Osservatorio Astronomico di Roma

colloquium - Fabrizio Nicastro
2018-11-08 11:45 - 12:45 (Europe/Rome) | Aula Gratton

Missing Baryons and the Warm-Hot Intergalactic Medium
2018-11-08 11:45 - 12:45
It has been known for decades that the observed number of baryons in the local Universe falls about 30-40% short of the total number of baryons predicted by Big-Bang Nucleosynthesis, inferred by density fluctuations of the Cosmic Microwave Background and seen during the first 2-3 billion years of the universe (redshift z>2-3) in the so called “Lyman-α Forest”. While theory provides a reasonable solution to this paradox, by locating the missing baryons in hot and tenuous filamentary gas connecting galaxies, it also sanctions the difficulty of detecting them because their by far largest constituent, hydrogen, is mostly ionized and therefore virtually invisible in ordinary signal-to-noise Far-Ultraviolet spectra. Indeed, despite the large observational efforts, only a few marginal claims of detection have been made so far.Here I will first review the observational efforts pursued over the past 15 years by several groups and will then present our recent results that show that the missing baryons are indeed found in a tenuous warm-hot and moderately enriched medium that traces large concentrations of galaxies and permeates the space between and around them. The detection of these baryons is hampered by foreground ISM contamination, which is hard to correct for, due to our poor knowledge of inner-shell resonant transitions from metals in the X-ray band. Despite these intrinsic difficulties, I will show that the number of OVII systems detected down to the sensitivity threshold of our data, agrees well with numerical simulation predictions for the long-sought hot intergalactic medium, and its detection adds a fundamental tile to the long-standing missing baryon puzzle. Finally, I will comment on the implications of these new results for future high resolution X-ray missions.

colloquium - Svetlana Zhukovska
2018-11-12 11:45 - 12:45

AGB stars and the cosmic dust cycle
2018-11-12 11:45 - 12:45
Theoretical and observational studies of dust condensed in outflows from AGB stars have substantially advanced the understanding of the dust mixture from individual stars. This detailed information incorporated into models of the lifecycle of interstellar grains allows us to evaluate the contribution of AGB stellar populations to the galactic dust budget, their role in the dust production in galaxies of various morphological types. I will highlight some questions of galactic evolution that can be answered by these models in combination with modern infrared observations. I will also present models of dust evolution in an inhomogeneous, multi-phase ISM that shed light on the dust mass growth in clouds, an important dust formation mechanism in evolved galaxies.

Characterizing the circum/inter-galactic gas in emission around z~2-3 quasars
2018-11-20 11:45 - 12:45
Recently, enormous (> 200 kpc) Lyman-alpha nebulae (ELAN) have been discovered around radio-quiet z~2-3 quasars. Being currently explained as powered by the ionizing radiation of quasars, these bright large-scale nebulosities suggest the possibility of studying the circum/inter-galactic gas in emission around individual systems on very large scales. Motivated by these discoveries, we have been conducting a statistical census of z~2-3 quasars using the narrow-band and IFU technique with the aim to determine the frequency of this phenomenon, as well as to study their size, luminosity, covering factor, and the gas physical properties.
In the first part of my talk I will present the results of the QSO MUSEUM survey
(Quasar Snapshot Observations with MUse: Searching for Extended Ultraviolet eMission), which comprises 61 z~3 quasars observed with the MUSE/VLT instrument.
In the second part of the talk I will then focus on one of these objects which suggests that
Lyman-alpha could be used to trace the inspiraling motions of the cool circum-galactic medium,
predicted to take place on hundreds of kpc within massive halos.
I will conclude by summarizing my on-going observational effort in characterizing the ELAN phenomenon, and large-scale gas structures around quasars.

colloquium - Fabrizio Arrigoni Battaia
2018-11-20 11:45 - 12:45

colloquium - Juie Shetye
2018-11-27 11:45 - 12:45

Exploring the solar chromosphere with ground-based telescopes
2018-11-27 11:45 - 12:45
The Sun’s atmosphere consists of the photosphere, chromosphere and corona. The solar chromosphere bridges the photosphere and the corona. This dynamic layer is filled with events that evolve in a fraction of time and are very small in spatial scales. We use the biggest solar telescopes to zoom into this layer in order to understand such dynamic events.

