Seminars


The PhD program in Astronomy Astrophysics and Space Science encourages students to follow the wide range of seminars organised by the institutes hosting the course:
- Sapienza University of Rome, Physics Department
- Tor Vergata University of Rome, Physics Department
- INAF, National Institute of Astrophysics

See below for a list of seminars

2024


Molecular Complexity in Solar-like Planetary Systems
22/05/2024
Our is the only planet known to have developed such a complex chemistry which led to life. Numerous evidence suggests that molecular complexity had begun and developed when the Solar System was an embryo inside a cold molecular cloud. In this presentation, I will review the overall picture of how molecular complexity builds up along with the evolution of the molecular cloud embryo into a protoplanetary system. I will also give an overview of the major chemical processes and the many challenges that remain to be overcome.
Experimental Studies of Black Holes: Status & Prospects
22/05/2024
The discovery of the Quasars in the 1960s led to the 'massive black hole paradigm' in which most galaxies host massive black holes of masses between millions to billions of solar masses at their nuclei, which can become active galactic nuclei and quasars when they accrete gas and stars rapidly. I will discuss the major progress that has happened in the last decades to prove the massive black hole paradigm through ever more detailed, high-resolution observations, in the center of our own Galaxy, as well as in external galaxies and even in distant quasars. In the Galactic Center such high-resolution observations can also be used to test General Relativity in the regime of large masses and curvatures.
Cosmic birefringence tomography from axion-like particles
22/05/2024
Cosmic birefringence -- a rotation of the linear polarization plane of the cosmic microwave background (CMB) as they travel through space -- is a key observational effect on CMB as it provides a way to search for parity-violating physics in cosmology. Recent measurements of the cross-correlation between the even-parity E-modes and odd-parity B-modes in the Planck polarization map suggest a tantalizing hint of cosmic birefringence. A possible candidate for the origin of cosmic birefringence is pseudoscalar "axionlike'' fields. In this talk, after briefly reviewing the observations of isotropic and anisotropic cosmic birefringence, I will discuss the importance of the time evolution of axionlike fields to explore the origin of cosmic birefringence.
Reading Physics from Stellar Spectra
21/05/2024
The Milky Way is host to hundreds of billions of stars. Of them, about 10 million, less than 0.01%, have so far been mapped by large-scale spectroscopic surveys. We will soon see major progress in the quantity, quality, and depth of data with next-generation astronomical facilities. In this seminar, I will focus on the frontiers in diagnostic stellar spectroscopy. First, I will summarize the key principles behind physical models that allow us to extract physical parameters of stars from their observed spectra. 3D non-equilibrium models of stellar atmospheres and spectra are poised to become workhorses of astronomy in the next decade. Second, I will show how we overcome another challenge: the innovative combination of the models and complex noisy data. Third, I will demonstrate how new data and new models drive progress in areas that rely on stellar parameters and chemical composition of stars. These include studies of exoplanets, gravitational wave sources, and Galaxy formation. I will close with a personal view of perspectives opening with large facilities of the next decade, such as SDSS-V, 4MOST, and ELT.
Revealing the Milky Way's Hidden Satellites: A KiDS Survey Exploration.
16/05/2024
In the past two decades, the exploration of Milky Way (MW) satellites has intensified due to the availability of wide-field deep panchromatic photometric surveys carried out with the new generation of telescopes. The application of high-performance overdensity detection techniques on extensive datasets has significantly increased our knowledge of stellar systems residing in the MW halo. These surveys have unlocked the exploration of the low-luminosity faint end of the galaxy luminosity function, which was previously inaccessible, encompassing dwarf galaxies and ultra-faint dwarf (UFD) galaxies. UFDs are not only renowned as the most dark-matter-dominated objects in the Universe but also as the oldest and least chemically evolved galaxies, making them invaluable probes for unraveling the MW's mass assembly history. To further expand the search for unidentified stellar systems, our study leverages the untapped potential of the Kilo-Degree Survey (KiDS), which has not yet been utilized in the quest for low-surface brightness satellites of the MW. This presentation showcases the outcomes of an extensive investigation encompassing the entire KiDS star catalog.
The highest resolution at the lowest radio frequencies: the LOFAR view of the radio sky
02/05/2024
The LOw Frequency ARray (LOFAR) is a radio interferometer with antennas in nine European countries. Its geographic spread of almost 2,000km provides a large effective 'lens'. With this, we can make images with exquisite resolution at low radio frequencies. We do this by combining the signals from all these distant antennas, a technique known as very long baseline interferometry (VLBI). VLBI with LOFAR is very challenging. Over the past few years we have developed special calibration techniques for VLBI with LOFAR. These new techniques are now used for a wide variety of science cases which would not otherwise be possible. We have now extended these techniques to image large areas of the sky, which provides a unique combiantion of resolution and field of view. In this talk I will provide a general introduction to LOFAR, and an overview of the challenges in making high resolution images. I will walk through how we overcome these challenges and show examples of our breakthrough successes and recent science results. I will finish by providing an overview on current and future plans. These include a Northen sky survey which will have higher resolution than any previous wide-area radio survey.
Advances in stellar and galactic evolution with the population of planetary nebula progenitors from the APOGEE DR17 survey
20/02/2024
Planetary nebulae (PNe) are the ejected gas and dust shells of Asymptotic Giant Branch (AGB) stars, which represent the late life of low- and intermediate-mass stars (LIMS). With the advent of the APOGEE DR17 survey, there is a purpose in comparing Red Giants (RGs) and PNe abundances to disclose their similarities and differences since such a comparison has been rarely, and not recently, done in the Milky Way. While we expect similarities in most of the alpha-element distributions across the two populations, given their limited evolution in LIMS, differences in Fe and S abundances allow us to determine their depletion due to grain condensation in post-AGB phases. Differences in N and C between PNe and their progenitors set new limits to their production in the late stages of LIMS evolution. Finally, we use radial metallicity gradients from RGs and PNe and Gaia-calibrated distances to constrain galaxy evolution in the framework of the current chemical evolution models.
Opening up the radio sky with VLBI
16/02/2024
In the past few decades, radio surveys have provided us with unique insights into many areas of astrophysics such as star formation, supernovae, active galactic nuclei, pulsars, cosmology and much more. A key aspect of these surveys is the technique of Very Long Baseline Interferometry (VLBI) which can provide some of the highest resolutions possible in astronomy. This method has been crucial in understanding the inner workings of galaxies such as AGN-star-formation feedback, dark-matter substructures in gravitational lenses, and providing the first two direct images of a black hole shadow. VLBI has been typically limited where the largest surveys require many years of observations to build up an extensive sample. However, computational improvements have enabled us to map multiple sources within a single VLBI survey and push into the lower frequency regime through the International LOFAR telescope. In this talk, I will talk about the scientific and technical discoveries arising from such surveys and focus on the bright future of VLBI surveys. This includes the transition from the current modus operandi of a small number of surveys of a few 'famous' deep fields to a ubiquitous VLBI survey instrument. I will conclude the talk by talking about the upcoming developments in VLBI, such as the incorporation of SKA and MeerKAT, ultra-wideband receivers, and GPU-accelerated correlation and calibration.
