arXiv subjects

Alessandro Trinca

Publications and source records attributed to Alessandro Trinca.

At least 19 recordsLinked to original sources

arXiv2026

How can we finally see the first light? Status and perspective in the search for Population III stars

Finding the first (Population III or Pop III) stars is one of the fundamental quests of astronomy, aiming to deliver the missing link in how stars form at early cosmic times. Yet their initial mass function, formation sites and feedback remain highly uncertain, as well as the timing and topology of the transition to metal-enriched star formation. The observability of their peculiar spectral features is also debated, due to their short lifetime and faintness. This review summarizes current theoretical expectations for Pop III star formation, and the main observational strategies that have been adopted to constrain their properties across cosmic time, including near-field cosmology studies, direct searches for extremely metal-poor star-forming complexes and/or hard-ionizing spectral signatures at high and intermediate redshifts, and prospects for identifying Pop III activity up to Cosmic Dawn. The combination of JWST spectroscopy, time-domain searches, lensing surveys, stellar archaeology, absorption-line studies, as well as improved simulations, is yielding a growing number of observational candidates and narrowing the allowed parameter space for the first stars, setting the stage for a ``golden era'' of Pop III searches.

astro-ph.GA↗

arXiv2026

The role of major mergers in triggering super-Eddington accretion

JWST observations have opened a new era in the exploration of the high-redshift Universe, revealing black holes (BHs) with masses of several million solar masses already at $z>8$, challenging our understanding of their growth mechanisms. In this context, super-Eddington (SE) accretion has emerged as a promising solution and has been widely adopted in both numerical simulations and semi-analytical models. In this work, we investigate whether a major merger between two relatively low-mass halos ($M_{\rm halo}\sim10^9\,\mathrm{M_\odot}$) at high redshift can trigger episodes of sustained SE accretion, with particular focus on the role of BH feedback. We employ state-of-the-art, high-resolution cosmological zoom-in simulations of a major merger at $z\sim11$. We explore different prescriptions for BH seeding and feedback, including physically motivated radiative and kinetic models (winds and jets) across the three main accretion regimes: advection-dominated accretion flows (ADAF), radiatively efficient sub-Eddington accretion, and SE accretion. For the relatively low-mass halos studied here, our feedback prescription efficiently suppresses gas accretion, preventing substantial BH growth. We find that, although the merger drives gas inflows towards the central regions, this is not sufficient to trigger sustained SE accretion. Post-merger SE accretion episodes are observed only when BH feedback is entirely switched off. Amongst the feedback channels considered, kinetic feedback is the primary mechanism regulating BH growth. Moreover, the only significant SE accretion episodes occur immediately after BH seeding, while the merger itself does not produce a substantial enhancement of the accretion rate.

astro-ph.GA↗

arXiv2026

The LISA Astrophysics MBHcatalogues Project: A comparison of predictions of simulated massive black hole binaries

In the hierarchical paradigm of galaxy formation, central massive black holes (MBHs) are expected to coalesce after the merger of their host galaxies. One of the main goals of the Laser Interferometer Space Antenna (LISA) is to constrain the origin and growth of MBHs through their merger rates and mass distribution. Predicting MBH merger rates requires not only tracing their statistical population from large to small physical scales (kpc to sub-pc) but also modelling their formation, accretion, dynamics, mergers, and their galactic physical processes across cosmic time. This project is the result of a large collaborative effort undertaken by the LISA Astrophysics Working Group, bringing together its collective expertise on MBH formation, evolution, and modelling, to build a comprehensive understanding of MBH merger rates across cosmic time. The project compares various theoretical predictions of MBH merger rates, quantifies the spread, and evaluates the global astrophysical uncertainties of the LISA event rates. To build a unique and complete view, our work is based on about 20 semi-analytical models and cosmological simulations from the literature, all employing distinct approaches to modelling MBH and galaxy physics. To compute the merger rates, we also incorporate delays arising from the dynamical phase of MBH hardening to coalescence. We present the expected LISA merger rates given current galaxy formation models and discuss how the merger rate depends on model assumptions, such as the seeding model and the resolution of cosmological simulations.

