Showing papers by "Andrea Comastri published in 2022"
TL;DR: In this article , the column density of the interstellar medium (ISM) rapidly increases toward early cosmic epochs with increasing redshift, and it may reach values as high as Compton-thick at z ∼ 6 quasar hosts.
Abstract: We combine results from deep ALMA observations of massive ( M ∗ > 10 10 M (cid:12) ) galaxies at di ff erent redshifts to show that the column density of their interstellar medium (ISM) rapidly increases toward early cosmic epochs. Our analysis includes objects from the ASPECS and ALPINE large programs, as well as individual observations of z ∼ 6 quasar hosts. When accounting for non-detections and correcting for selection e ff ects, we find that the median surface density of the ISM of the massive galaxy population evolves as ∼ (1 + z ) 3 . 3 . This means that the ISM column density toward 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 ∼ > 6. Remarkably, the median ISM column density is on the same order of what is measured from X-ray observations of large active galactic nucleus (AGN) samples already at z ∼ > 2. We have developed a simple analytic model for the spatial distribution of ISM clouds within galaxies, and estimate the total covering factor toward active nuclei when obscuration by ISM clouds on the host scale is added to that of parsec-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 , ∗ ∝ (1 + z ) γ . We show that, for γ = 2, such a model successfully reproduces the increase in the obscured AGN fraction with redshift that is commonly observed in deep X-ray surveys, both when di ff erent 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. We finally discuss the implications of our results and how they can be tested observationally with current and forthcoming facilities (e.g., VLT, E-ELT, ALMA, and JWST) and with next-generation X-ray imaging satellites. By extrapolating the observed X-ray nebulae around local AGN to the environments of supermassive black holes at high redshifts, we find ∼ < 1” nebulae impose stringent design constraints on the spatial resolution of any future X-ray imaging Great Observatory in the coming decades.
12 citations
TL;DR: In this article , the combined Chandra and Swift-BAT spectral analysis of nine low-redshift (z ≤ 0.10), candidate heavily obscured active galactic nuclei (AGN) selected from the Swift- BAT 150 month catalog was presented.
Abstract: We present the combined Chandra and Swift-BAT spectral analysis of nine low-redshift (z ≤ 0.10), candidate heavily obscured active galactic nuclei (AGN) selected from the Swift-BAT 150 month catalog. We located soft (1−10 keV) X-ray counterparts to these BAT sources and joint fit their spectra with physically motivated models. The spectral analysis in the 1−150 keV energy band determined that all sources are obscured, with a line-of-sight column density N H ≥ 1022 cm−2 at a 90% confidence level. Four of these sources show significant obscuration with N H ≥ 1023 cm−2 and two additional sources are candidate Compton-thick Active Galactic Nuclei (CT-AGNs) with N H ≥ 1024 cm−2. These two sources, 2MASX J02051994–0233055 and IRAS 11058−1131, are the latest addition to the previous 3 CT-AGN candidates found using our strategy for soft X-ray follow-up of BAT sources. Here we present the results of our methodology so far, and analyze the effectiveness of applying different selection criteria to discover CT-AGN in the local Universe. Our selection criteria has an ∼20% success rate of discovering heavily obscured AGN whose CT nature is confirmed by follow-up NuSTAR observations. This is much higher than the ∼5% found in blind surveys.
3 citations
TL;DR: In this article , the authors presented a new X-ray spectroscopic study of active galactic nuclei (AGNs) at intermediate-redshift (0.1c$) to characterize the various manifestations of winds in the X-rays driven from supermassive black holes in AGNs.
