Robust constraints on tensor perturbations from cosmological data: A comparative analysis from Bayesian and frequentist perspectives
20/12/2024
One of the central challenges in modern Cosmology is the precise characterization of the primordial tensor power spectrum, a cornerstone prediction of numerous cosmological models, particularly inflationary scenarios. These tensor perturbations carry distinctive imprints that can reveal their physical origins, making the robust reconstruction of their spectrum a pivotal goal for contemporary research. In this talk, I will present methods for constraining key parameters of the tensor power spectrum, such as the tensor-to-scalar ratio and the spectral tilt, with a particular emphasis on the statistical methodologies underpinning these inferences. I will critically examine the strengths and limitations of the standard Bayesian framework commonly employed in this context. Furthermore, I will demonstrate how complementary insights from a frequentist approach can deepen our understanding of the Bayesian results, offering a more nuanced perspective on the interplay between these statistical paradigms.
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Wave dark matter
17/12/2024
We will explore the possibility that dark matter is composed of sufficiently light particles that it effectively behaves as a collection of waves. We will review the particle physics motivations and the rich wave phenomenology, and discuss the implications for astronomical observations and experimental detection.
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Galaxy Clusters from adolescence to maturity: challenges for simulations
12/12/2024
In my talk I will review our understanding, through cosmological simulations, of the evolution of galaxy clusters from redshift z~2-3, to the recent cosmic epoch. Through a comparison with observational data at different wavelengths I will assess the capability of simulations to trace the fast evolution of such cosmic structures from their proto-cluster stage, characterized by a strongly star forming galaxy population embedded in a dynamically disturbed inter-galactic medium, to their relaxed stage at low redshift, characterized by a passive galaxy population immersed in a relatively relaxed intra-cluster medium. In this context, I will highlight successes of simulations, and critically assess their limitations and what we should learn from them.
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Lighting up Blazar Physics at the Spectrum’s Edge: VHE and VLBI Synergies
12/12/2024
Blazars, a class of active galactic nuclei with jets aligned towards Earth, offer a unique opportunity to study extreme astrophysical processes. Their powerful jets emit across the entire electromagnetic spectrum, providing data at all wavelengths for investigation. This presentation focuses on the synergy between Very High Energy (VHE) gamma-ray observatories and VLBI arrays—two distinct facilities operating at opposite ends of the spectrum—used to uncover the mechanisms driving the non-thermal emission of blazars. VHE observations probe the highest energy emissions from these objects, while VLBI provides high-resolution imaging of their jet structures. Together, they enable the study of particle acceleration processes, jet kinematics, and emission variability across multiple scales. I will introduce the basics of VHE observations and the tools employed at the two extremes of the spectrum. Finally, I will present studies showing how this combined approach deepens our understanding of blazar physics, from the origins of high-energy photons to the dynamic behaviour of jets in their most compact regions.
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Breaking the distance-duality relation to address cosmic tensions
11/12/2024
Persistent cosmic tensions arise from discrepancies in the cosmological distance ladder constructed from different distance observables, such as BAO and SnIa, which are calibrated using measurements from either the early or late Universe. These tensions are typically evaluated under the assumption that the distance-duality relation (DDR) holds, allowing for a direct comparison between measurements of the luminosity and angular diameter distances. In this talk, we will examine the implications of relaxing this assumption and considering more general relations. We will discuss how this approach impacts the interpretation of current cosmic tensions and its potential to clarify whether new physics is needed to address these discrepancies.
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Extended AGN jets as a direct test to the ΛCDM model
03/12/2024
Current small-scale cosmological controversies are coming down to the precision level of observations. The key point is whether a better understanding of baryonic physics, dark matter physics, or both is required to address these challenges. In this talk, I will describe how very long baseline interferometric observations of extended AGN jets (sometimes gravitationally lensed) are contributing to understanding some of these small-scale cosmological issues while simultaneously providing insights on the jet physics up to the earliest epochs (z>6).
