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Over the past decade, the IceCube Neutrino Observatory has detected a few hundreds of high-energy (HE) neutrinos from cosmic sources. Despite numerous studies searching for their origin, it is still not known which source populations emit them. A few confident individual associations exist with active galactic nuclei (AGN), mostly with blazars which are jetted AGN whose jet points in our direction. Nonetheless, on a population level, blazar-neutrino correlation strengths are rather weak. To definitively answer if jetted AGN systematically emit >~100 TeV neutrinos: (1) we compiled the largest catalog of blazars and their optical light curves to date; and (2) we searched for a spatio-temporal correlation between these blazar light curves and IceCube’s first catalog of >~100 TeV neutrino events while assuming that neutrinos are expected at the brightest optical outbursts. Under this phenomenological assumption, we found that a global blazar-neutrino correlation cannot be confidently established, inline with the result of our previous study in the radio band. We estimated that fewer than ~8% of >~100TeV neutrino events came from major blazar outbursts, alluding to substantial contributions from other systems. In my talk, I will present this state-of-the-art correlation study and outlook for further searches with next generation of instruments.

Speaker: Alberto Traina (INAF-OAS Bologna)

Title: SMBHs growth in overdense environments: AGN enhancement in protoclusters with enormous Ly⍺ nebulae

Abstract: SMBHs are almost ubiquitous in galaxies’ nuclei in the local and in the high-redshift Universe. However, the formation and growth processes that lead to such massive objects in relatively short timescales are still unclear. A crucial role in accelerating their evolution may be played by the surrounding environment: large quantities of gas and higher merger rates are key to understand how their growth occurs. Protoclusters of galaxies, the precursors of today’s galaxy clusters, represent the perfect laboratories to investigate this effect at high redshift. The hunt for the SMBHs population in protoclusters and its characterization requires a multi-wavelength effort to obtain a complete census: in this perspective the X-rays represent the best channel to investigate the AGN activity, even in the most obscured conditions. In this talk, I will present recent deep (>200ks) Chandra observations targeting three protoclusters at z ~ 2-3, that host enormous Ly⍺ nebulae. I will discuss the spectral properties of the detected AGN as well as the effects of overdense environment on the growth of SMBHs. In particular, I will show the fraction of AGN and the X-ray luminosity functions of the protoclusters, which are significantly larger (1 – 2 dex!) than those of their local counterparts. I will present new results on how the enhancement of SMBHs in overdense environments (x10 larger than SMGs) suggests that protoclusters are indeed optimal sites for promoting their growth. Finally, I will show preliminary results on the growth of SMBHs in hydrodynamical cosmological simulations.