In the talk, we discuss detailed observations of two different events guided by high-resolution and high-cadence observations. The first topic covers a statistical study of long thin jets called “spicules.” Spicules wiggle and sway around to give an impression of waves propagating along them. These waves can travel with speeds of hundreds of kilometres per second, energising the solar chromosphere. The second topic is about swirling-whirling events that look like tornadoes. These churn matter from the lower photosphere to the chromosphere. Studying the behaviour of these events is vital in understanding a decade-long question in solar physics, that addresses the heating of the Sun’s atmosphere.
A future goal is to support such observation by performing Magnetohydrodynamic (MHD) simulations using LareXd, developed here at Centre for Fusion Space and Astrophysics (CFSA), University of Warwick. In the end, we would have a glimpse of what the future of ground-based observations holds. We will see the latest progress on next-generation solar telescope Daniel K. Inouye Solar Telescope (DKIST) and what we at CFSA, Warwick are expecting from it.

Colloqium - Donatella Romano
2018-12-04 11:44 - 12:45

The evolution of CNO isotope ratios: a litmus test for stellar IMF variations in galaxies across cosmic time
2018-12-04 11:45 - 12:45
Determining the shape of the stellar initial mass function (IMF) and whether it is constant or varies in space and time is the Holy Grail of modern astrophysics, with profound implications for all theories of star and galaxy formation. On a theoretical ground, the extreme conditions for star formation (SF) encountered in the most powerful starbursts in the Universe are expected to favour the formation of massive stars. Direct methods of IMF determination, however, cannot probe such systems, because of the severe dust obscuration affecting their starlight. The next best option is to observe CNO bearing molecules in the interstellar medium at millimetre/submillimetre wavelengths, which, in principle, provides the best indirect evidence for IMF variations. In this talk, I discuss some recent findings on this issue. First, I reassess the roles of different types of stars in the production of CNO isotopes, by using a proprietary chemical evolution code and up-to-date Milky Way data from the literature. The model is then extended to discuss extragalactic data. I show that, though significant uncertainties still hamper our knowledge of the evolution of CNO isotopes in galaxies, compelling evidence for an IMF skewed towards high-mass stars can be found for galaxy-wide starbursts. In particular, I show the results for a sample of submillimetre galaxies observed by our team with the Atacama Large Millimetre Array at the peak of the SF activity of the Universe, for which we measure a ratio 13C/18O of about 1. This isotope ratio is especially sensitive to IMF variations, and little affected by observational uncertainties. At the end, ongoing and future developments of our work are briefly outlined.

Paolo Dal Pozzo Toscanelli, Cosimo de’ Medici and the Sky of the Magi: a new reading of the Florentine Celestial Hemispheres in the Sagrestia Vecchia at San Lorenzo and in the Pazzi Chapel at Santa Croce.
2018-12-06 11:45 - 12:45
After 30 years since the historical pubblication of the analysis
conducted by Forti, Lapi Ballerini, Monsignori Fossi and Ranfagni (1987), I
offer a careful re-examination of the two famous florentine starry vaults of
the early Renaissance, taking into account the recent restoration of the
hemisphere of the Pazzi Chapel and the almost coeval maps drawn by Paolo
Dal Pozzo Toscanelli for his studies of comets in 1456 (Halley) and 1457.
The authorship by the Tuscan cosmographer is confirmed in the Sagrestia
Vecchia on the basis of a comparison between a sample of stars from the
dome, Toscanelli’s maps and Ptolemy’s Catalogue. The Pazzi Chapel instead,
reveals on close inspection to be a clumsy, derivative later work.
While the double date proposed in 1987, the enigmatic 4/5 july 1442, still
remains astronomically the most probable, I will show that the exactness of
the planetary positions have been overestimated, unfairly provoking a lack of
attention for other candidate dates, more astrologically meaningful if not
depicted with satisfying correctness. Relying indeed on the astrological
techniques and interests of the time, I propose to assess the 1442 and the
1439 most probable candidate horoscopes following the very appropriate line
of reasoning introduced by Dieter Blume (2000), i.e. considering the
congruence of the sky charts with principles and rules of astral divination as
well as with the political situation in Florence and with the cultural needs of
the clients.
Finally, I single out as most probable the second date (even exhibiting a
marginal evidence for it on the basis of Lorenzo de’ Medici’s calendarial
concerns), and I offer a new hypothetical explanation for this preference,
linking medicean interest in the magian narrative and the Star of Bethlehem,
astrological speculation and political propaganda.