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The nature and fate of the most obscured high-z massive galaxies
28/11/2024
The early assembly of the most massive galaxies, and their contribution to the SFR density of the universe is currently one of the main challenges for galaxy formation models. Recently, a population of massive red sources already in place at z>2-3 have been discovered, and called HST-dark, because they are missed by optical/UV search but detected at MIR and often in the mm.
Their characterisation remains uncertain, due to limited information available, and to different selection techniques. JWST is now allowing us to investigate the nature of HST-dark galaxies,
and to reveal new populations of early massive galaxies.
I will discuss the main properties of HST-dark galaxies, compared to those of JWST NIR-dark.
For those ALMA detected, the molecular gas mass and depletion times show that they are
likely on the way to quenching their SF. For ALMA HST-dark, there is a consensus on the presence of large amounts of dust, posing the problem of high-z dust production.
To constrain dust properties and obscured SF at high-z we need to observe in the FIR.
I will present the recently selected NASA PRobe far-Infrared Mission for Astrophysics (PRIMA),
a FIR (25-235 μm) observatory operating in the 2030s in spectroscopy and imaging, that will allow us a leap forward in our knowledge of the high-z obscured universe.
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Gamma-Ray Burst Polarimetry: History and Future Prospects
25/11/2024
Gamma-Ray Bursts (GRB) are the brightest electromagnetic events in the Universe since the Big Bang. As such they have intrigued the astrophysical community since their accidental discovery in 1967. Despite almost 60 years of intense research, resulting in over 10000 GRB detections, very little remains known about these violent events. While we know that these events are related to the death of massive stars or the merger of compact objects, we still lack an understanding of how, and where, the gamma-rays which give these events their name, are produced. Attempts to understand this have thus far focussed primarily on measurements of the time of arrival, the direction and energy of the gamma-ray emission. Measurements of the 4th parameter, the polarization, are rare, despite their significant potential to resolve theoretical models. In this talk I will discuss this potential in detail, while in parallel addressing the reasons for the lack of polarization measurements. Finally, I will present an overview of past missions as well as the missions which aim to provide the first detailed measurements in the coming decade.
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Recent observations of the near-Earth radiation environment: a plethora of galactic, solar and magnetospheric particles
22/11/2024
The near-Earth radiation space is a unique environment where particle populations of different origins coexist and evolve dynamically over time and space, spanning a wide energy range. Galactic cosmic rays – entering the heliosphere – are continuously modulated by the change in the solar wind and the associated heliospheric magnetic field. Moreover, changes in galactic particle fluxes show a very clear time-dependence, which is directly related to the periodical activity of the Sun. However, the Sun acts as both a modulator and a source of space radiation – especially during maxima of solar activity – with powerful emissions of the so-called solar energetic particles (SEPs). Despite notable improvements in the latest decades, the complex mechanisms underlying their origin and transport still challenge the development of a comprehensive picture of SEP events. Many efforts have also been directed at modelling the Earth’s trapped charged particle environment, as in the case of the South Atlantic Anomaly (SAA). Observations of the SAA radiation environment are crucial to validate these models (e.g., the NASA AE9/AP9 models), as well as to investigate the temporal evolution of the geomagnetic field, to study perturbations generated by space weather events (such as geomagnetic storms), and, last but not least, to safeguard spacecraft systems and human crew health. After the foundational results of successful past (PAMELA) and present (AMS-02) spaceborne missions, the CSES (China Seismo-Electromagnetic Satellite) mission aims to continue the study of the near-Earth radiation environment, through a constellation of low-Earth orbit satellites. This presentation will review the main results achieved by the High-Energy Particle Detector (HEPD-01) on board the CSES-01 satellite, which will be followed by the launch of the improved HEPD-02 detector on the CSES-02 satellite in December 2024.