astro-ph.GA↗

arXiv2026

Gravitational Waves from the Cosmic Dawn: Tracing Cosmic Black Hole Binaries with ET, LGWA and LISA

Next generation detectors, such as LISA, LGWA, and ET will, for the first time, probe the high redshift Universe, offering unique insight into the birth, growth, and dynamics of the first black holes (BHs) during their earliest stages formation. We aim to predict merger rates and gravitational wave (GW) signatures of "cosmic" binary BHs, forming as a result of galaxy mergers, at z>=4. We investigate how BH seeding, accretion physics and dynamical delays affect their properties and detectability across cosmic epochs. We use the semi-analytic model Cosmic Archaeology Tool (CAT) to trace the evolution and delayed-mergers, driven by dynamical friction, of BH binaries formed from light, medium-weight and heavy seeds, under Eddington-limited (EL) and super-Eddington (SE) accretion prescriptions. We employ the GWFish package to evaluate their GW signals and detectability by LISA, LGWA and ET. Our results show the impact of BH accretion and seeding prescriptions on the properties and distribution of detectable sources. In the EL model, the detected populations are dominated by nearly equal-mass binaries. In contrast, SE growth leads to lower mass ratios for LISA detections and medium ratios for ET and LGWA. We present the total detection rates predicted under the two accretion scenarios. The SE model allows BHs to grow faster, transferring a significant fraction of detectable systems from the ET band to the LISA band, compared to the EL model. As a result, the predicted LISA detection rate increases from ~32 yr^-1 in the EL case to ~64 yr^-1 in the SE scenario, and the ET detection rate reduces from ~64 yr^-1 in the EL model to only ~4 yr^-1 in the SE scenario. LGWA yields comparable detection rates in both scenarios (~21 yr^-1 in EL and ~12 yr^-1 in SE). The combined information encoded in mass ratios, redshift evolution and merger rates emerge as a promising diagnostic of early BH growth.

astro-ph.GA↗

arXiv2026

You can't see me: Super-Eddington growth hindering X-ray detection in high-z broad-line active galactic nuclei

We revisit black hole mass estimates for high-redshift broad-line active galactic nuclei (AGNs) discovered with JWST by jointly analysing their broad emission lines and their systematic non-detections in deep Chandra imaging. Building upon a self-shadowed, super-Eddington accretion framework in which the corona undergoes efficient radiative over-cooling, we couple funnel-dependent Comptonisation physics with slim-disc spectral models and explore the resulting parameter space through a full MCMC inference. Using a recently compiled sample of JWST high-redshift broad-line AGNs, we show that the observed X-ray weakness - manifested as extreme bolometric corrections, suppressed 2-10 keV luminosities, and non-detections in the 0.5-5 keV Chandra band - naturally arises when the corona is confined and radiatively over-cooled inside a narrow super-Eddington funnel. The combined broad line+X-ray analysis yields strongly bimodal posteriors: either very massive, very low-Eddington black holes (physically disfavoured), or a population of low-mass ($\sim 10^{6}$-$10^{7} M_{\odot}$) black holes accreting at $f_{\rm Edd} \gg 1$. The latter solution is strongly preferred for nearly all objects and returns masses consistent with, or lower than, local $M_{\rm BH}$-$M_{\star}$ relations, mitigating the extreme mass ratios implied by single-epoch virial estimators. The predicted intrinsic spectra are redder and exhibit reduced hard-X-ray output but higher bolometric luminosities, implying bolometric corrections larger than those typical of the local AGN population, yet consistent with low-redshift highly accreting counterparts. These results support a picture in which many JWST broad-line AGNs are powered by rapidly growing, super-Eddington black holes whose suppressed coronal emission and self-shadowed BLR geometry combine to mimic overmassive black holes at $z \gtrsim 6$.