The long and winding road towards precise and accurate ages of stars: a traveller’s perspective
14/02/2024
Our understanding of the formation and evolution of the Milky Way and galaxies is often blurred and biased by the lack of precise and accurate stellar ages. Asteroseismology, i.e., the study of global, resonant oscillation modes in stars, is providing us with a formidable tool to unveil detailed insights into the internal structure of stars, paving the path for robust age determinations. In this presentation I will discuss the ongoing efforts and recent results of the asterochronometry project, which aims to test our knowledge of stellar physics while providing precise and accurate age estimates (within 10-20%) for stars in the regions of the Galaxy surveyed by the space telescopes Kepler, K2, CoRoT, and TESS. While I will showcase examples of asteroseismology's role in reconstructing the early assembly history of the Milky Way, I will also highlight the limitations we encounter emphasising that these hurdles can only be truly overcome via an improved understanding of stellar physics. Finally, I will discuss the prospects for extending these studies to larger samples, and outline the scientific rationale for a future space mission dedicated to asteroseismology in “controlled environments”. Such a mission would transform stars into laboratories, enabling us to test stellar physics catalysing the development of next-generation stellar models.
The Imaging X-ray Polarimetry Explorer: Making History in High-Energy Astrophysics
7/02/2024
IXPE represents the momentary culmination of a long history of determined scientists with the goal of introducing two brand-new observables to the usual ones in High Energy Astrophysics. In this talk, I will illustrate how this goal was achieved, starting from the late '80s, progressing to the development of IXPE, which began with the proposal in 2014 and led to the launch on December 9, 2021, amid a pandemic and an American Government shutdown. Over the past two years, IXPE has been actively observing a variety of celestial sources, such as neutron star and black hole binaries, AGNs, magnetars, Supernova Remnants and Pulsar Wind Nebulae, just to name a few categories. The main findings for each class of objects will be presented in a cycle of seminars, starting with this one, where I will focus specifically on the scientific results that have been obtained for galactic black hole binaries, AGNs, and magnetars.
SHARP - A Near-IR Multi-mode Spectrograph conceived for the Multi-Conjugate Adaptive Optics Module MORFEO@ELT
6/02/2024
The world's largest aperture combined with state-of-the-art Adaptive Optics systems will enable the ELT to capture better data than the JWST in both sharpness and depth. Therefore, the spectrograph intended for the 2nd port of the Multi-Conjugate Adaptive Optics (MCAO) system MORFEO@ELT will be the most powerful instrument of the JWST era, revealing phenomena beyond the reach of others. SHARP (http://sharp.brera.inaf.it) is a near-IR (0.95-2.45 mu) spectrograph designed for the 2nd port of MORFEO@ELT, intended to be submitted in the upcoming ESO instrument call. Comprising a Multi-Object Spectrograph, NEXUS, and a multi-Integral Field Unit, VESPER, SHARP extends its wavelength range to ~2.45 μ. Coupled with MCAO-assisted observations, it delivers unprecedented high angular (~30 mas) and spectral resolution, outperforming NIRSpec@JWST (100 mas). MORFEO-SHARP will allow us to study the nearby and the early Universe in unprecedented detail, resolving the first galaxies and the star forming regions within galaxies far back in cosmic time, and providing spectra of individual nearby young stellar objects. This presentation introduces the scientific rationale behind SHARP, showcasing its features and inviting those interested to join the SHARP team.
Rapidly-rotating Population III stellar models
1/02/2024
The first stars, also known as Population III stars, began the process of reionization in the Universe and contributed to the metal enrichment. It is believed that they might have been fast rotators, which can have significant consequences for their radiative, mechanical, and chemical feedback. In this talk, I will present recent models using the Geneva stellar evolution code (GENEC) with fast initial rotation velocity, corresponding to 70% of the critical one in the mass range of 9 to 120Msol. I will compare the outputs of these models with those obtained with lower initial rotations, focusing on the primary nitrogen production. Other aspects of the rapidly-rotating models will be discussed, including their impact on the early chemical evolution of galaxies. Moreover, I will discuss the possibility that rapidly-rotating Pop III stars may, at least in part, explain the high N/O ratios measured in certain high-redshift galaxies, such as GN-z11 and CEERS-1019.
Searching for light dark matter
31/01/2024
The Standard Model (SM) of particle physics has been highly successful in describing the fundamental particles and their interactions in the last decades. Nevertheless, the SM leaves unanswered questions, like the origin of matter over anti-matter asymmetry in the Universe, the strong CP problem. On the other hand, the existence of dark matter (DM) is required by the cosmological and astrophysical observations. The scenario in which DM is the thermal relic of the early Universe is thus well justified. Even though well justified if the governing force is the weak interaction, the parameter space available to GeV-TeV WIMPs has reduced over recent years, so that interest has grown in “hidden” or “dark" sector models. These models assume that DM is made of particles which interact feebly with SM particles via a portal particle, thus greatly enlarging the allowed parameter space. In addition to solving the DM problem, those models postulating light dark particles could also address some anomalies in particles physics, such as the discrepancy between the experimental results and the calculated SM value of the anomalous magnetic moment of the muon, or the strong CP problem. Another indication of the existence of new, light (MeV-GeV) states seems to come from anomalous e+e- pairs production in nuclear physics measurements of light even-even nuclei. A panorama of ongoing and proposed experiments, capable of testing different models, is presented; those experiments explore different mass ranges and sensitivities, using different production and detection techniques. In particular, the feeble interaction with SM particles opens the possibility of producing these new particles at accelerators.
RU Lup: the accretion environment of a prototypical Classical T Tauri star
30/01/2024
While it is well established that Classical T Tauri stars accrete material from a circumstellar disk through magnetic fields, the physics regulating the processes in the inner (0.1 AU) disk is still not well understood. With its long observational history and its rich emission line spectrum, RU Lup is a prime example to study this environment. RU Lup is a monitoring target within the ULLYSES survey for Classical T Tauri stars. Optical spectroscopic observations with CHIRON and ESPRESSO were obtained simultaneously with the two epochs of the ULLYSES monitoring program for RU Lup. In this talk, I will discuss the main results obtained by analyzing this collection of data, supplemented by the two TESS observations and the archival AAVSO photometry of RU Lup. Using the high resolution ESPRESSO spectra, we improved the measurements of the stellar parameters, especially the projected rotational velocity (vsini). We determined the veiling fraction for the ESPRESSO spectra, showing that the veiling consists of two components: a continuum emission likely originating in the accretion shock and line emission that fills in the photospheric absorption lines. We detected a periodic modulation in the narrow component (NC) of the He I 5876 line with a period that is compatible with the stellar rotation period, indicating the presence of a compact region on the stellar surface that we identified as the footprint of the accretion shock. Although the brightness of RU Lup changed drastically both on daily and yearly timescales, this region is overall stable over the 3 years covered by the observations. An analysis of the high-cadence TESS light curves revealed quasi-periodic oscillations (QPO) on timescales shorter than the stellar rotation period. This suggests that the accretion disk in RU Lup extends inward of the corotation radius and the star accretes through a magnetic boundary layer (MBL). The rich metallic emission line spectrum of RU Lup might be characteristic of this accretion regime.
Relativistic jets from black hole X-ray binaries: a MeerKAT view
30/01/2024
Black hole X-ray binaries (BH XRBs) can launch powerful outflows in the form of radio-emitting discrete jet ejecta, which are generally observed to be produced during bright outburst phases and to propagate at apparently superluminal speeds. However, little is known about the powering mechanism, the formation and composition of these jets, and studying them is important for understanding both their physics and their feedback on the surrounding environment. While discrete ejecta have been historically difficult to detect and to follow in their motion away from the central black hole, the MeerKAT radio-interferometer (precursor of the SKA) is now revolutionizing the field with its exceptional sensitivity at GHz frequencies. In this talk, I will present some of the most interesting advancements that we have obtained with MeerKAT observations of BH XRBs in the last five years, as part of the ThunderKAT collaboration. More in detail, I will present the MeerKAT detection of a number of new ejecta that we observed to interact with the interstellar medium (ISM) and to strongly decelerate at parsec scales far from the black hole. In this context, covering the deceleration phase is essential for the physical modelling of the jet kinematics, and I will discuss what is possible to learn from the application of these models on the jet physical parameters and on the properties of the environment surrounding BH XRBs.
