Search

We investigate the coalescence of massive black hole ($M_{\rm BH}\gtrsim 10^{6}~\rm {\rm M}_{\odot }$) binaries (MBHBs) at 6 < z < 10 by adopting a suite of cosmological hydrodynamical simulations of galaxy formation, zoomed-in on biased (>3σ) overdense regions (Mh ∼ 1012 M⊙ dark matter haloes at z = 6) of the Universe. We first analyse the impact of different resolutions and AGN feedback prescriptions on the merger rate, assuming instantaneous mergers. Then, we compute the halo bias correction factor due to the overdense simulated region. Our simulations predict merger rates that range between 3 and 15 $\rm yr^{-1}$ at z ∼6, depending on the run considered, and after correcting for a bias factor of ∼20−30. For our fiducial model, we further consider the effect of delay in the MBHB coalescence due to dynamical friction. We find that 83 per cent of MBHBs will merge within the Hubble time, and 21 per cent within 1 Gyr, namely the age of the Universe at z > 6. We finally compute the expected properties of the gravitational wave (GW) signals and find the fraction of LISA detectable events with high signal-to-noise ratio (SNR > 5) to range between 66 per cent and 69 per cent. However, identifying the electro-magnetic counterpart of these events remains challenging due to the poor LISA sky localization that, for the loudest signals ($\mathcal {M}_c\sim 10^6~{{\rm M}_{\odot }}$ at z = 6), is around 10 $\rm deg^2$.

We present the results of a spectroscopic campaign with the Multi-Object Double Spectrograph (MODS) instrument mounted on the Large Binocular Telescope (LBT), aimed at obtaining a spectroscopic redshift for seven Chandra J1030 sources with a photometric redshift >=2.7 and optical magnitude r_AB=[24.5-26.5]. We obtained a spectroscopic redshift for five out of seven targets: all of them have z_spec>=2.5, thus probing the reliability of the Chandra J1030 photometric redshifts. The spectroscopic campaign led to the serendipitous discovery of a z~2.78 large scale structure (LSS) in the J1030 field: the structure contains four X-ray sources (three of which were targeted in the LBT-MODS campaign) and two non-X-ray detected galaxies for which a VLT-MUSE spectrum was already available. The X-ray members of the LSS are hosted in galaxies that are significantly more massive (log(M_*/M_sun)=[10.0-11.1]) than those hosting the two MUSE-detected sources (log(M_*/M_sun)10, are among the best tracers of large scale structures and filaments in the cosmic web. Consequently, our result can explain why X-ray-detected AGN have also been shown to be efficient tracers of large scale structures., 16 pages, 9 Figures. Accepted for publication in Astronomy and Astrophysics

The large total infrared (TIR) luminosities ($L_{\rm TIR} \gtrsim 10^{12}~L_\odot$) observed in $z \sim 6$ quasars are generally converted into high star formation rates ($SFR \gtrsim 10^2~M_\odot$ yr$^{-1}$) of their host galaxies. However, these estimates rely on the assumption that dust heating is dominated by stellar radiation, neglecting the contribution from the central Active Galactic Nuclei (AGN). We test the validity of this assumption by combining cosmological hydrodynamic simulations with radiative transfer calculations. We find that, when AGN radiation is included in the simulations, the mass (luminosity)-weighted dust temperature in the host galaxies increases from $T\approx 50$ K ($T \approx 70$ K) to $T\approx 80$ K ($T\approx 200$ K), suggesting that AGN effectively heat the bulk of dust in the host galaxy. We compute the AGN-host galaxy $SFR$ from the synthetic spectral energy distribution by using standard $SFR - L_{\rm TIR}$ relations, and compare the results with the "true" values in the simulations. We find that the $SFR$ is overestimated by a factor of $\approx 3$ ($\gtrsim 10$) for AGN bolometric luminosities of $L_{\rm bol} \approx 10^{12}~L_\odot$ ($\gtrsim 10^{13}~ L_\odot$), implying that the star formation rates of $z\sim 6$ quasars can be overestimated by over an order of magnitude., Comment: 9 pages, 6 figures. Accepted for publication by MNRAS

