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The peculiar case of the active galactic nucleus in PBC J2333.9-2343 – 17 Settembre 2018, ore 11:00 Aula Gratton

Euniversity of VALPARAISO – CHILE

Lorena Hernandez

Abstract

Under unification schemes, active galactic nuclei (AGN) can be explained by orientation effects. However, some sources show properties at different

frequencies that led to incongruent classifications and cannot be explained by such unification scheme. This is the case of PBC J2333.9-2343; its optical

pectrum is of a type 2 AGN but its X-ray spectrum does not show signs of absorption, and in the radio it has many features typical of a blazar but it is a giant

radio galaxy. Using multiwavelength simultaneous data from XMM-Newton, San Pedro Mártir telescope and VLBA, we find that these classifications cannot

be attributed to variability. We propose that PBC J2333.2343 is a blazar that has undergone a restarting activity episode in its nucleus. Interestingly, it has

changed from being a radio galaxy to become a blazar, showing an exceptional change in the direction of the jet that, by chance, occurred in the plane of the sky.

Moreover, we have analyzed Swift and New Technology Telescope (NTT) data to study the variability of the source, revealing a change in the broad line region

BLR) clouds and increasing variability at all observed wavelengths and we have detected an outflow in its optical spectra.

Area Tor Vergata – IAPS
Via Fosso Del Cavaliere, 100

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Detection of the Missing Baryons in the Warm-Hot Intergalactic Medium – 19 Settembre 2018, ore 11:00 Aula IB09

INAF – Ossrvatorio Astronomico di Roma

Fabrizio Nicastro

It has been known for decades that the observed number of baryons in the local Universe falls about 30-40% short of the total number of baryons

predicted by Big-Bang Nucleosynthesis, inferred by density fluctuations of the Cosmic Microwave Background and seen during the first 2-3 billion

years of the universe (redshift z>2-3) in the so called “Lyman-α Forest”. While theory provides a reasonable solution to this paradox, by locating

the missing baryons in hot and tenuous filamentary gas connecting galaxies, it also sanctions the difficulty of detecting them because their by far

largest constituent, hydrogen, is mostly ionized and therefore virtually invisible in ordinary signal-to-noise Far-Ultraviolet spectra. Indeed, despite

the large observational efforts, only a few marginal claims of detection have been made so far.

Here I will first review the observational efforts pursued over the past 15 years by several groups and will then present our recent results that show

that the missing baryons are indeed found in a tenuous warm-hot and moderately enriched medium that traces large concentrations of galaxies

and permeates the space between and around them. I will show that the number of OVII systems detected down to the sensitivity threshold of our

data, agrees well with numerical simulation predictions for the long-sought hot intergalactic medium, and its detection adds a fundamental tile to

the long-standing missing baryon puzzle. Finally, I will comment on the implications of these new results for future high resolution X-ray missions

(e.g. Athena).

Area Tor Vergata – IAPS – Via Fosso Del Cavaliere, 100