ICY SATELLITES: A MULTI-SCALE ANALYSIS TO UNDERSTAND THEIR TECTONICS
24/01/2024
The icy satellites, such as Jupiter’s Europa and Ganymede or Saturn’s Enceladus, are first class targets for future missions focused on the search of biosignatures in the Solar System. In fact, evidence of subsurface oceans indicates that such bodies may harbor potentially habitable environments and the investigation of the surface features contributes to their detection. The icy satellites show widespread deformation structures that provide insights to infer the tectonics and the mechanical properties of their crusts. Such structures represent discontinuities between crustal layers and conduits for fluid circulation that connect the surface with the deep layers, such as the ocean. Therefore, structural investigation is pivotal for the understanding of icy satellite geology, which still presents open issues. Their surfaces show a large amount of extension and strike-slip that require balancing, which is not fulfilled by the paucity of compression recognized at present. Several approaches have been proposed to unravel the tectonics of the icy satellites from remote sensing of data acquired by the past missions to the support of terrestrial analogs. We show tectonic models that allow to explore multi-scale investigations of the deformation structures of the icy satellites, and in particular of Ganymede, which is the main target of the JUICE mission.
The ESA M7 candidate mission Plasma Observatory
08/05/2024
Particle energization and transport of energy are key open problems of space plasma physics. Strong particle energization and energy transport occur in the complex and highly dynamic plasma environment in the near Earth space: the Magnetospheric System. Previous multi-point observations from missions such as ESA/Cluster and NASA/MMS evidenced the fundamental role of cross-scales coupling in plasma processes. Simultaneous measurements at both large, fluid and small, kinetic scales are required to resolve scale coupling and ultimately understand plasma energization and energy transport processes. Such measurements are currently not available. Here we present the Plasma Observatory (PO) multi-scale mission concept tailored to study plasma energization and energy transport in the Earth’s Magnetospheric System through simultaneous measurements at both fluid and ion scales. PO baseline mission includes one mothercraft (MSC) and six identical smallsat daughtercraft (DSC) flying in a two tetrahedra formation. The two tetrahedra have different characteristic scale and the MSC is at the common vertex of the inner tetrahedra. PO orbit is an HEO 8x17 RE orbit, covering all the key regions of the Magnetospheric System including the foreshock, the bow shock, the magnetosheath, the magnetopause, the magnetotail current sheet, and the transition region. Along the orbit, the separations between the spacecraft range from fluid (5000 km) to ion (30 km) scales. The MSC payload provides a complete characterization of electromagnetic fields and particles in a single point with time resolution sufficient to resolve kinetic physics at sub-ion scales and to fully characterize wave-particle interactions (for both protons and heavy ions). The DSCs have identical payload, simpler than the MSC payload, yet giving a full characterization of the plasma at the ion and fluid scales and giving the context where energization and transport occur. PO is the next logical step after Cluster and MMS. It will allow us to resolve for the first time scale coupling in the Earth’s Magnetospheric System, leading to transformative advances in the field of space plasma physics with implications on research fields that span from space weather to the understanding of the farthest astrophysical plasmas. PO is one of the three ESA M7 candidates, which have been selected in November 2023 for a competitive Phase A with a mission selection planned in 2026 and launch in 2037.
Looking from micro- to macro-scale: how the exploration of the Solar System can benefit from laboratory experiments on analog and returned samples
30/04/2024
The exploration of the Solar System's rocky surfaces of planets and minor bodies using remote sensing benefits from multiple sources of data: from ground-based observations, to orbiter and lander flybys, to returned samples of extraterrestrial material. However, the more data we acquire, the more it becomes clear that our current interpretation techniques (both laboratory and modelling), although improving, are still not sufficient to fully understand our observations. Indeed, the interpretation of remote sensing data could not be separated from intensive laboratory work, which provides a powerful tool for revealing the surface physical state and composition of rocky surfaces. The analysis of complex mixtures of analogous materials remains one of the key laboratory investigations to support remote sensing interpretation, but it is also one of the most challenging experiments, especially when multiple components are used. This talk gives a general overview of the main results from the literature on the efforts to use laboratory data to interpret infrared observations. Some new measurements on the mixing effect of different grain sizes and dark materials are also presented.
Thermonuclear explosions on neutron stars reveal the speed of their jets
16/04/2024
Relativistic jets are observed from all accreting compact objects throughout the visible Universe. These jets have a profound impact on their surroundings, yet their launch mechanism remains unknown. For accreting neutron stars, jet speeds can reveal the dominant launching mechanism, showing whether the jets are powered by magnetic fields anchored in the accretion flow or in the star itself. These objects can display bright explosions on their surface due to unstable thermonuclear burning of recently accreted material, called type-I X-ray bursts. The seconds to minutes long X-ray bursts greatly impact the accretion flow, altering the properties of both the disk and corona. Here, I will present an intensive X-ray and radio monitoring program focused on two known bursting neutron star X-ray binaries, aiming to detect the impact that type I X-ray bursts may have on the emitted jets. Remarkably, we discovered a clear radio enhancement in the minutes immediately after each X-ray burst, lasting tens of minutes. The ongoing presence of the jet suggests that the magnetic field structure in the accretion flow collapses more slowly than the gas, providing crucial constraints for magnetohydrodynamics calculations. Importantly, the jet flares allow us to robustly measure the speed of the neutron star's jet, finding them to be much slower than those from black holes at similar luminosities. This discovery provides a powerful and repeatable new tool in which we can determine the role that individual system properties have on the jet speed, revealing the dominant jet launching mechanism. https://www.nature.com/articles/s41586-024-07133-5
Globular cluster formation and the high-redshift Universe
10/04/2024
Globular clusters are among the oldest objects we know of, many likely to have formed at the epoch of reionization, and may have even contributed to it. Their formation, with their ubiquitous multiple stellar generations, remains an intriguing puzzle in astrophysics. Direct evidence indicates that they formed in a series of bursts, and each burst did not prevent the occurrence of the following ones, as if there was no negative feedback on star formation. Moreover, second-generation stars exhibit different light-element abundances, but no sign of enhancement by supernova products which, together with the lack of feedback, indicates that formation took place before supernovae started to affect the ISM. This suggests that, above a critical mass, stars fail to produce supernova events, but rather sink into black holes without ejecting much energy and heavy metals. This scenario of globular cluster formation has the attractive implication of suppressing star formation feedback for some ~10 million years, in practice leading to runaway star formation, analog to overcooling that in the absence of feedback would have turned most baryons into stars in the early Universe. Under such conditions, multiple episodes of star formation, incorporating stellar ejecta from previous bursts, appear to be unavoidable, thus accounting for the ubiquity of the multiple-generation phenomenon in globular clusters. If this is indeed the way globular clusters formed, then a generic ~10 Myr delayed feedback would have important implications for star formation in general, and in particular for the very high redshift Universe, helping to account for the unexpected frequency of bright/massive galaxies at z=9-16 revealed by JWST.
