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The rapid assembly of the massive black holes that power the luminous quasarsobserved at $z \sim 6-7$ remains a puzzle. Various direct collapse models havebeen proposed to head-start black hole growth from initial seeds with masses$\sim 10^5\,\rm M_\odot$, which can then reach a billion solar mass whileaccreting at the Eddington limit. Here we propose an alternative scenario basedon radiatively inefficient super-critical accretion of stellar-mass holesembedded in the gaseous circum-nuclear discs (CNDs) expected to exist in thecores of high redshift galaxies. Our sub-pc resolution hydrodynamicalsimulations show that stellar-mass holes orbiting within the central 100 pc ofthe CND bind to very high density gas clumps that arise from the fragmentationof the surrounding gas. Owing to the large reservoir of dense cold gasavailable, a stellar-mass black hole allowed to grow at super-Eddington ratesaccording to the "slim disc" solution can increase its mass by 3 orders ofmagnitudes within a few million years. These findings are supported bysimulations run with two different hydro codes, RAMSES based on the AdaptiveMesh Refinement technique and GIZMO based on a new Lagrangian Godunov-typemethod, and with similar, but not identical, sub-grid recipes for starformation, supernova feedback, black hole accretion and feedback. The lowradiative efficiency of super-critical accretion flows are instrumental to therapid mass growth of our black holes, as they imply modest radiative heating ofthe surrounding nuclear environment.

The detection of gravitational waves has opened a new era for astronomy, allowing for the combined use of gravitational wave and electromagnetic emissions to directly probe the physics of compact objects, still poorly understood. So far, the theoretical modelling of these sources has mainly relied on standard numerical techniques as grid-based methods or smoothed particle hydrodynamics, with only a few recent attempts at using new techniques as moving-mesh schemes. Here, we introduce a general relativistic extension to the mesh-less hydrodynamic schemes in the code gizmo , which benefits from the use of Riemann solvers and at the same time perfectly conserves angular momentum thanks to a generalized leap-frog integration scheme. We benchmark our implementation against many standard tests for relativistic hydrodynamics, either in one or three dimensions, and also test the ability to preserve the equilibrium solution of a Tolman–Oppenheimer–Volkoff compact star. In all the presented tests, the code performs extremely well, at a level at least comparable to other numerical techniques. [ABSTRACT FROM AUTHOR]

The observation of a population of massive black hole binaries (MBHBs) is key for our complete understanding of galaxy mergers and for the characterization of the expected gravitational waves (GWs) signal. However, MBHBs still remain elusive with only a few candidates proposed to date. Among these, SDSSJ143016.05 + 230344.4 ('tick-tock' hereafter) is the only candidate with a remarkably well sampled light curve showing a clear reduction of the modulation period and amplitude over three years of observations. This particular feature has been recently claimed to be the signature of a MBHB that is about to merge. In this paper, we provide an optical follow-up of the tick-tock source using the Rapid Eye Mount (REM) telescope. The decreasing luminosity observed in our follow up is hardly explained within the binary scenario. We speculate about an alternative scenario that might explain the observed light curve through relativistic Lense-Thirring precession of an accretion disc around a single massive black hole. [ABSTRACT FROM AUTHOR]

Dissecting the underlying structure of galaxies is of main importance in the framework of galaxy formation and evolution theories. While a classical bulge + disc decomposition of disc galaxies is usually taken as granted, this is only rarely solidly founded upon the full exploitation of the richness of data arising from spectroscopic studies with integral field units. In this work, we describe a fully Bayesian estimation method of the global structure of disc galaxies which makes use of the wealth of photometric, kinematic, and mass-to-light ratio data, and that can be seen as a first step towards a machine-learning approach, certainly needed when dealing with larger samples of galaxies. Ours is a novel, hybrid line of action in tackling the problem of galactic parameter estimation, neither purely photometric nor orbit-based. Being rooted on a nested sampler, our code, which is available publicly as an online repository, 1 allows for a statistical assessment of the need for multiple components in the dissecting process. As a first case-study the GPU-optimized code is applied to the S0 galaxy NGC-7683, finding that in this galaxy a pseudo-bulge, possibly the remnant of a bar-like structure, does exist in the centre of the system. These results are then tested against the publicly available, orbit-based code dynamite , finding substantial agreement. [ABSTRACT FROM AUTHOR]

