Osservatorio Astronomico di Roma

workshop Stamerra
2019-11-25 08:00 - 2019-11-28 17:00 (Europe/Rome) | Aula Gratton

LSST: an opportunity for the Italian Community
2019-11-26 11:45 - 12:45 | Aula Gratton
We review the current status of the LSST project, its expected performances, the key science goals and the involvment of the Italian Community

Acoustic oscillations and dynamo action in giants
2019-12-03 11:45 - 12:45 | Aula Gratton
The role of the magnetic field in determining the angular momentum transport in stellar interior is still an open issue. Acoustic oscillations are directly affected by the presence of a large-scale magnetic field but their study can provide fundamental information on the properties of the magnetic fields in solar-like stars. As an example the case of EK Eridani, a slowly rotating, overactive G8 giant, will be presented. Moreover the possibility to use asteroseismology to solve the long-lasting mystery on the origin of magnetic fields in Ap stars will be discussed.

Characterizing multi-phase gas outflows and their powering mechanism in nearby AGN
2019-12-10 11:45 - 12:45 | Aula Gratton
Active Galactic Nuclei are thought to play a crucial role in
the evolution of massive galaxies. In particular, fast outflows are
frequently observed in AGN covering various gas phases which may remove
a significant fraction of the gas content from the galaxies. I will
review the current state of research in this very active field of
ongoing research together with the advantages and disadvantages of
previous approaches. In particular, I will highlight the importance of
multi-wavelength observations to unravel the true multi-phase nature of
outflows by combining state-of-the-art observational facilities. In this
context I will present the first results from the ongoing Close AGN
Reference Survey (CARS), a multi-wavelength survey of 39 luminous
low-redshift unobscured AGN with extensive observations from VLT/MUSE,
ALMA, VLA, Chandra, SOFIA and many more. In addition, I will present the
multi-phase view of the famous ultra-luminous Quasar 3C273 where we
unlocked a few unknown secrets.

Gamma-ray bursts under a new light: the TeV emission from GRB190114C seen by the MAGIC telescopes
2019-12-18 11:45 - 12:45 | Aula Gratton
Gamma-ray bursts (GRBs) are the most luminous sources of electromagnetic radiation known in the Universe. GRBs had been observed over a broad energy range from the radio band up to GeV gamma rays, but the TeV gamma-ray band had remained terra incognita for a long time. Thanks to the MAGIC telescopes, designed to catch the fast glimpses of the GRBs, the first ever clear detection in this band was achieved for GRB 190114C, a bright, long GRB. The TeV emission from GRB190114C belongs to a new energetic component, providing an energy output comparable at the one at lower energies. We will discuss the details of the observations by MAGIC and the accompanying multi-frequency measurements by more than 20 instruments, from radio to gamma- rays, and the inferences on the emission mechanisms. This historical, highly significant detection has followed an intriguing hint of TeV emission from GRB 160821B, a short GRB with an associated kilonova. This hint, if real, has potential multi-messenger implications on the detectability of gravitational wave alerts in high-energy gamma-rays.

The two-families scenario: what does it predict?
2020-01-14 11:45 - 12:45 | Aula Gratton
I will revisit the two-families scenario in which neutron stars coexist with strange quark stars, i.e. with compact objects made almost
entirely of deconfined quarks. I will outline the differences between this scenario and other schemes in which quark matter appears only at the center of compact stars and I will discuss how it compares with GW170817, GRB170817A, AT2017gfo and with the existing limits on masses and radii of compact stars.

colloquium - Matteo Bachetti
2020-01-21 11:45 - 12:45 | Aula Gratton

3D magnetic structure, and brightening in sunspot penumbra
2020-01-28 11:45 - 12:45 | Aula Gratton
We analyzed spectropolarimetric data in the Fe I 617.3 nm and Ca II 854.2 nm lines of the sunspot in AR 12546 observed with the IBIS at the Dunn Solar Telescope on 20th May 2016 and co-temporal filtergrams by space-borne (Hinode, IRIS and SDO) instruments. The observed sunspot is one among the largest such features occurred over the last solar cycle. The IBIS data, taken under excellent seeing conditions that lasted more than three hours, were inverted with the NICOLE code, in order to retrieve the temperature, magnetic field, and plasma velocity of the studied sunspot as a function of optical depth and time. The umbral and penumbral regions are for the most part stable in the photosphere, while co-spatial chromospheric areas show waves in the umbra-penumbra boundary and intense brightening along penumbral filaments. We explored the origin of these chromospheric processes and their relation to changes in the 3D magnetic structure of the observed sunspot.

