Cosmic Time Research Articles

Radio-AGN activity across the galaxy population: dependence on stellar mass, star-formation rate, and redshift

Abstract We characterise the co-evolution of radio-loud AGN and their galaxies by mapping the dependence of radio-loud AGN activity on stellar mass and star-formation rate (SFR) across cosmic time (out to z ∼ 1.5). Deep LOFAR radio observations are combined with large galaxy samples to study the incidence of radio-loud AGN across the galaxy population; the AGN are further split into low-excitation radio galaxies (LERGs) and high-excitation radio galaxies (HERGs). We find that LERG activity occurs over a wide range of SFRs, whereas HERGs are typically found in galaxies with ongoing star formation. The LERGs are then split based on their SFRs relative to the main sequence, across redshift. Within quiescent galaxies, LERG activity shows a steep stellar mass dependence with the same normalisation across the past ∼ 10 Gyr; this indicates that hot gas fuels LERGs in quiescent galaxies across cosmic time. In massive galaxies ($\log _{10}(M/\rm {{\rm M}_{\odot }}) \gtrsim 11$), the incidence of LERGs is roughly constant across the galaxy population, suggesting that LERGs in massive galaxies may be fuelled by hot gas regardless of the star-formation activity. At lower masses, however, LERG activity is significantly more enhanced (by a factor of up to 10) in star-forming galaxies compared to quiescent galaxies; this suggests that an additional fuelling mechanism, likely associated with cold gas, may fuel the LERGs in galaxies with higher SFRs. We find that HERGs typically accrete above 1percnt of the Eddington-scaled accretion rate, and the LERGs typically accrete below this level.

Compact object populations over cosmic time II. Compact object merger rates and masses over redshift from varying initial conditions

ABSTRACT We perform a first study of the impact of varying two components of the initial conditions in binary population synthesis of compact binary mergers – the initial mass function, which is made metallicity- and star formation rate-dependent, and the orbital parameter (orbital period, mass ratio, and eccentricity) distributions, which are assumed to be correlated – within a larger grid of initial condition models also including alternatives for the primary mass-dependent binary fraction and the metallicity-specific cosmic star formation history. We generate the initial populations with the sampling code bossa and evolve them with the rapid population synthesis code compas. We find strong suggestions that the main role of initial conditions models is to set the relative weights of key features defined by the evolution models. In the two models we compare, black hole–black hole (BHBH) mergers are the most strongly affected, which we connect to a shift from the common envelope to the stable Roche lobe overflow formation channels with decreasing redshift. We also characterize variations in the black hole–neutron star (BHNS) and neutron star–neutron star (NSNS) final parameter distributions. We obtain the merger rate evolution for BHBH, BHNS, and NSNS mergers up to $z=10$, and find a variation by a factor of $\sim 50\textnormal {--}60$ in the local BHBH and BHNS merger rates, suggesting a more important contribution from initial conditions than previously thought, and calling for a complete exploration of the initial conditions model permutations.

The cooler past of the intracluster medium in TNG-Cluster

Abstract The intracluster medium (ICM) today is comprised largely of hot gas with clouds of cooler gas of unknown origin and lifespan. We analyze the evolution of cool gas (temperatures ≲ 104.5 K) in the ICM of 352 galaxy clusters from the TNG-Cluster simulations, with present-day mass ∼1014.3 − 15.4 M⊙. We follow the main progenitors of these clusters over the past ∼13 billion years (since z ≲ 7) and find that, according to TNG-Cluster, the cool ICM mass increases with redshift at fixed cluster mass, implying that this cooler past of the ICM is due to more than just halo growth. The cool cluster gas at z ≲ 0.5 is mostly located in and around satellite galaxies, while at z ≳ 2 cool gas can also accrete via filaments from the intergalactic medium. Lower-mass and higher-redshift clusters are more susceptible to cooling. The cool ICM mass correlates with the number of gaseous satellites and inversely with the central supermassive black hole (SMBH) mass. The average number of gaseous satellites decreases since z = 2, correlating with the decline in the cool ICM mass over cosmic time, suggesting a link between the two. Concurrently, kinetic SMBH feedback shifts the ICM temperature distribution, decreasing the cool ICM mass inside-out. At z ≈ 0.5, the predicted Mg ii column densities are in the ballpark of recent observations, where satellites and other halos contribute significantly to the total Mg ii column density. Suggestively, a non-negligible amount of the ICM cool gas forms stars in-situ at early times, reaching ∼102 M⊙ yr−1 and an Hα surface brightness of ∼10−17 erg s−1 cm−2 arcsec−2 at z ≈ 2, detectable with Euclid and JWST.