Unlocking Cosmic Origins: LiteBIRD's quest for Inflationary GWs
15/04/2024
The LiteBIRD (Lite (Light) satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection) experiment is a space mission dedicated to studying the polarization of the Cosmic Microwave Background (CMB). Its primary objective is to detect the faint B-mode polarization patterns in the CMB, which are believed to be imprints of gravitational waves from the early universe, particularly from the period of cosmic inflation. LiteBIRD is equipped with a 30 arcmin beam width and an extraordinarily low polarization noise of 2.16μK-arcmin, making it uniquely capable of capturing large scale full-sky CMB polarization. Our studies address two significant challenges in detecting Inflationary B-modes: foregrounds and the weak gravitational lensing of the CMB. Foregrounds, varying with observation frequency, can be mitigated through multi-frequency sky observations. However, gravitational lensing of the CMB presents a different problem, as it is not frequency-dependent and causes E-mode polarization to convert to B-modes. This conversion masks the primordial B-modes we aim to detect. Our work concentrates on estimating the mass distribution from the CMB field to create a template of lensing B-modes. By removing this lensing-induced B-mode template from the observational data, we enhance the sensitivity towards detecting Inflationary gravitational waves. This talk will explore the methodologies used in this study, the challenges encountered, and the potential impact on the detection of the Inflationary gravitational waves.
Modification and transfer of the cosmic background spectrum due to the observer motion: perspectives from radio to far-infrared
11/04/2024
The peculiar motion of an observer relative to an ideal reference frame at rest with respect to the cosmic background produces boosting effects which modify and transfer at higher multipoles the frequency spectrum of the isotropic background. Analytical solutions of a system of linear equations are presented to explicitly compute the spherical harmonic expansion coefficients for background spectra described by analytical or semi-analytical functions, significantly alleviating the computational effort needed for accurate theoretical predictions. This approach is extended to generic (tabulated) functions, allowing to treat a wider range of realistic models. Precise inter-frequency calibration will provide the opportunity to constrain or even detect tiny imprints in the background spectrum from a variety of cosmological and astrophysical processes, mainly due to the frequency dependence of the dipole spectrum, without resorting to precise absolute calibration. Expectations of future all-sky differential surveys in retrieving the amplitude of the far-infrared background spectrum and the parameters of the cosmic microwave background spectral distortions are discussed. In principle, the presence of spectral distortions also offers the chance to alleviate, with dipole analyses alone, the degeneracy between intrinsic and kinetic dipoles. The dipole signal on small sky areas expected at radio frequencies from a variety of processes is compared with the sensitivity and resolution of next interferometric observations.
Globular cluster formation and the high-redshift Universe
10/04/2024
Globular clusters are among the oldest objects we know of, many likely to have formed at the epoch of reionization, and may have even contributed to it. Their formation, with their ubiquitous multiple stellar generations, remains an intriguing puzzle in astrophysics. Direct evidence indicates that they formed in a series of bursts, and each burst did not prevent the occurrence of the following ones, as if there was no negative feedback on star formation. Moreover, second-generation stars exhibit different light-element abundances, but no sign of enhancement by supernova products which, together with the lack of feedback, indicates that formation took place before supernovae started to affect the ISM. This suggests that, above a critical mass, stars fail to produce supernova events, but rather sink into black holes without ejecting much energy and heavy metals. This scenario of globular cluster formation has the attractive implication of suppressing star formation feedback for some ~10 million years, in practice leading to runaway star formation, analog to overcooling that in the absence of feedback would have turned most baryons into stars in the early Universe. Under such conditions, multiple episodes of star formation, incorporating stellar ejecta from previous bursts, appear to be unavoidable, thus accounting for the ubiquity of the multiple-generation phenomenon in globular clusters. If this is indeed the way globular clusters formed, then a generic ~10 Myr delayed feedback would have important implications for star formation in general, and in particular for the very high redshift Universe, helping to account for the unexpected frequency of bright/massive galaxies at z=9-16 revealed by JWST.
Extended sources in the age of IXPE
03/04/2024
The NASA-ASI Imaging X-ray Polarimetry Explorer (IXPE) launched in December 2021 and has since enabled, for the first time, the ability to perform spatially resolved X-ray polarimetry in the 2 - 8 keV band for a wide range of extended sources. Thanks to its unique capabilities, IXPE has allowed us to probe the magnetic-field geometry closer than ever to the particle acceleration sites in young supernova remnants (SNRs) shocks. It has also unveiled the level of magnetic turbulence and its distribution in pulsar wind nebulae (PWNe) and has even shed light on the recent past of our Galactic center (GC). Up to now, IXPE has observed six SNRs (Cas A, Tycho, SN 1006, RCW 86, RX J1713.7-3, and Vela Jr.), five PWNe (the Crab, Vela, MSH15-52, PSR B0540-69, and G21.5), the molecular clouds of the Sgr A complex near the GC, and the eastern lobe of the jet of the microquasar SS433. The X-ray polarimetric results from all the sources observed to date have exceeded, and in many cases subverted, our expectations. In this talk, I will present the latest, unprecedented insights offered by the new field of spatially resolved X-ray polarimetry.
Dust and molecules in dying AGB stars
26/03/2024
There is a large debate about how dust grains have been accumulated in the interstellar medium (ISM) of galaxies. One of the major sources of dust grains into the ISM is evolved stars, such as AGB stars, red supergiants and supernovae (SNe). On the other hand, fast-expanding SN blast waves could be so efficient that theoretical models predict that almost entire ISM dust grains ejected by stars can be wiped off by SN explosion. There are still uncertainties in dust evolution in the ISM. We present several results about studies of AGB stars, planetary nebulae (PNe) and SNe in my talk. The first part is GAIA studies of AGB stars, showing the distribution of local dust output from AGB stars. The second part is studies of dust in PN, using JWST, indicating the final re-processing of dust grains before they are integrated into the ISM. Finally, JWST observations capture how dust grains are destroyed by SN blast waves in Supernova 1987A.
Foreground removal in the upcoming CMB polarization data
20/03/2024
Multi-frequency observations are needed to separate the CMB from foregrounds and accurately extract cosmological information from the data. In the past decades, many ground-based, balloon- borne and satellite experiments have been dedicated to CMB observations. The latest results from the Planck satellite achieved a precise measurement not only for temperature anisotropies, but also for CMB polarization E- modes. As an outcome of these experiments, much cosmological information has already been extracted from the CMB. Recently, much attention has been focused on the CMB polarization anisotropies, especially the B-modes, which are of particular interest as they are expected to probe inflation. However, a precise measurement of these B-modes strongly depends on our ability to separate the signal from the astrophysical foregrounds. In this seminar, I will discuss the foreground cleaning performance considering CMB polarization experiments, mainly in the context of the Chinese ground-based Ali CMB Polarization Telescope.
The Central Problem of Star Formation: Why So Slow?
20/03/2024
The Central Problem of star formation has been clear for over 40 years: simple estimations predict star formation rates more than 100 times what is observed in the Milky Way and other galaxies. Much ingenious theoretical work has been expended to solve this problem, enhancing our understanding of turbulence and feedback in molecular clouds, but the fundamental problem remains. This situation suggests a reconsideration of the basic assumption that underlies the problem: that molecular clouds are bound entities. In the most complete catalog of structures from CO emission maps, most molecular clouds are unbound, ameliorating the problem. Combining this information with theoretical models of how the star formation rate depends on the initial virial parameter, along with considerations of how metallicity affects the conversion of CO luminosity into mass, provides a solution to the Central Problem for the Milky Way. The variation of star formation rate with Galactocentric radius can also be predicted and finds good agreement with the recent results obtained from the Hi-GAL survey.
