Galaxy Formation and Evolution

Our team aims at investigating the complex processes leading to the formation and evolution of galaxies, galaxy systems, and supermassive black holes in a cosmological framework. To this purpose, we develop physical models to interpret and understand the astrophysics of galaxies and black holes across cosmic times, exploiting their emission over the whole electromagnetic spectrum and in gravitational waves. We are also strongly focused on the cosmological analysis of large-scale structure data to help understanding the fundamental nature of dark matter, dark energy, and gravity.

PI: Andrea Lapi

Main collaborators in SISSA: Carlo BACCIGALUPI (APC), Alessandro BRESSAN (APC), Annalisa CELOTTI (APC), Luigi DANESE (APC), Darko DONEVSKI (APC Postdoc), Anna FELTRE (APC Postdoc), Paolo SALUCCI (APC), Matteo VIEL (APP).

Ph.D. students: Lumen BOCO, Lara PANTONI, Tommaso RONCONI, Sabyasachi GOSWAMI, Anirban ROY

Former students (most recent): Jingjing SHI (Univ. Beijing, China and Univ. Perth, Australia), Federico BIANCHINI (Univ.Melbourne, Australia), Claudia MANCUSO (INAF-IRA, Bologna,Italy), Rossella AVERSA (CNR, Trieste,Italy).

Involvement in international projects (most recent): Athena, Euclid, Herschel, Einstein Telescope.

Financial support (most recent): PRIN MIUR 2017 "Opening the ALMA window on the cosmic evolution of gas, stars and supermassive black holes", PRIN MIUR 2015 "Cosmology and Fundamental Physics: illuminating the Dark Universe with Euclid", ASI-COSMOS Project "Cosmic Orbital and Suborbital Microwave Observations", "Spanish MINECO I+D 2015 project "High-z sub-mm sources: the optimal sample to study the gravitational lensed Universe", PRIN INAF 2012 "Looking into the Dust Obscured Phase of Galaxy Formation through Cosmic Zoom Lenses in the Herschel-ATLAS Survey", INFN QGSKY and InDARK Initiatives.

Main research topics and available thesis projects:

• Galaxy formation

  - coevolution of galaxies and supermassive black holes

  - galaxy angular momentum and size evolution

  - chemical and dust production models



• Cosmology and large-scale structure

  - cosmic reionization history

  - cross-correlation of cosmic fields

  - simulated halo and galaxy catalogs



• Gravitational Waves

  - cosmological rates of GW from compact binaries

  - multimessenger astrophysics of GW sources

  - formation of BH seed and GW emission from intermediate/extreme mass ratio inspirals



• Dark matter

  - halo statistics via excursion set formalism

  - dynamical relaxation of halos

  - analysis of galaxy rotation curves



• Galaxy clusters

  - thermodynamics of the intracluster medium

  - shocks and turbulence in cluster outskirts

  - analysis of X-ray and Sunyaev-Zel'dovich data

Early Universe and CMB Data Analysis

The Early Universe is nowadays probed with unprecedented precision by Cosmic Microwave Background (CMB) and Large Scale Structure (LSS) experiments. This poses severe challenges to our comprehension of the physical processes occurred in the Early Universe, as well as the nature of the Dark Cosmological Components. The SISSA Astrophysics group, led by Carlo Baccigalupi, Nicoletta Krachmalnicoff, Davide Poletti, has coordination roles in data analysis, pipeline preparation, data exploitation and interpretation in operating ( PolarBear, Simons Array) and planned experiments (Simons Observatory, CMB-S4, LiteBird). Also, Carlo Baccigalupi coordinates the activities on cross-correlation between CMB and LSS for the forthcoming European Space Agency satellite, Euclid.

• Measuring the amplitude of Cosmological Gravitational Waves through the B-modes of CMB polarization
• Measuring the behavior of the Dark Energy, responsible for the Cosmic Acceleration, through the Gravitational Lensing effect on CMB and LSS
• Exploiting Data Science for designing new algorithms for the analysis at all levels of the data reduction of the quoted experiments.