astro-ph.GA↗

arXiv2026

Too many or too massive? Investigating the high-$z$ demography of active SMBHs from JWST

Recent JWST observations have unveiled a numerous population of low-luminosity active galactic nuclei (AGN) at $4< z<10$, with space densities roughly an order of magnitude above pre-JWST estimates, and many of these AGN have masses orders of magnitude above the local black hole mass-stellar mass ($M_{\rm BH}-M_{*}$) scaling relations. We investigate the consistency of these observations within a data-driven framework that links the galaxy stellar mass function to the supermassive black hole (SMBH) mass function and AGN luminosity functions using different $M_{\rm BH}-M_{*}$ relations and the observed Eddington-ratio distribution. By comparing our predictions against observed AGN luminosity functions at $z\sim 5.5$ we find that observations can be reproduced either by highly-elevated $M_{\rm BH}-M_{*}$ relations paired with low duty cycles, or moderate relations with higher duty cycles. Through the Soltan argument, we find that $M_{\rm BH}-M_{*}$ relations that are modestly above the local relation for AGN produce consistency between multiple tracers of the SMBH demography at $z\sim 5.5$, while more extreme normalisations would require a weakly-evolving luminosity function at $z> 5.5$. Continuity-equation modelling shows that initially high $M_{\rm BH}-M_{*}$ relations predict a strong two-phase evolutionary scenario and very steep low-mass SMBH mass functions in tension with several current estimates, while more moderate relations generate local SMBH mass functions in better agreement with present determinations and near-constant scaling relations. Our results favour a scenario where SMBHs at $z \sim 5$ on average lie modestly above local AGN scaling relations, with elevated but physically plausible duty cycles. Future wide-field clustering and demographic studies will help break the remaining degeneracies between SMBH scaling relations and AGN duty cycles at early cosmic times.

astro-ph.GA↗

arXiv2026

Hunting the first Cosmic Giants: formation and detectability of Direct Collapse Black Holes around high-redshift quasars

The rapid emergence of supermassive black holes (SMBHs) in the early Universe poses a challenge to current models of black hole growth. One promising formation pathway is the direct collapse black hole (DCBH) scenario, in which gas in pristine, low-metallicity halos forms supermassive (or quasi-) stars leading to massive black holes seeds under specific environmental conditions. In this work, we investigate the potential host environments of DCBHs by coupling a semi-analytic model tracing BH formation and galaxy co-evolution with high-resolution N-body dark matter merger trees. This allows us to trace the population of DCBHs formed during the hierarchical assembly of a $\sim 10^{12} ~\rm M_\odot$ dark matter halo hosting a bright $10^9 ~\rm M_\odot$ quasar at redshift $z \approx 7$. We find that, when accounting for local fluctuations in the UV radiation field within this early cosmic structure, massive BH seeds can form via direct collapse as early as $z \approx 22$. Even under more stringent conditions for heavy seed formation, tens of DCBHs are predicted to emerge within the simulated overdensity down to $z \sim 14$, at which point metal enrichment of the intergalactic medium inhibits further episodes of direct collapse. A significant fraction of the massive black hole population formed at $z > 14$ is expected to survive in satellite galaxies that do not merge with the central halo down to $z \approx 7$. We show that the existence of such a population of ungrown heavy BH seeds can be probed through deep JWST observations targeting regions surrounding bright high-redshift quasars, and we discuss tailored observational strategies to detect and identify these elusive systems.

