The Collapse of Atomically-Cooled Primordial Haloes. I. High Lyman-Werner Backgrounds

Pristine, atomically-cooled haloes are leading contenders for the sites of primordial quasar formation because atomic cooling triggers rapid baryon collapse that can create 10$^4$ - 10$^5$ M$_{\odot}$ black hole seeds. However, until now no numerical simulations with a wide range of halo spins and assembly histories have followed the collapse for the times required to form a black hole. We have now performed cosmological simulations of baryon collapse in atomically-cooled haloes for times that are sufficient for supermassive stars to form and die as direct-collapse black holes (DCBHs). Our simulations reveal that fragmentation of the accretion disk at the center of the halo after $\sim$ 500 kyr is nearly ubiquitous and in most cases leads to the formation of binary or multiple supermassive stellar systems. They also confirm that rapid baryon collapse proceeds for the times required for these stars to form DCBHs. Our discovery raises the exciting possibility of detecting gravitational waves from DCBH mergers with LISA and tidal disruption events in the near infrared with the James Webb Space Telescope and ground-based telescopes in the coming decade.Comment: 13 pages, 10 figures, submitted to MNRA

WISDOM project -- XVI. SMBH mass in the early-type galaxies NGC0612, NGC1574, and NGC4261 from CO dynamical modelling

We present a CO dynamical estimate of the mass of the super-massive black hole (SMBH) in three nearby early-type galaxies: NGC0612, NGC1574 and NGC4261. Our analysis is based on Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 3-6 observations of the $^{12}$CO(2-1) emission line with spatial resolutions of $14-58$ pc ($0.01''-0.26''$). We detect disc-like CO distributions on scales from $\lesssim200$ pc (NGC1574 and NGC4261) to $\approx10$ kpc (NGC0612). In NGC0612 and NGC1574 the bulk of the gas is regularly rotating. The data also provide evidence for the presence of a massive dark object at the centre of NGC1574, allowing us to obtain the first measure of its mass, $M_{\rm BH}=(1.0\pm0.2)\times10^{8}$ M$_{\odot}$ (1$\sigma$ uncertainty). In NGC4261, the CO kinematics is clearly dominated by the SMBH gravitational influence, allowing us to determine an accurate black hole mass of $(1.62{\pm 0.04})\times10^{9}$ M$_{\odot}$ ($1\sigma$ uncertainty). This is fully consistent with a previous CO dynamical estimate obtained using a different modelling technique. Signs of non-circular gas motions (likely outflow) are also identified in the inner regions of NGC4261. In NGC0612, we are only able to obtain a (conservative) upper limit of $M_{\rm BH}\lesssim3.2\times10^{9}$ M$_{\odot}$. This has likely to be ascribed to the presence of a central CO hole (with a radius much larger than that of the SMBH sphere of influence), combined with the inability of obtaining a robust prediction for the CO velocity curve. The three SMBH mass estimates are overall in agreement with predictions from the $M_{\rm BH}-\sigma_{\star}$ relation.Comment: Main text: 20 pages, 14 Figures; Appendix: 7 pages, 6 Figures. Accepted for publication in MNRAS on 2023 March 2

WISDOM project - XVIII. Molecular gas distributions and kinematics of three megamaser galaxies

The co-evolution of galaxies and supermassive black holes (SMBHs) underpins our understanding of galaxy evolution, but different methods to measure SMBH masses have only infrequently been cross-checked. We attempt to identify targets to cross-check two of the most accurate methods, megamaser, and cold molecular gas dynamics. Three promising galaxies are selected from all those with existing megamaser SMBH mass measurements. We present Atacama Large Millimeter/sub-millimeter Array (ALMA) 12CO (2–1) and 230-GHz continuum observations with angular resolutions of ≈0 5. Every galaxy has an extended rotating molecular gas disc and 230-GHz continuum source(s), but all also have irregularities and/or non-axisymmetric features: NGC 1194 is highly inclined and has disturbed and lopsided central 12CO (2–1) emission; NGC 3393 has a nuclear disc with fairly regular but patchy 12CO (2–1) emission with little gas near the kinematic major axis, faint emission in the very centre, and two brighter structures reminiscent of a nuclear ring and/or spiral; NGC 5765B has a strong bar and very bright 12CO (2–1) emission concentrated along two bisymmetric offset dust lanes and two bisymmetric nuclear spiral arms. 12CO (2–1) and 12CO (3–2) observations with the James Clerk Maxwell Telescope are compared with the ALMA observations. Because of the disturbed gas kinematics and the impractically long integration times required for higher angular resolution observations, none of the three galaxies is suitable for a future SMBH mass measurement. None the less, increasing the number of molecular gas observations of megamaser galaxies is valuable, and the ubiquitous disturbances suggest a link between large-scale gas properties and the existence of megamasers

WISDOM Project - X. The morphology of the molecular ISM in galaxy centres and its dependence on galaxy structure

