Deep Investigation of Neutral Gas Origins (DINGO) is a deep blind survey of atomic hydrogen (HI) using the Australian SKA Pathfinder (ASKAP). Its aim is to study the evolution of HI from the current epoch to a time when the Universe was two-thirds is present age (z ∼ 0.4), through HI 21 cm emission spectral line observations of the Galaxy And Mass Assembly (GAMA) survey regions. The survey employs a two-tiered strategy: starting with z ≤ 0.1 and then extending to 0.25 ≤ z ≤ 0.4. Most of the science for DINGO will be done using stacked detections of the HI emission, though it will also yield unprecedented numbers of direct detections. We are already midway though the DINGO Pilot survey. I will discuss the present status of the DINGO Pilot survey and the initial data and associated science coming out of it. I will particularly focus on a study of the gas content of galaxy groups and pairs as compared to isolated galaxies, done using a combination of archival ALFALFA and DINGO Pilot data. We are finding possible evidence for the presence of large amounts of inter-galactic gas in low mass galaxy groups.

The Galactic disk exhibits complex chemical and dynamical substructure thought to be induced by the bar, spiral arms, and satellites. Here, we explore the chemical signatures of bar resonances in action and velocity space and characterize the differences between the signatures of corotation and higher-order resonances using test particle simulations. Thanks to recent surveys, we now have large homogeneous datasets containing metallicities and kinematics of stars outside the solar neighborhood. We compare the simulations to the observational data from Gaia EDR3, LAMOST DR5, and APOGEE DR16 and find weak evidence for a slow bar that associates the ``hat'' moving group with its outer Lindblad resonance and ``Hercules'' with corotation. While constraints from current data are limited by their spatial footprint, stars closer in azimuth than the Sun to the bar's minor axis show much stronger signatures of the bar's outer Lindblad and corotation resonances in test particle simulations. Future datasets with greater azimuthal coverage, including the final Gaia​​ data release, will allow reliable chemodynamical identification of bar resonances.

We show results form state-of-the-art gas modelling within three-dimensional numerical simulations including time-dependent non-equilibrium atomic and molecular chemistry coupled to different UV backgrounds, as suggested by recent literature, and various physical processes taking place in cosmic gas during structure formation (gas self-shielding, dust grain catalysis, metal fine-structure cooling, photoelectric and cosmic-ray heating). We predict neutral-gas (ΩHI) and H2 (ΩH2) density evolution, as well as depletion times in light of the latest ALMA, VLA, NOEMA, UKIDSS observations up to redshift z~7 and discuss their main drivers over cosmological epochs. Our findings suggest that non-equilibrium molecular cooling is efficient at lowering cold-gas temperatures in a wide variety of environments and since the first half Gyr. Different physical processes can affect H2 evolution in a non-trivial way and, thus, in addition to HI, H2 data appear to be pivotal probes for assessing cold-gas abundances and the role of UV radiation.

Thick disks are ubiquitous in nearby spiral galaxies, and many mechanisms, including mergers, have been proposed to explain their formation. I will first use a suite of zoom cosmological simulations to explore the connection between a galaxy's formation history and the structure of its disc. I will discuss some results on the structure of the Milky Way's thick disc, and what we can infer about the formation history of our Galaxy. Finally, I will present MUSE observations of NGC 5746, a massive (~10^11 Msun) edge-on disc galaxy. We find that a massive and extended disc formed very early: 80 per cent of the galaxy's stellar mass formed more than 10 Gyr ago. Most of the thick disc formed during that early phase. Later on, around ~8 Gyr ago, a ~1:10 merger happened. The satellite did not cause significant vertical heating (and also did not contribute to the growth of a classical bulge). It was however an important event for the galaxy: by depositing its stars throughout the whole galaxy it contributed ~30 per cent of accreted stars to the thick disc. This work highlights the complexity of thick discs, and the need for further observations to probe the build-up of discs across a wide range of masses.

