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Observational Astronomy
Active Galactic Nuclei/QSO in the early Universe
Multi-wavelength study and characterization of high-z quasars, from radio to X-ray bands
Supermassive black hole growth and co-evolution with their host galaxy
Radio jets in high-z quasars
Environment of high-z quasars/ Protoclusters
Quasars are one of the most powerful source in the Universe. At high redshift they serve as a direct probe of the physical conditions of the early Universe. They allow us to understand the formation and growth of the first Supermassive Black Holes (SMBHs) and their co-evolution of their host galaxy, as well as the history of the reionization process and the formation of the large scale structure (protoclusters).
The search and characterization of z>7 quasars in the Euclid data:
The search and characterization of z>7 quasars in the Euclid data:
The ESA Euclid mission has started a deep visible and near-infrared survey of ~14000 sq deg in February 2024. The huge photometric datasets provided by the survey represents the ideal ground for pushing the quasars discovery toward the highest redshifts, well beyond z=7. My work is focused to select quasars candidates in the Euclid data and to spectroscopically confirm them at the largest ground based telescopes or space facilities. In the first 1.5 yrs of survey, our High-z Quasar Work Package has already discovered 31 new quasars at z>6.6, breaking the quasar redshift record twice! and this is only the beginning!
Euclid cutouts and LBT/LUCI spectrum of EUCL J1729 (z ≈ 7.77), the most distant quasar discovered to date. Top: Euclid visible and near-infrared cutout. Middle and Bottom: The 2D and the 1D discovery spectrum. The flux of high-redshift sources at wavelengths shorter than the Ly-α emission line is strongly absorbed by the intervening HI clouds along the line of sight. The absorption feature at the position of the Ly-α line creates a drop (i.e. the Ly-α break), which can be recognised with broad-band photometry. Image taken from Yang et. al (2026, including SB).
The host galaxy of a newly discovered Euclid UV-faint quasar. Left: dust emission at 1.3mm; Right: [CII] emission tracing the properties of the Interstellar Medium. Understand how the SMBH co-evolve with the host-galaxy is an important step to constrain the stages of the formation and growth of these systems. Observations in the sub-mm (with NOEMA/ALMA) are unique tools for this goal. Image taken from Belladitta et al. (2026).
The search and characterization of high-z Radio-Loud (jetted) quasars:
The search and characterization of high-z Radio-Loud (jetted) quasars:
Radio-loud (RL) active galactic nuclei (AGN) are those SMBHs that are able to expel part of the accreting matter into two relativistic bipolar jets. They are therefore usually referred to as jetted AGN and represent ~10-15% of the total AGN population. Understanding the mechanisms responsible for the launch and the emission of these jets is of crucial importance for studying their role in SMBH accretion and evolution, and for investigating their feedback on the intergalactic medium.
High-redshift RL quasars (QSOs) are indispensable tools for studying the early evolutionary stage of the first jetted SMBHs, their feedback on the host galaxy and the environment, and their contribution to the re-ionization epoch.
A systematic search for these objects and their subsequent multi-wavelength study is necessary to better constrain the properties of jetted SMBHs in the first giga-years following the Big Bang.
In an effort to enlarge the current sample of high-z RL QSOs, I am conducting different projects that combines optical (PanSTARRS, DES, DESI, Decals), infrared (WISE, UKIDSS, UHS, VIKING, VHS), and radio (NVSS, RACS, LOFAR, VLASS, EMU) datasets to identify distant radio sources all over the sky, by using the so-called dropout technique.
After their identification with spectroscopic follow up, a multi-wavelength analysis is necessary to reveal the properties of high-z RL QSOs and compare then to the lower redshift population. In my research I am particularly interested in radio and X-ray properties, the two spectral bands that trace the emission of the relativistic jet.
Radio
Radio
Analysis of radio images and archival radio data.
Estimation of radio-loudness (a parameter that described the intensity of the radio emission with respect to the optical one), radio spectral index (that provides information on the jet orientation), and radio luminosity.
Study the jet structures at different scales, thanks to the collaboration with radio-astronomers at IRA-Bologna (Dr. Cristiana Spingola and Prof. Daniele Dallacasa).
Figure: Radio jet of PSOJ0309+27, a blazar at z=6.1, observed with the Very Long Baseline Array (VLBA); image credit: Spingola et al. 2020 / Bill Saxton NRAO/AUI/NSF
X-ray
X-ray
Analysis of the X-ray data.
Estimation of X-ray jet propertises
Study of X-ray kpc jets
Collaboration with eROSITA members
Figure: Rest frame spectral energy distribution of PSO J0309+27 from radio to X-rays frequencies. The X-ray emission (green butterfly) is stronger with respect to the emission coming from a X-ray corona (red area).
SMBH mass
SMBH mass
Estimation of the central black hole mass by using the so-called Single Epoch (i.e. virial) method, thanks to the detection and analysis of broad emission lines (like CIV and MgII); estimation of the Eddington ratio, bolometric luminosity, lines parameters
Figure: Double Gaussian fit of the CIV emission line detected for PSOJ0309+27 with LBT/LUCI instrument which allow the estimation of its SMBH mass.
The environment of z>6 Radio-Loud quasars
The environment of z>6 Radio-Loud quasars
RL AGN are commonly found in rich environments at different cosmic epochs. Galaxies over-densities around both low-z (z∼0.5-2) and high-z (z∼3-5.8) RL AGN have been found by several authors. Theoretical models strongly support a preferential over-dense environment around RL AGN. All these results suggest that the presence of a relativistic jet may indeed be preferentially triggered in dense environments.
Therefore luminous radio sources are good beacons for finding protoclusters of galaxies at high redshifts.
With the aim of tracing the earliest stages of protocluster evolution in RL AGN field at the highest redshift, we started a pilot project to study the environment of z>6 RL QSOs: PSO J0309+27 at z=6.1 and ILTJ1037+40 at z=6.07, a blazar and a blazar candidate, respectively. We use LBT/LBC to imaging the field of these two QSOs in r,i, and z filter, with the aim of selectng candidates Lyman-Break Galaxies through the color-color technique (r-i vs i-z colours).
This project is in collaboration with M. Mignoli, R. Gilli, F. Vito and R. Decarli at INAF-OAS (Bologna) , with Prof. C. Mazzucchelli at Universidad Diego Portales (Chile) and with Maria Chillaron Victor (phd student at Complutense University of Madrid).
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