The X-ray universe at microarsec resolution: the power and promise of X-ray interferometry
2020-02-04 11:45 - 12:45 | OAR Monte Porzio Catone – aula Gratton, Via Frascati 33, Roma, RM, 00136, Italia
The spectacular image of a supermassive black hole `shadow’ taken by the Event Horizon Telescope last year highlights the potential of being able to resolve microarcsecond scale structures in astrophysical sources. Given the ~Angstrom scale of X-ray wavelengths, similar resolutions are theoretically possible with only a 1 m diameter telescope, which could be accommodated on a single spacecraft. Conventional X-ray imaging capability remains far from from this goal however.
In this talk I will explore the possibility, recently proposed to ESA’s Voyage 2050 program, of developing X-ray interferometry to break the resolution barrier in the X-rays, starting from X-ray fringes which have already been observed in the lab and examining what would be required for an X-ray interferometric space observatory, from the possibilities with single spacecraft to formation flyers which could push to sub-microarcsecond resolution. Such revolutionary observatories would enable detailed imaging-spectroscopy of stellar coronae and transiting exoplanets within ~100 pc, direct observation of X-ray binary orbits, supermassive black hole accretion flows and event horizons, and imaging of luminous transients and binary supermassive black holes across the observable universe.

The quest for observational evidence of the hierarchical formation process at the smallest galaxy scales
2020-02-11 11:45 - 12:45 | Aula Gratton
I will present our ongoing project devoted to the search and study of satellites, stellar streams, and substructures around dwarf galaxies. Deep, wide field imaging acquired with the Large Binocular Telescope and follow-up observations performed with the WFC3 on the Hubble Space Telescope provide evidence of multiple satellites associated with the very metal-poor star-forming dwarf galaxy DDO 68. This is a striking example of the few observed cases of hierarchical merging in action at the dwarf galaxy scales. To perform a systematic search of substructures around dwarf galaxies, we have started a Strategic Program at the LBT, named SSH (i.e. The Smallest Scales of Hierarchy Survey) to acquire deep, wide-field imaging of a sample of 45 late-type dwarf galaxies located within 10 Mpc. The survey, which is now close to completion, will provide one of the first systematic observational studies of the hierarchical formation process down to very small galaxy scales. In this talk I will introduce SSH and discuss the results obtained so far.

The interstellar medium at high redshift
2020-02-18 11:45 - 12:45 | Aula Gratton
The gaseous content of galaxies is one of the key ingredients of galaxy evolution: It fuels star formation and nuclear activity, and at the same time it is the main receiver of any feedback mechanism from these two processes. However, we have only very limited knowledge of the gas content and of its physical properties in galaxies beyond the local universe. As a result, no description of galaxy formation can be fully validated without a better understanding of 1) how much gas was available for star formation in different cosmic times; 2) how the star formation efficiency, i.e., the capability of a galaxy to form stars from a given amount of gas, evolve through cosmic history, and which are physical conditions that governed this evolution; 3) what was the interplay between the interstellar medium, star formation, and nuclear activity. These questions are particularly critical at the very high redshifts (z>6, when the universe was <1 Gyr old), where our census of galaxies is highly incomplete, especially at the high-mass end, and galaxies followed very different evolution according to the mass of their initial gas reservoir. In this talk I will present the results of various observational campaigns aimed at addressing these questions, in particular by capitalizing on the unprecedented capabilities offered by the Atacama Large Millimeter Array and the Northern Extended Millimeter Array. These findings will guide the next generation of simulations and theoretical models, thus marking a transformational step in our understanding of galaxy evolution.

