Osservatorio Astronomico di Roma

Star formation in the Local Group
2019-02-19 11:45 - 12:45 (Europe/Rome) | Aula Gratton
Using Hubble Space Telescope (HST) observations, we have identified and
characterised almost 50,000 pre-main sequence (PMS) stars in several
star-forming regions in the Milky Way and Magellanic Clouds. These objects
are still undergoing active mass accretion, as revealed by excess emission
in the Halpha band. Detailed knowledge of the extinction law in these
fields, which we derive directly from the observations, allows us to
accurately obtain stellar physical parameters (temperature, luminosity,
age, mass, and mass accretion rate). This is presently the largest and
most homogeneous sample of PMS objects, on which we are conducting the
first comprehensive and systematic study of the PMS phase, spanning a wide
range of masses (0.5-4 Msun), metallicities (0.1-1 Zsun) and ages (0.5-30
Myr).
I will discuss how star formation has proceeded in these regions over
multiple recent bursts and how the accretion process depends on the
physical properties of the individual stars and of the environment. We
have discovered an important dependence of the mass accretion rate on
metallicity: mass accretion rates for stars of the same mass and age are
systematically higher in the Magellanic Clouds than in the Milky Way and
are expected to have been equally high at redshift z~2, when star
formation was at its peak in the Universe. I will also show a surprising
anti-correlation between the variability and intensity of the Halpha
excess: this suggests a discrete and clumpy nature for the accretion
process and reveals that the characteristic mass of the infalling parcels
of gas is comparable to that of the moons of giant planets in the solar
system.
To close, I will illustrate how we plan to thoroughly verify these results
spectroscopically and to extend them to lower mass objects and to more
extinguished environments through already planned guaranteed-time
observations with the James Webb Space Telescope. Our measurements will
provide, for the first time, quantitative information on the nature,
excitation, and kinematics of the infalling gas in these dense environments.

When the going get tough... or: observation and laboratory work for life searching in other worlds
2019-02-26 11:45 - 12:45 | Aula Gratton
“…if we never search, the chance of success is zero”. This was the conclusion in the seminal paper of G. Cocconi and P. Morrison in 1959 about the search for life. Since then, a lot of progress in technology and a lot of exciting results in astrophysics have been reached. Today, we know that, out of there, there are more than 4000 new worlds showing a large diversity in their size and orbital characteristics. In the midst of all these strange new worlds, a very promising type of them, the super Earths, seems to be ubiquitous in the Galaxy. Moreover, in fashion there are super Earths orbiting M stars. But, such an odd couple could host life? And if it can, how to find it?

colloquium - Francesco Massaro
2019-03-05 11:45 - 12:45 | Aula Gratton

Flipping a fair coin to decipher the large-scale environment of radio galaxies
2019-03-05 11:45 - 12:45 | Aula Gratton
The role played by the large-scale environment in the nuclear activity of radio galaxies is still not completely understood. Accretion mode, jet power, and galaxy evolution are connected with their large-scale environment on scales from tens to hundreds of kiloparsecs. I am presenting a detailed statistical analysis of the large-scale environment for two samples of radio galaxies in the local Universe (i.e., up to redshift 0.15).
I will discuss on a direct search of galaxy-rich environments around radio galaxies by using them as beacons. To carry out this study a new method, that does not appear to suffer cosmological biases and artifacts, as other algorithms, was developed. I conclude that, despite their radio morphological classification (FRI versus FRII) and/or their optical classification (high- or low-excitation radio galaxy, i.e., HERG or LERG), radio galaxies in the local universe tend to live in galaxy-rich large-scale environments that have similar characteristics and richness. I will then show that properties of large-scale environments of both FRIs and FRIIs do not depend by the property of central radio galaxy. Finally, I will provide an estimate of the X-ray parameters that can be derived from optical observations to plan future follow up campaigns.

colloquium - Roberto Speziali
2019-03-12 11:45 - 12:45 | Aula Gratton

LBT - Italia
2019-03-12 11:45 - 12:45 | Aula Gratton
LBT – ITALIA è un’organizzazione formata da un team di ricercatori dell’INAF che ha come obiettivo la gestione delle osservazioni al LARGE BINOCULAR TELESCOPE. A distanza di sette anni dall’inizio delle operazioni, si fornirà una panoramica della strumentazione e si descriverà l’attività del gruppo illustrando i risultati ottenuti.
Al termine del seminario, ampio spazio verrà dato alla discussione al fine di ricevere feddback da parte degli utenti
che hanno già usufruito dei servizi di LBT-ITALIA e rispondere alle domande in vista della imminente apertura della call 2019-2020.

