In the upcoming decades large facilities, such as the SKA, will provide resolved observations of the kinematics of millions of galaxies. In order to assist in the timely exploitation of these vast datasets we have explored the use of self-supervised, physics aware neural networks capable of Bayesian kinematic modelling of galaxies. In this talk I will present the network's ability to model the kinematics of cold gas in galaxies with an emphasis on recovering physical parameters and accompanying modelling errors. The models discussed are able to recover rotation curves, inclinations and disc scale lengths for both CO and HI data which match well with those estimated in the literature. The models are also able to provide modelling errors over learned parameters thanks to the application of quasi-Bayesian Monte-Carlo dropout. This work shows the promising use of machine learning and, in particular, self-supervised neural networks in the context of kinematically modelling galaxies observed using interferomers such as ALMA and VLA as well as IFU instruments like SDSS (MaNGA).

Dwarf galaxies are the most common type of galaxies in the Universe at all epochs and they play a fundamental role in cosmic history, being responsible for the build up of massive galaxies and possibly driving the reionization and metal enrichment processes. High-redshift observations of such sources are not available yet, but we demonstrate that the James Webb Space Telescope (JWST), while targeting massive Lyman Break Galaxies (LBGs), will catch for the first time the light of the faint satellite dwarf galaxies orbiting around them.We use state-of-art cosmological simulations of a typical LBG at z=6 to uncover the properties of satellite galaxies and make predictions for the upcoming JWST observations. These dwarf galaxies cover a wide range of stellar masses (log(M⋆/M⊙)≃7−9). We find that, even in such extremely dense environments, internal supernovae feedback is the key mechanism regulatingtheir evolution, capable of completely quenching dwarf galaxies. Only the frequent merger events characterising these biased regions can effectively prolong the star-formation in the most massive satellites.Modelling the galaxies’ stellar emission we reconstruct their spectral energy distributions: these reveal how with the JWST/NIRCam instrument, through colour-magnitude diagrams, it will be possible to infer properties such as the galaxies’ stellar masses and ages. The instrument’s high resolution will allow us to spatially resolve these small systems from the nearby host. Thanks to JWST’s high sensitivities we will detect, for the very first time, faint satellite dwarf galaxies of high-z LBGs in less than 5 hours.

The investigation of the physical hot and energetic phenomena in the Universe will further improve our understanding of the assembly of the largest structures and massive halos of galaxies, and of the role of black holes in shaping the Universe as we see it. Spatially resolved X-ray high-resolution spectroscopy will be a crucial tool to achieve these scientific goals. The X-IFUinstrument onboard the Athena observatory will provide us with these capabilities through the use of arrays of Transition edge microcalorimeters detectors. These superconducting devices will deliver the required exquisite spectral resolution needed to achieve the core science objectives, such as the characterization of turbulence and bulk motions in the hot gaseous atmospheres of groups and clusters of galaxies in order to unveil the process of large scale structures assembly. I will present the TransitionEdge Sensors principle, the status of the instrumental development for the X-IFU instrument, and discuss their performance in view of the scientific objectives of the Athena mission. I will further present the case of a feasibility study and optimisation of the observing strategy for the characterization of the internal dynamics of the intra-cluster medium, through the use of mock simulations of observations with the X-IFU instrument.

One of the fundamental questions for planetary science is how surfaces of other planets similar to the rocky bodies in our solar system look like. What is the rock structure like? Will there be water? Are there any active atmospheric cycles? How can we detect these different conditions?The current space missions and ground based instruments allow the detection of specific gasspecies and some cloud compositions in atmospheres of giant exoplanets. With instruments  installed in the near future and space crafts currently being build or planned, these kind of observations will be available for planets with smaller sizes and an overall rocky composition. We aim to further understand the connection of the conditions of the upper atmosphere with the conditions on the crust of the planet (temperature, pressure, composition).Our equilibrium chemistry models allow us to investigate theexpected crust and near-crust-atmosphere composition based. With this, we investigate the conditions under which liquid water is actually stable at the surface of a planet and not incorporated in hydrated rocks. Based on this crust -near-crust-atmosphereinteraction we build an atmospheric model, which allows us to investigate what kind of clouds are stable and could be present in atmospheres of rocky exoplanets. This allows us to link the high altitude gas phase and cloud compositions to the surface conditions.

The host galaxies of z>6 quasars are ideal laboratories to investigate the interplay between the accreting black hole and star formation and to characterize the interstellar medium (ISM) at cosmic dawn. The unprecedented capabilities of ALMA and NOEMA have opened a new window to study the galaxy evolution at early epochs at (sub-)mm wavelengths. By surveying multiple ISM tracers, we can probe the different phases of the star-forming medium and put first quantitative constraints on their physical properties for which there is little information at such high redshifts. In this talk I will present an ALMA multi-line survey of two z>6 quasar host galaxies and their nearby serendipitous-discovered companions. These are among the most star-forming galaxies known to date at these redshifts that do not show evidence of AGN activity. By measuring the emission of various gas tracers (OH163𝜇m, H2O, mid-/high-J CO, [CI]369𝜇m, [CII]158𝜇m, [NII]205𝜇m), we study the impact of the luminous accreting black hole and intense star formation on the ISM of the quasar hosts and their companions. In addition, by combining continuum emission in different frequency bands we place constraints on the dust properties. In this talk, I will show the power of multi-line studies of far-infrared diagnostics in order to dissect the physical conditions in the first massive galaxies as they emerge at the end of the Epoch of Reionization. This study lays the foundation for a follow-up campaign using NOEMA aiming to probe the warm dense phase of the ISM at z>6.