colloquium - Roberta Zanin
2020-02-28 11:45 - 12:45 | Aula Gratton

colloquium - Ester Marini
2020-03-03 11:45 - 12:45 | Aula Gratton

The role of starburst galaxies and mergers in the distant Universe
2020-03-10 11:45 - 12:45 | Aula Gratton
Starburst galaxies are the most luminous star-forming powered objects in the Universe. A long standing problem in galaxy evolution is to understand whether these systems are caused by merger events, or they are just gas rich galaxies undergoing stochastic accretion events. To properly characterize them, we need infrared data, given the huge dust attenuations affecting their UV and optical emission.
I will present a unique set of near-infrared rest-frame spectral observations of star-forming galaxies at redshift ~ 0.7, and show how these can be used to understand the dust properties and origin of starbursts. Furthermore, I will explain how additional multiwavelength information (from radio to X-rays) is crucial to trace the whole sequence of mergers, test the merger-AGN connection and the formation mechanism of passive galaxies. Finally, I will exploit high-resolution HST images to investigate the role of mergers on the origin of bright star-forming clumps in high-redshift galaxies. A complete study of near-infrared rest-frame lines will allow JWST to probe the physical properties (e.g., dust attenuation, metallicity) and the nature of the most dust-embedded systems up to the reionization epoch.

colloquium - Brian Chaboyer
2020-03-17 11:45 - 12:45 | Aula Gratton

colloquium - Eleonora Fiorellino
2020-03-24 11:45 - 12:45 | Aula Gratton

colloquium - Matt Middleton
2020-04-07 11:45 - 12:45 | Aula Gratton

colloquium - Giovanni Miniutti
2020-04-20 11:45 - 12:45 | Aula Gratton

colloquium - Suzanne Ramsey
2020-04-28 11:45 - 12:45 | Aula Gratton

colloquium - Hans Van Winckel
2020-05-05 11:45 - 12:45 | Aula Gratton

The X-ray rise of primeval titans: HYPerluminous quasars at the Epoch of ReionizatION (HYPERION)
2021-01-13 11:30 - 12:30
The outstanding mass growth of the Supermassive Black Holes powering
luminous quasars at the Epoch of Reionization (EoR, z > 6) is one of
the most debated open problems of modern extragalactic
astrophysics. These quasars are current targets of extensive
multiwavelength campaigns with todays flagship observatories, in order
to understand their properties. The limited sensitivity of current
X-ray observatories, however, has so far provided mostly low quality
spectra (< 10 − 15 counts; 0.5-10 keV) and therefore a poor
characterization of their nuclear properties. I will present HYPERION,
a 2.4 Ms Multi-Year Heritage XMM programme on the titans among z = 6 −
7.5 quasars (i.e. the most luminous/massive at their epoch) designed
to dramatically improve the X-ray data quality to 100 counts for a
sample of 15 sources. HYPERION will deliver unprecedented constraints
on their nuclear properties, accretion, ejection, disc/corona complex,
and, while perfectly complementing observations at other wavelengths,
will enable X-ray spectroscopic population studies at EoR to begin.

colloquium - Flavia Dell'Agli
2021-01-19 11:30 - 12:30

colloquium - Michele Fabrizio
2021-01-26 11:30 - 12:30

colloquium Anita Zanella: The contribution of high-redshift star-forming regions to galaxy evolution
2022-01-25 11:30 - 12:30
Observations have shown that local galaxies have modest star formation rates and form the bulk of their stars in giant molecular clouds. In comparison, galaxies in the early Universe have high star formation rates and host large star-forming regions (dubbed “clumps”), 10 – 1000 times larger, brighter, and more massive than local giant molecular clouds. Interestingly, the formation phase of clumps has rarely been observed and their fate is highly uncertain. Are they born in-situ due to fragmentation of gas-rich disks or are they small satellite galaxies that merged with the host? Do they migrate inward and contribute to the formation of the galaxy bulge or are they rapidly disrupted by stellar feedback? Do they play a role in the mass assembly and structural evolution of the host galaxy? I will discuss our latest results derived from spatially-resolved HST, VLT/MUSE and ALMA datasets, as well as mock observations created from hydrodynamical simulations, which provide some answers to these open questions.