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Magnetic field amplification in neutron star mergers and the role of the MRI
21/11/2024
The first detection of a binary neutron star merger has made sharp reality the long-standing paradigm that these cosmic fireworks are exciting laboratories for extreme physics. To get the most out of present and future observations, however, we require accurate models of the merger dynamics, which can only be achieved through numerical relativity simulations. One of the key factors in these simulations is the magnetic field, which plays a crucial role in shaping the dynamics of the system. It is also instrumental in the launching of relativistic jets and the associated gamma-ray bursts. In this seminar I will discuss the main mechanisms responsible for the amplification of the magnetic field, with a particular focus on the magneto-rotational instability and its potential role in binary neutron star mergers."
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La materia oscura illuminata
20/11/2024
La materia oscura è la misteriosa componente che si pensa costituisca la grande maggioranza di tutta la materia dell’universo, e l' INFN le sta dando la caccia. Sotto il nome Dark Matter Day 2024, viene organizzata e presentata una serie di eventi, che in tutto il mondo festeggiano il lavoro di migliaia di scienziati, che cercano di accendere una luce sul lato più misterioso ed oscuro dell’Universo.
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Complex MgII broad line time evolution in a quasar: Clues for a subparsec binary supermassive black hole?
20/11/2024
Supermassive binary black hole (SMBBH) systems are believed to form during the mergers of galaxies. While their existence is strongly predicted, there are still no confirmed cases due to observational challenges, particularly at close separations. However, indirect evidence - such as periodic variability in quasar photometry and complexity in their spectral lines - supports their presence.
A search for long-period variability (100 < P [days] < 600) in the SDSS Stripe 82 region, potentially missed in previous studies, was conducted. We used precisely calibrated (1%-2%) photometry in the SDSS gri bands collected over roughly six years. Lomb-Scargle periodograms identified the most likely candidates for such periodic variability, which were then cross-matched with other surveys across the electromagnetic spectrum (both photometry and spectroscopy) to confirm their variability and classification. Additional time series data from Pan-STARRS and ZTF extended the observational baseline to over 20 years. All identified candidates were quasars, with the top-ranked one (P = 278 days) marked as a variable source in the Chandra X-ray catalog. Possible explanations for the quasars' periodic behavior include radio jet precession, tilted or warped accretion disks, tidal disruption events, and other accretion-related phenomena.
The to-ranked quasar was further analyzed using new MgII line observations and archived SDSS spectra, providing three epochs of MgII data. A key finding was that the MgII line displayed a double-peaked profile that evolved over time. By comparing synthetic magnitudes with photometric data and applying the PoSKI model, which examines emission lines and light curves of SMBBH candidates, a correlation was found that suggests the presence of a closely orbiting SMBBH. These sources are of significant scientific value, as their eventual merger would release a tremendous amount of energy as gravitational waves.
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The European Solar Telescope. Europe's bid for leadership in solar science
18/11/2024
This talk will introduce the project of the European Solar Telescope (EST),
considered a key European research infrastructure, and its role in advancing solar physics.
We'll discuss the relevant solar phenomena — like magnetic field interactions and solar
eruptions — that create space weather and solar storms on Earth. Their study requires
high-resolution, multi-layer observation. The EST, with its 4.2-meter Gregorian design and
adaptive optics system will provide unprecedented data in magnetic field measurements
and observations across a broad spectral range. These capabilities are set to transform our
understanding of solar activity by enabling detailed studies of solar magnetic fields and
plasma dynamics.
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Fiber networks in Orion: star formation and width variations
13/11/2024
The Herschel observations unveiled the complex organisation of the interstellar medium in networks of parsec-scale filaments over the past decade. Despite their variety of scales throughout the interstellar medium, the analysis of these same observations revealed filaments in nearby low-mass clouds to have a characteristic width of ~0.1 pc. The origin of this characteristic width and its impact on star formation, however, has been a matter of intense discussions in the past years. Even more with the identification of small-scale filamentary structures harboured inside the Herschel filaments. These networks of fibers have been recognised describing the gas structures in star-forming regions at sub-parsec scales, thus critically challenging the existence of a typical width for filaments. I am going to present our study of the dense gas organisation prior to the formation of stars in a sample of 7 star-forming regions within Orion. This EMERGE Early ALMA Survey includes OMC-1/-2/-3/-4 South, LDN 1641N, NGC 2023, and the Flame Nebula, all surveyed at high spatial resolution (4.5'' or ~2000 au) in N2H+ (1−0) using ALMA+IRAM-30m observations. I will present the star-forming gas spatial distribution, its column density variations, its thermal structure, and its internal motions across the152 fibers identified in our survey.