Blue straggler stars (BSS) were originally identified in the color-magnitude diagram (CMD) of the globular cluster M3, where they defined an extension of the cluster main sequence, blueward and above the turnoff (TO). Among the variety of objects that populate stellar clusters, BSS  are surely between those still presenting many puzzles to astronomers since they are considered crucial probes for the study of the complex interaction between stellar evolution and stellar dynamics. Further, their presence poses a challenge for the standard single-star evolution theory, since stars with masses higher than that of the cluster TO  should have evolved into the white dwarf regime long ago and, besides, the major formation scenarios for  BSS involve stellar interactions. At present, these exotic stars have been largely identified in different stellar systems, such as globular clusters (GCs), dwarf galaxies, open clusters (OCs), and even in the field populations of the Milky Way. In particular,  available catalogs of  BSS in OCs are purely based on photometric criteria,  namely only the location of a given star in the CMD dictates its BS nature. Nevertheless, systematic investigations of the properties of galactic OCs are hampered by the inhomogeneity of the data available by the date of the catalogs were published, and consequently, the  BSS reported in this catalog are mostly of uncertain membership. Thus, while useful, these compilations are not reliable enough to allow the derivation of statistical properties of BSS.The principal aim of this thesis was to create a catalog of BSs in OCs based on the astrometric solutions of Gaia DR2 and not only on photometric criteria. In addition, we have searched also for possible yellow stragglers stars (YSS) i.e possible evolved BSS.  Finally, we have complement Gaia DR2 data with multi-epoch spectroscopic data from FLAMES, which allowed us to have a closer look at the BS population in four OCs with very different properties: age, metallicity, mass, and location in the MW disk.

Transition disks with large inner dust cavities are thought to host massive companions. However, the disk structure inside the companion orbit and how material flows toward an actively accreting star remain unclear. We present a high-resolution continuum study of inner disks in the cavities of 38 transition disks. Measurements of the dust mass from archival Atacama Large Millimeter/Submillimeter Array observations are combined with stellar properties and spectral energy distributions to assemble a detailed picture of the inner disk. An inner dust disk is detected in 18 of 38 disks in our sample. Of the 14 resolved disks, 8 are significantly misaligned with the outer disk. The near-infrared excess is uncorrelated with the mm-dust mass of the inner disk. The size–luminosity correlation known for protoplanetary disks is recovered for the inner disks as well, consistent with radial drift. The inner disks are depleted in dust relative to the outer disk, and their dust mass is uncorrelated with the accretion rates. This is interpreted as the result of radial drift and trapping by planets in a low α (∼10−3) disk, or a failure of the α-disk model to describe angular momentum transport and accretion. The only disk in our sample with confirmed planets in the gap, PDS 70, has an inner disk with a significantly larger radius and lower inferred gas-to-dust ratio than other disks in the sample. We hypothesize that these inner disk properties and the detection of planets are due to the gap having only been opened recently by young, actively accreting planets

The Small Magellanic Cloud (SMC) is an excellent laboratory to investigate the chemical enrichment history of a galaxy that has experienced strong gravitational interactions with other systems, since it is in an early stage of a minor merger event with theLarge Magellanic Cloud. Despite its proximity (~60 kpc) and the possibility to resolve its stellar content, the chemical composition of the SMC is still poorly known. In order to fill this gap and the accurately reconstruct the chemical evolution of the stellar populations in the SMC, we analysed FLAMES@VLT high-resolution spectra of about 200 red giant stars belonging to the SMC field. Additionally, we analysed stars members of three SMC clusters with different ages (~11, ~6 and ~1 Gyr) covering the entire range of ages of the SMC clusters system. This dataset allows to reconstruct the role played by the different contributors to the chemical enrichment, i.e. Type II and Ia supernovae, hypernovae, AGB stars.

In particular, most of the stars (both in fieldand clusters) have solar-scaled [alfa/Fe] ratios, indicating that they formed from a gas already polluted by Supernovae Type Ia. Among the field stars we identified a bunch of rare SMC metal-poor stars ([Fe/H]<-2.0) that allow to study for the first time the early chemical enrichment of the galaxy. Finally, we found the evidence of the presence of a metallicity gradient within the SMC, with metallicity decreasing moving outward

We analyze the physical conditions (density and temperature), chemical abundances, dynamics and kinematics of gas in HH529II, HH529III and HH204, photoionized Herbig-Haro objects in the Orion Nebula. By using very high resolution spectroscopy obtained withUVES@VLT, we separate the Doppler-shifted emission of the velocity outflows from the main nebular emission, studying each object independently. To study the 3D dynamics and kinematics we complement our spectroscopic study with 20 years of archival of the Hubble Space Telescope (HST) imaging. In all cases, we were able to determine the physical conditions through several diagnostics. We analyze the chemical composition by using both recombination lines (RLs) and collisional excitation lines (CELs). We studyone of the most important problems in the photoionized nebulae: the discrepancy between abundances based on CELs and RLs. In HH204 we did not observe such discrepancy, while in HH529II and HH529III we did. Despite of the different physical conditions and ionization degrees, the chemical composition of HH204, HH529II and HH529III, based on CELs is consistent, presenting abundances of metals around 0.1 dex greater than those derived in the Orion Nebula. We also found direct evidence of destruction of dust inthe shock fronts, releasing elements such as Fe, Ni and Cr in the gas phase, increasing their abundances in these objects by several times the content of the Orion Nebula. Through the radial and tangential motions, we explored the dynamics and kinematics of each outflow, concluding that HH529II is an internal working surface of the HH529 flow.

Persistent tension between low-redshift observations and the Cosmic Microwave Background radiation (CMB) suggests residual systematics or new physics beyond the standard LCDM model. In this talk, I will show results obtained from local observations of supernovae and baryon acoustic oscillations combined with low-redshift distance calibrators, that provide constraints on the Hubble constant and the sound horizon in a cosmologically independent way. When these values are compared to constraints from the CMB, a tension up to 5 sigma arises. Several modifications of LCDM have been put forward to reconcile the tension, but how well do these models actually perform? I will talk about the current status of tensions between the CMB-based and local (based on gravitational time delays and classical distance ladder) distance calibrations. I will also critically review most popular extensions of LCDM proposedto reconcile these measurements.

