Osservatorio Astronomico di Roma

Escape of Lyman photons from galaxies
2016-04-12 11:45 - 12:45 (Europe/Rome) | Aula Gratton
One of the key questions in observational cosmology is the identification of the sources responsible for cosmic
reionization. The general consensus is that a population of faint low-mass galaxies must be responsible for the
bulk of the ionizing photons. However, until recently, attempts at identifying individual galaxies showing
Lyman continuum (LyC) leakage have only found very few such galaxies, both at high and low redshifts.
We recently proposed a new indirect diagnostic for LyC leakage based on the shape of the Lyman-alpha line,
that I will first review (Verhamme+15).
A breakthrough was recently achieved by our team (Izotov et al. 2016a,b), detecting LyC emission in
low-redshift (z~0.3) luminous compact star-forming galaxies (LCGs) with high LyC escape fractions
using HST/COS observations. I will present these new results, and the Lyman-alpha emission from these galaxies,
confirming our theoretical predictions.
Finally, I will propose another complementary Lyman-alpha signature for LyC leakage, discussing theoretical predictions
on the Lyman-alpha spatial extend of LyC emitters: LyC leakers should have no/faint Lyman-alpha halos.

The final wind: stars in retirement
2016-04-05 11:45 - 12:45 | Aula Gratton
Catastrophic mass loss is at the heart of 90% of all stellar
death. Low and intermediate mass stars lose their hydrogen envelope
while on the Asymptotic Giant Branch stars. At the end, there is
insufficient hydrogen left and the star rapidly evolves into a white
dwarf, briefly illuminating a planetary nebula on the way. The ejected
gas can be used to study the superwind, the nuclear burning and dredge
up processes in the star, and even (with some difficulties) the star
formation histories of the dying stellar population. In this talk I
will discuss the planetary nebulae of the Galactic bulge, briefly
mention AGB stars in globular clusters, and finally discuss the origin
of the mysterious AGB J-type stars, believed to be the cause of the
A+B grains in the proto-solar system.

AGN feedback studies: combining SINFONI and ALMA
2016-03-31 11:45 - 12:45
From a mere ornament in the center of the galaxy, the Super Massive
Black Holes (SMBHs) turned in a potential major actor in shaping the
final stellar mass of its host via the so-called AGN feedback. From
the observations there is mounting evidence that AGN outflows are
ubiquitous, but what is still largely missing are observational proofs
of the impact that such AGN-driven outflows have on their hosts. I
will discuss two complementary approaches to tackle this topic.
The first involve the use of Integral Field Spectroscopy in the
near-infrared to use kinematical maps of the ionized gas, as traced by
the [OIII] line, to constrain the energetics of AGN outflows. Our
group has already obtained several results using SINFONI and it has
now started a more systematical study via a recently approved Large
Programme at VLT. The second approach involve the use of ALMA band-3 observations to
measure molecular gas masses, via the 12CO(2-1) transition line, in a
representative sample of ‘main-sequence’ z~ 1.5 AGNs. We compare the
star-formation efficiency and gas fraction of their hosts with those of inactive
galaxies in the same range of stellar masses, SFR and redshifts.

Substructures in protostellar discs: spirals, gaps and warps
2016-03-29 11:45 - 12:45 | Aula Gratton
The advent of high resolution imaging of protostellar discs, both in the sub-mm (thanks to ALMA) and in the near infrared, has radically changed our understanding of the evolution of such discs and of the planet formation process occuring within them. While in the past disc were modeled as simplified, axi-symmetric structures, often characterized by simple radial power-law for density and temperature, we now need more advanced modeling, able to describe the substructures observed. Such modeling needs to take into account both the gas component, that dominates the dynamics and the line emission, and the dust, which is responsible for the continuum mm band emission. Here, I present several aspects of such modeling. I will discuss the theory and some hydrodynamical simulations describing: (a) spiral density waves, for example induced by gravitational instabilities in young and massive discs; (b) gaps induced by the presence of a forming planet in the disc, with particular emphasis on the spectacular case of HL Tau, that we have recently successfully modeled; (c) warps, which are expected to develop in circumbinary discs, or in discs where a planet has been put on a very inclined orbit.

