arXiv subjects

S. Marchesi

Publications and source records attributed to S. Marchesi.

At least 37 records · Page 2Linked to original sources

arXiv2022

Identifying the 3FHL Catalog. VI. Swift Observations of 3FHL Unassociated Objects with Source Classification via Machine Learning

The Third Catalog of Hard Fermi Large Area Telescope Sources (3FHL) reports the detection of 1556 objects at E > 10 GeV. However, 177 sources remain unassociated and 23 are associated with a ROSAT X-ray detection of unknown origin. Pointed X-ray observations were conducted on 30 of these unassociated and unknown sources with Swift-XRT. A bright X-ray source counterpart was detected in 21 out of 30 fields. In five of these 21 fields, we detected more than one X-ray counterpart, totaling 26 X-ray sources analyzed. Multiwavelength data was compiled for each X-ray source detected. We find that 21 out of the 26 X-ray sources detected display the multiwavelength properties of blazars, while one X-ray source displays the characteristics of a Galactic source. Using trained decision tree, random forest, and support vector machine models, we predict all 21 blazar counterpart candidates to be BL Lacertae objects (BL Lacs). This is in agreement with BL Lacs being the most populous source class in the 3FHL.

astro-ph.HE↗

arXiv2022

A deep 1.4 GHz survey of the J1030 equatorial field: a new window on radio source populations across cosmic time

We present deep L-Band observations of the equatorial field centered on the z=6.3 SDSS QSO, reaching a 1 sigma sensitivity of ~2.5 uJy at the center of the field. We extracted a catalog of 1489 radio sources down to a flux density of ~12.5 uJy (5 sigma) over a field of view of ~ 30' diameter. We derived the source counts accounting for catalog reliability and completeness, and compared them with others available in the literature. Our source counts are among the deepest available so far, and, overall, are consistent with recent counts' determinations and models. We detected for the first time in the radio band the SDSS J1030+0524 QSO (26 +/- 5 uJy). We derived its optical radio loudness R_O = 0.62 +/- 0.12, which makes it the most radio quiet AGN at z >~ 6 discovered so far and detected at radio wavelengths. We unveiled extended diffuse radio emission associated with the lobes of a bright FRII radio galaxy located close to the center of the J1030 field, which is likely to become the future BCG of a protocluster at z=1.7. The lobes' complex morphology, coupled with the presence of X-ray diffuse emission detected around the FRII galaxy lobes, may point toward an interaction between the radio jets and the external medium. We also investigated the relation between radio and X-ray luminosity for a sample of 243 X-ray-selected objects obtained from 500 ks Chandra observations of the same field, and spanning a wide redshift range (0 ~< z ~< 3). Focused on sources with a spectroscopic redshift and classification, we found that sources hosted by ETG and AGN follow Log(L_R)/Log(L_X) linear correlations with slopes of ~0.6 and ~0.8, respectively. This is interpreted as a likely signature of different efficiency in the accretion process. Finally, we found that most of these sources (>~87%) show a radio-to-X-ray radio loudness R_X < -3.5, classifying these objects as radio quiet.

astro-ph.GA↗

arXiv2022

X-ray spectral and timing analysis of the Compton Thick Seyfert 2 galaxy NGC 1068

We present the timing and spectral analysis of the Compton Thick Seyfert 2 active galactic nuclei NGC 1068 observed using {\it NuSTAR} and {\it XMM-Newton}. In this work for the first time we calculated the coronal temperature ($\rm{kT_{e}}$) of the source and checked for its variation between the epochs if any. The data analysed in this work comprised of (a) eight epochs of observations with {\it NuSTAR} carried out during the period December 2012 to November 2017, and, (b) six epochs of observations with {\it XMM-Newton} carried out during July 2000 to February 2015. From timing analysis of the {\it NuSTAR} observations, we found the source not to show any variations in the soft band. However, on examination of the flux at energies beyond 20 keV, during August 2014 and August 2017 the source was brighter by about 20\% and 30\% respectively compared to the mean flux of the three 2012 {\it NuSTAR} observations as in agreement with earlier results in literature. From an analysis of {\it XMM-Newton} data we found no variation in the hard band (2 $-$ 4 keV) between epochs as well as within epochs. In the soft band (0.2 $-$ 2 keV), while the source was found to be not variable within epochs, it was found to be brighter in epoch B relative to epoch A. By fitting physical models we determined $\rm{kT_{e}}$ to range between 8.46$^{+0.39}_{-0.66}$ keV and 9.13$^{+0.63}_{-0.98}$ keV. From our analysis, we conclude that we found no variation of $\rm{kT_{e}}$ in the source.