Recent studies have revealed a strong relation between sample-averaged black-hole (BH) accretion rate (BHAR) and star formation rate (SFR) among bulge-dominated galaxies, i.e., "lockstep" BH-bulge growth, in the distant universe. This relation might be closely related to the BH-bulge mass correlation observed in the local universe. To understand further BH-bulge coevolution, we present ALMA CO(2-1) or CO(3-2) observations of 7 star-forming bulge-dominated galaxies at z=0.5-2.5. Using the ALMA data, we detect significant ($>3σ$) CO emission from 4 objects. For our sample of 7 galaxies, we measure (or constrain with upper limits) their CO line fluxes and estimate molecular gas masses ($M_{gas}$). We also estimate their stellar masses ($M_{star}$) and SFRs by modelling their spectral energy distributions (SEDs). Using these physical properties, we derive the gas-depletion timescales ($t_{dep} = M_{gas}/SFR$) and compare them with the bulge/BH growth timescales ($t_{grow} = M_{star}/SFR \sim M_{BH}/BHAR$). Our sample generally has $t_{dep}$ shorter than $t_{grow}$ by a median factor of $\gtrsim 4$, indicating that the cold gas will be depleted before significant bulge/BH growth takes place. This result suggests that the BH-bulge lockstep growth is mainly responsible for maintaining their mass relation, not creating it. We note that our sample is small and limited to $z, 15 pages, 7 figures, and 3 tables. Accepted by ApJ

In my presentation, I review the expected performances of the Athena-WFI survey, with a particular focus on the high redshift Universe and the first SMBH science topic. I put these performances in the broader context of present and future missions and facilities in other wavelengths, from optical/IR large-area surveys to mm/sub-mm and radio observations. The unique capability of Athena-WFIto identify obscured sources up to very high redshift, where they are expected to be the vast majority of the AGN population and derive their intrinsic accretion properties,makes it competitive even with the rich landscape of the late '30s.

Quasars powered by supermassive black holes (MBH, $>10^8~M_{\odot}$) at $z\sim 6$ are predicted to reside in cosmic over-dense regions. However, observations so far could not confirm this expectation due to limited statistics. The picture is further complicated by the possible effects of quasar outflows (i.e. feedback) that could either suppress or stimulate the star formation rate (SFR) of companion galaxies, thus modifying the expected bias. Here we quantify feedback effects on the properties and detectability of companions by comparing cosmological zoom-in simulations of a quasar in which feedback is either included or turned-off. With respect to the no-feedback case, companions (a) directly impacted by the outflow have their SFR increased by a factor $2-3$, and (b) tend to be more massive. Both effects shift the [CII]158$\mu$m and UV luminosity functions toward brighter magnitudes. This leads us to conclude that quasar feedback slightly increases the effective quasar bias, boosting the number density of observable quasar companions, in agreement with what has been found around the brightest quasars of recent ALMA [CII] surveys. Deeper observations performed with JWST and/or ALMA will improve the statistical significance of this result by detecting a larger number of fainter quasar companions., Comment: 20 pages, 13 figures; Accepted for publications in MNRAS

W-CDF-S, ELAIS-S1, and XMM-LSS will be three Deep-Drilling Fields (DDFs) of the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST), but their extensive multi-wavelength data have not been fully utilized as done in the COSMOS field, another LSST DDF. To prepare for future science, we fit source spectral energy distributions (SEDs) from X-ray to far-infrared in these three fields mainly to derive galaxy stellar masses and star-formation rates. We use CIGALE v2022.0, a code that has been regularly developed and evaluated, for the SED fitting. Our catalog includes 0.8 million sources covering $4.9~\mathrm{deg^2}$ in W-CDF-S, 0.8 million sources covering $3.4~\mathrm{deg^2}$ in ELAIS-S1, and 1.2 million sources covering $4.9~\mathrm{deg^2}$ in XMM-LSS. Besides fitting normal galaxies, we also select candidates that may host active galactic nuclei (AGNs) or are experiencing recent star-formation variations and use models specifically designed for these sources to fit their SEDs; this increases the utility of our catalog for various projects in the future. We calibrate our measurements by comparison with those in well-studied smaller regions and briefly discuss the implications of our results. We also perform detailed tests of the completeness and purity of SED-selected AGNs. Our data can be retrieved from a public website., Comment: 49 pages, 39 figures, 9 tables, accepted for publication in ApJS

The Chandra Deep Field-South and North surveys (CDFs) provide unique windows into the cosmic history of X-ray emission from normal (nonactive) galaxies. Scaling relations of normal-galaxy X-ray luminosity (L X) with star formation rate (SFR) and stellar mass (M ⋆) have been used to show that the formation rates of low-mass and high-mass X-ray binaries (LMXBs and HMXBs, respectively) evolve with redshift across z ≈ 0–2 following L HMXB/SFR ∝ (1 + z) and L LMXB/M ⋆ ∝ (1 + z)2−3. However, these measurements alone do not directly reveal the physical mechanisms behind the redshift evolution of X-ray binaries (XRBs). We derive star formation histories for a sample of 344 normal galaxies in the CDFs, using spectral energy distribution (SED) fitting of FUV-to-FIR photometric data, and construct a self-consistent, age-dependent model of the X-ray emission from the galaxies. Our model quantifies how X-ray emission from hot gas and XRB populations vary as functions of host stellar-population age. We find that (1) the ratio L X/M ⋆ declines by a factor of ∼1000 from 0 to 10 Gyr and (2) the X-ray SED becomes harder with increasing age, consistent with a scenario in which the hot gas contribution to the X-ray SED declines quickly for ages above 10 Myr. When dividing our sample into subsets based on metallicity, we find some indication that L X/M ⋆ is elevated for low-metallicity galaxies, consistent with recent studies of X-ray scaling relations. However, additional statistical constraints are required to quantify both the age and metallicity dependence of X-ray emission from star-forming galaxies.