For more details about this work: https://arxiv.org/abs/1909.07986

The merger history of a galaxy has a direct impact on the structure of its geometrically defined thick disc. Among other effects, mergers induce flaring in the stellar populations in the disc, which can be reflected on the thick disc’s age structure. As weare studying the age structure of thick discs in the MW and nearby galaxies with an unprecedented level of detail, it is important to use simulations in order to have a more comprehensible picture of the diversity of thick disc age structures, and their connection to the galaxies' merger histories.

In this talk, I will present the results of an analysis performed on a sample of 27 simulated MW mass galaxies in their cosmological context, where we explore the connection between the flaring of mono-age populations (MAPs), thick disc flaring, thin/thick disc separation, and thick disc’s age structure. I will explain under which conditions MAPs create flat thick discs, and how these galaxies form a continuum thin/thick structure, have radial age gradients, and tend to have quiescent recent merger histories, similar to our understanding of the Galaxy. Conversely, I will show the different scenarios we find where MAPs can create flared thick discs, with these galaxies showing a wider variety of the aforementioned features.

In conclusion, the results presented in this talk are in agreement with the emerging picture of thick discs being diverse and complex components of external galaxies, which when studied in detail, can provide vital constrains for the formation and evolution of disc galaxies.

Cepheid stars play a considerable role as astronomical distances indicators thanks to the empirical relation between their pulsation period and intrinsic luminosity: the PL relation. The uncertainty on this relation is the largest contributor to the error budget of the Hubble constant, that describes the Universe's expansion. The value of the Hubble constant is currently at the center of a major controversy: while it is estimated at 67.4 +/-0.5 km/s/Mpc by the Planck satellite, the local measurement based on Cepheids is larger by 4 sigma, with a value of 74.0 +/-1.4 km/s/Mpc. This discrepancy may provide evidence for physics beyond the standard model: it is therefore critical to improve the PL calibration with precise and accurate distance measurements of Cepheids.

In 2018, the second data release of the Gaia satellite (Gaia DR2) provided parallaxes for 1.3 billion stars with an unprecedented precision. However, Cepheids are bright stars and are often saturated in detectors. Moreover, the variations in brightness and color that occurs for variable stars like Cepheids are not yet taken into account in the Gaia data reduction. Therefore, Cepheids parallaxes can be affected by systematics due to their photometric variability.

In order to avoid these issues, a solution is to find stable and faint companion stars in the close environment of Cepheids. Using 36 indirect, unbiased and accurate distances based on Gaia DR2, I calibrate the PL relation and revise a previous value of the Hubble constant based on HST measurements of Galactic Cepheids.

Our Milky Way still hosts remnants from the era of first star formation in the form of (very) metal-poor stars, which we can study in detail. They are useful to learn about the First Stars and the conditions in the early Universe, and they provide unique insights into the early formation and evolution of our Galaxy. Metal-poor stars are typically searched for in the Galactic halo and the dwarf galaxies surrounding the Milky Way. However, a prediction of simulations is that the fraction of metal-poor stars that are very old is highest towards the centers of galaxies: in their bulges.

The task of finding the most metal-poor stars in the inner Milky Way faces many challenges, including large dust extinction, severe crowding and a high average metallicity of the dominant stellar population in the bulge. In this talk, I will present the Pristine Inner Galaxy Survey (PIGS) which has reached unprecedented efficiency in finding metal-poor stars in the bulge region, employing metallicity-sensitive photometry to select candidates for spectroscopic follow-up.

For the first time, using PIGS, we can study the the kinematics of thousands of (very) metal-poor inner Galaxy stars, and investigate the occurrence of the chemically peculiar carbon-enhanced metal-poor (CEMP) stars in this region. I will present these results and discuss what they can teach us about the origin of the oldest component of our Galaxy.

Galaxy mergers play an important role in how galaxies evolve over time, however extragalactic astronomers do not yet totally understand the process by which those mergers happen.

The brightest galaxies of groups and clusters are extremely luminous galaxies, usually located in the centres of those systems –central galaxies. Simulations predict that these central galaxies have undergone more mergers than other similarly luminous galaxies, making them an excellent test of the merger process. The recent merger history of galaxies can be read through their stellar population gradients. Central galaxies with active merger histories are predicted to have shallower metallicity gradients than satellite galaxies of a similar mass. We examined the stellar population gradients (age, metallicity and alpha-element abundance ratios) of central galaxies in the SAMI galaxy survey to determine whether they are offset from similarly massive satellite galaxies in order to reach a better understanding of the role of mergers in galaxy formation and evolution.

Astronomical observations with ground-based telescopes are affected by differential atmospheric dispersion, a consequence of the wavelength-dependent index of refraction of the atmosphere. In high resolution astronomical instruments, an Atmospheric Dispersion Corrector (ADC) is mandatory to avoid wavelength dependent losses. Even though an ADC seems a simple component, but from the design phase to on-sky commissioning, several problems can occur. The design of an ADC is based on atmospheric models that, to the best of our knowledge, were never tested on-sky. Different models shows a variation of 50 milli-arcseconds (mas), a value close to the required residuals from current ADCs. During the commissioning, detecting a variation of 50 mas in a PSF of 1 arcseconds, is not an easy task. We will present a method to measure on-sky the atmospheric dispersion based on measuring the PSF centroid of each wavelength using cross-dispersed spectra. We are able to characterize different atmospheric models with an accuracy of 18 mas. As for the on-sky commissioning, we present a simple concept based on the ellipse fit of intensity contour plots of the PSF. This method will allow us to better align the ADC in terms of prisms angles and total dispersion direction using on-sky measurements. In this talk we show the study we did to improve the phases of an ADC from design to on-sky commissioning.

I will present the results of a unique multi-wavelength campaigns focused on the recently discovered LMXB Swift J1858. This system displayed extreme variability in both X-ray and optical bands, similar to the famous black hole binary V404 Cyg during its 2015 outburst. Our observations covered the full frequency range from X-ray to radio and were provided by observatories including XMM-Newton, NuSTAR, NICER, VLTs, Gemini, GTC, VLA, MeerKAT and HST. A key feature of the campaign is a 4-hour window during which we obtained time-resolved, strictly simultaneous observations across the whole electromagnetic spectrum.