Low surface-brightness galaxy population in the Centaurus Cluster from the VEGAS survey
14/03/2024
I present a new catalog of LSB galaxies in the Centaurus cluster, which is built from wide-field multi-band images from the VST Early Type Galaxy Survey (VEGAS). The VST mosaic covers a field of view of 2x3 deg^2 centered on NGC 4696. I developed a new detection tool to identify and analyse LSB galaxies in the g’ and r’ bands. Such a tool is based on segmentation maps for galaxy detection, machine learning for false positive selection, and Bayesian modelling for measuring galaxy structural properties. I detected 13 new UDGs and more than 200 LSB galaxies (more than 60 newly discovered). I also found three LSB galaxies with a bright nucleus, that were classified as UV sources by the GALEX telescope. This work is part of my PhD project, which aims at applying this detection tool to the entire VEGAS sample, which covers more than 100 deg^2. In this talk, I illustrate this new tool and preliminary results, and how it could be implemented for the future deep imaging surveys. Then, I discuss the spatial distribution of LSB galaxies in comparison to bright galaxies. Finally, I present the scaling relations and cluster-centric distance trends of the galaxy properties.
Biosignatures and Technosignatures. The Telescopic Search for Life Across Interstellar Distances
13/03/2024
The 2020 Astronomy Decadal Survey put a "Habitable Worlds Observatory" at the top of the community's projects for the next twenty years. In this talk I will discuss the current state of research and future plans in the search for life via "biosignatures" and "technosignatures". I will review the history of the field and discuss what advances have allowed the ancient question of "are we alone" to finally become one which science might answer.
A new dark age for radio astronomy?
26/03/2024
In recent years, the utilization of the radio spectrum has dramatically increased. Digital telecommunication applications, be it terrestrial cell-phone networks or new-space low-earth orbit satellite constellations, have not only acquired unprecedented amounts of spectrum but also use their frequencies everywhere on Earth. The consequences for radio astronomy and other scientific radio services are severe. A single cell-phone tower within hundreds of kilometers around a radio telescope can blind us and there is no place on Earth to escape the ubiquitous transmissions of satellite megaconstellations. Since 1988, the Committee on Radio Astronomy Frequencies (CRAF) has been advocating for our rights to use the spectrum. We do this by participation in the national and international regulatory frameworks - which is a truly endless endeavor. Hundreds if not thousands of documents need to be processed every year. We not only contribute to regulatory texts, but even more importantly, perform spectrum compatibility calculations. This can range from coordinating a single cell phone tower around your favorite radio telescope to massive-scale simulations involving thousands of satellites while accounting for transmitter and receiver antenna patterns, atmospheric losses, beam-forming, side-lobe contributions and out-of-band signal suppression. In this talk, we will present CRAF’s activities.
Astrochemistry: a powerful tool to understand the origin of complexity in the Universe
05/03/2024
Astrochemistry is a blend of different disciplines, from chemistry to astronomy, including computational sciences and biology. One of the fundamental questions in astrochemistry is related to the understanding of intricate physical processes like star- and planet-formation, and how these are connected to the emergence of chemical complexity. In this talk I will introduce the astrochemistry field, showing its different applications. I will present some recent exciting magneto-hydrodynamical simulations and introduce how the chemistry can help disentangling among the main processes which lead to the formation of stars. It will be a journey from the simple chemistry of diffuse gas to the complexity of the small and dense regions of the interstellar medium, where complex chemical processes play a fundamental role to unveil our astrochemical origins.
A multidisciplinary view of space plasma dynamics inspired by the stochastic process theory
06/03/2024
Turbulent plasmas are ubiquitous in space and astrophysical settings and display a variety of collective phenomena that, in turn, have a great impact in the dynamics of stellar atmospheres, stellar winds, solar coronal heating, etc. Most of these phenomena are related to the microphysics of nearly-collisionless plasmas, such as the ion-kinetic scale processes transferring energy from electromagnetic fields to particles and leading to energy dissipation and plasma energization. The solar wind, a strongly turbulent plasma flowing in the heliosphere from the expansion of the solar Corona, constitutes an excellent natural laboratory to get precious clues about ion-kinetic scale plasma dynamics. During the last decades, space missions provided in situ data of diverse space plasma environments with an increasingly higher resolution. This enabled the possibility to investigate peculiar properties of fluctuations in the magnetic field and plasma parameters, transitioning from the magnetohydrodynamic (MHD) to the ion-kinetic regime. The kinetic regime is characterized by a global self-similar statistics of the fluctuations, in other words their statistical properties at different scales can be simply superimposed by rescaling. This is a contrasting feature with respect to the local scale-invariance universally observed in the MHD range, where strongly non-Gaussian fluctuations tend to develop towards small scales thus producing the “fat tailed” distributions observed everywhere. In a series of works, we developed a data-driven approach based on the Langevin equation in order to model statistical features of space plasma kinetic fluctuations. In practical terms, the stochastic variable is represented by the fluctuation of the magnetic field and the process is its evolution through the scales. This rather simple framework allows us to make predictions about statistical properties observed in different space plasma environments which have been tested on several spacecraft data samples and numerical simulations. As far as such fluctuations are of the Langevin type, their statistics evolve according to a Fokker-Planck equation. A derivation of the ion-kinetic scale statistics based on this equation makes it possible to derive the invariant distribution function, which turns out to be a generalized kappa distribution. The aim of this contribution is to introduce the framework of stochastic modeling in the context of space plasma physics and to illustrate how this methodology is truly general, and thus suitable for applications in many different physical contexts.
Optical and X-ray Gamma-Ray Bursts Fundamental Planes as cosmological distance indicators
06/03/2024
Already Gamma-ray bursts (GRBs), can be employed as standardized candles, extending the distance ladder beyond Type Ia supernovae (SNe Ia, z = 2.26). We standardize GRBs using the three-dimensional (3D) Fundamental Plane relation (the Dainotti relation) among the rest-frame end time of the X-ray plateau emission, its corresponding luminosity, and the peak prompt luminosity. Combining SNe Ia and GRBs, we constrain ΩM = 0.299 ± 0.009 assuming a flat Λ cold dark matter (ΛCDM) cosmology with and without correcting GRBs for selection biases and redshift evolution. Using a 3D optical Dainotti correlation, we find this sample is as efficacious in the determination of ΩM as the X-ray sample. We trimmed our GRB samples to achieve tighter planes to simulate additional GRBs. We determined how many GRBs are needed as stand-alone probes to achieve a comparable precision on ΩM to the one obtained by SNe Ia only. We reach the same error measurements derived using SNe Ia in 2011 and 2014 with 142 and 284 simulated optical GRBs, respectively, considering the error bars on the variables halved. These error limits will be reached in 2038 and in 2047, respectively. Using a doubled sample (obtained by future machine learning approaches allowing a light-curve reconstruction and the estimates of GRB redshifts when z is unknown) compared to the current sample, with error bars halved we will reach the same precision as SNe Ia in 2011 and 2014, now and in 2026, respectively. I will also discuss in general about the importance of the intrinsic relations for the correct application and the role of selection biases have in the derivation of incorrect cosmological parameters.
Measuring the degree of anisotropy of the UV emission in super-Eddington accretion flows
27/02/2024
A major prediction of most super-Eddington accretion theories is the presence of highly anisotropic emission resulting from the wind/funnel structure formed due to the intense radiation pressure in supercritical discs. Understanding the exact emission pattern of such flows has strong implications on how super-Eddington accreting sources will affect their environments. A key breakthrough allowing to test such predictions was the discovery of high-excitation photoionized nebula around Ultraluminous X-ray sources (ULXs). In such circumstances one can study the emission lines from high-excitation nebulae to assess whether the nebula ‘sees’ the same SED as observed along the line of sight. In this talk, I will present our efforts to tackle the degree of anisotropy of the emission in ULXs, coupling multi-band spectroscopy of the source with Integral-Field Unit spectroscopy of the nebular emission. I will present our recent results on the emission of the famous ULX NGC 1313 X-1, where we find that in order to reproduce the lines in the surrounding nebula, the photoionizing SED must be a factor ∼ 4 dimmer in ultraviolet emission than the line-of-sight SED. I will discuss the implications of these results in the context of ULXs and present ongoing work on another ULX with similar properties. I will finalise with some thoughts on what improvements in instrumentation and methods are needed to reduce existing uncertainties and explore the degree of anisotropy at higher energies.