The cosmic black hole accretion density (BHAD) is critical for our understanding of the formation and evolution of supermassive black holes (BHs). However, at high redshifts ($z>3$), X-ray observations report BHADs significantly ($\sim 10$ times) lower than those predicted by cosmological simulations. It is therefore paramount to constrain the high-$z$ BHAD using independent methods other than direct X-ray detections. The recently established relation between star formation rate and BH accretion rate among bulge-dominated galaxies provides such a chance, as it enables an estimate of the BHAD from the star-formation histories (SFHs) of lower-redshift objects. Using the CANDELS Lyman-$\alpha$ Emission At Reionization (CLEAR) survey, we model the SFHs for a sample of 108 bulge-dominated galaxies at $z=$0.7-1.5, and further estimate the BHAD contributed by their high-$z$ progenitors. The predicted BHAD at $z\approx 4$-5 is consistent with the simulation-predicted values, but higher than the X-ray measurements (by $\approx$3-10 times at $z=$4-5). Our result suggests that the current X-ray surveys could be missing many heavily obscured Compton-thick active galactic nuclei (AGNs) at high redshifts. However, this BHAD estimation assumes that the high-$z$ progenitors of our $z=$0.7-1.5 sample remain bulge-dominated where star formation is correlated with BH cold-gas accretion. Alternatively, our prediction could signify a stark decline in the fraction of bulges in high-$z$ galaxies (with an associated drop in BH accretion). JWST and Origins will resolve the discrepancy between our predicted BHAD and the X-ray results by constraining Compton-thick AGN and bulge evolution at high redshifts., Comment: 10 pages and 5 figures; accepted for publication in ApJ

arXiv:2106.08345v1, SPICA Collaboration Team., In the black hole (BH)–galaxy co-evolution framework, most of the star formation (SF) and the BH accretion are expected to take place in highly obscured conditions. The large amount of gas and dust absorbs most of the UV-to-soft-X radiation and re-emits it at longer wavelengths, mostly in the IR. Thus, obscured active galactic nuclei (AGN) are very difficult to identify in optical or X-ray bands but shine bright in the IR. Moreover, X-ray background (XRB) synthesis models predict that a large fraction of the yet-unresolved XRB is due to the most obscured (Compton thick, CT: NH ≥ 1024 cm−2) of these AGN. In this work, we investigate the synergies between putative IR missions [using SPace Infrared telescope for Cosmology and Astrophysics (SPICA), proposed for European Space Agency (ESA)/M5 but withdrawn in 2020 October, and Origins Space Telescope, OST, as ‘templates’] and the X-ray mission Athena (Advanced Telescope for High ENergy Astrophysics), which should fly in early 2030s, in detecting and characterising AGN, with a particular focus on the most obscured ones. Using an XRB synthesis model, we estimated the number of AGN and the number of those which will be detected in the X-rays by Athena. For each AGN, we associated an optical-to-Far InfraRed (FIR) spectral energy distribution (SED) from observed AGN with both X-ray data and SED decomposition and used these SEDs to check if the AGN will be detected by SPICA-like or OST at IR wavelengths. We expect that, with the deepest Athena and SPICA-like (or OST) surveys, we will be able to photometrically detect in the IR more than 90% of all the AGN (down to L2−10keV ∼ 1042 erg s−1 and up to z ∼ 10) predicted by XRB synthesis modeling, and we will detect at least half of them in the X-rays. The spectroscopic capabilities of the OST can provide ≈51 000 and ≈3 400 AGN spectra with R = 300 at 25–588µm in the wide and deep surveys, respectively, the last one up to z ≈ 4. Athena will be extremely powerful in detecting and discerning moderate- and high-luminosity AGN, allowing us to properly select AGN even when the mid-IR torus emission is ‘hidden’ by the host galaxy contribution. We will constrain the intrinsic luminosity and the amount of obscuration for ∼20% of all the AGN (and ∼50% of those with L2−10keV > 3.2 × 1043 erg s−1) using the X-ray spectra provided by Athena WFI. We find that the most obscured and elusive CT-AGN will be exquisitely sampled by SPICA-like mission or OST and that Athena will allow a fine characterisation of the most luminous ones. This will provide a significant step forward in the process of placing stronger constraints on the yet-unresolved XRB and investigating the BH accretion rate evolution up to very high redshift (z ≥ 4)., FP, CV, CG, LB, and LS acknowledge financial support by the Agenzia Spaziale Italiana (ASI) under the research contract 2018-31-HH.0. FJC acknowledges financial support from the Spanish Ministry MCIU under project RTI2018-096686-B-C21 (MCIU/AEI/FEDER/UE), cofunded by FEDER funds and from the Agencia Estatal de Investigación, Unidad de Excelencia María de Maeztu, ref. MDM-2017-0765. MPS acknowledges support from the Comunidad de Madrid, Spain, through Atracción de Talento Investigador Grant 2018-T1/TIC-11035 and PID2019-105423GA-I00 (MCIU/AEI/FEDER,UE). AF acknowledges the support from grant PRIN MIUR2017-20173ML3WW_001.