High ionisation absorption in low mass X-ray binaries
2016-03-22 11:45 - 12:45 | Aula Gratton
The advent of the new generation of X-ray telescopes yielded a significant step forward in our understanding of ionised absorption generated in the accretion discs of X-ray binaries. It appears now clear that these relatively weak and narrow absorption features, sporadically present in the X-ray spectra of some systems, are actually the signature of equatorial outflows, which might carry away more matter than that being accreted. Therefore, they play a major role in the accretion phenomenon. These outflows (or ionised atmospheres) are ubiquitous during the softer states but absent during the power-law dominated, hard states, suggesting a strong link with the state of the inner accretion disc, presence of the radio-jet and the properties of the central source. I will review the current understanding of this field.

Cool, luminous stars to probe chemistry & kinematics in dusty-extincted stellar systems
2016-03-15 11:45 - 12:45 | Aula Gratton
Evolved, cool giants and supergiants are among the brightest stars in any stellar system and are
easily observable out to large distances.
When observed at infrared wavelengths, these cool stars can be also used to probe the stellar content
in environments severely obscured by dust, such as the central regions of galaxies.
Progress in our astrophysical comprehension of the stellar content in such extreme environments
goes together with the technological advance of IR instrumentation.
In this talk I will first present briefly the IR instrument context over the last two decades,
and then I will review some of the most recent results in probing stellar chemistry
and kinematics in the center of the Milky Way and in nearby galaxies.

Extreme adaptive optics at the Large Binocular Telescope
2016-03-01 11:45 - 12:45 | Aula Gratton
After a brief introduction about adaptive optics and the Large Binoculare Telescope, I will present the LBT’s extreme adaptive optic system. I will show its current capabilities, main scientific results and the performance improvement offered by the upcoming upgrade. Finally, I will show how the LBT AO technology impacted the design of the 8m-class and the next generation of ground based telescopes.

Linking massive black hole spin evolution to galactic dynamics
2016-02-23 11:45 - 12:45 | Aula Gratton
The evolution of the spin of massive black holes (MBHs) is driven by accretion of gas and/or by black hole binary coalescences. I will discuss the physical processes involved in the MBH spin evolution, and present the results of a semi-analytical model that manages to reproduce the distribution of spins obtained from X-ray spectroscopy.

Metals outside galaxies: what do we learn from observations?
2016-02-16 11:45 - 12:45 | Aula Gratton
The observed properties and evolution of galaxies in the Universe require the existence of feedback mechanisms regulating the star formation and finally quenching it. The presence of winds, possibly transporting the gas outside the viral radius, has been confirmed observationally in local and high redshift objects. In this talk, I will briefly review how scientist have confirmed the presence of heavy elements outside galaxies using the observation of QSO absorption lines and I will present and discuss new results based on the highest signal-to-noise ratio, high resolution QSO spectrum ever obtained.

May a single hypothesis to explain most of the mysteries of the universe?
2016-02-09 11:45 - 12:45 | Aula Gratton
A single hypothesis on the properties of the gravitational interaction
in the presence of antimatter could explain, simultaneously: the asymmetry
between matter and antimatter at cosmic level, the inflation, the effects attributed
to dark matter and dark energy, and at elementary particle level CPV and the arrow of time.

The early growth of (super)massive black holes
2016-02-02 11:45 - 12:45 | Aula Gratton
With detections of quasars powered by increasingly massive black holes
(BH) at increasingly early times in cosmic history over the past decade,
there has been correspondingly rapid progress made on the theory of early
BH formation and growth. I review the emerging picture of how the first
massive BHs formed from the primordial gas and then grew to supermassive
scales, and discuss the initial conditions for the formation of the
progenitors of these seed BHs, the factors dictating the initial masses
with which they form, and their initialstages of growth via accretion,
which may occur at super-Eddington rates.

Exploring the realm of an AGN
2016-01-26 11:45 - 13:00 | Aula Gratton
The environment of Active Galactic Nuclei (AGN) is the result of accretion and injection of matter in and around a supermassive black hole. Through high resolution X-ray spectroscopy of both present and future instruments, the most extreme gas environments of the AGN can be studied. In this talk I will present our recent results on outflows and obscuration in AGN. I will also illustrate the tremendous improvement that future instruments will offer in this field.