The thermal Sunyaev-Zeldovich (tSZ) effect is a powerful, roughly redshift independent tool for discovering clusters of galaxies. The mass function of these clusters is a sensitive probe of cosmology, particularly sigma_8. However, accurate parameter estimation from this mass function requires accurate, unbiased mass estimates for the clusters, as well as a thorough understanding of the selection function of the underlying cluster catalog. In particular, radio and dusty galaxies which are spatially correlated with clusters may bias tSZ mass estimates. Similarly, astrophysical processes and structures, including shocks and jets, can cause significant deviation of the actual cluster profile from the assumed cluster profile, biasing mass reconstruction. In this talk I will discuss a recent work wherein we calibrated the mass-richness relation for an IR selected, high redshift cluster catalog using tSZ derived masses from the Atacama Cosmology Telescope (ACT), a Cosmic Microwave Background survey instrument. I will in particular detail the efforts we made to de-bias the mass estimates from point source effects. Finally, I will cover ongoing efforts to detect AGN supported X-ray cavities in the cluster MS0735 using the high resolution, 90GHz MUSTANG-2 instrument on the Green Bank Telescope (GBT). In addition to helping us de-bias mass estimates, a tSZ measurement of the bubble in MS0735 would shed light on the support mechanism for that bubble, and hence on astrophysical feedback processes that counteract radiative cooling of the intercluster medium.

Galactic Archaeology is commonly referred to the studies of Galactic history using chemical abundances of long-lived stars as fossil records. Today, thanks to Gaia and the large spectroscopic surveys available to the community, this field of study is going through a revolution, as we now have information on about 20 different chemical elements, ages and kinematics for thousands of stars. However, putting this huge multidimensional information together is everything but straightforward. I will introduce a new method that takes advantage of this multidimensional information by literally using long-lived stars as fossil records and putting these into phylogenetic trees, like a biologist.

The star-formation rate density (SFRD) and metal density (ZD) of the Universe are key diagnostics for understanding galaxies, as they encode the relative significance of all the main astrophysical processes driving galaxy evolution.

In this talk, I will present new results on the evolution of the SFRD and ZD from z=7 to 0 from the TNG100, EAGLE, and L-GALAXIES 2020 cosmological simulations. I will show that, while these simulations are able to reproduce either the observed SFRD or ZD, none is able to simultaneously match both. For example, some simulations can reproduce the high metal content observed in the neutral gas of damped Lyman-alpha (DLA) systems at z~3-5 (e.g. Peroux & Howk 2020), but require cosmic star formation rates in excess of those currently observed from FUV data (e.g. Madau & Dickinson 2014) to do so.

I will discuss three scenarios in which observations and simulations could be resolved: A) the cosmic SFRD at high redshift is higher than that inferred from FUV-FIR data, in which case TNG100 could be correct. B) the mean mass of DLA host galaxies is higher than that of the underlying galaxy population, in which case L-GALAXIES 2020 could be correct. C) neither of the above are true, in which case EAGLE could be correct, although at the expense of over-estimating DLA metallicities. These results demonstrate the huge importance of considering the ZD alongside the SFRD when constraining galaxy evolution models.

Nuclear star clusters (NSC), dense and compact stellar systems located at the bottom of the galactic potential well, are important tracers of the dynamical state of galaxies and their evolution. Stellar kinematics, which brings the footprint of the dynamical history of galactic structures, helps us to disentangle between the two main formation scenarios proposed for NSCs: star-cluster infall or in-situ star formation. We present parsec-scale kinematics of 11 nearby galactic nuclei, derived from adaptive-optics assisted integral field spectroscopy at (near-infrared) CO band-head wavelengths. We focus our analysis on the balance between ordered rotation and random motions, which can provide insights into the dominant formation mechanism of NSCs. We divide our target sample into late- and early-type galaxies, and discuss the nuclear kinematics of the two subsamples, aiming at probing any link between NSC formation and host galaxy evolution. The results suggest that the dominant formation mechanism of NSCs is indeed affected by the different evolutionary paths of their hosts across the Hubble sequence. More specifically, nuclear regions in late-type galaxies are on average more rotation dominated, and the formation of nuclear stellar structures is potentially linked to the presence of gas funneled to the center. Early-type galaxies, in contrast, tend to display more slowly rotating NSCs with lower ellipticity. However, some exceptions suggest that in specific cases, early-type hosts can form NSCs in a way similar to spirals.