The discovery of hundreds of QSOs in the first Gyr of the Universe powered by already grown SMBHs challenges our knowledge of SMBH formation. In particular, investigations of $z>6$ QSOs presenting notable properties can provide unique information on the physics of fast SMBH growth in the early universe. We present the results of follow-up observations of the $z=6.515$ radio-quiet QSO PSO167-13, which is interacting with a close companion galaxy. The PSO167-13 system has been recently proposed to host the first heavily obscured X-ray source at high redshift. We observed PSO167-13 with Chandra/ACIS-S (177 ks), and obtained new spectroscopic observations (7.2 h) with Magellan/FIRE. No significant X-ray emission is detected from the PSO167-13 system, suggesting that the obscured X-ray source previously tentatively detected was either due to a strong background fluctuation or is highly variable. The upper limit (90% confidence level) on the X-ray emission of PSO167-13 ($L_{2-10\,\mathrm{keV}}6$ QSO. The ratio between the X-ray and UV luminosity of $\alpha_{ox}6$ times weaker than the expectation based on its UV luminosity. The new Magellan/FIRE spectrum of PSO167-13 is strongly affected by the unfavorable sky conditions, but the tentatively detected C IV and Mg II emission lines appear strongly blueshifted. The most plausible explanations for the X-ray weakness of PSO167-13 are intrinsic weakness or small-scale absorption by Compton-thick material. The possible strong blueshift of its emission lines hints at the presence of nuclear winds, which could be related to its X-ray weakness., Comment: Accepted for publication on A&A

By using a large highly obscured ($N_{\rm H} > 10^{23}\ \rm cm^{-2}$) AGN sample (294 sources at $z \sim 0-5$) selected from detailed X-ray spectral analyses in the deepest Chandra surveys, we explore distributions of these X-ray sources in various optical/IR/X-ray color-color diagrams and their host-galaxy properties, aiming at characterizing the nuclear obscuration environment and the triggering mechanism of highly obscured AGNs. We find that the refined IRAC color-color diagram fails to identify the majority of X-ray selected highly obscured AGNs, even for the most luminous sources with ${\rm log}\,L_{\rm X}\, \rm (erg\ s^{-1}) > 44$. Over 80% of our sources will not be selected as heavily obscured candidates using the flux ratio of $f_{\rm 24 ��m}\, /\,f_R > 1000$ and $R - K > 4.5$ criteria, implying complex origins and conditions for the obscuring materials that are responsible for the heavy X-ray obscuration. The average star formation rate of highly obscured AGNs is similar to that of stellar mass- ($M_*$-) and $z$-controlled normal galaxies, while the lack of quiescent hosts is observed for the former. Partial correlation analyses imply that highly obscured AGN activity (traced by $L_{\rm X}$) appears to be more fundamentally related to $M_*$, and no dependence of $N_{\rm H}$ on either $M_*$ or SFR is detected. Morphology analyses reveal that 61% of our sources have a significant disk component, while only 27% of them exhibit irregular morphological signatures. These findings together point toward a scenario where secular processes (e.g., galactic-disk instabilities), instead of mergers, are most probable to be the leading mechanism that triggers accretion activities of X-ray-selected highly obscured AGNs., 23 pages, 12 figures, 3 tables, resubmitted to ApJ after addressing referee's comments

Background: In Western society, discussions about death have shifted from the domain of the everyday to the domain of medicine. Such censorship does not reduce the fear of death; rather, it deprives people of the means to elaborate their experiences of death, generating negative effects such as difficult mourning and stigmatisation of palliative care environments. The objective of this follow-up study was to detect whether and how death education can help to improve individuals’ relationship with death. Methods: This was a qualitative research study based on grounded theory. We conducted semi-structured interviews with both palliative care professionals and teachers who had taken part in a death education intervention three years earlier. The interviews were interpreted through thematic analysis. Results: The results confirmed death education’s positive effect for both palliative care professionals and teachers. These individuals reported that the education initiative helped them to positively modify their perspectives on death and dying, as well as their attitudes towards life. It also helped to improve community attitudes towards the hospice and its workers. Conclusions: This study confirmed that school education initiatives can create continuity between hospices and local communities. The death education project provided an educational space in which it was possible to elaborate experiences linked to death and to re-evaluate and appreciate hospices and their staff.