X-Shooting ULLYSES: Massive stars at low metallicity. VI. Atmosphere and mass-loss properties of O-type giants in the Small Magellanic Cloud

Mass loss through a stellar wind is an important physical process that steers the evolution of massive stars and controls the properties of their end-of-life products, such as the supernova type and the mass of compact remnants. To probe its role in stellar evolution over cosmic time, mass loss needs to be studied as function of metallicity. For mass loss to be accurately quantified, the wind structure needs to be established jointly with the characteristics of small-scale inhomogeneities in the outflow, which are known as wind clumping. We aim to improve empirical estimates of mass loss and wind clumping for hot main-sequence massive stars, study the dependence of both properties on the metal content, and compare the theoretical predictions of mass loss as a function of metallicity to our findings. Using the model atmosphere code Fastwind and the genetic algorithm fitting method Kiwi-GA we analyzed the optical and ultraviolet spectra of 13 O-type giant to supergiant stars in the Small Magellanic Cloud galaxy, which has a metallicity of approximately one-fifth of that of the Sun. We quantified the stellar global outflow properties, such as the mass-loss rate and terminal wind velocity, and the wind clumping properties. To probe the role of metallicity, our findings were compared to studies of Galactic and Large Magellanic Cloud samples that were analyzed with similar methods, including the description of clumping. We find significant variations in the wind clumping properties of the target stars, with clumping starting at flow velocities $0.01 - 0.23$ of the terminal wind velocity and reaching clumping factors $f_ cl = 2 - 30$. In the luminosity ($ L / odot = 5.0 - 6.0$) and metallicity ($Z/Z_ odot = 0.2 - 1$) range we considered, we find that the scaling of the mass loss $ M $ with metallicity $Z$ varies with luminosity. At $ odot = 5.75$, we find $ M Z^m$ with $m = 1.02 0.30$, in agreement with pioneering work in the field within the uncertainties. For lower luminosities, however, we obtain a significantly steeper scaling of $m > 2$. The monotonically decreasing $m(L)$ behavior adds a complexity to the functional description of the mass-loss rate of hot massive stars. Although the trend is present in the predictions, it is much weaker than we found here. However, the luminosity range for which $m$ is significantly larger than previously assumed (at $ odot 5.4$) is still poorly explored, and more studies are needed to thoroughly map the empirical behavior, in particular, at Galactic metallicity.

Crimson Behemoth: A massive clumpy structure hosting a dusty AGN at z=4.91

Abstract The current paradigm for the co-evolution of galaxies and their supermassive black holes postulates that dust-obscured active galactic nuclei (AGNs) represent a transitional phase towards a more luminous and unobscured state. However, our understanding of dusty AGNs and their host galaxies at early cosmic times is inadequate due to observational limitations. Here, we present JWST observations of CID-931, an X-ray-detected AGN at a spectroscopic redshift of $z_{\rm spec}=4.91$. Multiband NIRCam imaging from the COSMOS-Web program reveals an unresolved red core, similar to JWST-discovered dusty AGNs. Strikingly, the red core is surrounded by at least eight massive star-forming clumps spread over ${1{^{\prime \prime}_{.}}6} \approx 10\,\,{\rm kpc}$, each of which has a stellar mass of $10^9$–$10^{10}\, M_{\odot }$ and a radius of $\sim$0.1–1 kpc. The whole system amounts to $10^{11}\, M_{\odot }$ in stellar mass, higher than typical star-forming galaxies at the same epoch. In this system, gas inflows and/or complex merger events may trigger clump formation and AGN activity, thus leading to the rapid formation of a massive galaxy hosting a supermassive black hole. Future follow-up observations will provide new insights into the evolution of the galaxy–black hole relationship during such transitional phases in the early universe.