We use the magnetic-hydrodynamical simulation TNG50 to study the evolution of barred massive disc galaxies. Massive spiral galaxies are already present as early as z  = 4, and bar formation takes place already at those early times. The bars grow longer and stronger as the host galaxies evolve, with the bar sizes increasing at a pace similar to that of the disc scalelengths. The bar fraction mildly evolves with redshift for galaxies with |$M_{*}\ge 10^{10}\rm M_{\odot }$|⁠ , being greater than |$\sim 40{{\ \rm per\ cent}}$| at 0.5 < z < 3 and |$\sim 30{{\ \rm per\ cent}}$| at z  = 0. When bars larger than a given physical size (⁠|$\ge 2\, \rm kpc$|⁠) or the angular resolution limit of twice the I -band angular PSF FWHM of the HST are considered, the bar fraction dramatically decreases with increasing redshift, reconciling the theoretical predictions with observational data. We find that barred galaxies have an older stellar population, lower gas fractions, and star formation rates than unbarred galaxies. In most cases, the discs of barred galaxies assembled earlier and faster than the discs of unbarred galaxies. We also find that barred galaxies are typical in haloes with larger concentrations and smaller spin parameters than unbarred galaxies. Furthermore, the inner regions of barred galaxies are more baryon-dominated than those of unbarred galaxies but have comparable global stellar mass fractions. Our findings suggest that the bar population could be used as a potential tracer of the buildup of disc galaxies and their host haloes. With this paper, we release a catalogue of barred galaxies in TNG50 at six redshifts between z  = 4 and 0. [ABSTRACT FROM AUTHOR]

In this paper, we systematically explore the impact of a galactic bar on the inspiral time-scale of a massive object (MO) within a Milky Way-like galaxy. We integrate the orbit of MOs in a multicomponent galaxy model via a semi-analytical approach that accounts for dynamical friction generalized to rotationally supported backgrounds. We compare the MO evolution in a galaxy featuring a Milky Way-like rotating bar to the evolution within an analogous axisymmetric galaxy without the bar. In agreement with previous studies, we find that the bar presence may significantly affect the inspiral, sometimes making it shorter by a factor of a few, and sometimes hindering it for a Hubble time. The erratic behaviour is mainly impacted by the relative phase at which the MO encounters the stronger bar-induced resonances. In particular, the effect of the bar is more prominent for initially in-plane, prograde MOs, especially those crossing the bar co-rotation radius or outer Lindblad resonance. In the barred galaxy, we find the sinking of the most massive MOs (⁠|$\gtrsim 10^{7.5}\, \mathrm{M}_{\odot {}}$|⁠) approaching the galaxy from large separations (≳8 kpc) to be most efficiently hampered. Neglecting the effect of global torques associated with the non-symmetric mass distribution is thus not advisable even within an idealized, smooth galaxy model; we further note that spiral patterns are unlikely to affect the inspiral due to their transient and fluctuating nature. We speculate that the sinking efficiency of massive black holes involved in minor galaxy mergers may be hampered in barred galaxies, making them less likely to host a gravitational wave signal accessible to low-frequency detectors. [ABSTRACT FROM AUTHOR]

We report on ALMA observations of D1, a system at z ∼ 6.15 with stellar mass |$M_{*} \sim 10^7 \, \mathrm{M}_{\odot }$| containing globular cluster (GC) precursors, strongly magnified by the galaxy cluster MACS J0416.1-2403. Since the discovery of GC progenitors at high redshift, ours is the first attempt to probe directly the physical properties of their neutral gas through infrared observations. A careful analysis of our data set, performed with a suitable procedure designed to identify faint narrow lines and which can test various possible values for the unknown linewidth value, allowed us to identify a 4 σ tentative detection of [C  ii ] emission with intrinsic luminosity |$L_{\rm [C\, \rm {\small II}]}=(2.9 \pm 1.4)~10^6 \, {\it L}_{\odot }$|⁠ , one of the lowest values ever detected at high redshift. This study offers a first insight on previously uncharted regions of the |$L_{\rm [C\, \rm {\small II}]}{-}{\rm SFR}$| relation. Despite large uncertainties affecting our measure of the star formation rate, if taken at face value our estimate lies more than ∼1 dex below the values observed in local and high redshift systems. Our weak detection indicates a deficiency of [C  ii ] emission, possibly ascribed to various explanations, such as a low-density gas and/or a strong radiation field caused by intense stellar feedback, and a low metal content. From the non-detection in the continuum, we derive constraints on the dust mass, with 3 σ upper limit values as low as ∼ a few 104 M⊙, consistent with the values measured in local metal-poor galaxies. [ABSTRACT FROM AUTHOR]