astro-ph.HE↗

arXiv2022

A New Emulated Monte Carlo Radiative Transfer Disk-Wind Model: X-Ray Accretion Disk-wind Emulator -- XRADE

We present a new X-Ray Accretion Disk-wind Emulator (\textsc{xrade}) based on the 2.5D Monte Carlo radiative transfer code which provides a physically-motivated, self-consistent treatment of both absorption and emission from a disk-wind by computing the local ionization state and velocity field within the flow. \textsc{xrade} is then implemented through a process that combines X-ray tracing with supervised machine learning. We develop a novel emulation method consisting in training, validating, and testing the simulated disk-wind spectra into a purposely built artificial neural network. The trained emulator can generate a single synthetic spectrum for a particular parameter set in a fraction of a second, in contrast to the few hours required by a standard Monte Carlo radiative transfer pipeline. The emulator does not suffer from interpolation issues with multi-dimensional spaces that are typically faced by traditional X-ray fitting packages such as \textsc{xspec}. \textsc{xrade} will be suitable to a wide number of sources across the black-hole mass, ionizing luminosity, and accretion rate scales. As an example, we demonstrate the applicability of \textsc{xrade} to the physical interpretation of the X-ray spectra of the bright quasar PDS 456, which hosts the best-established accretion-disk wind observed to date. We anticipate that our emulation method will be an indispensable tool for the development of high-resolution theoretical models, with the necessary flexibility to be optimized for the next generation micro-calorimeters on board future missions, like \textit{XRISM/resolve} and \textit{Athena/X-IFU}. This tool can also be implemented across a wide variety of X-ray spectral models and beyond.

astro-ph.HE↗

arXiv2022

Supermassive Black Holes at High Redshift are Expected to be Obscured by their Massive Host Galaxies' Inter Stellar Medium

We combine results from deep ALMA observations of massive ($M_*>10^{10}\;M_{\odot}$) galaxies at different redshifts to show that the column density of their inter stellar medium (ISM) rapidly increases towards early cosmic epochs. Our analysis includes objects from the ASPECS and ALPINE large programs, as well as individual observations of $z\sim 6$ QSO hosts. When accounting for non-detections and correcting for selection effects, we find that the median surface density of the ISM of the massive galaxy population evolves as $\sim(1+z)^{3.3}$. This means that the ISM column density towards the nucleus of a $z>3$ galaxy is typically $>100$ times larger than locally, and it may reach values as high as Compton-thick at $z\gtrsim6$. Remarkably, the median ISM column density is of the same order of what is measured from X-ray observations of large AGN samples already at $z\gtrsim2$. We develop a simple analytic model for the spatial distribution of ISM clouds within galaxies, and estimate the total covering factor towards active nuclei when obscuration by ISM clouds on the host scale is added to that of pc-scale circumnuclear material (the so-called 'torus'). The model includes clouds with a distribution of sizes, masses, and surface densities, and also allows for an evolution of the characteristic cloud surface density with redshift, $Σ_{c,*}\propto(1+z)^γ$. We show that, for $γ=2$, such a model successfully reproduces the increase of the obscured AGN fraction with redshift that is commonly observed in deep X-ray surveys, both when different absorption thresholds and AGN luminosities are considered. Our results suggest that 80-90\% of supermassive black holes in the early Universe ($z>6-8$) are hidden to our view, primarily by the ISM in their hosts. [abridged]

