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.
|
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.
|