Abstract: We present a new X-ray spectroscopic study of $22$ luminous ($2\times10^{45}\lesssim L_{\rm bol}\rm /erg\,s^{-1} \lesssim 2\times10^{46}$) active galactic nuclei (AGNs) at intermediate-redshift ($0.1 \lesssim z \lesssim 0.4$), as part of the SUpermassive Black hole Winds in the x-rAYS (SUBWAYS) sample, mostly composed of quasars (QSOs) and type\,1 AGN. Here, 17 targets were observed with \textit{XMM-Newton} between 2019--2020 and the remaining 5 are from previous observations. The aim of this large campaign ($1.45\,\rm Ms$ duration) is to characterise the various manifestations of winds in the X-rays driven from supermassive black holes in AGN. In this paper we focus on the search and characterization of ultra-fast outflows (UFOs), which are typically detected through blueshifted absorption troughs in the Fe\,K band ($E>7\,\rm keV$). By following Monte Carlo procedures, we confirm the detection of absorption lines corresponding to highly ionised iron (e.g., Fe\,\textsc{xxv}\,H$\alpha$, Fe\,\textsc{xxvi}\,Ly$\alpha$) in 7/22 sources at the $\gtrsim95\%$ confidence level (for each individual line). The global combined probability of such absorption features in the sample is $>99.9\%$. The SUBWAYS campaign extends at higher luminosity and redshifts than previous local studies on Seyferts, obtained using \xmm and \suzaku observations. We find a UFO detection fraction of $\sim30\%$ on the total sample that is in agreement with the previous findings. This work independently provides further support for the existence of highly-ionised matter propagating at mildly relativistic speed ($\gtrsim0.1c$) in a considerable fraction of AGN over a broad range of luminosities, which is expected to play a key role in the self-regulated AGN feeding-feedback cycle, as also supported by hydrodynamical multiphase simulations.
3 citations
TL;DR: In this article , the authors presented new joint XMM-Newton and NuSTAR observations of APM08279 + 5255, a gravitationally-lensed, broad absorption line quasar (Z = 3 . 91).
Abstract: We present new joint XMM-Newton and NuSTAR observations of APM08279 + 5255, a gravitationally-lensed, broad-absorption line quasar ( z = 3 . 91). After showing a fairly stable flux ( f 2 − 10 (cid:39) 4 − 5 . 5 × 10 − 13 ergs − 1 ) from 2000 to 2008, APM08279 + 5255 was found in a fainter state in the latest X-ray exposures ( f 2 − 10 (cid:39) 2 . 7 × 10 − 13 ergs − 1 ), which can likely be ascribed to a lower X-ray activity. Moreover, the 2019 data present a prominent FeK α emission line and do not show any significant absorption line. This fainter state, coupled to the first hard X-ray sampling of APM08279 + 5255, allowed us to measure X-ray reflection and the high-energy cuto ff in this source for the first time. From the analysis of previous XMM-Newton and Chandra observations, X-ray reflection is demonstrated to be a long-lasting feature of this source, but less prominent prior to 2008, possibly due to a stronger primary emission. The estimated high-energy cuto ff ( E cut = 99 + 91 − 35 keV) sets a new redshift record for the farthest ever measured and places APM08279 + 5255 in the allowed region of the compactness-temperature diagram of X-ray coronae, in agreement with previous results on high- z quasars.
2 citations
TL;DR: In this paper , a multi-epoch monitoring with NuSTAR and XMM-Newton of NGC 1358, a nearby Seyfert 2 galaxy whose properties made it a promising candidate X-ray changing-look active galactic nucleus (AGN), was presented.