astro-ph.GA↗

arXiv2022

The molecular gas properties in local Seyfert 2 galaxies

We present a multi-wavelength study of the molecular gas properties of a sample of local Seyfert 2 galaxies to assess if, and to what extent, the presence of an active galactic nucleus (AGN) can affect the Interstellar Medium (ISM) properties in a sample of 33 local Seyfert 2 galaxies. We compare the molecular gas content (MH2), derived from new and archival low-J CO line measurements of a sample of AGN and a control sample of star-forming galaxies (SFGs). Both the AGN and the control sample are characterised in terms of host-galaxy properties (e.g., stellar and dust masses, Mstar and Mdust, respectively; and star formation rate, SFR). We also investigate the effect of AGN activity onto the emission of polycyclic aromatic hydrocarbon (PAH) molecules in the mid-infrared (MIR), a waveband where the dust-reprocessed emission from the obscured AGN contributes the most. The AGN hosted in less massive galaxies (i.e., log(Mstar/Msun)<10.5; log(Mdust/Msun)<7.5) show larger molecular gas content with respect to SFGs matched in stellar and dust mass. When comparing their depletion time(tdep~MH2/SFR), AGN show tdep~0.3-1.0 Gyr, similar to those observed in the control sample of SFGs. Seyfert 2 galaxies show fainter PAH luminosity at increasingly larger dominance of the nuclear activity in the MIR. We find no clear evidence for a systematic reduction of the molecular gas reservoir at galactic scale in Seyfert galaxies with respect to SFGs. This is in agreement with recent studies showing that molecular gas content only is reduced in regions of sub-kpc size, where the emission from the accreting supermassive black hole dominates. Nonetheless, we show that the impact of AGN activity on the ISM is clearly visible as suppression of the PAH luminosity.

astro-ph.GA↗

arXiv2021

Multi-Wavelength Study of a Proto-BCG at z = 1.7

In this work we performed a spectral energy distribution (SED) analysis in the optical/infrared band of the host galaxy of a proto-brightest cluster galaxy (BCG, NVSS J103023+052426) in a proto-cluster at z = 1.7. We found that it features a vigorous star formation rate (SFR) of ${\sim}$570 $\mathrm{M_{\odot}}$/yr and a stellar mass of $M_{\ast} \sim 3.7 \times 10^{11}$ $\mathrm{M_{\odot}}$; the high corresponding specific SFR = $1.5 \pm 0.5$ $\mathrm{Gyr^{-1}}$ classifies this object as a starburst galaxy that will deplete its molecular gas reservoir in $\sim$ $3.5 \times 10^8$ yr. Thus, this system represents a rare example of a proto-BCG caught during the short phase of its major stellar mass assembly. Moreover, we investigated the nature of the host galaxy emission at 3.3 mm. We found that it originates from the cold dust in the interstellar medium, even though a minor non-thermal AGN contribution cannot be completely ruled out. Finally, we studied the polarized emission of the lobes at 1.4 GHz. We unveiled a patchy structure where the polarization fraction increases in the regions in which the total intensity shows a bending morphology; in addition, the magnetic field orientation follows the direction of the bendings. We interpret these features as possible indications of an interaction with the intracluster medium. This strengthens the hypothesis of positive AGN feedback, as inferred in previous studies of this object on the basis of X-ray/mm/radio analysis. In this scenario, the proto-BCG heats the surrounding medium and possibly enhances the SFR in nearby galaxies.

astro-ph.GA↗

arXiv2021

Compton-Thick AGN in the NuSTAR era VI: The observed Compton-thick fraction in the Local Universe