astro-ph.GA↗

arXiv2025

BlackTHUNDER: Evidence of three massive black holes in a z~5 galaxy

We present observational evidence of three massive, accreting black holes (BHs) in the z=5.0167 galaxy J0148-4214 from JWST/NIRSpec-IFU spectroscopy. The BHs are revealed through broad H$\alpha$ emission (FWHM=430-2920 km/s) without a forbidden-line counterpart in the bright [OIII] doublet. Channel maps of the asymmetric central H$\alpha$ profile isolate two spatially distinct broad-line regions (BLRs), separated by $190\pm40$ pc, while a third BLR is found in the galaxy outskirts with a projected separation of 1.7 kpc. We discuss whether this emission could be due to supernovae, shocks, winds, or massive stars, but find the BLR origin most likely. Using single-epoch virial relations, we estimated BH masses of $\log(M_\bullet/M_\odot)=7.9\pm0.4$ (primary), $5.8\pm0.5$ (secondary), and $6.3\pm0.5$ (third off-nuclear). We argue that the two central BHs will likely rapidly merge, with a simple dynamical friction time estimate of the order of $\lesssim700$ Myr. Assuming that the third off-nuclear BH is also in the process of sinking towards the centre, it will likely lead to a second merger, and we investigated the detection probability of such mergers with LISA. Alternatively, the third BH may be the result of a previous central three-body interaction or a gravitational recoil, where our observations would provide evidence that such BHs may retain their accretion discs and BLRs even in the aftermath of such extreme dynamical interactions. The possible discovery of a BH triplet at high z, together with other recent results on distant BH pairs, indicates that multiple massive BH systems were likely common in the early Universe. Our results highlight the importance of IFU observations for the detection of massive BH multiplets in distant galaxies, the progenitors of massive BH mergers that may be detected with next-generation gravitational wave observatories.

astro-ph.GA↗

arXiv2025

A direct black hole mass measurement in a Little Red Dot at the Epoch of Reionization

Recent discoveries of faint active galactic nuclei (AGN) at the redshift frontier have revealed a plethora of broad \Halpha emitters with optically red continua, named Little Red Dots (LRDs), which comprise 15-30\% of the high redshift broad line AGN population. Due to their peculiar spectral properties and X-ray weakness, modeling LRDs with standard AGN templates has proven challenging. In particular, the validity of single-epoch virial mass estimates in determining the black hole (BH) masses of LRDs has been called into question, with some models claiming that masses might be overestimated by up to 2 orders of magnitude, and other models claiming that LRDs may be entirely stellar in nature. We report the direct, dynamical BH mass measurement in a strongly lensed LRD at $z = 7.04$. The combination of lensing with deep spectroscopic data reveals a rotation curve that is inconsistent with a nuclear star cluster, yet can be well explained by Keplerian rotation around a point mass of 50 million Solar masses, consistent with virial BH mass estimates from the Balmer lines. The Keplerian rotation leaves little room for any stellar component in a host galaxy, as we conservatively infer $M_{\rm BH}/M_{*}>2$. Such a ''naked'' black hole, together with its near-pristine environment, indicates that this LRD is a massive black hole seed caught in its earliest accretion phase.

astro-ph.GA↗

arXiv2025

Super-Eddington accretion in protogalactic cores

The presence of massive black holes (BHs) exceeding $10^9\,{\rm M}_{\odot}$ already at redshift $z > 6$ challenges standard models of BH growth. Super-Eddington (SE) accretion has emerged as a promising mechanism to solve this issue, yet its impact on early BH evolution in tailored numerical experiments remains largely unexplored. In this work, we investigate the growth of BH seeds embedded in a gas-rich, metal-poor protogalaxy at $z \sim 15$ using a suite of high-resolution hydrodynamical simulations that implement a slim-disc-based SE accretion model. We explored a broad parameter space, varying the initial BH mass, feedback efficiency, and spin. We find that SE accretion enables rapid growth in all cases, allowing BHs to accrete up to $10^5\,{\rm M}_{\odot}$ within a few $10^3$-$10^4$ years, independent of seed properties. Feedback regulates this process, both by depleting central gas and altering BH dynamics via star formation-driven potential fluctuations, yet even the strongest feedback regimes permit significantly greater growth than the Eddington-limited case. Growth stalls after less than $\sim$1 Myr due to local gas exhaustion, as no large-scale inflows are present in the adopted numerical setup. Our results show that SE accretion naturally leads to BHs that are overmassive relative to their host galaxy stellar content, consistent with JWST observations. We conclude that short low-duty-cycle SE episodes represent a viable pathway for assembling the most massive BHs observed at early cosmic times, even when starting from light seeds.