Neutrinos from a blazar jet and the birth of non-stellar neutrino astronomy
2019-03-14 11:45 - 12:45 | OAR Monte Porzio Catone – aula Gratton, Via Frascati 33, Roma, RM, 00136, Italia
IceCube has recently reported the discovery of high-energy neutrinos of astrophysical origin,
opening up the PeV (10^15 eV) sky. These observations are challenging to interpret on the
astronomical side and have triggered a fruitful collaboration across particle and astro-physics.
I will discuss the very recent association between high-energy IceCube neutrinos and the
blazar TXS 0506+056, reporting on how this result fits with the work done by our group over
the past five years. I will then present the “big picture”, explain why this this association is
very important for astronomy, and discuss some very recent results on the nature of TXS 0506+056.
The talk is self-contained, requires no previous knowledge of neutrinos or blazars, and has been
prepared for a very broad audience.

How quasars affect the formation of the bright cluster galaxy and the circum-galactic medium
2019-03-19 11:45 - 12:45 | Aula Gratton
AGN activity is considered a fundamental phase of the evolution of the massive galaxies. The accretion onto a SMBH generates a great amount of energy in the form of radiation, outflows and radio jets that affects both the ISM and CGM. In this talk, I present the results of two multi-wavelength studies aimed at exploring how nuclear activity affect the formation of the bright cluster galaxy and the circum-galactic medium at high redshift. Firstly, I will report on the multi-band analysis of the galaxy population in the very dense core (~70 x 70 kpc^2) of one of the most massive galaxy clusters at z ~ 1.6. We are able to shed light on the early, poorly-explored phase of the assembly of the Brightness Cluster Galaxy (BCG) in a region with high AGN and merger activity.
I will also report on the properties of both an extended (150 kpc) and luminous (10^44 erg/s) Lya nebula and the associated CIV extended (70 kpc) emission around a hyper-luminous quasar at z~3.6. Our analysis of kinematics of the Lya nebula suggests the presence of a spatially coherent blueshifted (~1000 km/s) component on several tens of kpc scales which we interpret as one of the first indications of an AGN-driven outflow propagating on circum-galactic scales.

colloquium - Elena Valenti
2019-03-26 11:45 - 12:45 | Aula Gratton

A MUSE view of the multiple populations' chemistry in Galactic Globular Clusters
2019-04-09 11:45 - 12:45 | OAR Monte Porzio Catone – aula Gratton, Via Frascati 33, Roma, RM, 00136, Italia
Stars in Galactic globular clusters are known to exhibit abundance variations in specific elements such as He, C, N, O, Na, and Al. These variations can be observed via spectroscopy but also photometrically by using CMD constructed with various filter combinations. Although these multiple populations have been, and still are, the subject of many investigations, the origin of their elemental abundance variations remain rather mysterious.
I will present some of our recent results on that topic based on the spectroscopic survey of 26 globular clusters that is currently carried out as part of the MUSE GTO time. With the MUSE survey covering the central regions of the clusters for which HST photometry is available, we can use these photometric catalogs to separate the RGB stars into two or more populations based on their position in the pseudo-two-color diagrams. Although the MUSE spectra are of relatively low-resolution (R ~ 2500), by combining the spectra of the stars within a distinct populations, we are able to study their abundance variations and relate them directly with the populations distinguished on the pseudo-two-color diagrams.

Lithium Web in astrophysics: insights and problems
2019-04-16 11:45 - 12:45 | OAR Monte Porzio Catone – aula Gratton, Via Frascati 33, Roma, RM, 00136, Italia
Lithium (Li) is widely used as a test of the cosmological model, a probe of stellar structure, and an age indicator of young stellar clusters. It is the very element that presents deep insights, yet many problems to astrophysics.
I will discuss problems and puzzles that Li introduces in astrophysics, including cosmological Li problem (and a stellar solution to it), Li-rich giants problem (Galactic and extraGalactic), Li problem in the Sun, the Galactic Li evolution (in the thin and thick discs), and the interstellar Li content.

colloquium - Mauro Centrone
2019-05-07 11:45 - 12:45

colloquium - Francoise Combes
2019-05-14 11:45 - 12:45 | Aula Gratton

Molecular tori, black hole fueling and feedback in nearby AGN
2019-05-14 11:45 - 12:45 | Aula Gratton
Recent molecular line observations with ALMA in several nearby Seyferts have revealed the existence of molecular tori, and the nature of gas flows at 10-20pc scale. At 100pc scale, or kpc-scale, previous work on gravitational torques had shown that only about one third of Seyfert galaxies experienced molecular inflow and central fueling, while in most cases the gas was stalled in rings. At higher resolution, i.e. 10-20pc scale, it is possible now to see in some cases AGN fueling due to nuclear trailing spirals, influenced by the black hole potential. This brings smoking gun evidence for nuclear fueling. In our sample galaxies, the angular resolution of up to 80mas allows us to reach the BH-zone of influence and the BH mass can be derived more directly than with the M-sigma relation.