QSO MUSEUM

Extended Lyα emission is routinely found around single quasars across cosmic time. However, few studies have investigated how such emission changes in fields with physically associated quasar pairs, which should reside in dense environments and are predicted to be linked through intergalactic filaments. We present VLT/MUSE snapshot observations (45 minutes/source) to unveil extended Lyα emission on scales of the circumgalactic medium (CGM) around the largest sample of physically associated quasar pairs to date, encompassing eight pairs (14 observed quasars) at z ∼ 3 with an i-band magnitude between 18 and 22.75, corresponding to absolute magnitudes Mi(z = 2) between −29.6 and −24.9. The pairs are either at close (∼50–100 kpc, five pairs) or wide (∼450–500 kpc, three pairs) angular separation and have velocity differences of Δv ≤ 2000 km s−1. We detected extended emission around 12 of the 14 targeted quasars and investigated the luminosity, size, kinematics, and morphology of these Lyα nebulae. On average, they span about 90 kpc and are 2.8 × 1043 erg s−1 bright. Irrespective of the quasars’ projected distance, the nebulae often (∼45%) extend toward the other quasar in the pair, leading to asymmetric emission whose flux-weighted centroid is at an offset position from any quasar location. We show that large nebulae are preferentially aligned with the large-scale structure, as traced by the direction between the two quasars, and conclude that the cool gas (104 K) in the CGM traces well the direction of cosmic web filaments. Additionally, the radial profile of the Lyα surface brightness around quasar pairs can be described by a power law with a shallower slope (∼−1.6) with respect to single quasars (∼−2), indicative of increased CGM densities out to large radii and/or an enhanced contribution from the intergalactic medium (IGM) due to the dense environments expected around quasar pairs. The sample presented in this study contains excellent targets for ultra-deep observations to directly study filamentary IGM structures in emission. This work demonstrates that a large snapshot survey of quasar pairs will pave the way to direct statistical study of the IGM.

A Probe into the Evolution of Primordial Perturbations in the f(T) Gravity Framework with Chaplygin Gas

This work is focused on studying the cosmology of variable modified Chaplygin gas (VMCG) in the framework of exponential and logarithmic f(T) theory. The equation of state (EoS) for VMCG in exponential and logarithmic f(T) gravity shows quintom behavior. Primordial perturbations were studied for VMCG in both exponential and logarithmic f(T) gravity, and it was observed that the potential increases with cosmic time t, and the scalar field decreases toward the minimum value of the potential. The squared speed of sound was positive, meaning that VMCG in both exponential and logarithmic f(T) gravity shows stability against small gravitational perturbations.

On the Expanding Universe – Accurately Calculate the Hubble Constant by Lunar Laser Ranging

Hubble's Law is an empirical formula. We use the product of the speed of light and time instead of distance for differentiation, and obtain the theoretical differential equation dV=Wdt. Then, the expansion velocity, radius, total mass, singularity radius, and redshift formula of the universe were calculated, and the gravitational constant was derived and proved to be proportional to the fourth power of cosmic time. The mathematical relationship between lunar laser ranging data and Hubble constant was obtained. This is a newly discovered precise method for measuring the Hubble constant

Cascading Dark Energy

The standard cosmological model is in the midst of a stress test, thanks to the tension between supernova-based measurements of the Hubble constant H 0 and inferences of its values from cosmic microwave background (CMB) anisotropies. Numerous explanations for the present-day cosmic acceleration require the presence of a new fundamental scalar field, as do early dark energy solutions to the Hubble tension. This raises the possibility that multiple fields cooperatively contribute to the dark energy component in bursts throughout cosmic time due to distinct initial conditions and couplings. Here, this cascading dark energy scenario is illustrated through a realization that effectively reduces to a two-field model, with two epochs in which dark energy is cosmologically significant. The model is compared to measurements of the CMB and baryon acoustic oscillations, as well as both PANTHEON and SH0ES observations of Type Ia supernovae. Neglecting the linear perturbations, it is found that this scenario ameliorates the Hubble tension, improving over purely late-time models of dark energy and the agreement between the galaxy survey measurements of baryon acoustic oscillations.