We present the X-ray source catalog for the ∼479 ks Chandra exposure of the SDSS J1030+0524 field, which 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 (FRII) 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 (0.5-7.0 keV), soft (0.5-2.0 keV), and hard (2-7 keV) bands, respectively. We produce X-ray simulations that mirror our Chandra observation to filter our preliminary catalogs and achieve 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. The Chandra observation covers a total area of 335 arcmin2 and reaches flux limits over the central few square arcmins of ∼3 × 10-16, 6 × 10-17, and 2 × 10-16 erg cm-2 s-1 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 (LBT), near-infrared imaging data from the Canada France Hawaii Telescope WIRCam (CFHT/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 (r, z, J, and 4.5 μm) 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., We acknowledge the referee for a prompt and constructive report. We acknowledge financial contribution from the agreement ASI-INAF n. 2017-14-H.O. We thank P. Broos for providing great support for the analysis of our simulations with AE, and H. M. Günther for the support provided for using MARX. We also thank B. Luo for providing us the log(N)–log(S) of the 7Ms CDF-S. FV acknowledges financial support from CONICYT and CASSACA through the Fourth call for tenders of the CAS-CONICYT Fund, and CONICYT grants Basal-CATA AFB-170002. DM and MA acknowledge support by grant number NNX16AN49G issued through the NASA Astrophysics Data Analysis Program (ADAP). Further support was provided by the Faculty Research Fund (FRF) of Tufts University.

We report the discovery of an extreme X-ray flux rise (by a factor of > 20) of the weak-line quasar SDSS J153913.47+395423.4 (hereafter SDSS J1539+3954) at z = 1.935. SDSS J1539+3954 is the most-luminous object among radio-quiet type 1 AGNs where such dramatic X-ray variability has been observed. Before the X-ray flux rise, SDSS J1539+3954 appeared X-ray weak compared with the expectation from its UV flux; after the rise, the ratio of its X-ray flux and UV flux is consistent with the majority of the AGN population. We also present a contemporaneous HET spectrum of SDSS J1539+3954, which demonstrates that its UV continuum level remains generally unchanged despite the dramatic increase in the X-ray flux, and its C iv emission line remains weak. The dramatic change only observed in the X-ray flux is consistent with a shielding model, where a thick inner accretion disk can block our line of sight to the central X-ray source. This thick inner accretion disk can also block the nuclear ionizing photons from reaching the high-ionization broad emission-line region, so that weak high-ionization emission lines are observed. Under this scenario, the extreme X-ray variability event may be caused by slight variations in the thickness of the disk. This event might also be explained by gravitational light-bending effects in a reflection model., 8 pages, 3 figures. Accepted for publication in ApJL

We present a series of new, publicly available mock catalogs of X-ray selected active galactic nuclei (AGNs), non-active galaxies, and clusters of galaxies. They are based on up-to-date observational results on the demographic of extragalactic X-ray sources and their extrapolations.These mocks reach fluxes below 1E-20 erg s-1 cm-2 in the 0.5-2 keV band, i.e., more than an order of magnitude below the predicted limits of future deep fields, and therefore represent an important tool for simulating extragalactic X-ray surveys with both current and future telescopes. We use our mocks to perform a set of end-to-end simulations of X-ray surveys with the forthcoming Athena mission and with the AXIS probe, a sub-arcsecond resolution X-ray mission concept proposed to the Astro 2020 Decadal Survey. We find that these proposed, next generation surveys may transform our knowledge of the deep X-ray Universe. As an example, in a total observing time of 15\,Ms, AXIS would detect ~225,000 AGNs and ~$50,000 non-active galaxies, reaching a flux limit f_0.5-2~5E-19 erg/s/cm2 in the 0.5-2 keV band, with an improvement of over an order of magnitude with respect to surveys with current X-ray facilities. Consequently, 90% of these sources would be detected for the first time in the X-rays. Furthermore, we show that deep and wide X-ray surveys with instruments like AXIS and Athena are expected to detect ~20,000 z>3 AGNs and ~250 sources at redshift z>6, thus opening a new window of knowledge on the evolution of AGNs over cosmic time and putting strong constraints on the predictions of theoretical models of black hole seed accretion in the early universe., 19 pages, 13 figures. Accepted for publication in A&A. Mock catalogs available online at http://cxb.oas.inaf.it/mock.html

