C IVλ1549 blueshifts show very high amplitudes and a high degree of correlation. The line widths and shifts are correlated for both [O III]λλ4959,5007 and C IVλ1549, suggesting that emission from outflowing gas is providing a substantial broadening effect to both lines. Otherwise, the links between C IVλ1549 centroid velocity at half intensity (c(1/2)), Eddington ratio (L/LEdd), and bolometric luminosity are found to be in agreement with previous studies of high-luminosity quasars. Conclusions. Our analysis suggests that the behaviour of quasars of very high luminosity all along the main sequence is strongly affected by powerful outflows involving a broad range of spatial scales. The main sequence correlations remain valid at high redshift and high luminosity even if a systematic increase in line width is observed. Scaling laws based on UV Al IIIλ1860 and Hβ emission lines are equally reliable estimators of MBH.

Measuring photometric redshifts for high-redshift radio source surveys

Abstract With the advent of deep, all-sky radio surveys, the need for ancillary data to make the most of the new, high-quality radio data from surveys like the Evolutionary Map of the Universe (EMU), GaLactic and Extragalactic All-sky Murchison Widefield Array survey eXtended, Very Large Array Sky Survey, and LOFAR Two-metre Sky Survey is growing rapidly. Radio surveys produce significant numbers of Active Galactic Nuclei (AGNs) and have a significantly higher average redshift when compared with optical and infrared all-sky surveys. Thus, traditional methods of estimating redshift are challenged, with spectroscopic surveys not reaching the redshift depth of radio surveys, and AGNs making it difficult for template fitting methods to accurately model the source. Machine Learning (ML) methods have been used, but efforts have typically been directed towards optically selected samples, or samples at significantly lower redshift than expected from upcoming radio surveys. This work compiles and homogenises a radio-selected dataset from both the northern hemisphere (making use of Sloan Digital Sky Survey optical photometry) and southern hemisphere (making use of Dark Energy Survey optical photometry). We then test commonly used ML algorithms such as k-Nearest Neighbours (kNN), Random Forest, ANNz, and GPz on this monolithic radio-selected sample. We show that kNN has the lowest percentage of catastrophic outliers, providing the best match for the majority of science cases in the EMU survey. We note that the wider redshift range of the combined dataset used allows for estimation of sources up to $z = 3$ before random scatter begins to dominate. When binning the data into redshift bins and treating the problem as a classification problem, we are able to correctly identify $\approx$ 76% of the highest redshift sources—sources at redshift $z &gt; 2.51$ —as being in either the highest bin ( $z &gt; 2.51$ ) or second highest ( $z = 2.25$ ).

Model selection using time-delay lenses

ABSTRACT The sample of time-delay gravitational lenses appropriate for studying the geometry of the Universe continues to grow as dedicated campaigns, such as the Dark Energy Survey, the (Very Large Telescope) VLT Survey Telescope (VST) ATLAS survey, and the Large Synoptic Survey Telescope, complete their census of high-redshift sources. This catalogue now includes hundreds of strong lensing systems, at least 31 of which have reasonably accurate time-delay measurements. In this paper, we use them to compare the predictions of two competing Friedmann–Lemaître–Robertson–Walker models: flat Lambda cold dark matter (ΛCDM), characterized by two adjustable parameters (H0 and Ωm), and the Rh = ct universe (with H0 as the single free variable). Over the past decade, the latter has accounted for the data better than the standard model, most recently the emergence of well-formed galaxies discovered by JWST at cosmic dawn. Here, we show that the current sample of time-delay lenses favours Rh = ct with a likelihood of ∼$84{{\ \rm per\ cent}}$ versus ∼$16{{\ \rm per\ cent}}$ for the standard model. This level of accuracy will greatly improve as the ongoing surveys uncover many thousands of additional lens systems over the next several years.

A search for missing radio sources at z ≳ 4 using Lyman dropouts

ABSTRACT Using the Lyman Dropout technique, we identify 148 candidate radio sources at z ≳ 4–7 from the 887.5 MHz Australian Square Kilometre Array Pathfinder (ASKAP) observations of the GAMA23 field. About 112 radio sources are currently known beyond redshift z ∼ 4. However, simulations predict that hundreds of thousands of radio sources exist in that redshift range, many of which are probably in existing radio catalogues, but do not have measured redshifts, either because their optical emission is too faint or because of the lack of techniques that can identify candidate high-redshift radio sources (HzRSs). Our study addresses these issues using the Lyman Dropout search technique. This newly built sample probes radio luminosities that are 1–2 orders of magnitude fainter than known radio-active galactic nuclei (AGN) at similar redshifts, thanks to ASKAP’s sensitivity. We investigate the physical origin of radio emission in our sample using a set of diagnostics: (i) radio luminosity at 1.4 GHz, (ii) 1.4 GHz to 3.4 μm flux density ratio, (iii) Far-IR detection, (iv) WISE colour, and (v) SED modelling. The radio/IR analysis has shown that the majority of radio emission in the faint and bright end of our sample’s 887.5 MHz flux density distribution originates from AGN activity. Furthermore, ∼10 per cent of our sample are found to have a 250 μm detection, suggesting a composite system. This suggests that some high-z radio-AGNs are hosted by SB galaxies in contrast to low-z radio-AGNs, which are usually hosted by quiescent elliptical galaxies.

Constraints on compact dark matter from lensing of gravitational waves for the third-generation gravitational wave detector

ABSTRACT Since the first gravitational wave (GW) event from binary black hole (BBH) was detected by LIGO-Virgo, GWs have become a useful probe on astrophysics and cosmology. If compact dark matter (DM) objects e.g. primordial black holes, contribute a significant fraction of DM at wide mass range, they will cause microlensing in the GW signals with long wavelengths that are distinct from the lensing effects of electromagnetic signals from astrophysical objects. In this paper, we apply the lensing effect of GW from BBH to derive constraints on the abundance of compact DM for the Cosmic Explorer, a third-generation ground-based GW detector. We first consider two channels of formation of BBH that contribute to low- and high-redshift GW sources, including the astrophysical origin BBH scenario, and the primordial origin BBH scenario. Secondly, comparing with the method of optical depth, we use the Bayesian analysis to derive constraints on the abundance of compact DM with different mass function of lens taken into consideration. For a null search with 1000 detected GW events of BBH, we find that the abundance of compact DM could be constrained to $\lesssim 0.1\,\mathrm{ per}\,\mathrm{ cent}$ in the mass range $\ge 500\, {\rm M}_{\odot }$ at 68 per cent confidence level. In addition, if a GW event lensed by a compact DM object with $M_{\rm l}\in [100\, {\rm M}_{\odot },300\, {\rm M}_{\odot }]$ is detected in 100 detected GW events of BBH, we can derive that the estimation of the abundance of compact DM is from $2.3$ to $25.2$ per cent in this mass range with the Bayesian analysis.