We use high-resolution maps of the molecular interstellar medium (ISM) in the centres of 86 nearby galaxies from the millimetre-Wave Interferometric Survey of Dark Object Masses (WISDOM) and Physics at High Angular Resolution in Nearby GalaxieS (PHANGS) surveys to investigate the physical mechanisms setting the morphology of the ISM at molecular cloud scales. We show that early-type galaxies tend to have smooth, regular molecular gas morphologies, while the ISM in spiral galaxy bulges is much more asymmetric and clumpy when observed at the same spatial scales. We quantify these differences using non-parametric morphology measures (Asymmetry, Smoothness, and Gini), and compare these measurements with those extracted from idealized galaxy simulations. We show that the morphology of the molecular ISM changes systematically as a function of various large-scale galaxy parameters, including galaxy morphological type, stellar mass, stellar velocity dispersion, effective stellar mass surface density, molecular gas surface density, star formation efficiency, and the presence of a bar. We perform a statistical analysis to determine which of these correlated parameters best predicts the morphology of the ISM. We find the effective stellar mass surface (or volume) density to be the strongest predictor of the morphology of the molecular gas, while star formation and bars maybe be important secondary drivers. We find that gas self-gravity is not the dominant process shaping the morphology of the molecular gas in galaxy centres. Instead effects caused by the depth of the potential well, such as shear, suppression of stellar spiral density waves, and/or inflow, affect the ability of the gas to fragment

WISDOM project XX. - Strong shear tearing molecular clouds apart in NGC 524

Early-type galaxies (ETGs) are known to harbour dense spheroids of stars but scarce star formation (SF). Approximately a quarter of these galaxies have rich molecular gas reservoirs yet do not form stars efficiently. We study here the ETG NGC 524, with strong shear suspected to result in a smooth molecular gas disc and low star-formation efficiency (SFE). We present new spatially resolved observations of the 12CO(2-1)-emitting cold molecular gas from the Atacama Large Millimeter/sub-millimeter Array (ALMA) and of the warm ionized-gas emission lines from SITELLE at the Canada–France–Hawaii Telescope. Although constrained by the resolution of the ALMA observations (≈37 pc), we identify only 52 GMCs with radii ranging from 30 to 140 pc, a low mean molecular gas mass surface density 〈Σgas〉 ≈ 125 M⊙ pc−2 and a high mean virial parameter 〈αobs, vir〉 ≈ 5.3. We measure spatially resolved molecular gas depletion times (τdep ≡ 1/SFE) with a spatial resolution of ≈100 pc within a galactocentric distance of 1.5 kpc. The global depletion time is ≈2.0 Gyr but τdep increases towards the galaxy centre, with a maximum τdep, max ≈ 5.2 Gyr. However, no pure H II region is identified in NGC 524 using ionized-gas emission-line ratio diagnostics, so the τdep inferred are in fact lower limits. Measuring the GMC properties and dynamical states, we conclude that shear is the dominant mechanism shaping the molecular gas properties and regulating SF in NGC 524. This is supported by analogous analyses of the GMCs in a simulated ETG similar to NGC 524

WISDOM Project - XVI. The link between circumnuclear molecular gas reservoirs and active galactic nucleus fuelling

We use high-resolution data from the millimetre-Wave Interferometric Survey of Dark Object Masses (WISDOM) project to investigate the connection between circumnuclear gas reservoirs and nuclear activity in a sample of nearby galaxies. Our sample spans a wide range of nuclear activity types including radio galaxies, Seyfert galaxies, low-luminosity active galactic nuclei (AGN) and inactive galaxies. We use measurements of nuclear millimetre continuum emission along with other archival tracers of AGN accretion/activity to investigate previous claims that at, circumnuclear scales (<100 pc), these should correlate with the mass of the cold molecular gas. We find that the molecular gas mass does not correlate with any tracer of nuclear activity. This suggests the level of nuclear activity cannot solely be regulated by the amount of cold gas around the supermassive black hole (SMBH). This indicates that AGN fuelling, that drives gas from the large-scale galaxy to the nuclear regions, is not a ubiquitous process and may vary between AGN type, with time-scale variations likely to be very important. By studying the structure of the central molecular gas reservoirs, we find our galaxies have a range of nuclear molecular gas concentrations. This could indicate that some of our galaxies may have had their circumnuclear regions impacted by AGN feedback, even though they currently have low nuclear activity. Alternatively, the nuclear molecular gas concentrations in our galaxies could instead be set by secular processes

WISDOM Project - XVII. Beam-by-beam properties of the molecular gas in early-type galaxies

We present a study of the molecular gas of seven early-type galaxies with high angular resolution data obtained as part of the mm-Wave Interferometric Survey of Dark Object Masses (WISDOM) project with the Atacama Large Millimeter/submillimeter Array. Using a fixed spatial-scale approach, we study the mass surface density (Σ) and velocity dispersion (σ) of the molecular gas on spatial scales ranging from 60 to 120 pc. Given the spatial resolution of our data (20–70 pc), we characterize these properties across many thousands of individual sightlines (≈50 000 at our highest physical resolution). The molecular gas along these sightlines has a large range (≈2 dex) of mass surface densities and velocity dispersions higher than those of star-forming spiral galaxies. It has virial parameters αvir that depend weakly on the physical scale observed, likely due to beam smearing of the bulk galactic rotation, and is generally supervirial. Comparing the internal turbulent pressure (Pturb) to the pressure required for dynamic equilibrium (PDE), the ratio Pturb/PDE is significantly less than unity in all galaxies, indicating that the gas is not in dynamic equilibrium and is strongly compressed, in apparent contradiction to the virial parameters. This may be due to our neglect of shear and tidal forces, and/or the combination of three-dimensional and vertical diagnostics. Both αvir and Pturb anticorrelate with the global star-formation rate of our galaxies. We therefore conclude that the molecular gas in early-type galaxies is likely unbound, and that large-scale dynamics likely plays a critical role in its regulation. This contrasts to the giant molecular clouds in the discs of late-type galaxies, that are much closer to dynamical equilibrium