Locking in co-evolution between supermassive black holes and their host galaxies in the early Universe
23/02/2024
I will present the latest results from JWST on the detection of the host galaxies of z ~ 6 quasars. These observations enable us to establish the early mass relation between black hole mass and galaxy stellar mass using NIRCAM and NIRSPEC. This involves careful 2D decomposition of IR images with accurate characterization of the point-spread function, selection effects, and measurement uncertainties. Furthermore, rest-frame spectroscopy is revealing the timescales for galaxy and SMBH growth. I will also discuss the connection with lower mass black holes found in deep JWST surveys as reported in the literature and need to consider selection effects.

2023


Towards the geology of exoplanets
April 20, 2023, 16:30 CEST
Hot rocky exoplanets offer exciting opportunities to place terrestrial geology into Galactic context, through composition measurements with JWST and Ariel. To capitalise on these opportunities we must identify the very best targets for spectroscopic characterisation. The catastrophically disintegrating exoplanets (CDEs) are the most dramatic examples of mass loss from an ablating rocky surface. They were discovered by Kepler through the variable transits of dust co-existing with metal-rich vapour, and are particularly suitable for transmission spectroscopy because the ablated material is spread over a large scale-height. But the Kepler CDEs are too faint for transmission spectroscopy. The Dispersed Matter Planet Project (DMPP) is discovering the nearby analogues and progenitors of the Kepler CDEs. DMPP uses archival stellar spectra to identify stars we view through shrouds of diffuse, metal-rich, circumstellar gas. The underlying hypothesis is that the gas is ablated from hot, close-orbiting planets. DMPP searches for the putative planets with high-precision, high cadence radial velocity measurements. The approach has been extremely successful and efficient, with planet discoveries whenever 60 RV measurements have been collected. DMPP-1 is a compact multiplanet system orbiting a star brighter than V=8. A possible CDE transit has been discovered in TESS data. DMPP-2 b is the joint-first RV planet discovery orbiting a strongly pulsating star. DMPP-3 is an eccentric binary star system with the secondary at the mass threshold for sustaining hydrogen fusion. A 2.6 Earth mass planet orbits the K0V primary star in a 6.7 day orbit, with a second Earth-mass circumprimary planet marginally detected. DMPP-3AB is in a hitherto unpopulated parameter space for binary star planetary systems. I will include updates on our latest discoveries of around 20 short period planets, including planets orbiting a star of magnitude 6, and planets orbiting a young star. We may have caught the latter system in the act of evolving out of the Neptune desert through planetary ablation. DMPP planets are likely to be viewed edge-on as ablated material will remain concentrated near the planets’ orbital planes. Thus they have high transit probability. The subset of DMPP planets which transit are thus amenable to direct empirical determinations of mass, radius and composition.

2022


Annalisa Pillepich, Max Planck Institute for Astronomy, Heidelberg: The many diverse manifestations of supermassive black-hole feedback: from simulations to observations, and back
Oct 26th, 2022
Large-volume cosmological galaxy simulations, such as IllustrisTNG, provide a holistic view on galaxies and on how their evolution depends on the interplay of internal and external physical phenomena. Among the internal mechanisms, feedback from super massive black holes (SMBHs) is commonly invoked in such numerical models to halt star formation in massive galaxies. In fact, no other mechanism so far has been shown to be capable of returning entire populations of simulated massive quenched galaxies that are consistent with the observed galaxy red sequence and quenched fractions. With simulations like IllustrisTNG we are putting together ever more quantitative and plausible evidences as to the role that feedback from SMBH can have, not only in shaping galaxy structural properties and galaxy populations across 90 per cent of the Universe’s history, but also in regulating the thermodynamical, ionization, and metal enrichment properties of the cosmic gas across halo scales and beyond. In this talk, I will use the outcome of the IllustrisTNG and other simulations in combination with current and future observational data, chiefly SDSS galaxy data and eROSITA X-ray observations, to further our understanding of the tight interconnections between SMBHs, star-formation quenching, and the physical state of the circumgalactic medium.
Pascal Oesch, University of Geneva: Galaxy Build-up During the Cosmic Reionization Epoch
July 4th, 2022
Speaker: Pascal Oesch (University of Geneva) Title: Our Panchromatic View of Galaxy Build-up at Cosmic Dawn into the JWST Era Abstract: The first deep images with the Hubble Space Telescope (HST) have transformed our view of the Universe. Over the following more than two decades, HST continued to extend our cosmic horizon reaching to only ~400 Myr after the Big Bang at z~11. In combination with other observations across the electromagnetic spectrum, from the rest-frame optical with Spitzer/IRAC, and now all the way to (sub)mm wavelengths with ALMA/NOEMA, we are gaining a more and more complete census and understanding of galaxy build-up across 97% of cosmic history. Yet some critical gaps remain, mainly because (1) our galaxy samples are still mostly rest-UV selected at z>3, and (2) we still only have highly-incomplete spectroscopic information at z>6. In this talk, I will present an overview of our current understanding of star-forming galaxies at z>3 based on our panchromatic view from HST+Spitzer+ALMA/NOEMA data. This will be completely revolutionized over the next months, however, as the first observations with the JWST are being taken. In particular, JWST will provide deep rest-frame optical data out to z=10, both in imaging and spectroscopy, which is truly unprecedented. JWST will thus finally allow us to probe the physics of the first generations of galaxies that ended the cosmic Dark Ages and started the reionization of the Universe. Join Zoom Meeting https://uniroma1.zoom.us/j/81122901013?pwd=M1hnRHRXZkEyeW1QMFlPQ2FXa0dNZz09 ID riunione: 811 2290 1013 Passcode: 686688
Elena Maria Rossi, Leiden Observatory: A multi-tracer study of the Local Group of galaxies
June 8t, 2022
The Local Group, and the Milky Way in particular is a unique laboratory to study the process of galaxy assembly because of our vantage point. This is especially true in this era of current and up-coming (all sky) surveys like e.g. Gaia, WEAVE, 4MOST, DASI, LSST, and Euclid, that are delivering an unprecedented astrometric, spectroscopic and photometric view of the Galactic stellar population. In this talk, I will review my group's work --both theoretical and observational -- towards the understanding of the mass distribution and other properties of the Milky Way using different dynamical tracers such as stellar streams and hypervelocity stars. Looking at the future, I will also show my vision for Galactic studies in the LISA era, when gravitational waves will deliver complementary information with respect to electromagnetic waves.
