Osservatorio Astronomico di Roma

Extreme-Adaptive-Optics observations of protostellar jets
2016-11-15 11:45 - 12:45 (Europe/Rome) | Aula Gratton
The ejection of matter in form of protostellar jets/outflows plays a fundamental role in the star-formation process as it is tightly connected to the mass accretion mechanism and is expected to directly affect the evolution of the circumstellar disk in which planet formation occurs. Since the typical angular scales of the jet-formation region are of the order of tens of mas for the closest star-forming regions, such region has so far remained unknown from an observational point of view. New instruments equipped with extreme Adaptive Optics systems offer now the opportunity to observe the jets as close as possible to the driving sources so as to gather crucial pieces of information on the ejection process and its connection to the disk.
In this context, I will present the first VLT/SPHERE observations jets from a young object. Using the ZIMPOL instrument we have taken optical images of the young binary Z CMa, which is composed by two eruptive variables: a Herbig star showing recurrent EXor-like outbursts and a FUor source, both driving a jet. The morphology of the two jets, which we trace down to ~70 mas, looks fairly different: the Herbig star appears to emit a poorly collimated compact flow, while the FU Ori drives a highly collimated precessing jet.
For the FUor jet, we discuss the mechanism responsible for the observed jet precession and we provide the first direct measurement of the mass ejection rate and of the ejection efficiency in a FUor source, which we can compare to the same quantities measured in other classes of young stellar objects.
Finally, I will give an overview of what we can expect for protostellar jet observations with other upcoming extreme-AO instruments, such as SHARK at LBT.

Can supermassive black holes influence the evolution of galaxies?
2016-11-10 11:45 - 12:45
Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. A strong support of this “quasar mode” feedback came from the recent X-ray observations of a mildly relativistic accretion disk winds in an ultraluminous infrared galaxies and their connection with a large-scale molecular outflows, providing a direct link between the SMBH and the gas out of which stars form. Spectroscopic observations, especially in the X-ray band, show that such accretion disk winds may be common in local AGN and quasars. However, their origin and characteristics are still not fully understood. Detailed theoretical models and simulations focused on radiation, magnetohydrodynamic (MHD) or a combination of these two processes to investigate the possible acceleration mechanisms and dynamics of these winds. Some of these models have been directly compared to X-ray spectra, providing important insights into the wind physics. Fundamental improvements on these studies will come from the unprecedented energy resolution and sensitivity of upcoming X-ray missions, such as Athena, and the synergy with future large facilities at other wavelengths, such as ALMA, E-ELT, SKA.

AGILE highlights in gamma-ray astrophysics and the hunt for GW counterparts
2016-11-08 11:45 - 12:45

Swinging between accretion and rotation power in binary millisecond pulsars
2016-10-25 11:45 - 12:45
Neutron stars in low mass X-ray binaries are spun-up to millisecond spin periods during a Gyr-long phase of accretion of the matter transferred by a companion star. When the rate of mass transfer decreases at the end of this Gyr-long X-ray bright phase, a radio pulsar powered by the rotation of the neutron star magnetic field turns on. After decades of searches, the evolutionary link between these two classes of sources has been recently proven by the discovery of three sources that were observed to swing between accretion (X-ray bright) and rotation (radio bright) pulsar behaviour. These sources are the prototype of a new class of transitional systems that alternate between accretion and rotation-powered states in response to variations of the rate of mass in-flow, on time scales as short as a couple of weeks. Observations of this and other similar systems indicate that transitions to the accretion phase not only involve bright X-ray outbursts, but also a fainter intermediate X-ray state, possibly caused by centrifugal inhibition and ejection of the matter flow. Transitional ms pulsars are ideal test beds for theories describing the accretion-ejection coupling around a fast magnetized rotator, as well as the evolution of old binary systems. I will review the main observed properties, the prospects of catching more state transitions, and the possibilities to fully exploit the unique observable features of this newly established class.