We present a procedure to constrain the redshifts of obscured ($N_H > 10^{22}$ cm$^{-2}$) Active Galactic Nuclei (AGN) based on low-count statistics X-ray spectra, which can be adopted when photometric and/or spectroscopic redshifts are unavailable or difficult to obtain. We selected a sample of 54 obscured AGN candidates on the basis of their X-ray hardness ratio, $HR>-0.1$, in the Chandra deep field ($\sim$479 ks, 335 arcmin$^2$) around the $z=6.3$ QSO SDSS J1030+0524. The sample has a median value of $\approx80$ net counts in the 0.5-7 keV energy band. We estimate reliable X-ray redshift solutions taking advantage of the main features in obscured AGN spectra, like the Fe 6.4 keV K$\mathrm{\alpha}$ emission line, the 7.1 keV Fe absorption edge and the photoelectric absorption cut-off. The significance of such features is investigated through spectral simulations, and the derived X-ray redshift solutions are then compared with photometric redshifts. Both photometric and X-ray redshifts are derived for 33 sources. When multiple solutions are derived by any method, we find that combining the redshift solutions of the two techniques improves the rms by a factor of two. Using our redshift estimates ($0.1\lesssim z \lesssim 4$), we derived absorbing column densities in the range $\sim 10^{22}-10^{24}$ cm$^{-2}$ and absorption-corrected, 2-10 keV rest-frame luminosities between $\sim 10^{42}$ and $10^{45}$ erg s$^{-1}$, with median values of $N_H = 1.7 \times 10^{23}$ cm$^{-2}$ and $L_{\mathrm{2-10\, keV}} = 8.3\times10^{43}$ erg s$^{-1}$, respectively. Our results suggest that the adopted procedure can be applied to current and future X-ray surveys, for sources detected only in the X-rays or that have uncertain photometric or single-line spectroscopic redshifts., Comment: 22 pages, 18 figures

We report on the spectroscopic confirmation of a large-scale structure around the luminous z = 6.31 quasi-stellar object (QSO) SDSS J1030+0524, powered by a one billion solar mass black hole. The structure is populated by at least six members, namely, four Lyman-break galaxies (LBGs), and two Lyman alpha emitters (LAEs). The four LBGs were identified among a sample of 21 i-band dropouts with zAB < 25.5 selected up to projected separations of 5 physical Mpc (15 arcmin) from the QSO. Their redshifts were determined through multi-object spectroscopic observations at 8-10 m class telescopes lasting up to eight hours. The two LAEs were identified in a 6 h VLT/MUSE observation centered on the QSO. The redshifts of the six galaxies cover the range between 6.129-6.355. Assuming that the peculiar velocities are negligible, this range corresponds to radial separations of ±5 physical Mpc from the QSO, that is comparable to the projected scale of the observed LBG distribution on the sky. We conservatively estimate that this structure is significant at a level > 3.5σ and that the level of the galaxy overdensity is at least 1.5-2 within the large volume sampled (∼780 physical Mpc3). The spectral properties of the six member galaxies (Lyα strength and UV luminosity) are similar to those of field galaxies at similar redshifts. This is the first spectroscopic identification of a galaxy overdensity around a supermassive black hole in the first billion years of the Universe. Our finding lends support to the idea that the most distant and massive black holes form and grow within massive (>1012 M) dark matter halos in large-scale structures and that the absence of earlier detections of such systems is likely due to observational limitations., We acknowledge funding from the INAF main-stream (1.05.01.86.31) and from the agreement ASI-INAF n. 2017-14-H.O. This work is based on ESO program 0102.A-0263(A), on observations obtained at the W. M. Keck Observatory, and on data acquired using the Large Binocular Telescope (ID 2017/2018 #18).

For over 60 years, the scientific community has studied actively growing central super-massive black holes (active galactic nuclei -- AGN) but fundamental questions on their genesis remain unanswered. Numerical simulations and theoretical arguments show that black hole growth occurs during short-lived periods ($\sim$ 10$^{7}$ -10$^{8}$ yr) of powerful accretion. Major mergers are commonly invoked as the most likely dissipative process to trigger the rapid fueling of AGN. If the AGN-merger paradigm is true, we expect galaxy mergers to coincide with black hole accretion during a heavily obscured AGN phase (N$_H$ $ > 10^{23}$ cm$^{-2}$). Starting from one of the largest samples of obscured AGN at 0.5 $, Comment: 19 pages, 11 figures, accepted in ApJ