Tracing the peaks of the matter distribution in the Universe, galaxy clusters can be used as powerful cosmological probes, as well as fantastic astrophysical laboratories, due to the complex interplay between their constituents. Presently, cluster cosmology is limited by systematic on the mass measurements, also linked to their detection. High mass systems at low and intermediate redshifts (z<~0.6) have been extensively characterized, partly because it is simply easier to obtain direct mass measurements for high signal to noise data.

In this talk, I will discuss the necessity to explore the low mass/high redshift regime to better exploit the samples coming from next generation surveys, and the opportunities given by multi-wavelength data combination approaches. I will present an observational project aiming at mapping three below mass clusters in SZ with the millimeter camera NIKA2, and the optical +X-ray+SZ characterization of the first target, appearing as a “bullet like cluster” at z~1. Finally, I will conclude on how to use information about individuals systems to inform cosmological analyses of large samples, via the use of simulations.

S0 galaxies make up one of the largest population of galaxies in the Universe, yet how they form has remained an unresolved question. A number of formation pathways have been proposed and tested in idealised simulations, however which pathways (and their relative contribution) are actually occurring in a cosmological context remains an open question. Here we combine observations and simulations to argue that two main formation pathways are transforming spiral galaxies into S0s; galaxy mergers and gas stripping during cluster infalls. In the observational study, we use stellar kinematics to show that the range of rotational support in the S0 population is difficult to explain using a single formation pathway, suggesting multiple pathways are active. In a follow-up study using the IllustrisTNG simulation, we then traced the history of S0 galaxies and identified their formation mechanism. We found that 37 percent formed from spirals via mergers and 57 percent formed from the gas stripping of a spiral falling into a larger cluster environment, with the remainder forming due to gas exhaustion.

Recent observations show that cosmic expansion is dominated by an effective cosmological constant. This means that we live inside a trapped surface, which corresponds to a Black Hole (BH) event horizon. Such Black Hole Universe (BHU) is a solution to classical GR, where two nested FLRW metrics are connected by a BH event horizon. CMB observations show some anomalies which are consistent with this BHU idea.

This new solution can be used to model our full Universe or a stellar BH inside. Observed BHs (and possibly BHs making the Dark Matter, DM) also could be made of such BHUs. In comoving coordinates the BHU is expanding while in Schwarzschild coordinates it is asymptotically static and therefore timeless. Such frame duality allows for a Perfect Cosmological Principle where spacetime can be homogeneous both in space and time, in better agreement with the relativity principle (see also darkcosmos.com)

The jets of active galactic nuclei (AGN) can produce spectacular structures in the radio wavelengths known as a radio galaxy. The morphology and characteristics of the jets of a radio galaxy can be used as a diagnostic to understand the physics occurring within and surrounding it. In this talk, I will first present the results of several investigations of the interplay between radio AGN and their environment that use infrared (Spitzer), optical (Pan-STARRS), and radio observations (VLA, LOFAR) of AGN in massive galaxy clusters at z~1. Then, I will present a multi-wavelength study of the radio galaxy population in the galaxy cluster MOO J1507+5137, which has exceptional radio activity among the massive galaxy population. The data are suggestive that during the cluster-cluster merger phase radio activity can be dramatically enhanced. Lastly, using the radio morphology and excitation state of radio galaxies, I explore the possibility of AGN having spectral states analogous to those of X-ray binaries (XRBs) and find that different classes of radio-loud AGN occupy distinct areas of the state diagram with broad similarities to XRBs.