We present the analysis of simultaneous NuSTAR and XMM-Newton data of 8 Compton-thick (CT-) active galactic nuclei (AGN) candidates selected in the Swift-Burst Alert Telescope (BAT) 100 month survey. This work is part of an ongoing effort to find and characterize all CT-AGN in the local ($z\leq$0.05) Universe. We used two physically motivated models, MYTorus and borus02, to characterize the sources in the sample, finding 5 of them to be confirmed CT-AGN. These results represent an increase of $\sim19$% over the previous NuSTAR-confirmed, BAT-selected CT-AGN at $z\leq0.05$, bringing the total number to 32. This corresponds to an observed fraction of $\sim 8$\% of all AGN within this volume-limited sample, although it increases to $20\pm5$% when limiting the sample to $z\leq0.01$. Out of a sample of 48 CT-AGN candidates, selected using BAT and soft (0.3$-$10 keV) X-ray data, only 24 are confirmed as CT-AGN with the addition of the NuSTAR data. This highlights the importance of NuSTAR when classifying local obscured AGN. We also note that most of the sources in our full sample of 48 Seyfert 2 galaxies with NuSTAR data have significantly different line-of-sight and average torus column densities, favouring a patchy torus scenario.

astro-ph.GA↗

arXiv2021

Identifying the 3FHL catalog: V. Results of the CTIO-COSMOS optical spectroscopy campaign 2019

As a follow-up of the optical spectroscopic campaign aimed at achieving completeness in the Third Catalog of Hard Fermi-LAT Sources (3FHL), we present here the results of a sample of 28 blazars of uncertain type observed using the 4m telescope at Cerro Tololo Inter-American Observatory (CTIO) in Chile. Out of these 28 sources, we find that 25 are BL Lacertae objects (BL Lacs) and 3 are Flat Spectrum Radio Quasars (FSRQs). We measure redshifts or lower limits for 16 of these blazars, whereas it is observed that the 12 remaining blazars have featureless optical spectra. These results are part of a more extended campaign of optical spectroscopy follow-up of 3FHL blazars, where until now 51 blazars of uncertain type have been classified into BL Lac and FSRQ categories. Further, this campaign has resulted in redshift measurements and lower limits for 15 of these sources. Our results contribute towards attaining a complete sample of blazars above 10 GeV, which then will be crucial in extending our knowledge on blazar emission mechanisms and the extragalactic background light.

astro-ph.HE↗

arXiv2021

The properties of the AGN torus as revealed from a set of unbiased NuSTAR observations

The obscuration observed in active galactic nuclei (AGN) is mainly caused by dust and gas distributed in a torus-like structure surrounding the supermassive black hole (SMBH). However, properties of the obscuring torus of the AGN in X-ray have not been fully investigated yet due to the lack of high-quality data and proper models. In this work, we perform a broadband X-ray spectral analysis of a large, unbiased sample of obscured AGN (with line-of-sight column density 23$\le$log(NH)$\le$24) in the nearby universe which has high-quality archival NuSTAR data. The source spectra are analyzed using the recently developed borus02 model, which enables us to accurately characterize the physical and geometrical properties of AGN obscuring tori. We also compare our results obtained from the unbiased Compton thin AGN with those of Compton-thick AGN. We find that Compton thin and Compton-thick AGN may possess similar tori, whose average column density is Compton thick (N$\rm _{H,tor,ave}$ $\sim$1.4$\times$10$^{24}$ cm$^{-2}$), but they are observed through different (under-dense or over-dense) regions of the tori. We also find that the obscuring torus medium is significantly inhomogeneous, with the torus average column densities significantly different from their line-of-sight column densities (for most of the sources in the sample). The average torus covering factor of sources in our unbiased sample is c$_f$=0.67, suggesting that the fraction of unobscured AGN is $\sim$33%. We develop a new method to measure the intrinsic line-of-sight column density distribution of AGN in the nearby universe, which we find the result is in good agreement with the constraints from recent population synthesis models.

astro-ph.GA↗

arXiv2020

NuSTAR Survey of Obscured Swift/BAT-selected Active Galactic Nuclei: II. Median High-energy Cutoff in Seyfert II Hard X-ray Spectra