We investigate the population of high-redshift ($3\leq z < 6$) AGN selected in the two deepest X-ray surveys, the 7 Ms \textit{Chandra} Deep Field-South and 2 Ms \textit{Chandra} Deep Field-North. Their outstanding sensitivity and spectral characterization of faint sources allow us to focus on the sub-$L_*$ regime (log$L_{\mathrm{X}}\lesssim44$), poorly sampled by previous works using shallower data, and the obscured population. Taking fully into account the individual photometric-redshift probability distribution functions, the final sample consists of $\approx102$ X-ray selected AGN at $3\leq z < 6$. The fraction of AGN obscured by column densities log$N_{\mathrm{H}}>23$ is $\sim0.6-0.8$, once incompleteness effects are taken into account, with no strong dependence on redshift or luminosity. We derived the high-redshift AGN number counts down to $F_{\mathrm{0.5-2\,keV}}=7\times10^{-18}\,\mathrm{erg\,cm^{-2}\,s^{-1}}$, extending previous results to fainter fluxes, especially at $z>4$. We put the tightest constraints to date on the low-luminosity end of AGN luminosity function at high redshift. The space-density, in particular, declines at $z>3$ at all luminosities, with only a marginally steeper slope for low-luminosity AGN. By comparing the evolution of the AGN and galaxy densities, we suggest that such a decline at high luminosities is mainly driven by the underlying galaxy population, while at low luminosities there are hints of an intrinsic evolution of the parameters driving nuclear activity. Also, the black-hole accretion rate density and star-formation rate density, which are usually found to evolve similarly at $z\lesssim3$, appear to diverge at higher redshifts., Accepted 2017 September 15 (MNRAS). 31 Pages, 25 figures

We study the X-ray variability properties of distant AGNs in the Chandra Deep Field-South region over 17 years, up to $z\sim 4$, and compare them with those predicted by models based on local samples. We use the results of Monte Carlo simulations to account for the biases introduced by the discontinuous sampling and the low-count regime. We confirm that variability is an ubiquitous property of AGNs, with no clear dependence on the density of the environment. The variability properties of high-z AGNs, over different temporal timescales, are most consistent with a Power Spectral Density (PSD) described by a broken (or bending) power-law, similar to nearby AGNs. We confirm the presence of an anti-correlation between luminosity and variability, resulting from the dependence of variability on BH mass and accretion rate. We explore different models, finding that our acceptable solutions predict that BH mass influences the value of the PSD break frequency, while the Eddington ratio $\lambda_{Edd}$ affects the PSD break frequency and, possibly, the PSD amplitude as well. We derive the evolution of the average $\lambda_{Edd}$ as a function of redshift, finding results in agreement with measurements based on different estimators. The large statistical uncertainties make our results consistent with a constant Eddington ratio, although one of our models suggest a possible increase of $\lambda_{Edd}$ with lookback time up to $z\sim 2-3$. We conclude that variability is a viable mean to trace the accretion history of supermassive BHs, whose usefulness will increase with future, wide-field/large effective area X-ray missions., Comment: 15 pages, 9 Figures, 2 Tables, in press on MNRAS

Background The theme of death in Western society has been removed from everyday life and replaced with specialized medical language. Such censorship does not reduce the fear of death, especially among young people, and it limits the possibility to elaborate on experiences linked to death, generating negative effects, especially in cases of traumatic grief. The objective of this follow-up study was to detect how and if experiences of death education changed the relationship between the community and a local hospice. Furthermore, it was stressed the theme of representation of death, in order to see whether participants were able to remind any possible attitude change following the project. Finally, it was analysed how they considered how they remembered the effect of the elaboration of the trauma caused by the suicide of a student. Methods This was a qualitative research study based on semi-structured interviews with palliative care professionals and teachers of students who had taken part in a death education intervention 3 years earlier. The interviews were examined through thematic analysis. Results The results confirmed the efficacy of the death education intervention initiated 3 years earlier. The education initiative contributed to modifying the students’ and teachers’ perspectives of end-of-life professionals and their understanding of the structures within which palliative care is implemented. It also modified the participants’ perspectives on the representation of death and promoted a new outlook on life. The hospice staff also perceived a change in the attitudes of the community, and this change had a positive impact on their everyday work. Conclusions This study confirmed the usefulness of creating continuity between a hospice and the community through a school education initiative. The death education project provided an educational space in which it was possible to elaborate on experiences linked to death and to re-evaluate and appreciate the structures of end-of-life care and the professionals who work in the area. Keywords: Hospice, Palliative care, Death education, Adolescents, Suicide.

Neutron star-neutron star mergers are known to be associated with short gamma-ray bursts. If the neutron star equation of state is sufficiently stiff, at least some of such mergers will leave behind a supramassive or even a stable neutron star that spins rapidly with a strong magnetic field (i.e., a magnetar). Such a magnetar signature may have been observed as the X-ray plateau following a good fraction (up to 50%) of short gamma-ray bursts, and it has been expected that one may observe short gamma-ray burst-less X-ray transients powered by double neutron star mergers. A fast X-ray transient (CDF-S XT1) was recently found to be associated with a faint host galaxy whose redshift is unknown. Its X-ray and host-galaxy properties allow several possibleexplanations including a short gamma-ray burst seen off axis, a low-luminosity gamma-ray burst at high redshift, or a tidal disruption event involving an intermediate mass black hole and a white dwarf. Here we report a second X-ray transient, CDF-S XT2, that is associated with a galaxy at redshift z = 0.738. The light curve is fully consistent with being powered by a millisecond magnetar. More intriguingly, CDF-S XT2 lies in the outskirts of its star-forming host galaxy with a moderate offset from the galaxy center, as short bursts often do. The estimated event rate density of similar X-ray transients, when corrected to the local value, is consistent with the double neutron star merger rate density inferred from the detection of GW170817., Comment: 29 pages, 4 figures, 3 tables, published in Nature on 11 April 2019