astro-ph.GA↗

arXiv2025

JADES reveals a large population of low mass black holes at high redshift

JWST has revealed a large population of active galactic nuclei (AGN) in the distant universe, which are challenging our understanding of early massive black hole seeding and growth. We expand the exploration of this population to lower luminosities by stacking $\sim 600$ NIRSpec grating spectra from the JWST Advanced Deep Extragalactic Survey (JADES) at $3<z<7$, in bins of redshift, [OIII]5007 luminosity and equivalent width, UV luminosity and stellar mass. In various stacks, we detect a broad component of H$\alpha$ without a counterpart in [OIII], implying that it is not due to outflows but is tracing the Broad Line Region (BLR) of a large population of low-luminosity AGN not detected in individual spectra. We also consider the possible contribution from Supernovae (SNe) and Very Massive Stars and conclude that while this is very unlikely, we cannot exclude some potential contribution by SNe to some of the stacks. The detection, in some stacks, of high [OIII]4363/H$\gamma$, typical of AGN, further confirms that such stacks reveal a large population of AGN. We infer that the stacks probe black holes with masses of a few times $10^6~M_\odot$ accreting at rates $L/L_{Edd}\sim 0.02-0.1$, i.e. a low mass and dormant parameter space poorly explored by previous studies on individual targets. We identify populations of black holes that fall within the scatter of the local $M_{BH}-M_{*}$ scaling relation, indicating that there is a population of high-z BHs that are not overmassive relative to their host galaxies and which have been mostly missed in previous JWST observations. Yet, on average, the stacks are still overmassive relative the local relation, with some of them 1-2 dex above it. We infer that the BH mass function (BHMF) at $3<z<5$ rises steeply at low masses. The BHMF is consistent with models in which BHs evolve through short bursts of super-Eddington accretion.

astro-ph.GA↗

arXiv2025

A black hole in a near-pristine galaxy 700 million years after the Big Bang

The recent discovery of a large number of massive black holes within the first two billion years after the Big Bang, as well as their peculiar properties, have been largely unexpected based on the extrapolation of the properties of luminous quasars. These findings have prompted the development of several theoretical models for the early formation and growth of black holes, which are, however, difficult to differentiate. We report the metallicity measurement around a gravitationally lensed massive black hole at redshift 7.04 (classified as a Little Red Dot), hosted in a galaxy with very low dynamical mass. The weakness of the [OIII]5007 emission line relative to the narrow H$\beta$ emission indicates extremely low metallicity, about $4\times 10^{-3}$ solar, and even more metal poor in the surrounding few 100 pc. We argue that such properties cannot be uncommon among accreting black holes around this early cosmic epoch. Explaining such a low chemical enrichment in a system that has developed a massive black hole is challenging for most theories. Models assuming heavy black hole seeds (such as Direct Collapse Black Holes) or super-Eddington accretion scenarios struggle to explain the observations, although they can potentially reproduce the observed properties in some cases. Models invoking "primordial black holes" (i.e. putative black holes formed shortly after the Big Bang) may potentially explain the low chemical enrichment associated with this black hole, although this class of models also requires further developments for proper testing.

astro-ph.GA↗

arXiv2025

Super-Eddington accretion in high-redshift quasar hosts: Black-hole driven outflows, galaxy quenching, and the nature of little red dots