I will walk you through the findings obtained by monitoring programs of independent instruments, then we will step back into a multi-wavelength perspective to get insights in the geometry of the system and the physical mechanism driving its outflows, unveiled thanks to the unprecedented coordination of several major observatories across the globe. We will finish with an overview of the findings of the system and how coordinated multi-wavelength campaigns can help us to understand the physics of compact objects and how they interact with their environment.

All of the survey data products will be made available to the scientific community in a ready-to-use format accompanied by practical examples.

Brown dwarfs are a critical link between the realms of stars and planets. Their formation process is one of the crucial missing pieces in our understanding of how star and planet formation work. Understanding the origin of brown dwarfs is the main motivation for recent deep studies of star-forming regions and young clusters. The major question driving our studies is whether the birth environmentaffects their formation efficiency, as predicted in several formation scenarios. The expectation is that high gas or stellar densities or the presence of massive OB stars may be factors that boost the incidence of newly formed brown dwarfs with respect tostars. To address this question we investigate the stellar and sub-stellar objects in the drastically different environments of massive young clusters RCW 38 and NGC 2244 and that of nearby star-forming regions. Here we will present the current status ofyoung brown dwarf studies, compare the low-mass Initial Mass Functions in a variety of Milky Way environments. For RCW38, we will address the high-mass IMF and the shallow slope that we see in the center (mass segregation or not?). We will summarised theimplications of these results for our understanding of sub-stellar formation processes.

Nuclear star clusters (NSCs) are extremely dense stellar systems that reside in the centres of ~70% of galaxies, including our Milky Way. This nucleation fraction even reaches > 90% forgalaxy masses ~ 10^9 M_sun. NSCs have similar sizes to globular clusters (GCs), but are even more massive and dense. NSCs often co-exist with supermassive black holes and follow distinct scaling relations with properties of the host galaxy, but it is stilldebated how NSCs form and grow. Generally, two main scenarios are discusse: in-situ from gas at the galactic centre or via the dissipationless accretion of GCs that spiral inwards due to dynamical friction. Most likely, a mixture of both pathways is realized in nature, but the dominant channel nor how it relates with the host galaxy are known.

Constraining NSC formation in galaxies requires a complete view of both thekinematics and chemical properties of the host galaxy, the NSC, and the GC system. Sucha study is challenging, but possible with modern day integral-field spectroscopy. I will present how MUSE can be used to determine the dominant NSC formation channel for individual galaxies, in conjunction with a semi-analytical model of NSC formation. These complementary approaches reveal for the first time how the NSC formation depends on properties of the host galaxy and show a transition of NSC formation via GC-inspiral to in-situ star formation with increasing NSC mass.

The formation of supermassive black holes (MBH) is thought to be tightly linked to the formation and growth of their host galaxy bulges. MBH mass measurements of local galaxies based on stellar or gaseous motion reveal strong correlations of the MBH mass with bulge properties, such as bulge mass, stellar velocity dispersion and light concentration. However, the black hole sample and its covered mass range are limited, revealing an increased scatter for the high and low mass end of the scaling relations. While it is crucial to expand and constrain these regions in order to investigate on the universality of the scaling relations for different galaxy populations and possible different galaxy formation scenarios, the MBH measurements are challenging due to the need of time-expensive (preferable IFU) data and resolution arguments.

I present my dynamical MBH measurements of almost 20 galaxies expanding on both the high and low mass end of the scaling relations. For our measurements we made wide use of IFU data, such as SINFONI, NIFS, MUSE, ALMA, and more. We tooks special care in testing dynamical measurement methods on different tracers (stars vs gas) and other systematics. I will also discuss formation scenarios of galaxies harbouring strongly undermassive black holes or possibly no black holes at all. A strong tool to give implications about the formation and growth of MBHs is the analysis of the galaxy's central orbital distributions. I will conclude my talk with a discussion on what we can learn from examining orbital distributions in galaxy evolution and formation context and how measurement uncertainties are affecting our MBH results.

Despite the importance of massive stars and star clusters for the energy content, stellar population and evolution of galaxies, the mechanism that ignites their formation in molecular clouds is still poorly addressed. Infrared Dark Clouds (IRDCs) are the likely precursors of massive stars. It has been suggested that IRDC formation and dynamical processing by multiple shock episodes triggered by bubbles, such as HII regions and Supernova Remnants (SNRs), can efficiently initiate star formation within these clouds. It is thus important to understand the conditions of density and temperature set by large-scale shocks in IRDCs to constrain the ignition of star formation in these objects. In this work, I will present the large scale shock triggered by the SNR W44 in the IRDC G034. I will show how the shock, probed by Silicon Monoxide (SiO) and observed with ALMA, enhances the density of the processed gas to values compatible with those required for massive star formation and has helped to shape the cloud. Thanks to the high resolution achieved by ALMA, the internal physical structure of the shock was resolved for the first time, providing a direct test to Magneto-Hydro-Dynamic (MHD) shock theories. Moved by these results, we have initiated the large single-dish observing program SHREC, aimed to observe SiO(2-1) emission in SNRs interacting with molecular clouds. During the talk, I will briefly introduce the aim and technical aspects of SHREC and present preliminary results obtained toward the SNRs IC443 and W41.

Over the past decades, several important steps have been taken to understand the formation and evolution of first generations of galaxies. In particular, thanks to deep multi-wavelength observations by Hubble Space Telescope (HST), studies of early galaxies have now been pushed well into the Epoch of Reionization, i.e. up to z~10-11 only 500Myr after the Big Bang (e.g. Bouwens+15, Oesch+16, Atek+18). However, our current knowledge beyond z~2-3 is significantly biased to the rest-frame ultraviolet observations as it’s only accessible by deep optical/near-infrared observations, and dust-obscured properties of high-redshift galaxies hasremained mostly unknown. This situation was revolutionized by extremely sensitive and high-resolution far-infrared (FIR) interferometers such as ALMA and NOEMA. First ALMA observations showed us surprises by finding fainter FIR emission than expected fromlow-redshift galaxy observations, suggesting an evolution of dust-obscured galaxy properties at high-redshift (e.g. Capak+15, Bouwens+16). To understand this potential evolution with statistical sample and with wide range of galaxy parameters, large ALMA observations were required. In this talk, I will discuss the evolution of dust attenuation and dust-obscured star-formation of galaxies at z~3 to z~6 revealed by ALMA, including a recent ALMA large program: ALPINE and an on-going large program: REBELS.