colloquium - Marco Padovani
2018-12-11 11:45 - 12:45

The role of cosmic rays on physical and chemical processes of the interstellar medium
2018-12-11 11:45 - 12:45
The study of the interaction of cosmic rays with the interstellar matter is a multi-disciplinary investigation that involves the analysis of several physical and chemical processes: ionisation of atomic and molecular hydrogen, energy loss by elastic and inelastic collisions, energy deposition by primary and secondary electrons, gamma-ray production by pion decay, the production of light elements by spallation reactions, and much more. Cosmic-ray ionisation activates the rich chemistry of dense molecular clouds and determines the degree of coupling of the gas with the local magnetic field, which in turn controls the collapse timescale and the star-formation efficiency of a molecular cloud. In recent years a wealth of observations from the ground and from space has provided information and constraints that still need to be incorporated in a consistent global theoretical framework. My goal is to use the results of chemical models and state-of-the-art numerical simulations supplemented by dedicated observations to provide a unifying interpretation of the data with a model of cosmic-ray propagation specifically developed to make predictions that can be tested against the observations. Finally, I will talk about my most recent study: a mechanism able to accelerate local thermal particles in protostars that can be used to explain the high ionisation rate as well as the synchrotron emission observed towards protostellar sources.

colloquium - Gioia Rau
2018-12-18 11:45 - 12:45

How to tackle a giant Star: multi-wavelength studies of cool, evolved stars, using HST and VLTI
2018-12-18 11:45 - 12:45
The chemical enrichment of the Universe is considerably affected by the contributions of Giant stars. Giant and supergiant stars are surrounded by a hot layer called the chromosphere, which could likely powers Magneto-Hydrodynamic Alfven waves that could initiate their mass loss. Toward the end of their life, on the Asymptotic Giant Branch (AGB), stars produce heavy chemical elements, molecules, and dust, which, through the mass loss provided via their stellar winds, are placed into the interstellar medium.
This talk will explore ongoing work modeling high-resolution spectroscopic observations with Hubble Space Telescope instruments (Rau et al. 2018), to reveal the role of the chromosphere in driving K-M giant and supergiant winds. Our results include estimates of wind and chromospheric parameters, mass-loss rates, and fundamental stellar parameters.
In addition, ground-based interferometric measurements with high-angular resolution instruments from VLTI, such as MIDI (Rau et al. 2015, Rau et al. 2017), GRAVITY (Wittkowski, Rau et al. 2018), help to test geometrical and dynamical models describing the behavior of the outer AGB atmospheres at various spatial scales. In this way we are able to unravel the role of molecules and dust in their extended atmospheres.
Future plans include the use of high-angular resolution instruments such as VEGA at CHARA, and MATISSE at VLTI, to better understand the behavior of cool stars outer atmospheres at various spatial scales.

colloqium - Cristina Ramos Almeida
2019-01-15 11:45 - 12:45

An infrared and sub-mm view of AGN obscuration and feedback
2019-01-15 11:45 - 12:45
In the past 10-15 years our view of AGN has significantly evolved thanks to the combination of new observations and models. X-ray, infrared and sub-mm data have been crucial to peer into the inner region of AGN and study the properties of the tori, circum-nuclear disks and nuclear outflows. In this talk I will summarize our current view of nuclear obscuration in AGN, focusing on the variations of the torus properties with gas phase. I will also present preliminary results of a new project aimed to characterize nuclear outflows in three gas phases (ionized, coronal and molecular) in a sample of nearby type-2 quasars and study their impact in the stellar populations, on-going star formation and molecular gas reservoirs of the galaxies.

colloquium - Viola Allevato
2019-01-22 11:45 - 12:45

Clustering dependence of X-ray AGN on host galaxy properties
2019-01-22 11:45 - 12:45
The presence of a super massive BH in almost all galaxies in the Universe is an accepted paradigm in astronomy. How these BHs form and how they co-evolve with the host galaxy is one of the most intriguing unanswered problems in modern Cosmology and of extreme relevance to understand the issue of galaxy formation. Clustering measurements can powerfully test theoretical model predictions of BH triggering scenarios and put constraints on the typical environment where AGN live in, through the connection with their host dark matter halos. In this presentation I will talk about the clustering properties of X-ray AGN from both an observational and theoretical point of view, using the new catalog of AGN detected by Chandra in COSMOS and semi-empirical models. The Chandra COSMOS-Legacy catalog is one of the largest available sample of X-ray AGN for clustering studies, allowing clustering measurements as a function of obscuration, luminosity and AGN host galaxy properties.

colloquium - Antonio Stamerra
2019-01-29 11:45 - 12:45

Multimessenger astrophysics with active galactic nuclei: observational clues of gamma-neutrino connection in blazars
2019-01-29 11:45 - 12:45
The clear detection of an isotropic flux of very high energy neutrinos by the IceCube experiment has opened the quest for the identification of their possibile electro-magnetic (EM) counterparts. Active Galactic Nuclei (AGNs) of the blazar category are considered as the main cosmic neutrino source candidates, although contribution from other types of active galaxies and Galactic sources is expected. Observation of transient EM emission, spatially and temporally compatible with the IceCube neutrinos, is crucial to identify their possible counterpart. Since April 2016, the IceCube Collaboration alerts the astronomical community whenever a high-energy single neutrino-induced event – HESE – is detected. Thanks to the IceCube real time system and the fast space- and ground-based observations which followed the alert, a neutrino event recorded on Sept. 22nd, 2017, has been significantly associated for the first time to a quasi-simultaneous gamma-ray flare observed by Fermi-LAT, AGILE and the MAGIC experiment from the AGN blazar TXS 0506+056. In this talk, we will review this multi-messenger result, mainly focussing on the MAGIC detection, and we will present some new results about possible transient gamma-ray sources observed by AGILE, coincident in time and space with public IceCube HESE neutrino events.

