arXiv subjects

S. Marchesi

Publications and source records attributed to S. Marchesi.

At least 19 recordsLinked to original sources

arXiv2026

The WISSHFUL program: the highest redshift UFO discovered in a non-lensed QSO

We present the first results from the WISSHFUL program, an XMM-Newton heritage program targeting luminous QSOs at Cosmic Noon. We report on recent simultaneous XMM-Newton and NuSTAR observations of the Super-Eddington accreting quasar WISSH13 at z=3.294, which provide the highest quality broadband X-ray spectrum to date for a non-lensed QSO at this redshift. Physical modeling of the continuum reveals a soft photon index ($\Gamma\sim2$) and strong reflection ($R\sim1.4-1.8$), despite the weak narrow Fe emission, and a low high-energy cut-off ($E_{cut}\sim60-80$ keV, $kTe = 15-20$ keV, depending on the model adopted). Most notably, we detect two significant (at $96.7\%$ and $98.9\%$ confidence level, respectively) absorption features at $\sim7.5$ and $\sim10$ keV rest-frame, interpreted as a blueshifted blend of Fe XXV He$\alpha$ and Fe XXVI Ly$\alpha$. These features indicate the presence of two kinematic components of a highly ionized, high column Ultra-Fast Outflow (UFO) with a velocity of $v_{out}\sim0.1c$ and $v_{out}\sim0.3c$, respectively. The slower wind is consistently detected in an archival 2017 XMM-Newton observation, whereas the faster wind is detected only in 2024. This stratified and variable wind exhibits extreme energetics, with a mass outflow rate of $\dot{M}_{out}\sim20M_{\odot}/yr$ (corresponding to $15\% \dot{M}_{acc}$) for each component, and a kinetic power of the order of $\sim1$ and $\sim10\%$ of the bolometric luminosity, respectively. While this represents one of the most powerful UFOs ever detected, its kinetic power is a similar fraction of the QSO's bolometric luminosity compared to lower-redshift AGN. We present several theoretical frameworks to explain the peculiar accretion and ejection properties of this remarkable QSO at Cosmic Noon.

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arXiv2026

A Serendipitous NuSTAR Detection of a Giant Radio Source Harboring an Obscured Active Galactic Nucleus

Giant radio sources (GRSs) harbor the Universe's largest structures generated by individual galaxies, with projected source sizes exceeding 700 kpc. These enigmatic objects have been mainly studied at radio frequencies, and their physical properties in the high-energy domain are poorly understood. Here we present the results of a multiwavelength study focused on NuSTAR J112829+5831.8 (J1128+5831), the only known GRS serendipitously detected with the Nuclear Spectroscopic Telescope Array. Being located in proximity to the famous interacting galaxy system, Arp 299, J1128+5831 has been serendipitously observed also by the Chandra X-ray Observatory, Hubble Space Telescope, and XMM-Newton satellites. From radio observations with the Low Frequency Array, the NRAO VLA Sky Survey and the Very Large Array Sky Survey, we have determined that J1128+5831 has an overall steep radio spectrum ($\alpha=-0.86$; $F_\nu\propto\nu^\alpha$) and a low core dominance ($C_{\rm D}=-2.4$, in log-scale), indicating the source to be viewed at large angles. From the X-ray spectral analysis, we found J1128+5831 to harbor an obscured active galactic nucleus (AGN) with neutral hydrogen column density exceeding $10^{23}$ cm$^{-2}$. Its optical spectrum, taken with the Dark Energy Spectroscopic Instrument, exhibits prominent narrow emission lines but lacks broad components, thus confirming J1128+5831 to be a Type 2 AGN powered by a radiatively efficient accreting system. Overall, the broadband properties of J1128+5831 are consistent with those observed for the general GRS population.