A Physically Motivated Framework to Compare the Merger Timescales of Isolated Low- and High-mass Galaxy Pairs Across Cosmic Time

The merger timescales of isolated low-mass pairs (108 < M * < 5 × 109 M ⊙) on cosmologically motivated orbits have not yet been studied in detail, though isolated high-mass pairs (5 × 109 < M * < 1011 M ⊙) have been studied extensively. It is common to apply the same separation criteria and expected merger timescales of high-mass pairs to low-mass systems, however, it is unclear if their merger timescales are similar, or if they evolve similarly with redshift. We use the Illustris TNG100 simulation to quantify the merger timescales of isolated low-mass and high-mass major pairs as a function of cosmic time, and explore how different selection criteria impact the mass and redshift dependence of merger timescales. In particular, we present a physically motivated framework for selecting pairs via a scaled separation criterion, wherein pair separations are scaled by the virial radius of the primary’s Friends-of-Friends (FoF) group halo (r sep < 1 R vir). Applying these scaled separation criteria yields equivalent merger timescales for both mass scales at all redshifts. Alternatively, static physical separation selections applied equivalently to all galaxy pairs at all redshifts lead to a difference in merger rate of up to ∼1 Gyr between low- and high-mass pairs, particularly for r sep < 150 kpc. As a result, applying the same merger timescales to physical-separation-selected pairs will lead to a bias that systematically overpredicts low-mass galaxy merger rates.

Cosmology in modified f (𝒢) gravity: a late-time cosmic phenomena

ABSTRACT In this work, we present a method for numerically solving the Friedmann equations of modified $f(\mathcal {G})$ gravity in the presence of pressureless matter. This method enables us to predict the redshift behaviour of the Hubble expansion rate. To evaluate the credibility of the model, we applied a Bayesian MCMC technique using late-time cosmic observations to impose limitations on the free parameters of the Gauss–Bonnet model. Our results suggest that the $f(\mathcal {G})$ model can reproduce the low-redshift behaviour of the standard Lambda cold dark matter ($\Lambda$CDM) model, but there are significant differences at high redshifts, leading to the absence of a standard matter-dominated epoch. We also examined the profiles of cosmographic parameters using the model parameter values from the standard range to verify the intermediate epochs. Our analysis shows that the highly promising $f(\mathcal {G})$ model is a feasible candidate for explaining the current epochs. We presented a dynamical system analysis framework to examine the stability of the model. Our study identified critical points depicting various phases of the Universe and explained the evolutionary epochs. We demonstrated that the model effectively captures the evolution of energy components over cosmic time, supporting its validity as an alternate explanation for the observed acceleration of the Universe.

The significance of measuring cosmological time dilation in the Dark Energy Survey Supernova Program

In the context of the dispersion relation c=λν and considering an expanding universe where the observed wavelength today is redshifted from the emitted wavelength by λ0=λemit(1+z), to keep c constant, it must be that ν0=νemit/(1+z). However, although the theory for wavelength in the RW metric includes the cosmological redshift, the same is not simply deduced for frequency (the inverse of time). Instead, cosmological time dilation T0=Temit(1+z) is an additional assumption made to uphold the hypothesis of constant speed of light rather than a relation directly derived from the RW metric. Therefore, verifying cosmological time dilation observationally is crucial. The most recent data employing supernovae for this purpose was released recently by the Dark Energy Survey. Results from the i-band specifically support variations in the speed of light within 1-σ. We used these observations to investigate variations in various physical quantities, including c and G, using the minimally extended varying speed of light model. The speed of light was 0.4% to 2.2% slower, and Newton’s constant may have decreased by 1.7% to 8.4% compared to their current values at redshift 2. These findings, consistent with previous studies, hint at resolving tensions between different ΛCDM cosmological backgrounds but are not yet conclusive evidence of a varying speed of light, as the full-band data aligns with standard model cosmology. However, the data remains valuable for testing variations in fundamental constants over cosmic time. Future analyses, particularly with more refined redshift data, may provide clearer insights into these potential changes.