The most extreme phase of black holes growth and feedback
2023-02-21 11:30 - 12:30 | Aula Gratton
Deep surveys have revealed fully-grown supermassive black holes powering active galactic nuclei at very high redshifts, when the Universe was a few hundred Myr old, less than 10% of its current age. This challenges the theories of black holes growth, requiring long periods of high accretion, most likely above the Eddington limit. These objects will be difficult to study in detail, even with future advanced observatories. However, in the nearby Universe, there are several objects that shine beyond Eddington, can be studied in great detail and used as proxy for primordial black holes. In the supermassive regime we have some narrow line Seyfert 1 galaxies and tidal disruption events, whilst hundreds of stellar-mass black holes and neutron stars are known to power ultraluminous X-ray sources (ULXs). A common denominator to these stellar-mass and supermassive objects is the presence of extreme winds which confirm the predictions by theoretical models of super-Eddington accretion. These winds carry a huge amount of power owing to their mildly-relativistic speeds (~0.2c) and are able to significantly affect the surrounding medium and limit the amount of matter that can reach the central accretor. In this seminar I will discuss the state-of-art of super-Eddington accretion in different mass regimes and highlight future missions that will decisively boost this research field.

Connecting AGN and massive gas reservoir in protoclusters: the Chandra view of the Jackpot nebula at z=2
2023-02-28 11:30 - 12:30 | Aula Gratton
High-redshift, gas-rich galaxy protoclusters represent excellent laboratories
for investigating the effects of the environment on SMBH growth, nuclear
activity and onset of AGN feedback in overdense regions.
The detection of enormous (>200 kpc) Ly_alpha nebulae (ELANe) in some of these
systems, coupled with the presence of multiple AGN, has called for an extensive
follow-up observational campaign, including X-rays to properly census
the AGN population in these protocluster and, hence, determine their role in
powering ELANe.
In this talk, I will present an ongoing large Chandra program targeting some
high-redshift ELANe; in particular, I will focus on the properties of the
Jackpot nebula at z=2, showing four X-ray detected AGN in the inner part and
some additional AGN associated with Lyman alpha emitters on larger scales.
I will also report on the detection of diffuse X-ray emission in the inner
region of the nebula.

VVV Microlensing events as tracers of Galactic structure and kinematics
2023-03-07 11:30 - 12:30 | Aula Gratton
We report the discovery of ~1,000 microlensing events within an area covering 20.68 deg^2 between 2010 and 2015 in the zero-latitude region of the Galactic bulge using the VVV Survey near-IR data. We used the near-IR Color-Magnitude and Color-Color Diagram to analyze the extinction properties of the sample in the central region of the Galactic plane. We study the Einstein ring crossing time distribution as a strong dark mass indicator and study features of the Galactic structure. We found 20 distant microlensing events probably located in the far disk of the Galaxy. This is the first time a population of events has been discovered, allowing us to study the other side of the Milky Way. We also examine specific events, such as the long timescale events showing parallax that favor the presence of dark stellar remnants such as black holes and neutron stars, which are essential ingredients in our understanding of stellar evolution and mass distribution, galaxy evolution and structure, dark matter balance, etc.