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arXiv2026

Source identification for the Swift-BAT 150-month hard X-ray catalog using soft X-ray observations

We present a comprehensive catalog of 251 potential counterparts for 250 unassociated hard X-ray sources detected in the Swift Burst Alert Telescope (BAT) 150-month hard X-ray survey. Over 150 months of observation, BAT has detected 2339 sources in the 15-150 keV energy range. Among these, 344 do not have a previously identified low-energy counterpart. Our study focuses on the analysis of soft X-ray observations at energies below 10 keV, spatially overlapping with these new Swift-BAT hard X-ray sources. Such observations were taken with Chandra, Swift-XRT, eROSITA, and XMM-Newton. Within the sample of 251 potential counterparts, 94 (37 percent) are identified as active galactic nuclei and 58 (23 percent) as galaxies. The remaining 99 sources (40 percent) include pulsars, cataclysmic variables, and unclassified soft X-ray counterparts in the 0.5-10 keV band. Redshift information is available for 139 out of the 251 sources, and its distribution is in close agreement with the redshift distribution of previous BAT catalogs. We also present the results of a small optical spectroscopy campaign of 9 out of 58 galaxies. The majority of these are classified as Seyfert 2 galaxies at redshifts slightly larger than the median of the BAT AGN sample.

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arXiv2025

The properties of X-ray selected AGN in protoclusters pinpointed by Enormous Lya Nebulae

Protoclusters of galaxies are overdense regions of the Universe characterized by large gas reservoirs. Such environments make them perfect laboratories to investigate galaxy-AGN co-evolution and the growth of SMBHs. Galaxies living in such a dense regions are expected to growth efficiently their SMBH, resulting in a higher incidence of AGN than in the field. Some protoclusters exhibit extended Ly$\alpha$ nebulae in their central region, pinpointing the presence of massive gas reservoirs, but whose main powering mechanism is still debated. We aim to investigate the AGN population, and AGN enhancement, in three protoclusters at 2.3 < z < 3.2 which host enormous Ly$\alpha$ nebulae (ELANe). Additionally, we search for the presence of X-ray diffuse emission in the same region of the Ly$\alpha$ nebulae to reveal multi-phase gas in these protoclusters. We use deep (190-270 ks) Chandra observations to identify AGN among the protocluster members and perform X-ray spectral analysis to derive the properties of those sources. We compare the AGN fraction and space density with those observed in other known protoclusters and from the field environment. We find 11 X-ray detected AGN in the three protoclusters. Each structure hosts a central, X-ray powerful (log$(L_{\rm X}/{\rm erg \, s^{-1}}) \sim 45-46$), QSO, while the other X-ray sources are mostly moderately luminous (log$(L_{\rm X}/{\rm erg \, s^{-1}}) \sim 44$) and obscured Compton-Thin AGN. The fraction of AGN in our targets is comparable with estimates for other protoclusters, and significantly higher than what is found for low-redshift clusters. We also find a significant enhancement (2-4 dex) of AGN density with respect to the field and to non active galaxies in the protoclusters. Finally, we find no significant soft X-ray diffuse emissions from the nebulae, thus ruling out gravitational heating as the main powering mechanism of the ELANe.

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arXiv2025

The Compton-thick AGN Population and the $N_{\rm H}$ Distribution of Low-mass AGN in our Cosmic Backyard

We present a census of the Compton-thick (CT) active galactic nucleus (AGN) population and the column density ($N_{\rm{H}}$) distribution of AGN in our cosmic backyard using a mid-infrared selected AGN sample within 15 Mpc. The column densities are measured from broadband X-ray spectral analysis, mainly using data from $\textit{Chandra}$ and $\textit{NuSTAR}$. Our sample probes AGN with intrinsic 2-10 keV luminosities of $L_{\rm 2-10, int} = 10^{37}$-$10^{43}$ erg s$^{-1}$, reaching a parameter space inaccessible to more distant samples. We directly measure a 32$^{+30}_{-18}\%$ CT AGN fraction and obtain an $N_{\rm{H}}$ distribution that agrees with that inferred by the $\textit{Swift}$-BAT survey. Restricting the sample to the largely unexplored domain of low-luminosity AGN with $L_{\rm 2-10, int}$ $\leq$ $10^{42}$ erg s$^{-1}$, we found a CT fraction of 19$^{+30}_{-14}\%$, consistent with those observed at higher luminosities. Comparing the host-galaxy properties between the two samples, we find consistent star formation rates, though the majority of our galaxy have lower stellar masses (by $\approx 0.3$ dex). In contrast, the two samples have very different black hole mass ($M_{\rm BH}$) distributions, with our sample having $\approx$1.5 dex lower mean mass ($M_{\rm BH}$ $\sim$ 10$^{6}$ $M_\odot$). Additionally, our sample contains a significantly higher number of LINERs and H$_{\rm{II}}$-type nuclei. The Eddington ratio range probed by our sample, however, is the same as $\textit{Swift}$-BAT, although the latter dominates at higher accretion rates, and our sample is more evenly distributed. The majority of our sample with $\lambda_{\rm Edd} \ge$ 10$^{-3}$ tend to be CT, while those with $\lambda_{\rm Edd} <$ 10$^{-3}$ are mostly unobscured or mildly obscured.

