***********************************************************
OATS-UNI/TS SEMINAR
***********************************************************
Speaker: Isabella Prandoni (INAF - IRA Bologna)

Title: Current and Next-Generation Deep Radio Surveys: probing AGN activity down to the radio-quiet AGN regime
Date: Thursday, April 3rd, 2014
Time: 11:30
Venue: Villa Bazzoni
***********************************************************
Abstract To properly understand the detailed process of galaxy formation and evolution - indeed even to explain the most basic parameters such as the galaxy luminosity function - there is an urgent need to identify and quantify the role of AGN feedback. Completing the census of AGN activity, especially at redshifts where most of the accretion occurred, is therefore essential in order to understand the physical link between supermassive black-holes (SMBH) and galaxies, and their cosmic co-evolution. In particular we need to identify the contribution of obscured accretion activity in bolometric surveys and quantify its impact on the evolution of star formation. The two main processes that contribute to the extragalactic continuum radio emission at 1.4 GHz are the non-thermal emission associated with relativistic electrons powered by active galactic nuclei (AGNs) and the synchrotron emission from relativistic electrons in supernova remnants. The latter is therefore a tracer of star formation activity in galaxies. While the bright radio sky is dominated by the emission driven by radio-loud (RL) AGNs, at fainter flux densities (0.5-1 mJy) the contribution from star-forming galaxies (SFGs) becomes increasingly important. Moreover, recent work has revealed the presence of a third population of sources at 10-100 microJy levels, the radio-quiet (RQ) AGNs. The unexpected detection of large numbers of RQ AGNs, traditionally studied at optical/IR or X-ray wavelengths, opens new exciting perspectives for deep continuum-radio surveys, providing a unique and powerful dust/gas-obscuration-free tool to get a global census of both star formation and AGN activity up to high redshifts; hence tracing the apparently simultaneous development of the stellar populations and the black hole growth in the first massive galaxies. It is worth to note that RQ AGNs show the presence of AGN activity in one or more bands of the electromagnetic spectrum (e.g., optical, mid-infrared, X-ray), while the origin of their radio emission is hotly debated. It can originate from star formation, low level AGN activity or, more interestingly, from a combination of the two processes. In the lead-up to the SKA, several new-generation radio telescopes and upgrades are coming on line around the world, including APERTIF (The Netherlands), eMERLIN (UK), EVLA (USA), e-EVN (based in Europe), LOFAR (The Netherlands), MWA (Australia), and the two SKA precursors: ASKAP (Australia) and Meerkat (South Africa). Large and/or deep continuum surveys are ongoing or being planned for many of these telescopes. Such surveys will allow us to observationally address the AGN role in galaxy evolution in incremental steps. I will discuss our current understanding of the the physical properties of faint radio-selected AGNs, based on the exploitation of multi-wavelength information available for several deep radio fields, and the role that the SKA and its pathfinders can play in answering the several open questions in this research field, including the nature of RQ AGN radio emission. In addition, I will briefly outline the ongoing work at international level to fine-tune the design of the SKA, in order to optimize it for continuum extra-galactic surveys. In particular I will discuss the issue of spatial resolution, which appears to be critical for a variety of science cases (from AGN/SFG studies to weak lensing).
***********************************************************
Contact: Stefano Borgani (OATs)