Broadband X-ray spectroscopy of the X-ray emission produced in the coronae of active galactic nuclei (AGN) can provide important insights into the physical conditions very close to their central supermassive black holes. The temperature of the Comptonizing plasma that forms the corona is manifested through a high-energy cutoff that has been difficult to directly constrain even in the brightest AGN because it requires high-quality data at energies above 10 keV. In this paper we present a large collection of coronal cutoff constraints for obscured AGN based on a sample of 130 AGN selected in the hard X-ray band with Swift/BAT and observed nearly simultaneously with NuSTAR and Swift/XRT. We find that under a reasonable set of assumptions regarding partial constraints the median cutoff is well constrained to 290$\pm$20 keV, where the uncertainty is statistical and given at the 68% confidence level. We investigate the sensitivity of this result to our assumptions and find that consideration of various known systematic uncertainties robustly places the median cutoff between 240 keV and 340 keV. The central 68% of the intrinsic cutoff distribution is found to be between about 140 keV and 500 keV, with estimated uncertainties of 20 keV and 100 keV, respectively. In comparison with the literature, we find no clear evidence that the cutoffs in obscured and unobscured AGN are substantially different. Our analysis highlights the importance of carefully considering partial and potentially degenerate constraints on the coronal high-energy cutoff in AGN.

astro-ph.HE↗

arXiv2020

Gamma-ray emission revealed at the western edge of SNR G344.7-0.1

We report on the investigation of a very high energy (VHE), Galactic gamma-ray source recently discovered at >50GeV using the Large Area Telescope (LAT) on board the Fermi Gamma-Ray Space Telescope. This object, 2FHL J1703.4-4145, displays a very hard >50GeV spectrum with a photon index ~1.2 in the 2FHL catalog and, as such, is one of the most extreme sources in the 2FHL sub-sample of Galactic objects. A detailed analysis of the available multi-wavelength data shows that this source is located on the western edge of the supernova remnant (SNR) G344.7--0.1, along with extended TeV source, HESS J1702-420. The observations and the spectral energy distribution modeling support a scenario where this gamma-ray source is the byproduct of the interaction between the SNR shock and the dense surrounding medium, with escaping cosmic rays (CRs) diffusing into the dense environment and interacting with a large local cloud, generating the observed TeV emission. If confirmed, an interaction between the SNR CRs and a nearby cloud would make 2FHL J1703.4-4145 another promising candidate for efficient particle acceleration of the 2FHL Galactic sample, following the first candidate from our previous investigation of a likely shock-cloud interaction occurring on the West edge of the Vela SNR.

astro-ph.HE↗

arXiv2020

Co-evolution of black hole accretion and star formation in galaxies up to z=3.5

We study the co-evolution between the black hole accretion rate (BHAR) and the star formation rate (SFR) in different galaxy life phases: main sequence star-forming galaxies, quiescent and starburst galaxies at different cosmic epochs. We take advantage of the X-ray data from the Chandra COSMOS-Legacy survey and of the extensive multiwavelength ancillary observations in the COSMOS field presented in the COSMOS2015 catalog. We perform an X-ray stacking analysis and combine it with detected sources, in a broad redshift interval ($0.1<z<3.5$). The X-ray luminosity is used to predict the BHAR, while a similar stacking analysis on far-infrared Herschel maps is used to measure the corresponding SFR. We focus on the evolution of the average SFR-stellar mass (M*) relation and compare it with the BHAR-M* relation. We find that the ratio between BHAR and SFR does not evolve with redshift, although it depends on stellar mass. For the star-forming populations, this dependence on M* has a logarithmic slope of $\sim0.6$, for the starburst sample of $\sim0.4$, both at odds with quiescent sources where it remains constant ($\log(\rm {BHAR}/{\rm SFR})\sim -3.4$). By studying the specific BHAR and specific SFR we find signs of downsizing for both M* and black hole mass (M$_{\rm BH}$): quiescents grew their super-massive black hole at very early times, while star-forming and starburst galaxies had an accretion that endured until more recent times. Our results support the idea that the same physical processes feed and sustain both star formation and black hole accretion. Our integrated estimates of the M*-M$_{\rm BH}$ relation at all redshifts are consistent with independent determinations of the local M*-M$_{\rm BH}$ relation, thus adding key evidence to a weak evolution in the BHAR/SFR, and its low normalization compared to local dynamical M*-M$_{\rm BH}$ relations.

astro-ph.GA↗

arXiv2020

$NuSTAR$ Observations of Four Nearby X-ray Faint AGN: Low Luminosity or Heavy Obscuration?