Recent high-resolution interferometric images of submillimetre galaxies (SMGs) reveal fascinatingly complex morphologies. This raises a number of questions: how does the relative orientation of a galaxy affect its observed submillimetre emission, and does this result in an `orientation bias' in the selection and analysis of such galaxies in flux-limited cosmological surveys? In this talk I'll describe our recent paper investigating these questions, using the Simba cosmological simulation paired with the dust radiative transfer code Powderday. We found that galaxies exhibit significant scatter in their emission close to the peak of the thermal dust emission, with variation in flux density of up to ∼50 mJy at the peak. This results in an appreciable dispersion in the inferred dust temperatures and infrared luminosities (16th−84th percentile ranges of 5 K and 0.1 dex, respectively) and therefore a fundamental uncertainty in derived parameters such as dust mass and star formation rate (∼30% for the latter using simple calibrations). Using a Monte Carlo simulation we also assessed the impact of orientation on flux-limited surveys, and found a bias in the selection of SMGs towards those with face-on orientations, as well as those at lower redshifts.

We predict that the orientation bias will affect flux-limited single-dish surveys, most significantly at THz frequencies, and I will discuss how this bias should be taken into account when placing the results of targeted follow-up studies in a statistical context.

Dome C in Antarctica offers exceptional conditions for time-series photometry thanks to the continuous night during the Antarctic winter and favourable atmospheric conditions. We developed a pilot project to search and characterise transiting exoplanets from this site and qualify it for visible photometry. Our instruments have been running for several years and provide excellent data. The main telescope is undergoing a major upgrade that will increase its throughput and enable simultaneous observations in two colours. I will present the project, the results, the ongoing observations, and the upgrade we are implementing.

With the very recent discovery of radio luminous AGN at z>6, a new window of opportunity is finally opening in the study of the galaxy evolution at the end of the Epoch of Reionization. Our pilot programme in the 60 deg^2 GAMA-09 field uses a new selection technique taking advantage of the large frequency coverage of GLEAM by selecting compact, steep and curved sources at low-frequency (70-230MHz). Out of four candidates, one new powerful radio galaxy, 0856+0224, is confirmed at z=5.55, finally overtaking the z=5.2 20 year-old record for distant radio galaxies (albeit just falling short of the new recent z=5.7 record). Interestingly, 0856+0224 presents similarities with existing z<5 redshift samples, giving confidence in the success of our selection technique. Our recent progress on a second source, 0917-0012, thanks to the extensive multi-wavelength coverage from follow-up observations with ALMA and JVLA, supplemented with publicly available data, place this source at a promising z>5. I will also discuss the refinement of our selection technique over the full 1200 deg^2 sky area covered by the ESO VIKING near-infrared survey, leading to 55 new high-redshift candidates. This sample aims to provide us with the first statistically significant radio luminous active galactic nuclei sample at z > 6.5 during the Epoch of Reionization. The nature of radio selection presents the advantage of being insensitive to orientation-dependent obscuration, it allows us (i) to study simultaneously the co-evolution of the supermassive black hole and host galaxy and (ii) to enable the study of the IGM through the HI absorption line.

Astrophysical jets are frequently observed phenomena in the Universe, which play an important feedback role in the evolution of their host systems. Long-term monitoring of post-AGB binary systems has revealed periodic variations in their Balmer lines, indicating that jets are also common in these systems. To harness the wealth of information hidden in these observations, we developed a spatio-kinematic model of the jet to recreate the observed Balmer line variations. I will present our results for 15 jet-creating post-AGB binaries, where we determined the full 3D, velocity, and density structure of the jets and their mass-outflow momenta. I will also present how these results can be linked to the mass-transfer in the binary system, which reveals that the circumbinary disk feeds the accretion onto the jet-launching companion. With this work, we gain crucial insights into the structures of jets launched by these post-AGB binary systems and their mass-transfer history.​

Nowadays, the development of the observational instruments is so high that became very sensitive to the details of stellar physics. The interpretation of the stellar surfaces images, the fundamental parameters, the stellar variability and the hosting planet detection & characterisation needs realist simulations of stellar convection. In this context, three-­dimensional radiative hydrodynamics simulations of cool stars are essential to a proper and quantitative analysis of these observations. I will present how these simulations across the Hertzsprung-Russel diagram have been (and will be) crucial to prepare and interpret the spectrophotometric, interferometric, astrometric, and imaging observations.