colloquium - Sonia Fornasier: Latest results on 67P/Churyumov-Gerasimenko comet from the OSIRIS instrument onboard the ROSETTA mission
2023-03-21 11:30 - 12:30 | Aula Gratton
The Rosetta space mission of the European Space Agency Rosetta has observed comet 67P/Churyumov-Gerasimenko for about 2 years, delivering the lander Philae on the comet surface for the first time in the history of the space exploration. Ended in September 2016, the Rosetta/Philae mission, acquired an incredible amount of unique data of comet 67P, allowing the most detailed study ever attempted of a comet.
Rosetta had a large complement of scientific experiments including the OSIRIS imaging system which consists of a Wide Angle Camera (WAC) and a Narrow Angle Camera (NAC). More than 80000 images were acquired with the OSIRIS imaging system with spatial resolution ranging from several meters to a few centimeters per pixel during Rosetta’s descent to the comet in late September 2016. In particular, the high dynamics of the cameras detectors permitted to distinguish morphological structures on shadowed areas as well as frost layers, and to monitor at the same time the very dark surface, faint jets (with lifetimes shorter than a few minutes), and ices exposures.
An extensive catalogue of volatiles exposure was recently created permitting to investigate the link between composition, morphology and activity. It also indicates that ices exposures are typically sub-meter sized, information which is relevant for cometary models.
Detailed analysis of highly active regions revealed that the small lobe has different physical and mechanical properties than the big one and a lower volatile content, at least in its uppermost layers. These findings support the hypothesis that comet 67P originated from the merging of two distinct bodies in the early Solar System, as previously suggested by the geomorphological analyses of the comet terrains.
Finally, the reconstructed Philae orbit revealed that it had a second landing site located only 30 m apart from the final one. Philae stamped within a boulder for 25 cm depth, indicating that the cometary material is extremely soft and highly porous. This collision exposed the primordial water ice embedded within the boulder, providing an accurate measurement of the refractory to volatile ratio in comet 67P.

colloquium - Giulia De Somma: The classical Cepheids modelling in the Gaia Era
2023-03-28 11:30 - 12:30 | Aula Gratton
Classical Cepheids are the most used primary distance indicators to calibrate
the cosmic distance ladder and reliable stellar population tracers. These stars
have been adopted to probe galactic evolution and star formation, thanks to
their intrinsic variability and the link between pulsation properties and
evolutionary parameters. A theoretical approach to the study of these objects
is crucial to interpret observed behaviors and fully exploiting the accuracy of
observed oscillation characteristics in terms of stellar properties and distances.
By using the Stellingwerf hydrodynamical code, we recently provided detailed
homogeneous nonlinear Classical Cepheid pulsation models. We take into
account variations of chemical composition, mass-luminosity (ML) relation, and
efficiency of super-adiabatic convection.
The predicted pulsation observables included the instability strips, multi-filter
light curves, and the corresponding mean magnitudes and colors.
We used these quantities to derive metal-dependent period-luminosity-color
(PLC) and period-Wesenheit (PW) relations. The latter were applied to a
sample of Gaia Early Data Release 3 (DR3) Galactic Cepheids. The inferred
theoretical parallaxes were tested against Gaia astrometric results. By
combining this pulsational scenario with updated stellar evolution
predictions and using the BASTI code, we derived new and accurate metal-
dependent Period-Age and Period-Age-Color relations, which were applied to
the same sample of Galactic Cepheids in the Gaia DR3 to constrain their age
distribution. These results are all discussed in view of the incoming SPECTRUM
project that will represent the first attempt to systematically compute
nonlinear convective pulsation models along stellar evolutionary tracks.

Colloquium - Gianluca Castignani: Processing of gas in galaxies within the cosmic web
2023-04-04 11:30 - 12:30 | Aula Gratton
Galaxies are distributed in a complex filamentary network of matter called the cosmic web. Several studies showed that galaxy properties can be influenced by their large scale environments: spiral galaxies may interact and merge into an elliptical galaxy, they can be stripped from their gas by ram pressure and see their star formation quenched, they can be harassed in small groups, even before entering into clusters. However, it remains debated which is the overall impact of the cosmic web in processing cold gas of galaxies, as they move through large-scale filaments around the clusters down to the densest regions of the cluster cores. To evaluate the degree of such processing it is essential to study the reservoirs of molecular gas as it is the raw material from which stars form. I will present the results of a large observational campaign, mainly exploiting IRAM millimeter facilities, with the goal of quantifying the processing of galaxies’ gas in the cosmic web and with cosmic time. I will discuss the degree of such processing in a variety of dense megaparsec-scale environments for: i) galaxies in the cosmological filaments around Virgo, the nearest cluster in the Universe, ii) galaxies in and around clusters at intermediate redshifts, iii) distant brightest cluster galaxies (BCGs) at the center of clusters. Finally, I will discuss the potential of such studies for next generation multi-wavelength facilities. Thousands of distant clusters and BCGs will be detected with Euclid, enabling an unprecedented leverage to constrain galaxy evolution in clusters.