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From clouds to fragments: on the multi-scale interplay between gravity and turbulence
08/11/2024
The star formation mechanism occurs in well defined structures that can be identified and studied in great details in our own Galaxy: the process starts in giant molecular clouds, objects extended up to several tens of parsecs, within which elongated sub-structures, called filaments, may form. Inside filaments, round-like condensations extended up to ~1pc in radius, the so-called clumps, are the natural birth site of the pre- and proto- stellar fragments, inside which will origin the future stars.
There are still many open questions in this hierarchical view of the star formation process: are these structures relatively confined from each other, or is the large-scale environment affecting the dynamics of the formation down to clumps and fragments? Is there a continuous interplay of the various forces involved in the process, namely turbulence, gravity (and magnetic fields), at all scales? Or is there a relevant scale at which gravity will start to dominate the collapse, with critical implications on the star-formation mechanism?
After a general overview of the problem, I will present in details some recent results focused on the interplay between gravity and turbulence at the filament, clump and fragment scales. To investigate this interplay at the larger scales, we have combined the dynamics of so-called 70 micron quiet clumps, i.e. very pristine regions not yet strongly affected by feedbacks, with the dynamics of the parent filaments in which they are embedded. At smaller scales, I will discuss the different scenarios of fragments formation in light of the most recent results from the SQUALO (Star formation in QUiescent And Luminous Objects) project. This ALMA survey has been designed to investigate the formation properties in a sample of massive clumps selected to be at various evolutionary stages and with the common feature that they are all accreting at the clump scales.
Our results show that a large scales we observe a continuous interplay between turbulence and gravity, where the former creates structures at all scales and the latter takes the lead above a critical value of the surface density is reached, ~ 0.1 g cm^-2. At the same time, the fragmentation properties show several indications that the fragment are "clump-fed", i.e. the process is dynamical and the gravity dominates the collapse inside our massive clumps.
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The EVN, JIVE and SKA through the decades – history, people and politics
24.10.2024
I will give an overview of the historical development of these three pillars of global radio astronomy from their origins in the 1970s, 1980s and 1990s respectively to the current day. All three have travelled along different routes to maturity, the EVN as a global “grass roots” collaboration, JIVE as a European Research Infrastructure Consortium (ERIC), and SKA as an Inter-Governmental (Treaty) Organisation. I will also touch on key issues in these collaborations including the interactions between the radio astronomy community and their funding agency and government counterparts as well as the political environments at national, regional and global level that created the opportunities for new infrastructures.
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Unleashing the Fury: The Power and Impact of Supermassive Black Hole Winds
23/10/2024
Supermassive black hole (SMBH) winds are powerful outflows, capable of reaching velocities up to half the speed of light, driven by the immense energy near these massive objects. These ultra-fast outflows (UFOs) carry significant mass and energy, playing a potential role in shaping galaxy evolution over cosmic time. In this talk, we will present the latest insights into SMBH winds, leveraging X-ray and multi-wavelength observations along with advanced modeling techniques. We’ll also explore their connection to other high-energy phenomena such as variable AGN, SMBH binaries, and tidal disruption events. In particular, we'll highlight new findings on quasi-periodic outflows (QPOuts) in close binary black hole systems, which may serve as electromagnetic precursors to LISA gravitational wave sources. Finally, we’ll offer a sneak peek at groundbreaking results from XRISM/Resolve’s spectroscopic observations of the powerful UFO in quasar PDS 456.