With the help of the APOGEE survey and Gaia EDR3, we review the dependency of metallicity and alpha-elements with orbital parameters and velocities for an unprecedented coverage and precise sample of stars in the inner Galaxy (28 000 stars within |XGal| < 5 kpc, |YGal| < 3.5 kpc, |ZGal| < 1 kpc, and 8000 stars more restricted to the innermost regions). These samples allow us to characterize the different coexisting populations in the region via joint analysis of the distributions of velocities, metallicities, orbital parameters and chemical abundances.  The chemo-kinematic data dissected on the orbital plane maps the bar, the inner disk, and the pressure supported component, showing that the Galactic bar consists of metal-poor and metal-rich stars. It clearly shows that all these components are much more complex and that the classical definitions of the galactic components are blurred.  We also detect a tail of counter-rotating stars, suggesting a merger or proto Galactic disk remnants. The analysis would not have been possible without the high-resolution spectroscopic survey APOGEE, the parallaxes and proper motions from Gaia EDR3, and the StarHorse tool, which can combine spectra, photometry and astrometry to derive precise distances even for this challenging area.

Relic galaxies, i.e., massive, compact and old galaxies which have formed most of their stars in a short time are the remnants of high-z red nuggets. Most of the high-z galaxies are supposed to merge with smaller companions and systematically increase their size becoming the big monsters in the local Universe. But, due to the stochastic nature of galaxy mergers, few of them should survive untouched for their entire life, these are the relics. The time has finally come: although extremely rare, it is now possible to find them and study their properties in very details. They will provide a unique look at the high-z red nuggets, the stellar populations in the cores of the largest local galaxies and the role of mergers and environment on the evolution of the most massive and passive galaxies.

I will bring you through the "Relics' revolution", starting from the discoveries of the first relic galaxies in the local Universe, and then I discuss our contribution to the field. KiDS@VST survey and a campaign of spectroscopic follow-ups have provided us with an unprecedented sample of relic candidates, the so called ultra-compact galaxies (UCMGs), i.e. galaxies with stellar masses > 8 * 10^10 solar masses, and sizes < 1.5 kpc, at redshifts z < 0.5. We have studied their abundance in terms of redshift and environment.

We are now approaching the innermost cave, with the INSPIRE large program, which aims at determining, within the UCMG sample, the stellar populations of relic candidates using XShooter@VLT. The first results of this project, i.e. stellar population parameters and velocity dispersions for 19 relic candidates, are reported in recent works. Thanks to INSPIRE, we seize the sword: we confirm the discovery of the first 10 relics ever found at 0.15 < z < 0.4, which add to the only three existing in the local Universe and already characterized in very detail. I will finally go through the current state of our project and future prospects.

Carbon is next to H, He, and O, the most abundant element in the Universe and is extensively used (usually in combination with O) when probing the  chemical evolution of stellar populations and galaxies. However, the origin of carbon is not yet settled and some studies favor low-mass stars while others favor high-mass stars. The situation is further complicated as the surface composition of carbon in evolved stars might have been altered by the internal burning processes of the star. Therefore, reliable carbon abundances  that trace the composition of carbon of the gas cloud the star was born from requires spectral analysis of un-evolved dwarf and subgiant stars.

In this talk I will present new measurements of carbon in a sample of 91 microlensed dwarf and subgiant stars in the Galactic bulge and discuss how we can use these to probe the origin and evolution of the Galactic bulge as well as some hints of which stars that are the main contributors to the C enrichment of the interstellar medium.

Star formation in massive clusters is a major route of star formation, particularly in extreme environments as encountered in starburst galaxies or in the early universe. In these environments an intimate relation between massive reservoirs of gas and the population of young stars can be expected, among them numerous hot and luminous early type stars.