Effect of the local and large-scale environment on the star formation histories of galaxies

The specific environment of galaxies may play a key role in their evolution. Large extragalactic surveys make it possible to study galaxies not only within their local environment, but also within the large-scale structure of the Universe. We aim to investigate how the local environment influences the star formation history (SFH) of galaxies across a range of large-scale environments. We categorised a sample of 9384 galaxies into the three primary large-scale structures (voids, walls and filaments, and clusters). We further classified them based on their local environment (as either 'singlets' or group members) through a search of companion galaxies within sky-projected distances of $ r_p &lt; 0.45$ Mpc and velocity differences of $ v &lt; 160$ $ km s $. Subsequently, we explored these subsamples using SFH data from previous works. Throughout this study, we divided galaxies into long-timescale SFH galaxies (LT-SFH), which assemble their mass steadily along cosmic time, and short-timescale SFH galaxies (ST-SFH), which form their stars early on. We then compared their characteristic mass assembly look-back times. The distributions of mass assembly look-back times in ST-SFH galaxies are statistically different for singlets and groups. These differences are only found in LT-SFH galaxies when studying these distributions in stellar mass bins. Our results indicate that the large-scale environment is related to a delay in mass assembly of up to sim 2 Gyr, while this delay is $&lt;$1 Gyr in the case of local environment. The effects of both types of environment are more significant in less massive galaxies and in LT-SFHs. Our results are consistent with galaxies in groups assembling their stellar mass earlier than in singlets, especially in voids and lower mass galaxies. Local environment plays a relevant role in stellar mass assembly times, although we find that large-scale structures also cause a delay in mass assembly, and all the more so in the case of cluster galaxies.

Emission-line Ratios and Ionization Conditions of CEERS Star-forming Galaxies with JWST/NIRSpec

Galaxy emission-line fluxes can constrain star formation rates (SFRs) and interstellar medium (ISM) ionization. We investigate rest-frame optical emission lines of 71 star-forming galaxies (SFGs) at redshift 0.7 < z < 7 using JWST/NIRSpec measurements from the Cosmic Evolution Early Release Science survey. We use Hα to measure SFR and utilize Hubble Space Telescope CANDELS stellar mass estimates to determine specific SFR (sSFR) and compare with the SFG main sequence (MS). We create [O iii]λ5008/Hβ versus [Ne iii]λ3870/[O ii]λ3728 line ratio diagrams. The line ratios appear to correlate with sSFR, and our results suggest that sSFR is the parameter that governs ionization conditions rather than SFR or a galaxy’s distance from the MS. These measurements reveal a rich diversity of ISM conditions and physical galaxy properties throughout cosmic time.

Modelling absorption and emission profiles from accretion disc winds with WINE

Fast and massive winds are ubiquitously observed in the UV and X-ray spectra of active galactic nuclei (AGNs) and other accretion-powered sources. Several theoretical and observational pieces of evidence suggest they are launched at accretion disc scales, carrying significant mass and angular momentum. Thanks to such high-energy output, they may play an important role in transferring the energy released by accretion to the surrounding environment. In the case of AGNs, this process can help to set the so-called co-evolution between an AGN and its host galaxy, which mutually regulates their growth across cosmic time. To precisely assess the effective role of UV and X-ray winds at accretion disc scales, it is necessary to accurately measure their properties, including mass and energy rates. However, this is a challenging task, due to both the limited signal-to-noise ratio of available observations and the limitations of the models currently used in the spectral analysis. We aim to maximise the scientific return of current and future observations by improving the theoretical modelling of these winds through our Winds in the Ionised Nuclear Environment (WINE) model. WINE is a spectroscopic model specifically designed for disc winds in AGNs and compact accreting sources, which couples photoionisation and radiative transfer with special relativistic effects and a three-dimensional model of the emission profiles. We explore with WINE the main spectral features associated with the disc winds in AGNs, with a particular emphasis on the detectability of the wind emission in the total transmitted spectrum. We explore the impact of the wind ionisation, column density, velocity field, and geometry in shaping the emission profiles. We simulated observations with the X-ray microcalorimeter Resolve on board the recently launched XRISM satellite and the X-IFU on board the future Athena mission. This allows us to assess the capabilities of these telescopes in the study of disc winds in X-ray spectra of AGNs for the typical physical properties and exposure times of the sources included in the XRISM performance verification phase. The wind kinematic and geometry (together with the ionisation and column density) deeply affect both shape and strength of the wind spectral features. Thanks to this, both Resolve and, on a longer timescale X-IFU will be able to accurately constrain the main properties of disc winds over a broad range of ionisation, column densities, and covering factors. We also investigate the impact of the spectral energy distribution (SED) on the resulting appearance of the wind. Our findings reveal a dramatic difference in the gas opacity when using a soft, Narrow Line Seyfert 1-like SED compared to a canonical powerlaw SED with a spectral index of $