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arXiv2025

X-ray polarization observations of NGC 2110 with IXPE

X-ray polarimetric observations from the Imaging X-ray Polarimeter Explorer (IXPE) is an excellent tool for probing the geometry and dynamics of X-ray emitting corona in active galactic nuclei (AGN). This work aims to investigate the geometry of the X-ray corona in the Seyfert 2 AGN, NGC 2110, using its first polarimetric observation with IXPE, conducted over a net exposure of 554 ks beginning on October 16, 2024. We performed a model-independent analysis of the 2-8 keV IXPE polarimetric observation to estimate the polarization properties of NGC 2110. Furthermore, we performed spectral and spectro-polarimetric analyses combining IXPE data with archival observations from NuSTAR, XMM-Newton, and Swift-XRT to derive detailed spectral and polarization properties. From the spectro-polarimetric analyses, an upper limit on the polarization degree (PD) of 7.6% (at the 99% confidence) was estimated in the 2-8 keV band. The spectro-polarimetric analysis in the 5.66-8 keV band yielded a looser upper limit of 27% at the 99 % confidence. Comparing the measured polarization properties, coronal parameters, and inclination angle of NGC 2110 with the Monte Carlo radiative transfer (MONK) simulations suggest that the current polarization measurements lack the sensitivity to place definitive constraints on the coronal geometry. The upper limits on PD, as derived from our analysis at the 99% confidence level, indicate that polarization remains undetected at a statistically significant level. Consequently, we are unable to determine whether the corona is elongated along the disk or more compact and spherical. Future observations with improved sensitivity will be crucial to breaking these degeneracies and providing deeper insight into the coronal structure of NGC 2110.

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arXiv2025

Swift-XRT and NuSTAR Monitoring of Obscuration Variability in Mrk 477

We present the analysis of 15 X-ray observations of Mrk 477, a nearby Seyfert 2 active galactic nucleus, with the objective to monitor its obscuring column density variability. The full dataset consists of five archival observations, split into two XMM-Newton, two NuSTAR and one Chandra observation, plus two dedicated monitoring campaigns. The monitoring campaigns were performed with Swift-XRT and NuSTAR, containing five observations each. We performed a simultaneous analysis using self-consistent torus models, deriving geometric properties of the torus as well as the obscuration along the line of sight. Mrk 477 is best modeled with a torus with large covering factor yet low column density (on average). Its line of sight column density oscillates between $1.5-7\times10^{23}$~cm$^{-2}$. Mrk~477 presents frequent obscuring column density variability, on timescales as short as $\sim2$~weeks. The probability of drawing a pair of obscuration-variable observations for Mrk~477 when having 2, 3, and 4 observations is 40\%, 78\% and 95\%, respectively. Adding the results of this work to those of another 26 sources, we find a trend of increasing obscuration variability with time (from $\sim20$\% at $\Delta t<10$~days, to $\sim60-70$\% at timescales larger than 5 years). We discuss whether this is compatible with the majority of obscuration variability coming from broad line region clouds.