These stars will have a profound impact on the surrounding gas, via their UV radiation, winds, and ultimately via supernova explosions. It is not clear, however, what the consequences of this impact will be. Further star formation could be triggered, suppressed, or ultimately terminated by feedback, and the physical conditions of the dense gas forming new stars can be changed, possibly changing the fragmentation properties and the resulting stellar mass function.

We here present an APEX study of the temperature distribution within the dense gas reservoir in the NGC3603 region. NGC3603 harbours the most massive young cluster associated with substantial amounts of molecular gas known in our Galaxy and may serve as a template for its more massive extragalactic counterparts.

We find a clear gradient in dense gas temperatures, decreasing with distance from the starburst cluster, testifying to the potential of a starburst cluster to skew the outcome of further star formation in its environment . Major sites of ongoing massive star formation are found at the far ends of the giant molecular cloud, indicating that indeed the story in NGC3603 goes on.

Will a newborn star feel a difference between being born in Orion today, and in a massive, dusty galaxy 10 billion years ago? Forming stars at rates 100x higher than any present-day galaxy, the dust-enshrouded, sub-mm bright galaxies (SMGs) play a key role in the stellar mass assembly in the early Universe. However, our understanding of physical conditions in the star-forming regions in SMGs has been very limited, chiefly due to the coarse (> 1 kpc) resolution of mm-wave observations. Even with the full power of ALMA, multi-tracer (dust, [CII], CO) studies of the ISM in SMGs remain an extremely expensive undertaking.

I will present the recent results of molecular gas studies of probably the best-studied SMG: SDP.81 (z = 3.0), a spectacular, strongly gravitationally lensed starburst. Combining ∼40 hours of ALMA long-baseline, multi-band observations, lens modelling, and radiative transfer models, we mapped the physical conditions in this SMG at an unprecedented, ∼100 pc resolution. These results provide the first view of the physical conditions in SMGs on scales comparable to nearby galaxies and their variation on sub-kpc scales. I will also discuss the limitations of the current data, on-going VLA and ALMA studies targeting the HCN, HCO+ and radio emission in this unique source, and future survey of ISM physics of large samples of SMGs.

The merging rate of double neutron stars (DNS) has a great impact on many astrophysical issues, including the interpretation of gravitational waves signals, of the short Gamma Ray Bursts (GRBs), and of the chemical properties of stars in galaxies. Such rate depends on the distribution of the delay times (DDT) of the merging events. In this paper we derive a theoretical DDT of merging DNS following from the characteristics of the clock controlling their evolution. We show that the shape of the DDT is  governed by a few key parameters, primarily the lower limit and the slope of the distribution of the separation of the DNS systems at birth. With a parametric approach we investigate on the observational constraints on the DDT from the cosmic rate of short GRBs and the Europium to Iron ratio in Milky Way stars, taken as tracer of the products of the explosion. We find that the local rate of DNS merging requires that $\sim 1 \%$ of neutron stars progenitors live in binary systems which end their evolution as merging DNS within a Hubble time. The redshift distribution of short GRBs does not yet provide a strong constraint on the shape of the DDT, although the best fitting models have a shallow DDT. The chemical pattern in Milky Way stars requires an additional source of Europium besides the products from merging DNS, which weakens the related  requirement on the DDT. At  present both constraints can be matched with the same DDT for merging DNS.

In this talk I will present one of most recent papers of the TIMER project with MUSE at the VLT. We have obtained high signal-to-noise and spatial resolution integral-field spectroscopy data of the inner few kpc of 21 nearby massive barred galaxies, allowing studies of the stellar kinematics and population properties with unprecedented spatial resolution. We establish the presence of nuclear discs in virtually all galaxies and show that their kinematics and structural properties are consistent with the bar-driven secular evolution picture for their formation. We also show that such nuclear discs are recovered as exponential, photometric "bulges" in careful, state-of-the-art image decompositions. Finally, I put these observations in the context of recent results concerning the central region of our own Milky Way.