Stellar Structure and Evolution

Stellar evolution keeps a unique role for deciphering the visible properties of the universe, from the solar neighborhoods to the primeval galaxies. A new Renaissance for the stellar structure theory is approaching, due to the challenging results of asteroseismology, that are disclosing the invisible star's secrets, and to the beginning of the multi-messenger astronomy with the detection of gravitational waves from merging compact stellar remnants and their follow-ups.

PI: Alessandro Bressan

Main collaborators in SISSA: Guglielmo Costa (PhD student), Sabyasachi Goswami (PhD student), Milena Valentini (PhD student), Mirouh Giovanni (APC, postdoc), Luigi Danese (APC), Antonio Lanza (APC), Andrea Lapi (APC), Francesca Perrotta (APC), Paolo Salucci (APC).

Recent former students: Yang Chen (Univ. Padova), Xiaoting Fu (Univ. Bologna), Ambra Nanni (Univ. Padova), Ikechukwu Anthony Obi (Univ. Enugu, Nigeria) , Alessandra Slemer (Univ. Padova), Jing Tang (NAO, Beijing), Alessandro Trani (Univ. Tokyo).

Financial support: PRIN INAF, 2015 Euclid grant, ERC "STARKEY" (P.I. Paola Marigo, Univ. Padova).

• Stellar evolution for population synthesis studies

  - stellar physics (mixing, rotation, mass-loss, element abundances)

  - evolutionary tracks , binary evolution

  - resolved stellar populations

  - demography of compact remnants

  - gravitational waves from stellar black holes and neutron star mergers



• Stellar dust ejecta

  - dust formation in circumstellar envelopes

  - stellar populations in the mid infrared



• Spectro-photometric evolution of galaxies

  - chemical evolution of galaxies

  - effects of dust reprocessing

  - panchromatic spectra of galaxies

  - properties of the inter-stellar medium

High Energy Astrophysics

The formation and the evolution of extremely compact stellar objects and Black Holes in the Universe are signaled by exceptional phenomena such as production of particles accelerated to energies much higher than those reachable by the most powerful accelerators on Earth. Often these particles are collimated in extremely energetic jets. Extraordinary X-ray and gamma-ray luminosity is also associated with these objects. High Energy Astrophysics is devoted to study the extremely energetic phenomena occurring in the Universe, in order to understand these extraordinary cosmic settings and to test the fundamental physics at its frontiers.

• Active galactic nuclei (in coll. with Luigi Danese, Andrea Lapi)
• Accretion onto supermassive black holes (in coll. with Luigi Danese, Andrea Lapi)
• Gamma-ray bursts (in coll. with Lara Nava)
• Extragalactic backgrounds (in coll. with Luigi Danese)

Dark Matter

Dark matter is a main protagonist in Cosmology. Its presence, proven by observations, implies the existence of physics yet undiscovered, moreover such a component is likely to rule the formation and the evolution of any Cosmological Structure. In galaxies, groups and clusters of glaxies, the observed ordinary baryonic matter, gas and stars, had, over the whole history of the Universe, a complex interplay with this invisible component. The detailed lines of research are:

• The distribution of dark and visible matter in galaxies (in coll. with Andrea Lapi)
• The nature of the dark matter phenomenon: leads from observations and from galactic gamma-ray emissions and underground detections
• Ellipticals: crossroads between DM halos, their inner stellar spheroid and their central supermassive black holes (in coll. with Luigi Danese)
• The change of paradigm: from LCDM to LWDM
• Dark matter halo formation and statistics (in coll. with Andrea Lapi)

Gravitation and Gravitational Waves

Almost 100 years after Einstein introduced General Relativity, the theory still remains puzzling. Systems were gravity is strong, such as compact stars and black holes, and the phenomena taking place in their vicinity can provide new insight in both astrophysics and fundamental physics. The recent detection of Gravitational Waves from Black-Hole and Neutron Star systems opens unprecedented windows on the regime of strong gravity, and enforces the need to study emitters and progenitors in astrophysical systems. Moreover, the thorny issues of quantum gravity and potentially even classical deviations from General Relativity are most pertinent than ever.

• Astrophysics of Emitters and Progenitors (in coll. with Alessandro Bressan, Andrea Lapi)
• Alternative and Analogue Theories of gravity, Quantum Gravity and Astroparticle (see here)
• Gravitational Waves (in coll. with Enrico Barausse, Andrea Lapi)

Galaxy Clusters...