Massive stars play a critical role in the evolution of galaxies and star clusters. Recent observations of the latter have highlighted the need for systematic studies dedicated to probing the impact of massive stellar evolution on the properties of stellar populations. While the use of fitting formulae to stellar tracks remains a popular choice for modelling stellar evolution in population synthesis codes, these formulae are not adaptable to changes. In this talk, I will discuss and present results from an alternative approach, one that is more adaptable: Method of Interpolation for Single Star Evolution (METISSE). It can readily make use of stellar models computed with different stellar evolution codes and compare their predictions for populations of stars. Using METISSE with data from different stellar evolution codes, I will show how various physical ingredients used in the evolution of massive stars, such as the treatment of their radiation dominated envelopes, can lead to differences in their evolutionary properties. I will discuss the implications of these differences on the evolution and interaction of stars inbinaries, and how they can impact compact binary mergers and the properties of gravitational wave events.

Massive black holes at the centers of galaxies can launch powerful wide-angle winds, which if sustained over time, can unbind the gas from the stellar bulges of galaxies. These winds, also known as ultra-fast outflows (UFOs), may be responsible for the observed scaling relation between the masses of the central black holes and the velocity dispersions of stars in galactic bulges. Propagating through the galaxy, the wind should interact with the interstellar medium creating a strong shock, similar to those observed in supernovae explosions, which is able to accelerate charged particles to high energies. In this talk I'll present the Fermi Large Area Telescope detection of gamma-rayemission from these shocks in a small sample of galaxies exhibiting energetic winds. The detection implies that energetic black-hole winds transfer ~0.04% of their mechanical power to gamma rays and that the gamma-ray emission represents the onset of the wind-host interaction.

Massive stars play a critical role in the evolution of galaxies and star clusters. Recent observations of the latter have highlighted the need for systematic studies dedicated to probing the impact of massive stellar evolution on the properties of stellar populations. While the use of fitting formulae to stellar tracks remains a popular choice for modelling stellar evolution in population synthesis codes, these formulae are not adaptable to changes. In this talk, I will discuss and present results from an alternative approach, one that is more adaptable: Method of Interpolation for Single Star Evolution (METISSE). It can readily make use of stellar models computed with different stellar evolution codes and compare their predictions for populations of stars. Using METISSE with data from different stellar evolution codes, I will show how various physical ingredients used in the evolution of massive stars, such as the treatment of their radiation dominated envelopes, can lead to differences in their evolutionary properties. I will discuss the implications of these differences on the evolution and interaction of stars inbinaries, and how they can impact compact binary mergers and the properties of gravitational wave events.

Despite the long history of dark matter, its nature is still unknown.Cold dark matter (CDM) remains the generally accepted workinghypothesis.  Apparent shortcomings in the ability of CDM to explainvarious observations have been noted and have led to the development ofalternative hypotheses, but so far none have been able to dethrone CDM. This is partly due to the presence of baryons in galaxies, whose feedback processes and radiative properties are far more complex thanthe physics of dark matter. In the presence of baryonic feedback, many dark-matter models start losing their distinctive profiles, leaving usunable to distinguish between them.

One promising way out of this conundrum is to study dark matter in environments with as few baryons as possible. Ultra-faint dwarf galaxies (UFDs) are the faintest, least massive, and most dark matter–dominated galaxies known. They are predicted to have dark-matter distributions unchanged by baryonic feedback.

In this colloquium I will present the current state of research to constrain the nature and properties of dark matter using UFDs, includingthe first results from a novel 100-hour MUSE survey of UFDs. I will address the constraints on primordial black holes from their dynamical effects on stellar distributions, as well as the constraints on various types of particulate dark matter (weakly interacting massive particles, axion-like particles, self-interacting dark matter, and fuzzy dark matter) from emission-line searches and the first determined dark matter–density profile of a UFD. I will end with an outlook for the near future of this field.

Bars are a major driver of secular evolution in disc galaxies, promoting the inflow of gas to the centre, where stellar structures, such as nuclear discs are built. We constrain the formation of these structures by deriving their stellar kinematics and mean population properties. To this end, we use observations with unprecedented spatial resolution, obtained with the MUSE integral-field spectrograph for a sample of 21 Milky Way-type galaxies in the local Universe. We show that nuclear discs are characterised by a high rotational support, i.e. near-circular orbits with low velocity dispersions, and are significantly younger, more metal-rich, and less [α/Fe]-enhanced, as compared to their surroundings. These findings are consistent with the picture of bar-driven secular evolution and contrast with the formation of old and kinematically hot classical bulges in violent accretion events. Moreover, nuclear discs exhibit well-defined radial gradients of the population properties with single slopes, suggesting that they are continuous components from their outer edge to the galaxy centre. We argue that these continuous (stellar) nuclear discs may form from a series of bar-built (gas-rich) nuclear rings that grow in radius, as the bar evolves. In this picture, nuclearrings are simply the star-forming outer edge of nuclear discs. Finally, we do not find evidence for the presence of classical bulges in the centres of these galaxies. This could result from feedback processes efficiently preventing the formation of classical bulges or may challenge the paradigm of hierarchical structure formation, questions we will address in a dedicated MUSE survey.