We present $NuSTAR$ observations of four active galactic nuclei (AGN) located within 15 Mpc. These AGN, namely ESO 121-G6, NGC 660, NGC 3486 and NGC 5195, have observed X-ray luminosities of $L_{\rm 2-10\ keV, obs} \lesssim$ 10$^{39}$ erg s$^{-1}$, classifying them as low luminosity AGN (LLAGN). We perform broadband X-ray spectral analysis for the AGN by combining our $NuSTAR$ data with $Chandra$ or $XMM-Newton$ observations to directly measure their column densities ($N_{\rm H}$) and infer their intrinsic power. We complement our X-ray data with archival and new high angular resolution mid-infrared (mid-IR) data for all objects, except NGC 5195. Based on our X-ray spectral analysis, we found that both ESO 121-G6 and NGC 660 are heavily obscured ($N_{\rm H}$ > 10$^{23}$ cm$^{-2}$; $L_{\rm 2-10\ keV,\ int} \sim$ 10$^{41}$ erg s$^{-1}$), and NGC 660 may be Compton-thick. We also note that the X-ray flux and spectral slope for ESO 121-G6 have significantly changed over the last decade, indicating significant changes in the obscuration and potentially accretion rate. On the other hand, NGC 3486 and NGC 5195 appear to be unobscured and just mildly obscured, respectively, with $L_{\rm 2-10\ keV,\ int} <$ 10$^{39}$ erg s$^{-1}$; i.e., genuine LLAGN. Both of the heavily obscured AGN have $L_{\rm bol} >$ 10$^{41}$ erg s$^{-1}$ and $λ_{\rm Edd} \gtrsim$ 10$^{-3}$, and are detected in high angular resolution mid-IR imaging, indicating the presence of obscuring dust on nuclear scale. NGC 3486 however, is undetected in high-resolution mid-IR imaging, and the current data do not provide stringent constraints on the presence or absence of obscuring nuclear dust in the AGN.

astro-ph.HE↗

arXiv2020

Morphological and spectral study of 4FGL J1115.1-6118 in the region of the young massive stellar cluster NGC 3603

We report a detailed study of an unidentified gamma-ray source located in the region of the compact stellar cluster NGC 3603. This is a star-forming region (SFR) powered by a massive cluster of OB stars. A dedicated analysis of about 10 years of data from 10 GeV - 1 TeV, provided by the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope, yields the detection of a pointlike source at a significance of 9$σ$. The source photon spectrum can be described by a power-law model with best fit spectral index of $2.35 \pm 0.03$. In addition, the analysis of a deep Chandra image in the 0.5 - 7 keV band reliably rules out an extragalactic origin for the gamma rays. We also conclude that the broadband spectral energy distribution of the point source can be explained well with both leptonic and hadronic models. No firm evidence of association with any other classes of known gamma-ray emitters is found, therefore we speculate that 4FGL J1115.1-6118 is a gamma-ray emitting SFR.