Ascende superius - Seek higher things - Moving to higher order statistics in weak lensing
2016-10-18 11:45 - 12:45
Weak lensing has emerged as one of the most promising tool to constrain
cosmological parameters and modified gravity theories by measuring second
order statistical probes such as the cosmic shear two points correlation
function and tomographic power spectra. Thanks to both the wide area and
large redshift range probed, future surveys will deliver such an exquisite
quality dataset that it is worth wondering whether one can move to higher
order statistics. We review here some interesting possibilities showing
that they can be recovered with sufficient precision from future data and
shed further light on the dark energy mystery.

Quasars and their host galaxies in the first Gyr of the Universe
2016-10-12 11:45 - 12:45
Quasars are the brightest (non-transient) objects observed at the highest
redshifts, z>7. Such high redshift quasars are important for several
reasons. Firstly, detailed analysis of quasar spectra provide unique
information about the baryonic and physical condition of the Universe
during the epoch of reionisation. Furthermore, the density of high
redshift quasars puts powerful constraints on the mechanisms that are
required to seed and grow >10^9 Msun supermassive black holes less than a
Gyr after the Big Bang. Lastly, as these massive black holes are thought
to be located in the progenitors of the massive early type galaxies we see
in the local Universe, studying the host galaxies of the most distant
quasars enables us to probe the formation of massive galaxies in the early
Universe.
Because high redshift quasars are rare, multi-band surveys covering large
areas on the sky are required to discover such objects. In this talk I
will describe our successful programme aimed at discovering quasars at the
highest redshifts in various optical and near-infrared surveys, such as
Pan-STARRS1, UKIDSS and VIKING. I will highlight the results of our
search, which includes the discovery of more than 100 new quasars in the
first Gyr of the Universe. I will describe our on-going multi-wavelength
follow-up observations to characterise the distant quasars, their power
source and their environment, in particular our ALMA programmes to study
the galaxies hosting these luminous objects. I will present the results of
these observations, and discuss the implications for massive galaxy and
black hole formation at high redshift and our understanding of the
relation between the black hole mass and the bulge mass of galaxies.

Gamma-ray busrts as probes of high redshift galaxies and their environments
2016-10-11 11:45 - 12:45
The launch of the Swift mission has revolutionised the study
of the Gamma-Ray Bursts, enabling the optical follow-up of the early afterglow.
Thanks to the fast broadcast of the GRB coordinates
and to the rapid response mode systems built up in 8-meter class
telescopes, these afterglows have be observed from hours down to a few
minutes after the GRB explosion. The high signal-to noise achievable
allows us to acquire medium-to-high resolution spectra, which carry a lot of
information both on the GRB environment and the Inter-Stellar Medium
of high redshift galaxies. I will give a short review of what we have
learned through the medium-to-high resolution spectroscopy of GRB afterglows,
mainly with UVES and X-shooter at the VLT.

Cosmic rays, gamma-rays, and neutrinos from AGN winds
2016-10-04 11:45 - 12:00
Galaxy scale outflows driven by active galactic nuclei (AGN) are likely to play a key role in the evolution of galaxies. In fact, they can perturb and possibly expel most of the gas out of the galaxy, offering a plausible physical origin for the close connection between the properties of black holes and their host galaxies. AGN-driven outflows can also induce shocks in the interstellar medium, which, in turn, can accelerate relativistic particles.
I will present a study of the non-thermal emissions produced by relativistic particles accelerated by the AGN-driven shocks in NGC 1068. NGC 1068 is a nearby prototypical Seyfert 2 galaxy which shows both starburst and nuclear activities in its central region. NGC 1068 is a strong gamma-ray emitter. It is the brightest of the few non-blazar galaxies detected by the Fermi gamma-ray space telescope.
I will show the gamma-ray and radio spectra predicted by the AGN outflow model, and I will discuss how these results compare with those corresponding to other commonly assumed sources of gamma-ray and radio emissions, like Supernova remnants or AGN jets.
I will compare the neutrino flux expected in the AGN outflow model with constraints from current experiments, and I will provide predictions for the detections by the upcoming KM3NeT neutrino telescope.