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The atmospheric remote-sensing infrared exoplanet large-survey (Ariel) sensitivity, performance, and detrending techniques
17/10/2024
ESA's M4 Ariel mission, scheduled for launch in 2029, will spectroscopically characterize the atmospheres of a large and diverse sample of hundreds of exoplanets. Using a 1-m class all-aluminum Cassegrain telescope, Ariel will detect the atmospheric signatures of the small, < 100 ppm, modulation induced by exoplanets on the bright host star signals using transit, eclipse, and phase curve spectroscopy. Three photometric and three spectroscopic channels with Nyquist sampled focal planes simultaneously cover the 0.5-7.8 micron region of the electromagnetic spectrum to maximize observing efficiency and reduce systematics of astrophysical and instrumental origin. The jitter in the spacecraft’s line of sight is an especially significant source of disturbance when measuring the spectra of exoplanet atmospheres, if left uncorrected. This contribution reviews the predicted performance of Ariel, the design solutions implemented, and an improved detrending technique to correct for the jitter disturbance post-processing that will allow Ariel to achieve the required sensitivity and control of systematics.
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Stellar obliquity of gas giant planets
16/10/2024
The Rossiter-McLaughlin effect allows us to determine the stellar obliquity. This parameter is indicative of formation and evolutionary pathways of exoplanetary systems. In this talk, I will present stellar obliquity measurements of six gas giant planets obtained with HARPS and discuss their potential histories. Additionally, I will outline plans for upcoming atmospheric characterization using JWST and Ariel, highlighting how these observations will complement the obliquity findings. Furthermore, I will show ESPRESSO time series of HD 110067c, resonant chain similar to TRAPPIST-1. The orbit of HD 110067c is well aligned. This result is indicative that the current architecture of the system has been reached through convergent migration without any major disruptive events. Finally, I detect rather small transit-timing variation in this system for the first time from a significant offset of 19 minutes.
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Nucleosynthesis of the first stellar generations
15/10/2024
The first stellar generations in the Universe were sources of ionizing radiation and
of newly synthesized elements. They played a key role in the reionization process
as well as initiating the chemical evolution of the Universe. The talk will begin by
recalling the expected main physical properties of the first stellar generations
that likely make them evolve significantly differently from stars in the present-day
Universe. We will then focus on aspects dealing with the chemical enrichments
by the first stellar generations. Comparisons between predictions of models with
the observed surface composition of halo stars will be presented.
The special case of the Carbon-Enhanced Metal- Poor Stars (CEMP), especially
the most iron-poor ones, provides precious and interesting clues about the early
chemical enrichment processes. The talk will end by discussing the exciting
cases of nitrogen-rich regions in high redshift galaxies observed by the James
Webb Space Telescope.
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A sharper view: observations of planet-forming disks with JWST
09.10.2024
Low-mass X-ray binary (LMXB) outbursts are often first detected by X-ray all-sky monitors like MAXI or Swift/BAT. Only after the detection of new outbursts by these instruments can observations with more sensitive multi-wavelength telescopes be triggered. This causes a gap in the coverage of the rising parts of the outbursts, limiting our knowledge of their early stages. Here we introduce the "X-ray Binary New Early Warning System (XB-NEWS)", which aims to detect and announce new LMXB outbursts within days of their first optical rise. This results in triggering multi-wavelength campaigns during the very early stages of outbursts and understanding their origin. As a demonstration of the project, we further present the results of a comprehensive multi-wavelength campaign of the neutron star LMXB MAXI J1807+132 during its 2023 outburst which was triggered by XB-NEWS. Observations were made with several ground and space-based observatories spanning radio to X-ray wavebands. We are able to characterize the broadband (optical and X-ray) spectral and timing properties during different stages of the outburst and uncover a few peculiar features in the phenomenology. We detect a delay of nearly 5 days in the rise of X-rays compared to the optical rise suggesting involvement of viscous timescales from a truncated accretion disk. As the source transitions to different canonical states, we trace the evolution of the accretion disk and corona. A large radius of the last stable orbit, suggests the possibility of the source harboring a stronger-than-usual magnetic field, albeit without any pulsations. In the intermediate and hard state during the outburst we detect signatures of synchrotron emission from a jet that extends well into the optical wavelengths. The end of the main outburst marks the beginning of several re-flares which display a complex behavior, of unknown origin, with high variability but low hardness.