The first image of a black hole
2019-05-21 11:45 - 12:45 | Aula Gratton
I will briefly discuss how the first image of a black hole was obtained
by the EHT collaboration. In particular, I will describe the theoretical
aspects that have allowed us to model the dynamics of the plasma
accreting onto the black hole and how such dynamics was used to generate
synthetic black-hole images. I will also illustrate how the comparison
between the theoretical images and the observations has allowed us to
deduce the presence of a black hole in M87 and to extract information
about its properties. Finally, I will describe the lessons we have
learned about strong-field gravity and alternatives to black holes.

Protoclusters of galaxies: from Planck to the Euclid and JWST era
2019-05-28 11:45 - 12:45 | Aula Gratton
Clusters of galaxies are key structures for our understanding of galaxy
evolution physics in denser environments, for constraining the structure
formation scenario and some cosmological parameters independantly of
other techniques like CMB. Despite the difficulties to observe, detect
and model them, there are successes in studying and using galaxy
clusters. In the recent years, many hight-redshift galaxy clusters (z>1)
were detected as well as many high-redshift protoclusters (z>1.5),
progenitors of todays’s clusters. These objects help answering crucial
questions like how and when the clusters formed stars ? In a
synchroneous way ? What is the fate of the gas in clusters ?
After a review of the current status of protoclusters search and
properties and the latest results, I will focus on the original program
we are performing with Planck, Herschel, Spitzer, IRAM, ALMA and other
facilities.
We selected an original sample of about 2000 highly star-forming
structures candidates in Planck, deep in the Cosmic Infrared Background.
Selection was not done in SZ, but by colors of the redshifted peak of
thermal far-infrared emission of galaxies. We observed about 200 of them
with Herschel/SPIRE, about 80 of them with Spitzer/IRAC, and about a
dozen in the near-infrared and millimeter ranges. We have a few redshift
confirmations, and I will highlight our main findings, work in progress,
and perspectives of the SPHerIC subsample (Spitzer, Planck, Herschel
infrared clusters).
A colleague said wisely about high-redshift clusters and protoclusters
in a review talk, « we need more than one object at a time. » Euclid and
JWST will make evolve this field (and other) after 2021 with increasing
statistics and a sharp, detailed view of these structures at the
« cosmic noon » epoch and earlier.

Orlando Luongo - colloquium
2019-06-11 11:45 - 12:45 | Aula Gratton

Probing Dark Matter and Dark Energy with strong gravitational lensing
2019-06-13 11:45 - 12:45 | Aula Gratton
Evidence from different cosmological probes have lead to the establishment of the dark matter and dark energy paradigm. Dark matter dominates the matter budget at cosmological scales and drives the formation of structure and dark energy is responsible for the late time acceleration of the universe. To date, these phenomenas have purely been described as gravitational effects and no other evidence have provided convincing evidence for their underlying physical nature – remaining one of the most striking mysteries the universe has not yet revealed.
In my talk, I will describe the phenomena of strong gravitational lensing and how we can use this unique probe to constrain the physical nature of dark matter and dark energy. I am going to highlight recent results in both domains. I will then look in the near future and highlight the prospects of this technique with increasing sample size, analysis techniques and instrumentation.

The eye of Gaia on globular clusters dynamics
2019-06-18 11:45 - 12:45 | Aula Gratton
I present the results of a survey of the kinematics of a large sample of Galactic globular clusters performed thanks to the synergy between the 2nd Gaia data release and the most extensive collection of radial velocities. This unprecedented dataset of 3D velocities of thousand of stars in more than 100 globular clusters has been used to investigate both the internal (masses, anisotropy and rotation patterns) and the systemic dynamics (orbits, tides) of these stellar systems providing also insight into the overall structure of the Galactic globular cluster system.