Galaxy clusters are the most recent and largest collapsed objects in the universe. Their formation and evolution rate is a strong function of the background cosmology, thus making galaxy clusters useful probes to constrain cosmological models. The formation of a galaxy cluster is a complex non-linear phenomenon which involves many physical aspects such as gravity which drives the collapse, the hydrodynamic of the baryons which are shock heated to virial temperatures by the processes of accretion and merging of substructures. Additionally, the gas can cool radiatively and subsequently form stars which in turn will return energy and metals to the gas through supernovae explosions. At virial equilibrium most of the baryons in the cluster will reside in the form of a hot X-ray emitting gas, which is commonly referred to as the intracluster medium (ICM). To follow in a self-consistent manner the complex hydrodynamical flows that take place during the evolution of the ICM it is then necessary the use of N-body/hydrodynamic codes. To this end, a Lagrangian state-of-the art parallel SPH code has been developed over the years and then applied to the study of a number of problems, such as the impact of turbulence in the ICM. Turbulent motions are expected to affect ICM properties in a variety of ways. For instance, the accuracy of cosmological constraints extracted from galaxy clusters relies on accurate measurements of their gravitating mass. X-ray estimates of cluster masses are based on the assumption of spherical symmetry and hydrostatic equilibrium. However, turbulent motions will provide additional non-thermal pressure support which will bias the hydrostatic equilibrium assumption. Additionally, non-thermal pressure support also has a significant effect on the shape and amplitude of the thermal SZ power spectrum. Finally, turbulence in the ICM has been also proposed as a possible heating source to solve the so-called cooling flow problem.

• N-body/hydrodynamical simulations of GCs
• X-ray properties of GCs
• Turbulence in GCs and Sunyaev Zel'dovich signal

Present Large Scale Structure simulations in cosmology are compared with data from existing and planned (Euclid) surveys, allowing to gain unprecedented insight into the role of hydrodynamics, the main properties and dynamics of the Dark Matter and Dark Energy, as well as to constrain Gravity Modifications. The LSS group at SISSA is active in the following directions:

• LSS, gravity modifications and screening mechanisms (in coll. with Carlo Baccigalupi, Stefano Liberati)
• Weak lensing in N-body simulations (in coll. with Carlo Baccigalupi)
• Interplay between Astrophysical Tracers, CMB lensing and Constraining Power on Dark Energy, Matter (in coll. with Carlo Baccigalupi, Andrea Lapi)
• Preparatory work for the Euclid Satellite mission for the Cross-Correlation with CMB data (in coll. with Carlo Baccigalupi, Andrea Lapi)

Astrochemistry and Astrobiology

Astrobiology is a multidisciplinary science facing one of the most fundamental topics nowadays, the origin of life. It lies at the intersection of astronomy, physics, chemistry, geology, and biology. Initially organic compounds form in the interstellar medium, and their interaction with radiation and surfaces - from grains of sand to growing planetesimals - facilitates the steady growth of complex molecules. In this way, they form chemical systems (prebiotic molecules) that can combine to create genetic material and metabolism. We focus on the search of complex organic molecules in the interstellar medium and, particularly, on the search of chiral molecules (molecules that can exist in two forms which are mirror images of each other, named enantiomers), which have a particular importance for life. Indeed, any biological system on Earth relies on key chiral molecules (sugars, aminoacids, nucleic acids) which, remarkably, exist almost exclusively as single enantiomers: homochirality seems to be a striking signature of life. The search for chiral molecules and the possible measurements of their enantiomeric excess in astronomical compounds in the ISM will proceed through the spectroscopical analysis of IR and sub-mm data from existing radiotelecopes and interferometers, such as ALMA.

Main collaborators: : Laura Silva & Giovanni Vladilo (INAF/OATS, Trieste, Italy), Marcella Massardi (INAF/IRA, Bologna, Italy), Massimo Maris (Univ. Bologna, Italy), Alessandra Magistrato (INFN Trieste, Italy)

• identification of complex organic molecules in the ALMA surveys, search for chiral molecules


• polarization-based methods to characterize an enantiomeric imbalance in an astronomical molecular cloud and development of new techniques.