arXiv subjects

Samuele Campitiello

Publications and source records attributed to Samuele Campitiello.

4 recordsLinked to original sources

arXiv2021

Toward measuring the spin of obscured supermassive black holes: a critical assessment with disk megamasers

Mass and spin are two fundamental properties of astrophysical black holes. While some established, indirect methods are adopted to measure both these properties of active galactic nuclei (AGN) when viewed relatively face-on, very few suggested methods exist to measure these properties when AGN are viewed highly inclined and potentially obscured by large amounts of gas. In this context, we explore the accuracy and performance of a recently proposed method to estimate the spin of AGN through fitting their accretion disk spectral energy distribution, when adapted for highly inclined and obscured systems, and in particular to a sample of six, local water megamasers. For these sources, both the accretion rate and inclination angle are known, allowing us to rely only on the AGN bolometric luminosity to infer their spin. Using the bolometric luminosity as a proxy for the accretion disk peak luminosity, we derive the expected bolometric luminosity as a function of spin. Then, we measure the bolometric luminosity of each source through X-ray spectroscopy, and compare it with the expected value to constrain the spin of the AGN. The quality of the constraints depend critically on the accuracy of the measured bolometric luminosity, which is difficult to estimate in heavily obscured systems. Three out of six sources do not show consistency between the expected and measured bolometric luminosities, while other three (four, when considering the [OIII] line as tracer of the bolometric luminosity) are formally consistent with high spin values. Our results suggest that this method, although promising (and possibly considered as a future calibrator for other methods) needs better observational data and further theoretical modeling to be successfully applied to obscured AGN and to infer robust results.

astro-ph.GA↗

arXiv2021

The disk-torus system in active galactic nuclei: possible evidence of highly spinning black holes

We study the ratio $R$ between the luminosity of the torus and that of the accretion disk, inferred from the relativistic model KERRBB for a sample of approximately 2000 luminosity-selected radio-quiet Type I active galactic nuclei from the Sloan Digital Sky Survey catalog. We find a mean ratio $R \approx 0.8$ and a considerable number of sources with $R \gtrsim 1$. Our statistical analysis regarding the distribution of the observed ratios suggests that the largest values might be linked to strong relativistic effects due to a large black hole spin ($a > 0.8$), despite the radio-quiet nature of the sources. The mean value of $R$ sets a constraint on the average torus aperture angle (in the range $30^{\circ} < θ_{\rm T} < 70^{\circ}$) and, for about one-third of the sources, the spin must be $a > 0.7$. Moreover, our results suggest that the strength of the disk radiation (i.e., the Eddington ratio) could shape the torus geometry and the relative luminosity ratio $R$. Given the importance of the involved uncertainties on this statistical investigation, an extensive analysis and discussion have been made to assess the robustness of our results.

astro-ph.HE↗

arXiv2020

Estimating black hole masses: Accretion disk fitting versus reverberation mapping and single epoch

We selected a sample of 28 Type 1 AGNs for which a black hole mass has been inferred using the reverberation mapping technique and single epoch scaling relations. All 28 sources show clear evidence of the "Big Blue Bump" in the optical-UV band whose emission is produced by an accretion disk (AD) around a supermassive black hole. We fitted the spectrum of these sources with the relativistic thin AD model KERRBB in order to infer the black hole masses and compared them with those from Reverberation mapping and Single epoch methods, discussing the possible uncertainties linked to such a model by quantifying their weight on our results. We find that for the majority of the sources, KERRBB is a good description of the AD emission for a wide wavelength range. The overall uncertainty on the black hole mass estimated through the disk fitting procedure is $\sim 0.45$ dex (which includes the uncertainty on fitting parameters such as e.g. spin and viewing angle), comparable to the systematic uncertainty of reverberation mapping and single epoch methods; however, such an uncertainty can be $\leq 0.3$ dex if one of the parameters of the fit is well constrained. Although all of the estimates are affected by large uncertainties, the masses inferred using the three methods are compatible if the dimensionless scale factor $f$ (linked to the unknown kinematics and geometry of the Broad Line Region) is assumed to be larger than one. For the majority of the sources, the comparison between the results coming from the three methods favors small spin values. To check the goodness of the KERRBB results, we compared them with those inferred with other models, such as AGNSED, a model that also accounts for the emission originating from an X-ray corona: using two sources with a good data coverage in the X band, we find that the masses estimated with the two models differ at most by a factor of $\sim 0.2$ dex.

astro-ph.HE↗

arXiv2019

Black hole mass and spin estimates of the most distant quasars

We investigate the properties of the most distant quasars ULASJ134208.10+092838.61 ($z = 7.54$), ULASJ112001.48+064124.3 ($z = 7.08$) and DELSJ003836.10-152723.6 ($z = 7.02$) studying their Optical-UV emission that shows clear evidence of the presence of an accretion disk. We model such emission applying the relativistic disk models KERRBB and SLIMBH for which we have derived some analytical approximations to describe the observed emission as a function of the black hole mass, accretion rate, spin and the viewing angle. We found that: 1] our black hole mass estimates are compatible with the ones found using the virial argument but with a smaller uncertainty; 2] assuming that the virial argument is a reliable method to have a black hole mass measurement (with no systematic uncertainties involved), we found an upper limit for the black hole spin of the three sources: very high spin values are ruled out; 3] our Eddington ratio estimates are smaller than those found in previous studies by a factor $\sim 2$: all sources are found to be sub-Eddington. Using our results, we explore the parameter space (efficiency, accretion rate) to describe the possible evolution of the black hole assuming a $\sim 10^{2-4} M_{\odot}$ seed: if the black hole in these sources formed at redshift $z = 10 - 20$, we found that the accretion has to proceed at the Eddington rate with a radiative efficiency $η\sim 0.1$ in order to reach the observed masses in less than $\sim 0.7$ Gyr.

astro-ph.HE↗