astro-ph.HE↗

arXiv2020

A broadband X-ray study of a sample of AGNs with [OIII] measured inclinations

In modeling the X-ray spectra of active galactic nuclei (AGNs), the inclination angle is a parameter that can play an important role in analyzing the X-ray spectra of AGN, but it has never been studied in detail. We present a broadband X-ray spectral analysis of the joint NuSTAR-XMM-Newton observations of 13 sources with [OIII] measured inclinations determined by Fischer et al. 2013. By freezing the inclination angles at the [OIII] measured values when modeling the observations, the spectra are well fitted and the geometrical properties of the obscuring structure of the AGNs are slightly better constrained than those fitted when the inclination angles are left free to vary. We also test if one could freeze the inclinations at other specific angles in fitting the AGN X-ray spectra as commonly did in the literatures. We find that one should always let the inclination angle free to vary in modeling the X-ray spectra of AGNs, while fixing the inclination angle at [OIII] measured values and fixing the inclination angle at 60$^\circ$ also present correct fits of the sources in our sample.Correlations between the covering factor and the average column density of the obscuring torus with respect to the Eddington ratio are also measured, suggesting that the distribution of the material in the obscuring torus is regulated by the Eddington ratio, which is in agreement with previous studies. In addition, no geometrical correlation is found between the narrow line region of the AGN and the obscuring torus, suggesting that the geometry might be more complex than what is assumed in the simplistic unified model.

astro-ph.GA↗

arXiv2020

The deep Chandra survey in the SDSS J1030+0524 field

We present the X-ray source catalog for the 479 ks Chandra exposure of the SDSS J1030+0524 field, that is centered on a region that shows the best evidence to date of an overdensity around a z > 6 quasar, and also includes a galaxy overdensity around a Compton-thick Fanaroff-Riley type II radio galaxy at z = 1.7. Using wavdetect for initial source detection and ACIS Extract for source photometry and significance assessment, we create preliminary catalogs of sources that are detected in the full, soft, and hard bands, respectively. We produce X-ray simulations that mirror our Chandra observation to filter our preliminary catalogs and get a completeness level of > 91% and a reliability level of 95% in each band. The catalogs in the three bands are then matched into a final main catalog of 256 unique sources. Among them, 244, 193, and 208 are detected in the full, soft, and hard bands, respectively. This makes J1030 field the fifth deepest extragalactic X-ray survey to date. The field is part of the Multiwavelength Survey by Yale-Chile (MUSYC), and is also covered by optical imaging data from the Large Binocular Camera (LBC) at the Large Binocular Telescope, near-IR imaging data from the Canada France Hawaii Telescope WIRCam, and Spitzer IRAC. Thanks to its dense multi-wavelength coverage, J1030 represents a legacy field for the study of large-scale structures around distant accreting supermassive black holes. Using a likelihood ratio analysis, we associate multi-band counterparts for 252 (98.4%) of the 256 Chandra sources, with an estimated reliability of 95%. Finally, we compute the cumulative number of sources in each X-ray band, finding that they are in general agreement with the results from the Chandra Deep Fields.

astro-ph.GA↗

arXiv2020

NuSTAR perspective on high-redshift MeV blazars

With bolometric luminosities exceeding $10^{48}$ erg s$^{-1}$, powerful jets and supermassive black holes at their center, MeV blazars are some of the most extreme sources in the Universe. Recently, the Fermi-Large Area Telescope detected five new $γ$-ray emitting MeV blazars beyond redshift $z=3.1$. With the goal of precisely characterizing the jet properties of these extreme sources, we started a multiwavelength campaign to follow them up with joint NuSTAR, Swift and SARA observations. We observe six high-redshift quasars, four of them belonging to the new $γ$-ray emitting MeV blazars. Thorough X-ray analysis reveals spectral flattening at soft X-ray for three of these objects. The source NVSS J151002$+$570243 also shows a peculiar re-hardening of the X-ray spectrum at energies $E>6\,\rm keV$. Adopting a one-zone leptonic emission model, this combination of hard X-rays and $γ$-rays enables us to determine the location of the Inverse Compton peak and to accurately constrain the jet characteristics. In the context of the jet-accretion disk connection, we find that all six sources have jet powers exceeding accretion disk luminosity, seemingly validating this positive correlation even beyond $z>3$. Our six sources are found to have $10^9 \rm M_{\odot}$ black holes, further raising the space density of supermassive black holes in the redshift bin $z=[3,4]$.

astro-ph.HE↗