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UNRAVELING SPACE WEATHEIRNG ON PLANETARY AND ASTROPHYSICAL SURFACES
04/10/2024
It is well known that the interaction of energetic ions, electrons and
photons with surfaces and interfaces leads to non-thermal desorption via
a process typically referred to as desorption induced by electronic
transitions (DIET). When DIET involves either electrons or photons,
these processes are generally referred to as electron-stimulated
desorption and photon-stimulated desorption (PSD), respectively. Recent
attention has focused on understanding the role of non-thermal “space
weathering” in the processing of interstellar grains and ices.
Specifically, there is deep interest in understanding the radiation
processing of carbon grains in the solar nebula and unraveling the H2O
formation mechanisms in solar nebula and planetary systems, including
the Moon. Using graphite grains, the VUV photon-simulated oxidation of
carbon grains via reactive scattering of water fragments produced by
dissociative electron attachment at the buried interface was examined.
The results suggested that VUV PSD at the buried water:carbon grain
interface may help control the carbon inventory during planet formation.
The inverse process, (i.e, the formation of water) may happen on
metal-oxide samples such as mineral grains and lunar regolith samples,
that contain or are terminated by hydroxyl groups. Solar wind space
weathering experiments of several Apollo lunar samples demonstrated that
thermally activated recombinative desorption (RD) can be H2O sources
[2,3] and that electron-stimulated reactive scattering to produce water
may also be occurring, especially when the Moon is in the magnetopause
[4]. RD can occur on a diurnal basis on the Moon and is prevalent
during meteoroid impacts. The latter is simulated by laser irradiation
studies followed by state and velocity resolved detection of the
produced water. Finally, evidence of space weathering and surface
alteration has also been revealed using spatially resolved,
high-resolution nanoscale Fourier transform infrared
imaging/spectroscopy correlated with photoluminescence (PL) on Apollo
samples with different origins and history.
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Beyond the standard quantum limit: applications of single photon counting detectors for axion detection, intensity interferometry and interstellar communications
03/10/2024
The standard quantum limit for sensing is related to the quantum noise from coherent detection of two conjugate quantities such as amplitude and phase. One way to beat this limit is with a technique called squeezing which increases the uncertainty along one axis in exchange for reducing it along the complementary axis. Another way to beat the limit is to use incoherent detection which is essentially phase insensitive. In the limit of low photon occupation number, single photon detection can achieve much better sensitivity than the standard quantum limit. I will describe several applications of single photon detection and the associated technology development including: i) microwave single photon counting detectors for axion searches, ii) single photon counting intensity interferometry with small telescopes and iii) deep space and interstellar optical communication.
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Cosmology in the era of Cosmic Microwave Background Polarization
06/09/2024
We discuss the opportunities for cosmology in light of the start of the Stage III+ CMB observations, targeting primordial gravitational waves and lensing. We highlight the near and far future objectives, describing the opportunities for combining CMB probes, in this and the next decade, with Large Scale Structure surveys.
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The spiral structure of the Milky Way using Cepheids with new mid-IR distances
11/07/2024
Classical Cepheids (DCEPs) are potentially excellent tracers of the young stellar population that is responsible for shaping the visible aspect of our Galaxy, the Milky Way. We estimate new distances for 3427 Cepheids based on mid-IR photometry from WISE, which suffers minimally from extinction, and by adopting a 3D extinction map to calculate the necessary (albeit small) extinction corrections.