We report the discovery of disappearance of Mg ii, Al iii, C iv, and Si iv broad absorption lines (BALs) at the same velocity, accompanied by a new Civ BAL emerging at a higher velocity, in the quasar J0827+4252 at z = 2.038. This is the first report of BAL disappearance (i) over Mg ii, Al iii, C iv, and Si iv ions and (ii) in a weak emission-line quasar (WLQ). The discovery is based on four spectra from the SDSS and one follow-up spectrum from HET/LRS2. The simultaneous Civ BAL disappearance and emergence at different velocities, together with no variations in the CRTS light curve, indicate that ionization changes in the absorbing material are unlikely to cause the observed BAL variability. Our analyses reveal that transverse motion is the most likely dominant driver of the BAL disappearance/emergence. Given the presence of mildly relativistic BAL outflows and an apparently large C iv emission-line blueshift that is likely associated with strong bulk outflows in this WLQ, J0827+4252 provides a notable opportunity to study extreme quasar winds and their potential in expelling material from inner to large-scale regions., Comment: Published in 2019 ApJL, 870, 2

While theoretical arguments predict that most of the early growth of supermassive black holes (SMBHs) happened during heavily obscured phases of accretion, current methods used for selecting $z>6$ quasars (QSOs) are strongly biased against obscured QSOs, thus considerably limiting our understanding of accreting SMBHs during the first Gyr of the Universe from an observational point of view. We report the $Chandra$ discovery of the first heavily obscured QSO candidate in the early universe, hosted by a close ($\approx5$ kpc) galaxy pair at $z=6.515$. One of the members is an optically classified type 1 QSO, PSO167-13. The companion galaxy was first detected as a [C II] emitter by ALMA. An X-ray source is significantly ($P=0.9996$) detected by $Chandra$ in the 2-5 keV band, with $2\times10^{24}\,\mathrm{cm^{-2}}$ and $N_H>6\times10^{23}\,\mathrm{cm^{-2}}$ at $68\%$ and $90\%$ confidence levels, respectively. Thus, regardless of which of the two galaxies is associated with the X-ray emission, this source is the first heavily obscured QSO candidate at $z>6$., Comment: A&A Letters, accepted

X-ray emission from QSOs has been used to assess SMBH accretion properties up to $z$~6. However, at $z>6$ only ~15 QSOs are covered by sensitive X-ray observations, preventing a statistically significant investigation of the X-ray properties of QSOs in the first Gyr of the Universe. We present new Chandra observations of 10 $z>6$ QSOs, selected to have virial black-hole mass estimates from Mg II line spectroscopy. Adding archival X-ray data for an additional 15 $z>6$ QSOs, we investigate the X-ray properties of the QSO population in the first Gyr of the Universe, focusing in particular on the $L_{UV}-L_{X}$ relation, which is traced by the $\alpha_{ox}$ parameter, and the shape of their X-ray spectra. We performed photometric analyses to derive estimates of the X-ray luminosities, and thus the $\alpha_{ox}$ values and bolometric corrections ($K_{bol}=L_{bol}/L_{X}$). We compared the resulting $\alpha_{ox}$ and $K_{bol}$ distributions with the results found for QSO samples at lower redshift. Finally, we performed a basic X-ray spectral analysis of the brightest $z>6$ QSOs to derive their individual photon indices, and joint spectral analysis of the whole sample to estimate the average photon index. We confirm a lack of significant evolution of $\alpha_{ox}$ with redshift, extending the results from previous works up to $z>6$, and the trend of an increasing bolometric correction with increasing luminosity found for QSOs at lower redshifts. The average power-law photon index of our sample ($\Gamma=2.20_{-0.34}^{+0.39}$ and $\Gamma=2.13_{-0.13}^{+0.13}$ for sources with $30$ net counts, respectively) is slightly steeper than, but still consistent with, typical QSOs at $z=1-6$. All these results point toward a lack of substantial evolution of the inner accretion-disk/hot-corona structure in QSOs from low redshift to $z>6$. Our data hint at generally high Eddington ratios at $z>6$., Comment: 15 pages. 10 figures. 7 tables. Accepted for publication in A&A