Unravelling the Andromeda Galaxy's most important merger
2019-06-25 11:45 - 12:45
The Andromeda Galaxy (M31), our nearest large galactic neighbour, offers a unique opportunity to test how mergers affect galaxy properties. M31’s stellar halo caused by the tidal disruption of satellite galaxies is the best tracer of the galaxy’s accretion history. Despite a decade of effort in mapping out M31’s large stellar halo, we are unable to convert M31’s stellar halo into a merger history. Here we use cosmological models of galaxy formation to show that M31’s massive and metal-rich stellar halo containing intermediate age stars implies that it merged with a large (M* ~ 2.5 x 10^10 M_sun) galaxy ~2 Gyr ago. The simulated properties of the merger debris help to interpret a broader set of observations of M31’s stellar halo and satellites than previously considered: its compact and metal-rich satellite M32 is the tidally-stripped core of the disrupted galaxy, M31’s rotating and flattened inner stellar halo contains most of the merger
debris, and the giant stellar stream is likely to have been thrown out during the merger. This accreted galaxy was the third largest member of the Local Group. This merger may explain the global burst of star formation ~2 Gyr ago in the disk of M31 in which ~1/5 of its stars were formed. Moreover, M31’s disk and bulge were already in place before its most important merger, suggesting that mergers of this magnitude do not dramatically affect galaxy structure.

Absorption and accretion properties of local Active Galactic Nuclei
2019-09-16 11:45 - 12:45 | Aula Gratton
Active Galactic Nuclei (AGN) are powered by accretion onto supermassive black holes and, besides being among the most luminous sources of radiation in the Universe, are also widely believed to play an important role in the evolution of their host galaxies.
X-ray emission is an ubiquitous property of AGN and, being produced within a few gravitational radii from the supermassive black hole, can provide fundamental information about the structure and geometry of the circumnuclear material, as well as on the characteristics of the accretion flow. In my talk I will present recent studies of the obscuration and accretion properties of local AGN in the X-ray band, focussing on the results obtained from the Swift/BAT AGN Spectroscopic Survey.

Lars Mattsson - colloquium
2019-09-24 14:30 - 15:30 | Aula Gratton

Modeling stellar winds on the asymptotic giant branch accurately
2019-09-26 11:45 - 12:45 | Aula Gratton
I present the latest progress on our ongoing work with our state-of-the-art
models of stellar winds of asymptotic giant branch stars. I will both depict
features and assumptions of our model code T-800 and show some of the results
that set our work apart; because, results are in several a case drastically
different from earlier results. In particular, I focus on effects of
gas-to-dust drift and higher-than-before spatial resolution.

colloquium - Chris Sneden
2019-10-01 11:45 - 12:45 | Aula Gratton

Early galaxy formation and its large-scale effects
2019-10-03 11:45 - 12:45 | Aula Gratton
Galaxy formation in the first billion years mark a time of great upheaval in the history of the Universe: as the first sources of light, these galaxies ended the ‘cosmic dark ages’ and produced the first photons that could break apart the hydrogen atoms suffusing all of space starting the process of cosmic reionization. As the earliest building blocks, the galaxies that formed in the first billion years also determine the physical properties of all subsequent galaxy populations. I will start by introducing the reionization process and detail the reasons foe which the history and topology of reionization remain debated. I will then show how cross-correlations of 21cm data with the underlying galaxy population, in the forthcoming era of 21cm cosmology, will yield tantalising constraints on the average intergalactic medium ionization state as well as the reionization toplogy (outside-in versus inside-out). Time permitting, I will try to give a flavour of how the assembly of early galaxies, accessible with the forthcoming James Webb Space Telescope, can provide a powerful testbed for Dark Matter models beyond “Cold Dark Matter”.

Dynamic relations in sampled processes
2019-10-10 11:45 - 12:45 | Aula Gratton
I will start my talk by a short description of a historical connection between my university, Shanghai Jiao Tong University (SJTU), and Collegio Romano. There is an interesting chain from Clavius, who led the Gregorian calendar reform, via Matteo Ricci and Xu Guangqi, the first modern scientist of China, to the founding of the two elite universities on Shanghai, Fudan and SJTU. The technical part of my talk is based on joint work with Tryphon Georgiou. Linear dynamical relations that may exist in continuous-time, or at some natural sampling rate, are not directly discernable at reduced observational sampling rates. Indeed, at reduced rates, matrix-valued spectral densities of vector-valued time series have maximal rank and thereby cannot be used to ascertain potential dynamic relations between their entries. This hitherto undeclared source of inaccuracies appears to plague off-the-shelf identification techniques seeking remedy in hypothetical observational noise. In this paper we explain the exact relation between stochastic models at different sampling rates and show how to construct stochastic models at the finest time scale that data allows. We then point out that the correct number of dynamical dependences can only be ascertained by considering stochastic models at this finest time scale, which in general is faster than the observational sampling rate.