Indirect Dark Matter searches with the MAGIC telescopes and prospects with the ASTRI mini-array and the Cherenkov Telescope Array
2016-09-27 11:45 - 12:45

Gas accretion and star formation in disk galaxies
2016-09-13 11:45 - 12:45
Numerical simulations predict that metal-poor gas accretion from the cosmic web fuels the
formation of disk galaxies. My presentation will summarize observational evidence
for this gas accretion process driving star formation. In particular, I will discuss
a number of properties characterizing large samples of star-forming galaxies that
can be explained by metal-poor gas accretion (e.g., the fundamental metallicity relation,
or the relationship between galaxy morphology and metallicity). Some properties of the
(neutral and ionized) gas around galaxies will be examined too. I will also review the
properties of the extremely metal poor galaxies. They show chemical and dynamical
inhomogeneities that can be naturally explained as due to star-formation feeding from
infall of external metal-poor gas.

The Milky Way bulge: chemical content, kinematics and 3D structure
2016-06-30 11:45 - 12:45
During the last decade large observational efforts have been focused on understanding the formation and evolution of the Milky Way bulge by studying the spectroscopic and photometric properties of its stellar population over large and unexplored regions.
The emerging picture is substantially different from what previously thought and by far more complicated.
I will review the results obtained by the recent surveys focusing in particular on the observational evidences concerning the Bulge chemical content, kinematics and 3D structure.

Stellar evolution modeling of low-mass stars with magnetic fields: advances and challenges
2016-06-14 11:45 - 12:45
Though magnetic fields are commonly believed to play an important role
on the structure and evolution of stars, there have been few attempts so
far to include their effects on stellar evolution models. Specifically
in the case of low-mass stars, those effects could account for some
disparities between standard stellar models predictions and
observations, such as their radii and effective temperatures. In this
talk I will briefly review the modeling techniques for considering the
magnetic field effects on 1-D evolution codes, and also present some
recent results of those techniques as implemented in the ATON stellar
evolution code. Some theoretical and observational challenges to those
results will also be highlighted.

The two-families scenario of compact stars: signatures and implications on GRBs
2016-06-09 11:45 - 12:45
In the last years the possibility of discriminating between the various theoretically possible compositions of a compact “neutron” star has become more and more convincing and it is based on the measure of a few fundamental quantities, such as the radii (NICER, LOFT), the moment of inertia (SKA) and/or the gravitational wave signal before and after the merging of two compact stars (VIRGO, LIGO).
I will outline the so-called two-families scenario in which both stars having very small radii (of the order of about 10.5 km) and stars having very large masses (of the order or larger than about 2 Ms) can exist. In that scenario very dense stars, having small radii, are made of neutron, protons, hyperons and other hadronic resonances, while the most massive stars are strange-quark stars, i.e. objects entirely made of deconfined quark matter. I will discuss the implications of the two-families scenario on short and long Gamma Ray Bursts within the proto-magnetar model of GRBs, showing that quark deconfinement can be responsible both of the rapid termination of the prompt emission in short GRBs and of late time activity in long GRBs.

Dust-driven stellar winds in stellar evolution models
2016-05-31 11:45 - 12:45
Mass loss from stars during their evolution in the HR-diagram is an essential ingredient in stellar evolution models. Mass loss on the AGB is of particular interest when dust production is included in the model, since it is well established that the winds of AGB stars are largely dust driven. For practical reasons, the wind models adopted in stellar evolution codes are relatively simplistic: the actual mass-loss rate is prescribed and net effect of thermal gas pressure is usually not taken into account. In this talk I will discuss how wind these models can be improved without turning them into inhibiting computational challenges. I will also discuss (or speculate about) the effects such an improved wind model can have on the resultant dust yields for AGB stars.

The square kilometre array
2016-05-24 11:45 - 12:45
Building on the major scientific achievements of the current generation of centimetre and metre-wavelength telescopes, phase 1 of the Square Kilometre Array (SKA1) will be the next global radio astronomy observatory. It is currently being designed by engineers and scientists from around the world, with the aim of beginning construction in 2018 and early science operations in 2020. SKA1 will conduct key tests of general relativity through surveys and timing of pulsars in our Galaxy. It will help answer fundamental questions related to the evolution of atomic Hydrogen in the Universe, from the present day back to the Cosmic Dawn. I will give an overview of the wide breadth of science objectives that could be addressed by SKA1, along with a description of the planned telescopes and the sites that will host them