Since the first direct detection in 2015, gravitational waves havecompletely changed the landscape of known stellar mass black holes(BH). This gives unprecedented constraints on the evolution and deathof the most massive stars, which are otherwise hard to study dueto their rarity. In particular, stellar evolution predicts theexistence of a gap in the BH mass distribution, due topair-instability evolution. Its location between ~45-125 Msun is oneof the most robust predictions of stellar theory, primarily sensitiveonly to uncertain nuclear reaction rates. This will allow for the useof gravitational-wave detectors as nuclear astrophysicsexperiments. On the other hand, ~3% of the population of BHs inferredhave masses within the pair-instability gap. Explaining these BHsrequires either dynamics, gas accretion, or exoticphysics.

Pair-instability should also produce visible electromagnetictransient, however, an uncontroversial detection is stilllacking. Upcoming large time-domain surveys will soon be able toreveal even very rare transients and should identify these.

In this talk, I will review the physics of (pulsational) pair-instability inthe context of the latest gravitational-wave and time-domainsurveys. I will show the wide range of theoretical predictions andtheir trends with stellar mass, and highlight what we have alreadylearned from the binary BH mergers detected. Finally, I will discuss possible ways to populate the pair-instability gap andpotential open problems with some of the scenarios that have been
proposed.

Most massive stars spend their lives in so close orbit with a companion star that severe mass exchange or even coalescence is inevitable as the stars evolve and swell. A third of massive stars are thus stripped of their fluffy, hydrogen-rich envelopes, leaving the compact helium core exposed. These stripped stars are so hot that most of their radiation is emitted in the ionizing regime. Using evolutionary and spectral models of stripped stars, I will show how they sometimes dominate the ionizing emission from full stellar populations and even significantly contribute to cosmic reionization. With their hard ionizing spectra, stripped stars possibly leave observable traces, for example in the nebular spectrum of distant galaxies. Apart from being ionizing sources, stripped stars are also interesting to consider as gravitational wave emitters. Creating a population model, we predict that several stripped stars orbiting compact objects will be detectable by LISA.

The ultimate goal in galaxy studies is to have a complete picture of galaxy formation and evolution across the history of the Universe. A robust determination of the abundance of massive (even quiescent) galaxies at high-redshift is essential to constrain current galaxy formation models.

In this context, this work addresses the challenge of studying the build-up of massive galaxies adding a new population of optically faint (HST-dark) Balmer Break Galaxies (BBGs), which are bright at longer wavelengths (even in the sub-mm regime), to the general population of massive galaxies at z > 3. We study in detail the physical properties of the general population of known massive galaxies at z > 3 and we analyze the sample of BBGs by comparing them with a mass-limited (M > 10^10M☉and z > 3) sample and a color-selected (H −[3.6] > 2.5) sample extracted from the CANDELS catalogs published for these fields.

We have therefore detected a new population of previously unknown optically dark massive red galaxies and provide a more complete sample of the general population of massive galaxies at z > 3. This population of massive distant galaxies may represent the progenitors of most massive local galaxies. In the context of the current paradigm of galaxy formation, it is essential to constrain and confirm the number density of high redshift massive galaxies, which will provide crucial information to expand our understanding of galaxy evolution. The existence of this numerous population of massive galaxies at high redshifts represents a challenge for existing cosmological models and state-of-the-art simulations.

In a cosmological setting, the disk of a galaxy is expected to continuously experience gravitational torques and perturbations from a variety of sources, which can cause the disc to wobble, flare and warp. Specifically, the study of galactic warps and their dynamical nature can potentially reveal key information on the formation history of galaxies and the mass distribution of their halos. Our Milky Way presents a unique case study for galactic warps, thanks to detailed knowledge of its stellar distribution and kinematics. Using a simple model of how the warp’s orientation is changing with time, we measure the precession rate of the Milky Way’s warp using 12 million giant stars from Gaia Data Release 2, finding that it is precessing at 10.86 ± 0.03 (statistical) ± 3.20 (systematic) km/s/kpc in the direction of Galactic rotation, about one third the angular rotation velocity at the Sun’s position in the Galaxy. The direction and magnitude of the warp’s precession rate favour the scenario that the warp is the result of a recent or ongoing encounter with a satellite galaxy, rather than the relic of the ancient assembly history of the Galaxy. Using N-body simulations, we analyse the vertical response of the Galactic disc to the repeated impacts of a satellite similar to the Sagittarius dwarf galaxy, finding that the instantaneous vertical pattern speeds in the disc have a constraining power in the context of a Milky Way-satellite interaction.

I present results from high-resolution, "genetically modified", cosmological simulations quantifying the diversity in the structural properties of faint dwarf galaxies.

Ultra-faint dwarf galaxies are the least luminous objects in the Universe. Their shallow potential well makes them highly sensitive to the interaction between dynamical mass growth and internal, feedback processes. Thissensitivity provides an ideal laboratory for testing galaxy formation models, while also generating significant scatter in their stellar and gaseous properties. Quantifying the expected scatter will be essential to interpret findings in the next generation of deep, wide sky, surveys (e.g. LSST).

To begin this quantification, I present a suite of simulated low-mass, field dwarf galaxies, evolved with cosmological zoom simulations capable of resolving the explosions of individual supernovae (Rey et al. 2019, 2020). These high-resolution simulations are complemented with the "genetic modification" approach, allowing us to resimulate chosen galaxies making targeted changes to their cosmological mass growth history.This unique combination of abilities providesa complete overview of the interaction between feedback and assembly in these systems.

I will show how this interplay regulates the ability of the lowest-mass galaxies to accrete fresh gas at late times, leading to diverse cold gas content at similar stellar masses. I will further show how this accretion can allow dwarfs to re-ignite and sustain continuous, low levels of star formation until today, highly reminiscent of observed star-forming low-mass dwarfs (e.g. Leo T, Leo P).

One of the most intriguing outcomes of the young field of exoplanet research is the emergence of highly-irradiated planets, located much closer to their host star than any of the Solar System planets. These planets, which give us a glimpse into the future of our Solar System once the Sun reaches its final life stages, have been studied in-depth, allowing us to learn more about their temperature profiles and present molecules and atoms. However, the characterisation of atmospheric dynamics, a crucial part totruly understand an atmosphere, has severely lagged behind.