Horizontal Branch morphologies in the age of multi-band photometry
2019-10-15 11:45 - 13:45
The Horizontal Branch (HB) stars have always played a crucial role in the study of the galactic globular clusters (GC). They are the direct offspring of the low mass, Red Giant Branch (RGB) stars and the final product of the helium flash taking place at the Tip of the RGB. The colour and the luminosity of a HB star are tied to its mass which, in turn, is tied to the mass of the star undergoing the flash. The sensitivity of this value to the chemistry of the cluster allows for a large variety of HB morphologies which is one of the culprits that led to the discovery of the multiple populations phenomenon. A leap forward in our understanding of GCs has been made when recent works, based on a large collection of HST data, measured, albeit indirectly, the helium abundance in a large collection of GCs, allowing the characterization of these old stellar populations in unprecedented ways. In spite of this richness of information, however, we still lack the key to fully understand the populations hosted along the HB, especially due to the complex interplay between the parameters regulating their evolution. In this talk, I will provide a review of the current state of the HB study and discuss how the synergy with the recent advancements in the field of multi-band photometry can provide solutions to some new and decades-old problems.

Linear spectropolarimetry in stars different than the Sun: what can we learn?
2019-10-22 11:45 - 12:45 | Aula Gratton
Polarimetry is considered as an important searching tool in Astronomy and it deserves to be a standard observational technique for a variety of astrophysical contexts: from stellar photospheric inhomogeneities to protoplanetary nebulae, as well as in the exoplanet research field. Despite this, however, the difficulties involved in the measurements and in the theoretical interpretation made this technique not as widespread as it deserves. In this talk I will review the results of my research about the diagnostic potential of optical high resolution linear spectropolarimetry in stars different than the Sun. At this purpose, after an introduction on the observational technique, I will focus on the polarised spectrum of the post-AGB binary system 89 Herculis: from the very inner regions of the stellar envelope to the first observational evidence of a micro-Gauss level magnetic field. Finally, I will discuss on the applicability and future prospect of this technique in the more general context of stellar physics.

Post-AGB stars as tracers of the origin of elements in the Universe
2019-10-29 11:45 - 12:45 | Aula Gratton
The chemical evolution of galaxies is governed by the chemical yields from stars, especially from Asymptotic Giant Branch (AGB) stars. This underlines the importance of understanding how AGB stars produce their elements by obtaining accurate stellar nucleosynthetic yields. Although AGB nucleosynthesis has general validity, critical uncertainties (such as the treatment of convective-driven mixing processes and mass loss) exist in current stellar models. Observations from Post-Asymptotic Giant Branch (post-AGB) stars serve as excellent tools to confront predictions from a dedicated suite of stellar models, quantify the strongest discrepancies, and eliminate crucial uncertainties that hamper stellar modelling. Our recent studies of post-AGB stars have shown an intriguing chemical diversity that ranges from stars that are extremely enriched in carbon and s-process elements to the discovery of the first post-AGB star with no traces of carbon nor s-process elements. Additionally, our studies have also shown that AGB nucleosynthesis is significantly affected by a binary companion. These results reflect the complexity that surrounds the element production in AGB stars. In this talk, I will present the intriguing chemical diversity observed in post-AGB stars and its implications on element/isotope production in AGB stars and stellar nucleosynthetic yields.

The impact of AGB stars on the life of stellar systems
2019-11-05 11:45 - 12:45 | Aula Gratton
During the latest phases of their lives, low-intermediate mass stars (M<8Msun) evolve through the Asymptotic Giant branch (AGB) phase. Although very rapid, the AGB phase represents a crucial step for the chemical evolution of the system where these stars form. The reason is that AGB stars undergo an advanced nucleosynthesis and experiment dredge-up events, while they progressively lose the majority of their mass through stellar winds. Furthermore, the low temperature and high densisty of their stellar winds prove extremely favourable conditions for dust condensation in the circumstellar envelopes. All the reprocessed gas and dust lost by the AGB stars enrich the insterstellar medium of the host system. Detailed modelling of these complex physical processes are essential to reconstruct the impact that these stars had on the history of formation and chemical evolution of stellar clusters and galaxies. In this talk I will present how the latest generation of AGB+dust evolutionary models has been recently used to this scope in different environments: from globular clusters, to unveil the origine of multiple populations, to Local Group dwarf galaxies, to infer star formation history and dust production rate.