On the origin of star formation quenching in massive galaxies at ≳ in the cosmological simulations IllustrisTNG

ABSTRACT Using the cosmological simulations IllustrisTNG, we perform a comprehensive analysis of quiescent, massive galaxies at $z \gtrsim 3$. The goal is to understand what suppresses their star formation so early in cosmic time, and how other similar mass galaxies remain highly star forming. As a first-order result, the simulations are able to produce massive, quiescent galaxies in this high-redshift regime. We find that active galactic nucleus (AGN) feedback is the primary cause of halting star formation in early, massive galaxies. Not only do the central, supermassive black holes (SMBHs) of the quenched galaxies have earlier seed times, but they also grow faster than in star-forming galaxies. As a result, the quenched galaxies are exposed to AGN feedback for longer, and experience the kinetic, jet mode of the AGN feedback earlier than the star-forming galaxies. The release of kinetic energy reduces inflows of gas while likely maintaining outflows, which keeps a low cold gas fraction and decreases the star formation of the galaxies down to a state of quiescence. In addition to AGN feedback, we also investigate the influence of the large-scale environment. While mergers do not play a significant role in the quenching process, the quenched galaxies tend to reside in more massive haloes and denser regions during their evolution. As this provides a greater initial amount of infalling gas to the galaxies, the large-scale environment can mildly affect the fate of the central SMBH growth and, via AGN feedback, contribute to star formation quenching.

Measuring neutron star radius with second and third generation gravitational wave detector networks

Abstract The next generation of ground-based interferometric gravitational wave detectors will observe mergers of black holes and neutron stars throughout cosmic time. A large number of the binary neutron star merger events will be observed with extreme high fidelity, and will provide stringent constraints on the equation of state of nuclear matter. In this paper, we investigate the systematic improvement in the measurability of the equation of state with increase in detector sensitivity by combining constraints obtained on the radius of a $1.4 \, \mathrm{M}_{\odot}$ neutron star from a simulated source population. Since the measurability of the equation of state depends on its stiffness, we consider a range of realistic equations of state that span the current observational constraints. We show that a single 40km Cosmic Explorer detector can pin down the neutron star radius for a soft, medium and stiff equation of state to an accuracy of 10m within a decade, whereas the current generation of ground-based detectors like the Advanced LIGO-Virgo network would take $\mathcal{O}(10^5)$ years to do so for a soft equation of state. &amp;#xD;