The advent of the James Webb Space Telescope has revolutionised our understanding of the high-redshift Universe through its detection of bright, massive galaxies up to $z\gtrsim 10$ and its identification of peculiar sources called `little red dots' (LRDs). The origin of both classes of objects remains uncertain but is likely linked to the formation and early growth of the first massive black holes (MBHs), which may be more easily explained by invoking phases of super-Eddington accretion. In this study, we used a state-of-the-art zoom-in cosmological simulation of a quasar host to investigate whether these objects could resemble any of the peculiar sources observed with JWST during their assembly. We find that the impact of MBH feedback on star formation is typically moderate, with outflows preferentially escaping perpendicular to the galactic disc. However, for approximately ten percent of the galaxy's lifetime, the system enters a distinct quenched phase following rapid MBH growth driven by super-Eddington accretion. This phase culminates in a powerful feedback event, during which the MBH jet and disc-driven winds interact directly with the galactic disc and carve out a central cavity. We also find that, during the history of the quasar host progenitor, the spectral properties of the system can resemble both LRDs and quenched galaxies, depending on the specific evolutionary stage considered. These findings suggest that both conditions may represent transient phases in the life cycle of high-redshift galaxies.

astro-ph.GA↗

arXiv2025

Predicting the number density of heavy seed massive black holes due to an intense Lyman-Werner field

The recent detections of a large number of candidate active galactic nuclei at high redshift (i.e. $z \gtrsim 4$) has increased speculation that heavy seed massive black hole formation may be a required pathway. Here we re-implement the so-called Lyman-Werner (LW) channel model of Dijkstra et al. (2014) to calculate the expected number density of massive black holes formed through this channel. We further enhance this model by extracting information relevant to the model from the $\texttt{Renaissance}$ simulation suite. $\texttt{Renaissance}$ is a high-resolution suite of simulations ideally positioned to probe the high-$z$ Universe. Finally, we compare the LW-only channel against other models in the literature. We find that the LW-only channel results in a peak number density of massive black holes of approximately $\rm{10^{-4} \ cMpc^{-3}}$ at $z \sim 10$. Given the growth requirements and the duty cycle of active galactic nuclei, this means that the LW-only is likely incompatible with recent JWST measurements and can, at most, be responsible for only a small subset of high-$z$ active galactic nuclei. Other models from the literature (e.g. rapid assembly; relative velocities between baryons and dark matter) seem therefore better positioned, at present, to explain the high frequency of massive black holes at high $z$.

astro-ph.CO↗

arXiv2025

BlackTHUNDER -- A non-stellar Balmer break in a black hole-dominated little red dot at $z=7.04$

Recent observations from JWST have revealed an abundant population of active galactic nuclei (AGN) and so-called ``Little Red Dots'' (LRDs) at $2\lesssim z \lesssim 11$, many of which are characterized by V-shaped UV-to-optical continua with turnovers around the Balmer limit. The physical nature of these LRDs is unclear, and it remains debated whether the peculiar spectral shape originates from AGN, compact galaxies, or both. We present the analysis of new NIRSpec-IFU data from the BlackTHUNDER JWST Large Programme and archival NIRSpec-MSA data of a lensed LRD at $z=7.04$. The spectra confirm the presence of a smooth Balmer break and a broad H$\beta$ tracing the Broad Line Region (BLR) of an AGN. The small velocity dispersion of the H$\beta$ narrow component indicates a small dynamical mass of the host galaxy of $M_{\rm dyn}<4 \times 10^8~M_{\odot}$, which implies that the stellar population cannot contribute more than 10% to the optical continuum. We show that the Balmer break can be well described by an AGN continuum absorbed by very dense ($n_{\rm H}\sim 10^{10}~{\rm cm^{-3}}$) and nearly dust-free gas along our line-of-sight (possibly gas in the BLR or its surrounding). The same gas is expected to produce H$\beta$ absorption, at a level consistent with a tentative detection ($3\sigma$) in the high-resolution spectrum. Such a non-stellar origin of the Balmer break may apply to other LRDs, and would alleviate the issue of extremely high stellar mass surface densities inferred in the case of a stellar interpretation of the Balmer break. We note that this is a rare case of a black hole that is overmassive relative to both the host galaxy stellar and dynamical masses. We finally report indications of variability and the first attempt of AGN reverberation mapping at such an early epoch.