Until recently, our only glimpse into the winds on exoplanets was restricted to global circulation models (e.g. Showman et al. 2009, Parmentier et al. 2018), probing only the lowest layers of the atmosphere, and atmospheric escape models, which describe the mass outflow far out in the exosphere (e.g. Lecavelier des Etangs et al. 2010, Bourrier et al. 2017). Thanks to these techniques, we know that the lower atmosphere is dominated by zonal winds,while the exosphere expands into space. But what happens in the vast area between these regimes?

This pressing question has been answered in my PhD work, where I, for the first time, utilise resolved spectral lines which probe the missing layers of the atmosphere to understand their atmospheric dynamics (Seidel et al. 2019, 2020a, 2020d submitted). During my talk, I will present a consolidated view of highly-irradiated exoplanet atmosphere dynamics, focussing on the connection between the different atmospheric layers.

I present the Stromlo Stellar Tracks, a set of stellar evolutionary tracks, computed by modifying the Modules for Experiments in Stellar Astrophysics (MESA) 1D stellar evolution package, to fit the Galactic Concordance abundances for hot massive Main-Sequence stars. Until now, all stellar evolution tracks are computed at solar, scaled-solar, or alpha-element enhanced abundances, and none of these models correctly represent the Galactic Concordance abundances at different metallicities. This paper is the first implementation of Galactic Concordance abundances to the stellar evolution models. The Stromlo tracks cover massive stars (10<Msun<300) with varying rotations evolved from the pre-main sequence to the end of Carbon burning. I find that the implementation of Galactic Concordance abundances is critical for the evolution of main-sequence, massive hot stars in order to estimate accurate stellar outputs (L, T, g), which, in turn, have a significant impact on determining the ionizing photon luminosity budgets.I additionally support prior findings of the importance that rotation plays on the evolution of massive stars and their ionizing budget. The evolutionary tracks for our Galactic Concordance abundance scaling provide a more physically motivated approach than simple uniform abundance scaling with metallicity for the analysis of HII regions and have considerable implications in determining nebular emission lines and metallicity. Therefore, it is important to refine the existing stellar evolutionary models forcomprehensive high-redshift extragalactic studies.

High-mass stars inject a large amount of energy and momentum -stellar feedback -into the interstellar medium (ISM) during their relatively short lifetimes. The feedback from these stars can influence the ISM both locally (<1pc) and across their entire host galaxy (~1kpc), and occurs through a variety of feedback processes; e.g. protostellar outflows, stellar winds, ionizing radiation. The most important of these feedback mechanisms for the overall energy and momentum budget of ISM occurs at the end of thestars lifetime, when they explode as supernovae. However, the efficiency with which SNe couple with their environment strongly depends on their local gas density distribution. Hence, the early pre-SNe feedback processes from high-mass stars play a crucialrole in setting this environment into which SNe later explode, and, therefore, in effect limit the efficiency of SNe feedback. In this talk, I will discuss our recent efforts in a quantitative study of pre-SNe feedback mechanisms within both the centre Milky Way, and a large sample of nearby extragalactic systems. In these analyses, we focus on the balance of various internal and external pressures within young HII regions. The study of the Galactic Centre represents the first such study in a high-pressureenvironment, which has important implications for high-redshift environments. The study of extragalactic systems is the first to attempt such a study on a statistically significant sample of HII regions (>2000). Together, these make key advancements in our understanding of young stellar feedback as a function of environment.

Many galaxies in the local Universe do not live alone, but in groups or even clusters. With many galaxies in little space, as well as the presence of a hot intracluster medium (ICM), the evolution of these galaxies is different from their isolated counterparts. In particular, galaxy clusters host a relatively high number of passive galaxies. Several mechanisms play a role in this, related tothe ICM (e.g. ram pressure stripping) or the galaxy number density (e.g. galaxy-galaxy interactions). That these mechanisms affect the atomic gas in galaxies (HI) is well known. However, whether it also affects the more tightly bound and centrally locatedmolecular gas (H2) is less obvious. In this talk I will present results from the ALMA Fornax Cluster Survey (AlFoCS), an ALMA survey of the CO in Fornax cluster galaxies. I will discuss the molecular gas content in these galaxies, show resolved images of its morphology and kinematics, and show how it differs from galaxies in the field at fixed stellar mass. Furthermore, I will present results from the collaboration I lead between AlFoCS and the MUSE survey Fornax3D, in which we exploit the powers of ALMA and MUSE to study the resolved star formation relation (Kennicutt-Schmidt relation) in Fornax galaxies. Lastly, I will show some surprising recent results of a study of gas-to-dust ratios in the Fornax cluster compared to the Virgo cluster and the field, using data from ALMA, Herschel, ATCA, and MUSE.

The properties of the most massive galaxies in the Universe provide fundamental constraints on both galaxy evolution physics and cosmology. However, extracting subtle physical properties, such as galaxy star formation histories (SFHs) and metallicities, from observations is highly challenging, owing to the age-metallicity-dust degeneracy in galaxy spectral shapes and the challenges involved in obtaining high-SNR, well calibrated spectroscopy.

I will discuss past, present and future efforts to constrain the physical properties of massive quiescent galaxies, and what these tell us about galaxy evolution. In particular I will present results from the VANDELS ESO Public Spectroscopic Survey (arXiv:1903.11082), reporting the analysis of 75 high-SNR rest-UV spectra for massive quiescent galaxies at 1.0 < z < 1.3 to extract detailed SFHs using a sophisticated Bayesian statistical approach. I will then discuss ongoing efforts to constrain the stellar metallicities of these galaxies with rest-optical KMOS observations, allowing us to probe the evolution of the stellar mass-metallicity relation across 9 Gyr of cosmic history.