DUNE: Dust depletion UNified method across cosmic time and Environments

We present a novel method to characterize dust depletion, namely, the depletion of metals into dust grains. We used observed correlations among relative abundances combining a total of 17 metals in diverse galactic environments, including the Milky Way (MW), Large Magellanic Cloud (LMC), Small Magellanic Cloud (SMC), and damped Lyman-alpha absorbers (DLAs) towards quasars and gamma-ray bursts (GRBs). We only considered the relative abundances of metals that qualify as tracers of dust and we used all available dust tracers. We find linear correlations among all studied dust tracers in a multidimensional space, where each dimension corresponds to an individual dust tracer. The fit to the linear correlations among the dust tracers describes the tendencies of different elements when depleting into dust grains. We determined the overall strength of dust depletion, Delta , along individual lines of sight, based on the correlations among different dust tracers. We avoided any preference for specific dust tracers or any other assumptions by including all available dust tracers in this multidimensional space. We also determined the dust depletion of Kr, C, O, Cl, P, Zn, Ge, Mg, Cu, Si, Fe, Ni, and Ti. Finally, we offer simple guidelines for the application of the method to the study of the observed patterns of abundances and relative abundances. This has allowed for a straightforward determination of the overall strength of depletion and the dust depletion of individual elements. We also obtained an estimate for the gas-phase metallicity and identified any additional deviations due to the nucleosynthesis of specific stellar populations. Thus, we have established a unified methodology for characterizing dust depletion across cosmic time and diverse galactic environments, offering a valuable new approach to the study of dust depletion in studies of the chemical evolution of galaxies.

A unified model for the clustering of quasars and galaxies at z ≈ 6

ABSTRACT Recent observations from the EIGER JWST program have measured for the first time the quasar–galaxy cross-correlation function at $z\approx 6$. The autocorrelation function of faint $z\approx 6$ quasars was also recently estimated. These measurements provide key insights into the properties of quasars and galaxies at high redshift and their relation with the host dark matter haloes. In this work, we interpret these data building upon an empirical quasar population model that has been applied successfully to quasar clustering and demographic measurements at $z\approx 2\!-\!4$. We use a new, large-volume N-body simulation with more than a trillion particles, FLAMINGO-10k, to model quasars and galaxies simultaneously. We successfully reproduce observations of $z\approx 6$ quasars and galaxies (i.e. their clustering properties and luminosity functions), and infer key quantities such as their luminosity–halo mass relation, the mass function of their host haloes, and their duty cycle/occupation fraction. Our key findings are (i) quasars reside on average in $\approx 10^{12.5}\, {\rm M}_{\odot }$ haloes (corresponding to $\approx 5\sigma$ fluctuations in the initial conditions of the linear density field), but the distribution of host halo masses is quite broad; (ii) the duty cycle of (UV-bright) quasar activity is relatively low ($\approx 1~{{\ \rm per\ cent}}$); (iii) galaxies (that are bright in [O iii]) live in much smaller haloes ($\approx 10^{10.9}\, {\rm M}_{\odot }$) and have a larger duty cycle (occupation fraction) of $\approx 13~{{\ \rm per\ cent}}$. Finally, we focus on the inferred properties of quasars and present a homogeneous analysis of their evolution with redshift. The picture that emerges reveals a strong evolution of the host halo mass and duty cycle of quasars at $z\approx 2\!-\!6$, and calls for new investigations of the role of quasar activity across cosmic time.

Systematic collapse of the accretion disc across the supermassive black hole population

ABSTRACT The structure of the accretion flow on to supermassive black holes is not well understood. Standard disc models match to zeroth-order in predicting substantial energy dissipation within optically thick material producing a characteristic strong blue/ultraviolet continuum. However, they fail at reproducing more detailed comparisons to the observed spectral shapes along with their observed variability. Based on stellar mass black holes within our Galaxy, accretion discs should undergo a transition into an X-ray hot, radiatively inefficient flow, below a (mass scaled) luminosity of $\sim 0.02\, L_{\rm {Edd}}$. While this has been seen in limited samples of nearby low-luminosity active galactic nuclei (AGN) and few rare changing-look AGN, it is not at all clear whether this transition is present in the wider AGN population across cosmic time. A key issue is the difficulty in disentangling a change in spectral state from increased dust obscuration and/or host galaxy contamination, effectively drowning out the AGN emission. Here, we use the new eROSITA eFEDS Survey to identify unobscured AGN from their X-ray emission, matched to excellent optical imaging from Subaru’s Hyper Suprime-Cam; allowing the subtraction of the host galaxy contamination. The resulting, uncontaminated, AGN spectra reveal a smooth transition from a strongly disc-dominated state in bright AGN, to the collapse of the disc into an inefficient X-ray plasma in the low-luminosity AGN, with the transition occurring at $\sim 0.02\, L_{\rm {Edd}}$; revealing fundamental aspects of accretion physics in AGN.