Osservatorio Astronomico di Roma

Zooming into Dark Matter and primordial Star Formation with massive Lensing Clusters
2018-05-15 11:45 - 12:45 (Europe/Rome) | Aula Gratton

seminar by Cristina Raimos Almeida
2018-06-12 11:45 - 12:45 | Aula Gratton

CTA: Scientific perspective and current status
2018-09-04 11:45 - 12:45 | Aula Gratton
The Cherenkov Telescope Array (CTA) is the major ground-based gamma-ray observatory planned for the next
decade and beyond. Consisting of two large atmospheric Cherenkov telescope arrays (one in the southern
hemisphere and one in the northern hemisphere), CTA will have superior energy and angular resolutions, a much
wider energy range, and up to an order of magnitude improvement in sensitivity, as compared to existing
instruments. The CTA science program will be rich and diverse, covering the major aspects of cosmic particle
acceleration, understanding extreme astrophysical environments, and probing physics frontiers beyond the
Standard Model. This talk will outline the scientific persective for CTA and will cover the most recent status of the project.

The planet formation seen through high-resolution images of protoplanetary disks
2018-09-11 11:45 - 12:45 | Aula Gratton
The high occurrence of exoplanets around solar-type stars suggests that planets form very efficiently in protoplanetary disks. Yet, numerical simulations and laboratory experiments show that the planet formation is a complicated process. The onset of optical/NIR and (sub-)mm surveys of young stars has been a game changer for our understanding of protoplanetary disks and planet formation. Thanks to the contributed effort of VLT/SPHERE, GPI, and ALMA we could resolve with unprecedented resolution several sub-structures at the disk surface and midplane from few to hundreds of au from the star. I show the method and the recent improvement of this type of observations and discuss the implications to the recurrent existence of these disk features.

SHARK-VIS: the upcoming high-resolution high-contrast visible imager for LBT
2018-09-18 11:45 - 12:45 | Aula Gratton
SHARK-VIS is the visual channel (400-1000 nm) of SHARK, the upcoming extreme-AO instrument for the LBT optimized for high-contrast observations. The project is led by the OAR AO group and the instrument is currently being built at OAR with the first light foreseen in 2019.
SHARK-VIS will provide LBT with unprecedented high-contrast and high-resolution imaging capabilities in the visible band, thanks to both several technical solutions, aimed at optimizing the PSF stability, and its “fast cadence imaging” approach, based on the use of a high-frame-rate low-noise camera exploited by specific custom algorithms. The instrument will produce diffraction-limit images with an angular resolution down to 15 mas and with frame rates up to 1kHz.
In the first part of the talk, instrument details, expected performances, and the project status will be discussed.
In the second part of the presentation, we will present a summary of the main scientific cases for which SHARK-VIS is expected to provide breakthrough results, also considering the simultaneous use of the SHARK-NIR companion instrument (built at OAPd) and LMIRCAM, which will turn LBT into a unique high-resolution facility with continuous wavelength coverage from 0.4 to 3.5 um. Main science cases include identification of accreting planets in star-forming regions, morphology of jets and disks in young stars, characterization of minor bodies of the Solar system, and investigation of the central regions of bright AGNs.

Four years of science with SPHERE/VLT
2018-10-02 11:45 - 12:45 | Aula Gratton
SPHERE/VLT is an extreme adaptive optics instrument designed to directly image exoplanets. It was designed and build by a European consortium (including laboratories from France, Italy, Germany, Switzerland and the Netherlands) from and saw its first light in 2014. Most of the guaranteed time observations (GTO) are related to exoplanets and young disk. I will briefly present some results from these programs. I will then focus on the “Other Science” part of the GTO, aiming at showing that SPHERE is a versatile instrument able to answer key question in a variety of topics. I will present the results obtained via this program, ranging from 3D mapping of asteroids to star clusters via jets from young stars and evolved stars, including the first direct image of the surface of stars.

The MESSIER surveyor: lifting the veil on the ultra low surface brightness universe
2018-10-09 11:45 - 12:45 | Aula Gratton
The MESSIER satellite has been designed to explore the extremely low surface brightness universe at UV and optical wavelengths. The two driving science cases target the mildly- and highly non-linear regimes of structure formation to test two key predictions of the LCDM scenario: (1) the detection of the putative large number of galaxy satellites, and (2) the identification of the filaments of the cosmic web. The science requirements imply challenging instrumentation issues which have only recently been solved. The satellite will drift scan the entire sky in 6 bands covering the 200-1000 nm wavelength range to reach the unprecedented surface brightness levels of 34 mag/arcsec^2 in the optical and 37 mag/arcsec^2 in the UV. As usual when uncovering new volumes in parameter space, many important secondary science cases will also result as free by-products and will be discussed in some detail: the actual luminosity function of galaxies, the contribution and role of intracluster light, the fluctuations of the cosmological background radiation at UV and optical wavelengths, the warm molecular hydrogen content of galaxies at z=0.25, time-domain studies of supernovae and tidal disruption events, the chemical enrichment of the interstellar medium through mass loss of red giant stars and the accurate measure of the BAO scale at z=0.7 with over 30 million galaxies detected in Lyman-alpha at this redshift. It will provide the first space-based reference UV-optical photometric catalogue of the entire sky, and synergies with GAIA, EUCLID and WFIRST will also be discussed.