Finally, I will discuss the prospectsfor furthering our understanding with upcoming instrumentation. The Multi-Object Optical and Near-infrared Spectrograph (MOONS) for the VLT will provide a million high quality spectra at z~1, and I am heavily involved in preparations for the ~200 night extragalactic GTO survey MOONRISE. I will also discuss our first steps towards learning about the earliest quiescent galaxies at z > 3 (arXiv:2001.11975), a field that will be revolutionised by the upcoming James Webb Space Telescope.

One of the most important tools to investigate the chemical history of our Galaxy and our own Solar System is to measure the isotopic fractionation of chemical elements. This is the process that distributes the less abundant stable isotopes of an element in different molecules. The isotopic ratios are governed by two main processes: 1. chemical evolution of the whole Galaxy due to stellar nucleosynthesis; and 2. local fractionation effects.For the case of nitrogen (N), the 14N/15N isotopic ratio found for the proto-Solar nebula, 440, is significantly higher than that measured in pristine Solar System materials, like comets (around 140). This suggests a local chemical enrichment of 15N during the Solar System formation. However, the causes of the 15N-enrichment are still uncertain.In this talk I will briefly review the state-of-the-art of the astronomical observations and theoretical chemical models devoted to the study of nitrogen fractionation. I will show the overall behavior of the 14N/15N ratio across the Galaxy. In particular, based on a large survey of star-forming regions, we have confirmed that the 14N/15N ratio increases with thegalactocentric distance. This overall trend can be explained by nucleosynthesis Galactic chemical evolution models.Furthermore, I will present the first interferometric maps of N-fractionation of N2H+ towards a star-forming region. Our results highlight the importance of local effects, and in particular of isotope-selective photodissociation of N2, in determining the 15N-enrichments in star-forming regions.

I present theoretical work done using the AMR MHD code FLASH on the formation of binary stars and the evolution of their discs in these systems. I simulated the collapse of molecular cores until the formation of protostars and followed the early evolution of these systems. I investigated the influence that binarity has on the global evolution of a young stellar system, including looking at mechanisms such as accretion of material, jets and outflows, and dynamical interactions. I find that while in some scenarios binary stars may produce hostile environments for planet formation via the destruction of circumstellar discs, the formation of large circumbinary discs ispossible. This can lead to the formation of planets around binary stars to be just as likely as the their formation around single stars. I also observe a dependence of accretion on episodic accretion, independent of separation. I will also present preliminary work on reproducing observed statistics of protostellar binary separations, and what it means for understanding binary formation pathways.

Galaxy clusters are the largest gravitationally bound structures in the Universe. Their formation out of small initial density fluctuations holds important clues to the behaviour of gravity over large distances and long timespans. The standard cosmological paradigm (ΛCDM) makes precise predictions for the frequency of galaxy clusters with different mass, and for how often they interact. We recently showed that these predictions are ruled out at over six standard deviations by the observed properties of El Gordo (MNRAS, 500, 5249). Such a massive pair of galaxy clusters should not have formed so early in the universe's history, as demonstrated using two statistical analysis methods focusing on how many objects similar to El Gordo are expected in the surveyed region. We also considered the main alternative to ΛCDM, which is called Milgromian dynamics (MOND). The main assumption of MOND is that once the gravity from a point mass falls below some threshold a_0, it then declines only inversely with distance instead of continuing to follow the inverse square law. In this way, MOND can explain the unexpectedly fast rotation curves of galaxies. On larger scales, MOND would significantly enhance structure formation and thereby explain El Gordo, as demonstrated using a previous cosmological MOND simulation. The lack of similarly extreme objects to El Gordo in the low-redshift Universe might indicate that we are in a large void. There is actually quite strong evidence for such a void, which would also naturally explain the unexpectedly fast local expansion of the Universe (MNRAS, 499, 2845).

Understanding the magnetic field strength and morphology of astrophysical regions is of great importance in understanding their dynamics. There exist a number of methods astronomers can employ to trace magnetic field structures, and each have their own limitations. A promising technique to trace the magnetic field morphology around evolved stars, or on the smallest scales of (high-mass) star forming regions, is (sub-)millimeter spectral line polarization observations. Line (linear) polarization can either arise in association with maser radiative transfer, or alternatively, molecular lines polarize through the Goldreich-Kylafis effect. In both cases, the polarization angle traces the magnetic field with a 90-degree ambiguity. In order to remove this ambiguity, and to estimate the observational viability of particular line polarization measurements, polarized line radiative transfer needs to be employed.

In this talk, I present

(i) polarized radiative transfer tools that quantify the polarization of maser radiation,

(ii) a three-dimensional polarized line radiative transfer tool: PORTAL. PORTAL simulates the emergence of thermal molecular line polarization in astrophysical objects of arbitrary geometry and magnetic field morphology,

(iii) A novel polarization mechanism: collisional polarization. Which provides the possibility of directly detecting ambipolar diffusion in disks through the polarization of molecular ions,

and I will discuss observations of molecular line polarization around evolved stars andon the smallest scales of (high-mass) star forming regions.

Merging between galaxy clusters are the most energetic events in the Universe. Part of the energy released during these events is channeled into shocks and turbulence that accelerate particles in the Intra Cluster Medium (ICM) and produce diffuse cluster-scale radio emission. These sources have been studied for decades using observations at GHz-frequency, however, under many aspects, their origin remains unclear. Given the steepness of the spectrum of these sources, low frequency observations were the crucial, albeit missing, piece of the puzzle to understand these non-thermal phenomena. In this respect, the Low Frequency Array (LOFAR), recently opened a new frequency window (10-240 MHz) in the radio sky, which is the most promising window in this field. On one hand, this is leading to the discovery of new types of diffuse sources and physical interactions in the ICM, such as gently re-energised tails and even beyond the cluster-scale, such as bridges connecting pairs of galaxy clusters. On the other hand, thanks to the superior survey speed and sensitivity of LOFAR, we now have the possibility to analyse large samples of galaxy clusters, even in mass and redshift ranges that were previously inaccessible. In this talk, I will review some of the most important results that have been achieved in the past few years with LOFAR observations of galaxy clusters and I will discuss the ongoing and future work on the largest samples of clusters observed at low frequency.