Abstract: We present the multi-epoch monitoring with NuSTAR and XMM-Newton of NGC 1358, a nearby Seyfert 2 galaxy whose properties made it a promising candidate X-ray changing-look active galactic nucleus (AGN), i.e., a source whose column density could transition from its 2017 Compton-thick (having LOS hydrogen column density N H,LOS > 1024 cm−2) state to a Compton-thin (N H,LOS < 1024 cm−2) one. The multi-epoch X-ray monitoring confirmed the presence of significant N H,LOS variability over timescales of weeks to years, and allowed us to confirm the changing-look nature of NGC 1358, which has most recently been observed in a Compton-thin status. Multi-epoch monitoring with NuSTAR and XMM-Newton is demonstrated to be highly effective in simultaneously constraining three otherwise highly degenerate parameters: the torus average column density and covering factor, and the inclination angle between the torus axis and the observer. We find a tentative anticorrelation between column density and luminosity, which can be understood under the framework of chaotic cold accretion clouds driving recursive AGN feedback. The monitoring campaign of NGC 1358 has proven the efficiency of our newly developed method to select candidate N H,LOS-variable, heavily obscured AGN, which we plan to soon extend to a larger sample to better characterize the properties of the obscuring material surrounding accreting supermassive black holes, as well as to constrain AGN feeding models.
2 citations
TL;DR: In this paper , the authors presented X-ray follow-up observations of a z ≈ 6 quasi-stellar objects (QSOs) J1641 + 3755, which was found to be remarkably Xray bright in a 2018 Chandra dataset, implying that its X-rays decreased by a factor (cid:38) 7 on a notably short timescale (i.e., ≈ 115 rest-frame days).
Abstract: Explaining the existence of supermassive black holes (SMBHs) with M BH (cid:38) 10 8 M (cid:12) at z (cid:38) 6 is a persistent challenge to modern astrophysics. Multi-wavelength observations of z (cid:38) 6 quasi-stellar objects (QSOs) reveal that, on average, their accretion physics is similar to that of their counterparts at lower redshift. However, QSOs showing properties that deviate from the general behavior can provide useful insights into the physical processes responsible for the rapid growth of SMBHs in the early universe. We present X-ray ( XMM-Newton , 100 ks) follow-up observations of a z ≈ 6 QSO, J1641 + 3755, which was found to be remarkably X-ray bright in a 2018 Chandra dataset. J1641 + 3755 is not detected in the 2021 XMM-Newton observation, implying that its X-ray flux decreased by a factor (cid:38) 7 on a notably short timescale (i.e., ≈ 115 rest-frame days), making it the z > 4 QSO with the largest variability amplitude. We also obtained rest-frame UV spectroscopic and photometric data with the Large Binocular Telescope ( LBT ). Surprisingly, comparing our LBT photometry with archival data, we found that J1641 + 3755 became consistently brighter in the rest-frame UV band from 2003 to 2016, while no strong variation occurred from 2016 to 2021. Its rest-frame UV spectrum is consistent with the average spectrum of high-redshift QSOs. Multiple narrow absorption features are present, and several of them can be associated with an intervening system at z = 5 . 67. Several physical causes can explain the variability properties of J1641 + 3755, including intrinsic variations of the accretion rate, a small-scale obscuration event, gravitational lensing due to an intervening object, and an unrelated X-ray transient in a foreground galaxy in 2018. Accounting for all of the z > 6 QSOs with multiple X-ray observations separated by > 10 rest-frame days, we found an enhancement of strongly (i.e., by a factor > 3) X-ray variable objects compared to QSOs at later cosmic times. This finding may be related to the physics of fast accretion in high-redshift
2 citations
TL;DR: In this article , preliminary results of the BeppoSAX observation of the radio-quiet AGN 1H0419-577 are presented, showing that despite its broad line optical spectrum, the intermediate X-ray spectrum (i.e. 2 − 10 keV) is flatter than typically observed in Seyfert 1s and no iron line is significantly detected.
Abstract: The preliminary results of the BeppoSAX observation of the radio-quiet AGN 1H0419-577 are presented. Despite its broad line optical spectrum, the intermediate X–ray spectrum (i.e. 2–10 keV) is flatter than typically observed in Seyfert 1s and no iron line is significantly detected. Even more intriguingly, a 1992 ROSAT pointed observation suggests a dramatic (∆Γ ≃ 1) change in the spectral shape for E < ∼ 2 keV . Such behavior is briefly discussed in the framework of our current understanding of Comptonization scenarios in the nuclear regions of radio–quiet AGN.