arXiv subjects

Francesco Ziparo

Publications and source records attributed to Francesco Ziparo.

4 recordsLinked to original sources

arXiv2026

A Selection Aware View of Black Hole-Galaxy Coevolution at High Redshift

The large population of broad-line Active Galactic Nuclei (AGN) observed with the James Webb Space Telescope (JWST) at $z \gtrsim 4$ opens a new window onto the black hole-galaxy connection in the first Gyr of cosmic history. We use the JADES survey-level dataset and develop a forward-modeling Bayesian framework that explicitly accounts for broad H$\alpha$ detectability, ensuring that selection effects are incorporated into the likelihood function. With this approach, we constrain the black hole-stellar mass ($M_{\mathrm{BH}}$-$M_\star$) relation to be $\log M_{\rm BH} = -4.06^{+0.50}_{-0.51} + 1.17^{+0.06}_{-0.06}\,\log M_\star$, with an intrinsic orthogonal scatter of $\sigma_{\rm int} = 0.63^{+0.14}_{-0.11}$ dex. The slope and normalization are consistent with local determinations, indicating that the average scaling was already established by $z \sim 4$-6. This suggests that the primary evolution of the relation occurs in its dispersion rather than in its mean normalization. In contrast, the substantially larger intrinsic scatter relative to the nearby Universe reveals a wider diversity of black hole-galaxy growth histories, likely driven by bursty accretion, delayed feedback, and differences in merger or seeding histories. Future JWST samples will be crucial to test whether this increased scatter is a persistent feature of the high-redshift Universe.

astro-ph.GA↗

arXiv2024

Primordial black holes as supermassive black holes seeds

The presence of supermassive black holes (SMBHs, $M_{\bullet}\sim 10^{6-10}~M_{\odot}$) in the first cosmic Gyr ($z\gtrsim 6$) challenges current models of BH formation and evolution. We propose a novel mechanism for the formation of early SMBH seeds based on primordial black holes (PBHs). We assume a non-Gaussian primordial power spectrum as expected in inflationary models; these scenarios predict that PBHs are initially clustered and preferentially formed in the high-$\sigma$ fluctuations of the large-scale density field, out of which dark matter (DM) halos are originated. Our model accounts for (i) PBH accretion and feedback, (ii) DM halo growth, and (iii) gas dynamical friction. PBHs lose angular momentum due to gas dynamical friction, sink into a dense core, where BH binaries form and undergo a runaway merger, eventually leading to the formation of a single, massive seed. This mechanism starts at $z\sim 20-40$ in rare halos ($M_h\sim 10^7\ M_\odot$ corresponding to $\sim 5-7\sigma$ fluctuations), and provides massive ($\sim 10^{4-5}~ M_{\odot}$) seeds by $z\sim 10-30$. We derive a physically-motivated seeding prescription that provides the mass of the seed, $ M_{\rm seed}(z)=3.1\times 10^{5}\ { M_{\odot}}[(1+z)/10]^{-1.2}$, and seeded halo, $ M_{h}(z)=2\times 10^{9}\ {M_{\odot}}[(1+z)/10]^{-2}e^{-0.05z}$ as a function of redshift. This seeding mechanism requires that only a small fraction of DM is constituted by PBHs, namely $f_{\rm PBH}\sim 3 \times 10^{-6}$. We find that $z\sim 6-7$ quasars can be explained with $6\times 10^4 M_{\rm \odot}$ seeds planted at $z\sim 32$, and growing at sub-Eddington rates, $\langle\lambda_{\rm E}\rangle\sim 0.55$. The same scenario reproduces the BH mass of GNz11 at $z=10.6$, while UHZ1 ($z=10.1$) and GHZ9 ($z=10$) data favour instead slightly later ($z\sim 20-25$), more massive ($10^5~M_{\rm \odot}$) seeds. [Abridged]

astro-ph.CO↗

arXiv2023

Blue Monsters. Why are JWST super-early, massive galaxies so blue?

The recent JWST tentative discovery of a population of super-early (redshift $z> 10$), relatively massive (stellar mass $M_* = 10^{8-9} M_{\odot}$) and evolved (metallicity $Z \approx 0.1 Z_{\odot}$) galaxies, which nevertheless show blue ($β\simeq -2.6$) spectra, and very small dust attenuation ($A_{\rm V} \leq 0.02$), challenges our interpretation of these systems. To solve the puzzle we propose two solutions in which dust is either (a) ejected by radiation pressure, or (b) segregated with respect to UV-emitting regions. We clarify the conditions for which the two scenarios apply, and show that they can be discriminated by ALMA observations, such as the recent non-detection of the $88μm$ dust continuum in GHZ2 ($z\simeq 12$) favouring dust ejection.

astro-ph.GA↗

arXiv2022

Cosmic radiation backgrounds from primordial black holes

Recent measurements of the cosmic X-ray and radio backgrounds (CXB/CRB, respectively) obtained with Chandra and ARCADE2 report signals in excess of those expected from known sources, suggesting the presence of a yet undiscovered population of emitters. We investigate the hypothesis that such excesses are due to primordial black holes (PBHs) which may constitute a substantial fraction of dark matter (DM). We present a novel semi-analytical model which predicts X-ray and radio emission due to gas accretion onto PBHs, assuming that they are distributed both inside DM halos and in the intergalactic medium (IGM). Our model includes a self-consistent treatment of heating/ionization feedback on the surrounding environment. We find that (i) the emission from PBHs accreting in the IGM is subdominant at all times ($1\% \leq I_{\rm IGM}/I_{\rm tot} \leq 40\% $); (ii) most of the CXB/CRB emission comes from PBHs in DM mini-halos ($M_h \leq 10^6\ M_{\odot}$) at early epochs ($z>6$). While a small fraction ($f_{\rm PBH} \simeq 0.3\%$) of DM in the form of PBHs can account for the total observed CXB excess, the CRB one cannot be explained by PBHs. Our results set the strongest existing constraint on $ f_{\rm PBH} \leq 3\times 10^{-4}\ (30/M_{\rm PBH})$ in the mass range $1-1000\, M_\odot$. Finally, we comment on the implications of our results on the global $\rm H_I$ 21cm signal.

astro-ph.CO↗