Ultraviolet imager with wide-field & deep for astronomical observation and study
2019-01-30 11:45 - 12:45
Base on the ultraviolet radiation characteristics of cosmic celestial models and different morphological materials, the astronomical ultraviolet band observation has important scientific significance and research value for the study of astronomical scientific problems such as searching for the cosmic missing baryons, studying the transport process of stellar and galaxies in the cosmic environment. China is currently developing the space station optical facility with an observation band covering near ultraviolet to infrared range. The wide-field deep ultraviolet imager (WDUI) is proposed on the optical facility of the China space station (CSS), which can overcome the influence of the Earth’s atmosphere and obtain the remarkable astronomical observation efficiency in the ultraviolet band. It promotes the development level of the astronomical ultraviolet band observation instrument and promotes the observation of the ultraviolet astronomical section of the space astronomical science. Output of scientific achievements has a positive effect. This talk reviews the background of the payload proposal, the astronomical observation capability of the CSS optical facility, the scientific goals of the payload, the preliminary system design and technical characteristics of the payload, and possible other band observations.

colloqium - Eva Villaver
2019-02-05 11:45 - 12:45

From AGB stars to Planetary Nebulae: what the ISM, stellar rotation, and companions can do
2019-02-05 11:45 - 12:45
Asymptotic giant branch (AGB) stars lose their envelopes by means of heavy mass-loss rates. Besides the mass-loss process itself there are other mechanisms that influence the evolution of the star and of what we see as Planetary Nebulae. Among them are the interaction of the ejecta with the interstellar medium (ISM), the inclusion of stellar rotation and/or the presence of a companion. I will present our simulation of the interaction process between AGB stars and the ISM. I will show what we can expect for the planetary nebula formation when we include rotation in stellar evolution models and finally I will describe how these stars are influenced by the presence of external companions

Stellar Populations in Local and high redshift Universe
2019-02-12 11:45 - 12:45
Synthetic stellar libraries are quite popular to constrain the stellar pop-
ulations (age and metallicity distribution) of unresolved systems like high redshift galaxies.
However, they are typically based on theoretical Spectral Energy Distributions (SEDs).
It is important to build up empirical synthetic stellar li-
braries, calibrated on local systems and
covering a broad range in ages (globular clusters, old open clusters),
chemical compositions (iron, alpha, CNO) and dynamical properties (nearby
dwarf galaxies), able to improve our SED fitting codes to deeply investigate
high redshift galaxies.
To do that, I am taking advantages of a sample of 65 Galactic globular clus-
ters (GGCs) for which we have accurate and homogeneous optical photometry
based on space (ACS at HST, innermost regions) and ground-based
(up to the tadial radius).
In particular, I will present the results on the study of the Horizontal Branch
(HB) morphology for 64 GGCs in our sample.
I will introduce a very new photometric morphology index based
on the cumulative density function of the stars along the HB,
useful to investigate the well known “second
parameter problem” affecting age estimations and so, stellar libraries.
I will also discuss the results of the analysis on galaxy
evolution through the Galaxy Stellar Mass Function (GSMF) up to redf-
shift 4, obtained combining all the five CANDELS fields (GOODS-South,
GOODS-North, EGS, COSMOS, UDS), the Frontier Fields Parallels (Abell 2744,
MACSJ0416, MACSJ0717, MACSJ1149) and the Ultravista/COSMOS
field. Stellar masses have been estimated fitting the photometry to syn-
thetic models: these surveys are characterized by multi-wavelength (deep
optical/near-infrared/mid-infrared) coverage (CANDELS), very high limiting magnitudes
(Frontier Fields) and large areas (UltraVista), allowing to explore the GSMF
from low masses to the high-mass end.

Colloquium - Marianna Torelli
2019-02-12 11:45 - 12:45

colloquium - Giuseppe Tanzella-Nitti
2019-02-14 11:45 - 12:45

colloquium - Guido De Marchi
2019-02-19 11:45 - 12:45

Star formation in the Local Group
2019-02-19 11:45 - 12:45
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
“…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?