Samaya Nissanke, University of Amsterdam: Gravitational waves and multi-messenger astrophysics
May 26th, 2022
Abstract: Since the revolutionary discovery of gravitational wave (GW) emission from a binary black hole merger in 2015, the exquisite GW detectors LIGO, Virgo and KAGRA have detected more than 90 compact object mergers. Most notably, one of these mergers corresponds to the first binary neutron star merger, dubbed GW170817. This event has been transformative because it was observed in both gravitational and electromagnetic radiation, thus opening up a new era in multimessenger astrophysics. The multi-messenger characterisation of such an event has enabled major advances into diverse fields of modern physics from gravity, high-energy and extragalactic astrophysics, nuclear physics, to cosmology. In this talk, I will discuss work in strong-field gravity astrophysics and how combining observations, theory and experiment is key to make progress in this field. I will present the opportunities and challenges that have emerged in multi-messenger astrophysics, and what the future holds in this new era. Join Zoom Meeting https://uniroma1.zoom.us/j/81122901013?pwd=M1hnRHRXZkEyeW1QMFlPQ2FXa0dNZz09 ID riunione: 811 2290 1013 Passcode: 686688
Rachel Somerville, Center for Computational Astrophysics Flatiron Institute: Developing new galaxy formation models that will help us Learn the Universe
May 5th, 2022
Understanding and simulating galaxy formation from first principles is a huge computational challenge because of the vast range of scales and rich array of physics involved. Upcoming experiments will map galaxies and gas across unprecedented volumes and probe further back into cosmic time than ever before. These experiments have the potential to probe fundamental physics questions such as the nature of dark matter and dark energy, and the initial conditions of the Universe. But in order to extract the full scientific potential from these data, we need to understand how luminous tracers (stars and gas) are related to the underlying matter density field, and we must develop techniques that can accurately forward model the galaxy formation process with a computational efficiency that is orders of magnitude higher than standard numerical hydro/N-body techniques. I will describe the philosophy and status of the SMAUG (Simulating Multiscale Astrophysics to Understand Galaxies) project, and how it will form a pillar in the new Simons Collaboration "Learning the Universe", which will combine new galaxy formation models, new machine learning techniques, and simulation based inference to obtain constraints on cosmology and astrophysics.
Georges Meynet, University of Geneva: Stars at the Extreme: First Stars, Spinstars and Supermassive Stars
April 6th, 2022
The presentation will focus on stars at some extreme either from the point of view of their mass (supermassive stars), rotation (spinstars) or initial composition (Pop III stars). The talk will begin by a general overview of the main challenges faced by the modeling of massive stars with a special focus on the transport processes in convective and radiative zones. Then the presentation will continue discussing recent results about the binary statistics of Pop III populations, the chemical and radiative feedback of Pop III stars, the evolution of very massive stars i.e. stars with masses between 150 and 300 solar masses at different metallicities addressing the question of the progenitor of Pair Instability supernovae and the limits of the mass domain for the black hole mass gap. Finally, new models for the formation of supermassive stars that are candidates as seeds for the formation of supermassive black holes at high redshift will be presented
Felix Aharonian, Dublin Institute for Advanced Studies and Max-Planck-Institute for Nuclear Physics (MPIK), Heidelberg, Germany: PeVatrons and the "Century-old-Mistery" of Galactic Cosmic Rays
March 2, 2022
Despite the recent advances in Cosmic Ray studies, the origin of Galactic Cosmic Rays (CRs) is still considered a "century-old mystery" - we do not know yet which sources contribute to CR fluxes measured in the Earth's vicinity. Identifying the major CR contributors with astronomical source populations is one of the highest priorities of the field. The best carriers of information about CR factories are gamma-rays and neutrinos - the only stable and neutral secondary products of CR interactions pointing to the CR production sites. The recent years' outstanding achievement of gamma-ray astronomy was the discovery of TeV gamma-radiation from SNRs generally supporting the SNR paradigm of the origin of Galactic CRs. On the other hand, the lack of the extension of gamma-ray spectra of young SNRs well beyond 10 TeV raises doubts about their ability to contribute to the highest energy galactic CR spectrum in the so-called "knee" region above 1 PeV. Meanwhile, the ultra-high-energy (UHE; E> 100 TeV) gamma-ray observations of the clusters of young massive stars demonstrate mounting evidence of these objects (and related superbubbles) being prime contributors to Galactic CRs at PeV energies. I will discuss these observations in the context of the concept of "Young Stars versus Dead Stars". The hunt for CR PeVatrons cannot be reduced merely to the identification of the sources contributing to the local "CR fog". The term 'cosmic rays' has broader implications; after matter, radiation and magnetic fields, the relativistic nonthermal plasma constitutes the fourth substance of the observable Universe. The localisation and exploration of physical conditions and processes in these extreme CR factories, independent of their relative contributions to the 'CR fog', is a fundamental issue in its own right. I will highlight the recent exciting achievements of UHE gamma-ray astronomy in elucidating the cites of extreme CR accelerators in the Milky Way and discuss the implications of the discovery of a large number of CR PeVatrons by the LHAASO collaboration.
Volker Bromm, University of Texas at Austin: What do we know about the first stars and galaxies?
Feb 8, 2022
I will review the emerging theoretical framework for how stars, galaxies, and black holes transformed the early universe. Predictions for the enrichment of the intergalactic medium with heavy chemical elements, the rate of supernova explosions and gamma-ray bursts, as well as the number density and properties of the first galaxies, sensitively depend on the particle-physics nature of dark matter. To constrain the elusive first generation of stars, we can bring to bear a powerful combination of probes at high redshifts and in our local neighborhood. The latter approach, known as “stellar archaeology” holds particular promise in light of ongoing and planned large surveys of metal-poor stars, both in the Milky Way and its dwarf satellites. It is exciting to contemplate the decade ahead, when the James Webb Space Telescope (JWST) will allow us to confront theory with observations at the edge of time.

2021


Licia Verde, ICREA and Institute of Cosmological Sciences, University of Barcelona: "The future beyond precision cosmology"
14/12/2021
The standard cosmological model (the LCDM model) has been established and its parameters are now measured with unprecedented precision. This model successfully describes observations from widely different epochs of the Universe, from the first few minutes, all the way to the present day. However, there is a big difference between modelling and understanding. The next decade will see the era of large surveys; a large coordinated effort of the scientific community in the field is on-going to map the cosmos producing an exponentially growing amount of data. But precision is not enough: accuracy is also crucial. The "unreasonable effectiveness” of the LCDM model offers challenges and opportunities. I will present some of the lines of enquiry explored by my group in this direction.
Samaya Nissanke, University of Amsterdam: "Gravitational waves and multi-messenger astrophysics"
30/11/2021

Giovanna Tinetti, Department of Physics and Astronomy, University College London: "Decoding the light from other worlds"
09/11/2021
Thousands of planets orbiting stars other than our own are being discovered (extrasolar planets). Since their discovery in the 1990s this field of astronomy and planetary science has exploded, being today one of the most exciting and dynamic. Even within the limits of our current observational capabilities, studies of extrasolar planets have provided a unique contribution to improving our view of the place that the Solar System and the Earth occupy in the galactic context. The arrival of more performing and dedicated facilities from space and the ground in the coming decade, will provide an unprecedented opportunity to study these worlds in great detail. In this talk, I will review highlights and pitfalls of our current knowledge of this topic and discuss the scientific and technical steps to be taken in this fascinating journey of remote exploration of the planets in our Galaxy.
Pavel Kroupa, University of Bonn and Charles University of Prague: How observations of stellar populations constrain cosmological models
19/10/2021
Quasars are found to appear a few hundred Myr after the Big Bang, but pressing matter together into super-massive black holes (SMBHs) so quickly appears to be impossible. At a later stage, the spheroidal component of a galaxy (its bulge if it is not an elliptical galaxy) is observed to show a correlation between its mass and that of the central SMBH it harbours, although spheroids with a mass lower than a few 1E9 Msun appear to only host a nuclear star cluster. I will discuss a theory for the formation of SMBHs which accounts for these observations using standard, non-exotic physics.