astro-ph.GA↗

arXiv2024

Episodic super-Eddington accretion as a clue to Overmassive Black Holes in the early Universe

Early JWST observations are providing growing evidence for a ubiquitous population of accreting supermassive black holes (BHs) at high redshift, many of which appear overmassive compared to the empirically-derived local scaling relation between black hole mass and host galaxy stellar mass. In this study, we leverage predictions from the semi-analytical Cosmic Archaeology Tool (CAT) to reconstruct the evolutionary pathways for this overmassive BH population, investigating how they assemble over cosmic time and interact with their host galaxies. We find that the large $M_{\rm BH}-M_{\rm star}$ ratios can be explained if light and heavy BH seeds grow by short, repeated episodes of super-Eddington accretion, triggered by major galaxy mergers. On average, we find that BH-galaxy co-evolution starts in earnest only at $z < 8$, when $\simeq 30\%$ of the final galaxy stellar mass has formed outside the massive black hole host. Our model suggests that super-Eddington bursts of accretion last between $0.5-3$ Myr, resulting in a duty cycle of $1-4 \%$ for the target BH sample. The boost in luminosity of BHs undergoing super-Eddington accretion helps explaining the luminosity function of Active Galactic Nuclei observed by JWST. At the same time, a large population of these overmassive BHs are predicted to be inactive, with Eddington ratio $\lambda_{\rm Edd} < 0.05$, in agreement with recent observations.

astro-ph.GA↗

arXiv2024

Size matters: are we witnessing super-Eddington accretion in high-redshift black holes from JWST?

Observations by the James Webb Space Telescope of the Universe at $z\gtrsim 4$ have shown that massive black holes (MBHs) appear extremely overmassive compared to the local correlation for active galactic nuclei. In some cases, these objects might even reach half the stellar mass inferred for the galaxy. Understanding how such objects formed and grew to this masses has then become a big challenge for theoretical models, with different ideas ranging from heavy seed to super-Eddington accretion phases. Here, we take a different approach, and try to infer how accurate these MBH mass estimates are and whether we really need to revise our physical models. By considering how the emerging spectrum (both the continuum and the broad lines) of an accreting MBH changes close to and above the Eddington limit, we infer a much larger uncertainty in the MBH mass estimates relative to that of local counterparts, up to an order of magnitude, and a potential preference for lower masses and higher accretion rates, which i) move them closer to the local correlations, and ii) might indicate that we are witnessing for the first time a widespread phase of very rapid accretion.

astro-ph.HE↗

arXiv2024

A dormant, overmassive black hole in the early Universe

Recent observations have found a large number of supermassive black holes already in place in the first few hundred million years after Big Bang. The channels of formation and growth of these early, massive black holes are not clear, with scenarios ranging from heavy seeds to light seeds experiencing bursts of high accretion rate. Here we present the detection, from the JADES survey, of broad Halpha emission in a galaxy at z=6.68, which traces a black hole with mass of ~ 4 * 10^8 Msun and accreting at a rate of only 0.02 times the Eddington limit. The host galaxy has low star formation rate (~ 1 Msun/yr, a factor of 3 below the star forming main sequence). The black hole to stellar mass ratio is ~ 0.4, i.e. about 1,000 times above the local relation, while the system is closer to the local relations in terms of dynamical mass and velocity dispersion of the host galaxy. This object is most likely the tip of the iceberg of a much larger population of dormant black holes around the epoch of reionisation. Its properties are consistent with scenarios in which short bursts of super-Eddington accretion have resulted in black hole overgrowth and massive gas expulsion from the accretion disk; in between bursts, black holes spend most of their life in a dormant state.

astro-ph.GA↗