Transient spiral arms and galaxy rotation curves
2018-10-16 11:45 - 12:45 | Aula Gratton
The complex spatial structure evident in spiral galaxies is understood either in terms of instabilities of quasi-stationary states, or a result of dissipative non-gravitational interactions. We illustrate here, using numerical simulations, that purely self-gravitating systems evolving from quite simple initial configurations can give rise easily to structures of this kind of which the lifetime can be large compared to the dynamical characteristic time, but short compared to the collisional relaxation time scale. More specifically, for a broad range of non-spherical and non-uniform rotating initial conditions, gravitational relaxation gives rise quite generically to long-lived non-stationary structures of a rich variety, characterized by spiral-like arms, bars and even ring-like structure in special cases. These structures are a feature of the intrinsically out-of-equilibrium nature of the system’s collapse, associated with a part of the system’s mass while the bulk is well virialized. They are characterized by predominantly radial motions in their outermost parts, but also incorporate an extended flattened region which rotates coherently about a well virialized core of triaxial shape with an approximately isotropic velocity dispersion. We briefly discuss the possible relevance of these simple toy models to the observed structure of real galaxies. On the one hand, we discuss the determination of the velocity fields of THINGS galaxies. On the other hand we consider recent observations in our Galaxy (APOGEE and GAIA) that show that the galactic disk seems not to be a time-independent axisymmetric system. We conclude by stressing that these simple models illustrate the possibility that the observed apparent motions of spiral galaxies might be explained by non-trivial non-stationary mass and velocity distributions without invoking a large amount of dark matter halo or a modification of Newtonian gravity.

What is the role of the environment in shaping early-type galaxy sizes? Has it changed in the last 10 Gyr?
2018-10-18 15:00 | Aula Gratton
Understanding galaxy evolution requires understanding the impact of cosmic time, environment, mass, and halo growth at least, because likely a combination of them leads to the quenching of star formation and the emergence of the galaxy populations we see in the nearby Universe. In the talk, I will present the picture coming out from two mass-selected samples of red-sequence early-type galaxies in the general field.

Highlights from the ESA Rosetta mission
2018-10-23 11:45 - 12:45
The Rosetta/Philae mission of the European Space Agency marked a turning point in cometary space exploration. Launched on March 2004, Rosetta needed 10 years of interplanetary journey to arrive around its main target, the comet 67P/Churyumov-Gerasimenko. Rosetta orbited around the comet for about two years, providing the unique opportunity to continuously investigate the 67P nucleus composition, activity, and its evolution during the orbit. For the first time in the history of the space exploration, Rosetta delivered a lander, Philae, on a cometary surface.
A large complement of scientiﬁc experiments designed to complete the most detailed study of a comet ever attempted are on board Rosetta, including cameras, spectrometers, radio science, dust and plasma analyser and so on. More than 80,000 images of the comet have been acquired with the OSIRIS imaging system with a spatial resolution ranging from several meters to a few centimeters per pixel. I will present the main scientific results of this extraordinary space mission on the structure, geomorphology, and surface composition of the comet, and their implications on the formation of our solar system.

Cepheid variables in the Gaia Data Release 2 and the extragalactic distance scale
2018-10-30 11:45 - 12:45
Classical Cepheids are the most important primary indicators for the extragalactic distance scale.
Establishing the precise zero points of their Period-Luminosity and Period-Wesenheit (PL/PW) relations
has profound consequences on the estimate of H0. Type II Cepheids are also important distance indicators and tracers of old stellar populations. The recent Data Release 2 (DR2) of the Gaia Spacecraft includes photometry and parallaxes for
thousands of classical and type II cepheids. Adopting a subsample of well studied objects, we use the Gaia parallaxes to derive new optical/Near Infra-Red PL/PW relations for the Galactic Cepheids. We use these information, coupled with proprietary data from the Vista Magellanic Cloud (VMC) survey, to discuss the zero point of the Gaia parallaxes and its impact on the extragalactic distance scale and the measurement of H0.

eROSITA: Stellar science with a new X-ray All-Sky Survey
2018-11-06 11:45 - 12:45 | Aula Gratton
Nearly 30 years after ROSAT, the german-russian mission eROSITA, planned for
launch in spring 2019, is going to perform a new X-ray All-Sky Survey.
The majority of sources that will be detected with eROSITA are
late-type stars. I present eROSITA science cases for pre-main sequence and
for hydrogen-burning stars based on current studies with other
X-ray instruments. New momentum is expected from eROSITA especially
for stellar population and variability studies. These comprise a wide range
of topics including studies of the dynamics of stellar coronae (through
flares and activity cycles), search for X-rays from accretion outbursts
in young stars, and the use of X-rays as diagnostics for
stellar angular momentum evolution and the structure of the galactic
stellar disk.

colloquium - Beate Stelzer
2018-11-06 11:45 - 12:45 | Aula Gratton

colloquium - Fabrizio Nicastro
2018-11-08 11:45 - 12:45 | Aula Gratton

Missing Baryons and the Warm-Hot Intergalactic Medium
2018-11-08 11:45 - 12:45 | Aula Gratton
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 | Aula Gratton

AGB stars and the cosmic dust cycle
2018-11-12 11:45 - 12:45 | Aula Gratton
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.

colloquium - Fabrizio Arrigoni Battaia
2018-11-20 11:45 - 12:45 | Aula Gratton

Characterizing the circum/inter-galactic gas in emission around z~2-3 quasars
2018-11-20 11:45 - 12:45 | Aula Gratton
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.