Ralf Klessen, Institute for Theoretical Astrophysics, University of Heidelberg: Star formation through space and time
23/09/2021
Stars and star clusters are the fundamental visible building blocks of galaxies at present days as well as in the early universe. They form by gravitational collapse in regions of high density in the complex multi-phase interstellar medium. The process of stellar birth is controlled by the intricate interplay between the self-gravity of the star-forming gas and various opposing agents, such as supersonic turbulence, magnetic fields, radiative feedback, gas pressure, and cosmic rays. Turbulence plays a dual role. On global scales it provides support, while at the same time it can promote local collapse. This process is modified by the thermodynamic response of the gas, which is determined by the balance between various heating and cooling processes, which in turn depend on the chemical composition of the material. In this talk I will try to give an overview of the our understanding of the star-formation process, discuss some examples of the recent progress in the field, and speculate about the implications for stellar birth in the high-redshift universe.
Piero Madau, Department of Astronomy and Astrophysics, University of California Santa Cruz: The dark and luminous side of structure formation
22/06/2021
The beaded filamentary network of intergalactic gas in which galaxies form and evolve, and which gives origin to a “forest” of hydrogen Lyman-alpha absorption lines in the spectra of distant quasars, encodes information on the physics of structure formation, the nature of the dark matter, the temperature and ionization state of baryons in the Universe. The potential of the Lyman-alpha forest for constraining with percent accuracy the matter density distribution on medium to small cosmological scales has motivated the construction of the Dark Energy Spectroscopic Instrument (DESI), which will measure absorption line spectra backlit by nearly a million high-redshift (z >2) quasars. In this talk I will describe the multiple steps needed to connect flux fluctuations in quasar spectra to physical parameters, present an unprecedented suite of hundreds of high-resolution hydrodynamical simulations of structure formation with different thermal histories, and use it to perform a statistical comparison of mock spectra with the observed 1D flux power spectrum and other data. A likelihood analysis shows that, over the last 13 billion years, gas in the cosmic web experienced four main heating and cooling epochs.
Debora Sijacki, Institute of Astronomy, University of Cambridge, UK: The evolution of massive black holes through cosmic times
01/06/2021
In this talk I will review current theoretical efforts in understanding supermassive black hole formation, accretion and feedback throughout cosmic time. Specifically, I will discuss possible links between large scale cosmological environments and supermassive black hole assembly and outline several possible interaction channels between active black holes and their host galaxies. In the second part of the talk I will focus on novel computational methods that allow us to follow black hole physics on much smaller scales in full galaxy formation simulations to unravel how black hole mass and spin evolve during the binary hardening stages or during launching of powerful jets.
Roberto Maiolino, Cavendish Laboratory, University of Cambridge, UK: Quenching star formation in galaxies
18/05/2021
In the local universe stars only make up about 7% of all baryons, indicating that star formation has been extremely inefficient across the cosmic epochs. Within this context, even more impressive is the fact that in a significant fraction of galaxies star formation has been totally “quenched”, resulting into the population of passive and quiescent local galaxies. Understanding what are the mechanisms responsible for suppressing or even quenching star formation in galaxies has been one of the main challenges of astrophysics in recent years and it is one of the research areas in which most of the efforts have been directed, both in terms of cosmological simulations and in terms of observing campaigns. I will give an overview of the potential causes and physical processes that might be responsible for regulating or even leading to the complete suppression of star formation in galaxies. I will illustrate that there are a variety of possible culprits. Among these I will show that supernova explosions can play a role, but the energy injected in the insterstellar and intergalactic medium by accreting supermassive black holes can have a truly dramatic effect on their host galaxies. The environment in which galaxies live (e.g. galaxy groups or clusters) can also play an important role, by suppressing star formation especially in satellite galaxies. I will discuss observational evidence for these various effects by using results from extensive multi-wavelength datasets. I will conclude by emphasizing open, outstanding problems and the possibility of tackling them with the next generation of observing facilities.
Joseph Silk, Institut d’Astrophysique de Paris, The Johns Hopkins University, University of Oxford: The future of cosmology
16/04/2021
One of the greatest challenges in cosmology is understanding the origin of the structure of the universe. The cosmic microwave background and large-scale surveys of galaxies have provided unique windows for probing cosmology and its inflationary origin. But where do we go next? Future experiments are planned with the next generation of observatories that will increase the current precision of cosmological measurements by an order of magnitude. However we need to do far better if there is to be a guaranteed science return that will definitively probe our cosmic origins. I shall argue that the ultimate goal for our future strategy must be astronomy from lunar-based telescopes.
Benedetta Ciardi, Max Planck Institute for Astrophysics: Exploring cosmic reionization with 21cm telescopes
09/03/2021
Cosmic reionization is the last major phase transition undergone by our Universe. Although most studies agree on the general characteristics of H reionization (for example that is driven by stars and it is mostly if not fully complete by z ≈ 6), its details are still largely unknown, among which the contribution from and role played by more energetic sources. In this talk, I will discuss the ingredients needed for a correct modeling of cosmic reionization and present results from recent radiative transfer simulations accounting for a variety of source types (such as stars, quasars, X-ray binaries). I will then discuss the observability of reionization in terms of various diagnostics associated to the 21cm signal from neutral hydrogen and present the latest results from the LOFAR radio telescope. Join Zoom Meeting https://uniroma1.zoom.us/j/89931306878?pwd=WG5RYlYyZzRSMzJsOFpSRHczWEFCZz09
Razmik Mirzoyan, Max Planck Institute for Physics, Munich, Germany: Gamma-Ray Astronomy: The Cross-Road Between Physics and Astrophysics
23/02/2021
hirty-two years ago a report about the measurement of unusual, so-called teraelectronvolt signal from the Crab Nebula captured the attention of the world scientific community. The authors reported a flux of so-called gamma-ray photons, where each carried an incredible amount of energy, exceeding that of the well-known X-rays by billion times. How and in which processes the nature managed to pack such a huge energy content into single photons remained a mystery for the coming years. Researchers used for observations a special technique and instrumentation dubbed as imaging atmospheric Cherenkov telescopes. In the following couple of years not much has happened and the community started speculating about the new science of a single source. More researchers joined that effort and already ten years after the initial discovery ~10 sources of teraelectronvolt gamma-rays were known. Today this discipline boasts to know more than 200 sources of very different origin, from supernova remnants to pulsars, from supermassive active galactic nuclei with black holes in their centre to gamma-ray busts, from binary systems to pulsar wind nebulae. A new discipline, the so-called astro-particle physics with diverse instrumentation appeared in the cross-roads between physics and astrophysics. In this lecture we will have a closer look to the details of this rapidly evolving, fascinating frontier science. Join Zoom Meeting https://uniroma1.zoom.us/j/89931306878?pwd=WG5RYlYyZzRSMzJsOFpSRHczWEFCZz09
Cecilia Ceccarelli, Université Grenoble Alpes, IPAG: The astrochemical trail of our origin
02/02/2021
The Solar System was born 4.5 billions years ago, after a complex process whose details are not fully understood. The large number of detected extrasolar planets tells us that they are a common product of the star formation process, their variety that there are many ways of building them. How can then we recover the path followed by the Solar System? Understanding the Solar-type star formation process currently taking place in the Milky Way is mandatory to answer this question. Astrochemistry, the science of how atoms and molecules combine and evolve in the interstellar medium, is a powerful diagnostics to follow the evolution that turns a molecular cloud dense clump into a planetary system. But it can only be exploited once we know how to interpret the chemistry occurring in the exotic conditions of the interstellar medium, where quantum chemical effects dominate. In this presentation, I will provide an overview of the major progresses of our understanding in astrochemistry and, more specifically, the one involved in the Solar System formation history.

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