Besides the Galactic Center, GRAVITY’s dual-feed mode also enables observations of faint companions to nearby stars, such as exoplanets and brown dwarfs. By combining the light of four telescopes, precise astrometry and high-quality spectra of these companions can be obtained. In this talk, I will first illustrate the setup of exoplanet observations with GRAVITY. Then, I will show that GRAVITY’s spectrographs are affected by correlated errors and how they can be mitigated in order to increase the achievable contrast. In the second half of the talk, I will focus on the reddest known sub-stellar companion HD 206893 B and what we can learn about its orbit and atmosphere from our GRAVITY data. Due to its extremely red color, this specific object represents a benchmark case for atmospheric models and highlights the challenges in revealing the nature of a companion (exoplanet or brown dwarf) in direct imaging.

The variability of AGN is stochastic in its nature (e.g. Vaughan et al. 2003). It is well modelled as local fluctuations in the accretion flow propagating inwards, where most of the energy is dissipated but the flow contains the memory of all the local time-scales. However, apart from this regular, low-level stochastic variability, some AGN occasionally show exceptionally large changes in the luminosity, spectral shape and/or X-ray absorption. The most notable are the changes of the spectral type, when the source classified as a Seyfert 1 becomes a Seyfert 2 galaxy, or vice versa.Thus a name was coined of 'Changing-Look AGN' (CL AGN).

Only a few cases were recorded in the past (e.g. NGC 5548, Peterson et al. 1987). Recently the number of new CL AGN is growing rapidly (MacLeod et al. 2019), so the phenomenon is apparently not so rare as previously thought. The origin of this phenomenon is still unknown, but for most of the sources there are strong arguments in favor of the intrinsic changes (e.g., Kynoch et al. 2019, Hutsemekers et al. 2019). Understanding the nature of such rapid changes is a challenge to the models of accretion flow onto the black hole. The time-scales are much shorter than the usual viscous time-scales in the accretion disks (of order of hundreds of years, or longer, depending on the black hole mass and the Eddington ratio). There are no convincing models of this phenomena, although some mechanisms are already proposed (e.g. Ross et al. 2018, Sniegowska et al. 2020).

In recent years, ALMA has allowed for probing the the Sunyaev-Zeldovich (SZ) effect at unprecedented sensitivity and angular resolution, thus opening a millimetre-wave window - complementary to X-ray observations - on the evolution of galaxy clusters and the physics of the intracluster medium. I will present the recent results from a high-resolution multi-wavelength study of one of the most massive clusters ever observed at a redshift larger than 1, SPT-CL J2106-5844. The unique capabilities of ALMA+ACA allow one to resolve the bimodal structure of the ICM, corresponding to the peaks in the mass distribution but difficult to identify in the X-ray data alone. The radio observations by ASKAP and ATCA further revealed the presence of an extended complex of radio sources, of which part is associated with strong star formation activity within the cooling cluster core. All this demonstrates how the combination of SZ information at high angular resolution with data spanning the whole electromagnetic spectrum can be pivotal in the characterization of dynamical and thermodynamical properties of galaxy clusters.

Surveys of bright sub-millimetre sources with ALMA have provided the first unbiased view of intense star formation at high redshift and have allowed for detailed studies of their structures and star formation triggers. I will present a detailed analysis of high resolution (0.18") 870um continuum maps of ~150 sub-mm galaxies (SMGs) selected from the ALMA-SCUBA-2 UDS survey. These observations resolve the dust which traces ongoing star formation within the interstellar medium of these galaxies, and typically have infrared light profiles consistent with exponential discs. The profiles also reveal an axis ratio distribution best described by triaxial shapes. This suggests that the sub-millimetre emission is tracing bars, which are funnelling cold gas from the outer part of the galaxies into the centres. Previous studies have suggested that SMGs may be the high-redshift analogs to local merger-dominated ultra-luminous infrared galaxies (ULIRGs). However, these results and other recent studies, suggest that SMGs instead have disc morphologies. This means that ALMA - once again - is revealing important differences between high-redshift SMGs and local ULIRGs.