We show that our distances are consistent with Gaia’s parallaxes for the subset with relative parallax errors smaller than 10%, verifying that our mean distance errors are less than 15% and that the mean parallax zeropoint for this sample is about 7 microarcseconds in magnitude.
We use the new distances for a subset of dynamically young DCEPs to trace the spiral arms of the Milky Way, deriving pitch angles for four spiral arms: the Perseus, Local (Orion), Sagittarius-Carina and Scutum arms.
These arms are traced by the DCEPS well into the third and fourth galactic quadrants where there is currently a lack of masers with astrometric parallaxes, thus significantly extending our picture of the spiral structure of our Milky Way on large-scales.
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A quantitative search for life in the Solar System beyond Mars
27/06/2024
Several bodies in the outer Solar System are likely to have water oceans beneath their surface, and in two cases (Europa and Enceladus), the evidence is very strong. Indeed, the plume of gas and solids coming from Enceladus has been analyzed and indicates a subsurface ocean that could sustain life. Europa’s ocean is less well known but that will hopefully change with the Europa Clipper and JUICE missions to the Galilean moons at the end of the decade. In this talk I will explain how and when one would obtain quantitative information on the biological potential and existence of life within these and other oceans of the outer solar system.
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The multifaceted connection between the atmospheric composition of giant planets and their native disc
19/06/2024
Planet formation shapes the composition of giant planets and is expected to leave chemical fingerprints in their atmospheres. We have traced these fingerprints in the atmospheric abundances of carbon, oxygen, nitrogen, and sulphur. I will discuss how the abundance ratios of these elements in planetary atmospheres are influenced by the physical and chemical evolution of the natal protoplanetary disc and the process of planet formation and migration. Disc evolution strongly influences the distribution of carbon and oxygen between gas and solids in the disc, challenging the interpretation of the planetary C/O ratio. The joint comparison of multiple elemental ratios, including the refractory-to-volatile ratio, with the host star's composition constraints various aspects of planet formation, including the accretion of planetesimals, gas, and/or volatile-enriched gas due to the sublimation of drifting icy grains. I will also present the first applications of our interpretative framework to spectroscopic observations of hot and warm Jupiters.
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Near-Field Cosmology with a New Photometric System
12/06/2024
The discovery of the ubiquitous nature of the multiple populations (MPs) in globular clusters (GCs) in our Galaxy and nearby galaxies is a great achievement in the fields of stellar and galactic astrophysics. One of the remarkable aspects of the GC MPs is that the second generation (SG) of stars, showing the chemical compositions that experienced proton capture processes at high temperature and being the major component of the most of normal GCs with MPs, formed in more spatially concentrated inner regions of GCs out of interstellar media polluted by the first generation (FG) of stars, with the chemical compositions similar to abundance patterns observed in Galactic field stars with the similar metallicity. Over the past decades, we developed a new photometric system to study such lighter elemental abundance anomalies in GC MPs. With our system, we will be able to simultaneously measure accurate [Fe/H], [C/Fe] and [N/Fe] (hopefully [O/Fe] in near future), which are the barometers of GC MPs, for the complete sample in crowded regions. In our talk, we will discuss the current status and the future perspective of our long-term survey program.
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Emergence of low- and high-mass stars in complex fiber networks
05/06/2024
The filamentary nature of the Interstellar Medium plays a fundamental role on the star formation process. Filaments dominate the gas structure inside molecular clouds and promote the formation of stars in them, from low-mass stars formed in isolated filaments to high-mass objects found in hub-filament associations. Still, the origin and evolution of these different gas structures are matter of strong debates. Recent high resolution studies highlighted the complex gas kinematics inside filamentary regions, typically exhibiting a rich hierarchical structure of sub-filaments (or fibers) forming densely populated networks. During my talk I will discuss how both low- and high-mass star formation regimes can naturally emerge in fiber networks of different complexity paving the way for a unified scenario of star formation.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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