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arXiv2024

A Multi-Wavelength Characterization of the Obscuring Medium at the Center of NGC 6300

Most of the super-massive black holes in the Universe accrete material in an obscured phase. While it is commonly accepted that the "dusty torus" is responsible for the nuclear obscuration, its geometrical, physical, and chemical properties are far from being properly understood. In this paper, we take advantage of the multiple X-ray observations taken between 2007 and 2020, as well as of optical to far infra-red (FIR) observations of NGC 6300, a nearby ($z=0.0037$) Seyfert 2 galaxy. The goal of this project is to study the nuclear emission and the properties of the obscuring medium, through a multi-wavelength study conducted from X-ray to IR. We perform a simultaneous X-ray spectral fitting and optical-FIR spectral energy distribution (SED) fitting to investigate the obscuring torus. For the X-ray spectral fitting, physically motivated torus models, such as borus02, UXClumpy and XClumpy are used. The SED fitting is done using XCIGALE. Through joint analysis, we constrain the physical parameters of the torus and the emission properties of the accreting supermassive black hole. Through X-ray observations taken in the last 13 years, we have not found any significant line-of-sight column density variability for this source, but observed the X-ray flux dropping $\sim40-50\%$ in 2020 with respect to previous observations. The UXClumpy model predicts the presence of an inner ring of Compton-thick gaseous medium, responsible for the reflection dominated spectra above 10 keV. Through multi-wavelength SED fitting, we measure an Eddington accretion rate $\lambda_{\rm{Edd}}\sim2\times10^{-3}$, which falls in the range of the radiatively inefficient accretion solutions.

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arXiv2024

Hydrogen Column Density Variability in a Sample of Local Compton-Thin AGN II

We present the multi-epoch analysis of 13 variable, nearby (z<0.1), Compton-thin (22<logN_H<24) active galactic nuclei (AGN) selected from the 105-month BAT catalog. Analyzing all available archival soft and hard X-ray observations, we investigate the line-of-sight hydrogen column density (N_H) variability on timescales ranging from a few days to approximately 20 years. Each source is analyzed by simultaneously modeling the data with three physical torus models, providing tight constraints on torus properties, including the covering factor, the cloud dispersion, and the torus average hydrogen column density (N_H,av). For each epoch, we measure the N_H and categorize the source as `N_H Variable', `Non-variable in N_H', or `Undetermined' based on the degree of variability. Our final sample includes 27 variable, Compton-thin AGN after implementing another 14 AGN analyzed in our previous work. We find that all sources require either flux or N_H variability. We classify 37% of them as `N_H Variable', 44% as `Non-variable in N_H', and 19% as `Undetermined'. Noticeably, there is no discernible difference between geometrical and intrinsic properties among the three variability classes, suggesting no intrinsic differences between the N_H-variable and non-variable sources. We measure the median variation in N_H between any observation pair of the same source to be 25% with respect to the lowest N_H measure in the pair. Furthermore, 48% of the analyzed sources require the inclusion of a Compton-thick reflector in the spectral fitting. Among these, the 30% exhibits recorded 22 GHz water megamaser emission, suggesting a potential shared nature between the two structures.

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arXiv2024

COSMOS2020: Investigating the AGN-obscured accretion phase at $z\sim 1$ via [NeV] selection

We investigated the properties of 94 [NeV]3426AA-selected type 2 AGN in COSMOS at z=0.6-1.2, performing optical-to-far-infrared spectral energy distribution fitting. In addition, we analyze the X-ray spectra of the X-ray-detected sources to obtain reliable values of the AGN obscuration and intrinsic luminosity. We found that more than two-thirds of our sample is composed of very obscured sources, with about 20% of the sources being candidate CT-AGN and half being AGNs in a strong phase of accretion. With respect to non-active galaxies, we find a higher fraction of sources within the main sequence and little evidence for AGNs quenching the SF. The comparison with the prediction from the in situ co-evolution model suggests that [NeV] is an effective tool for selecting galaxies in the obscured growth phase of the BH-galaxy co-evolution paradigm. We find that the "quenching phase" is still to come for most of the sample and only few galaxies show evidence of quenched SF activity.

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arXiv2024

Winds of change: the nuclear and galaxy-scale outflows and the X-ray variability of 2MASS 0918+2117

Powerful outflows from active galactic nuclei (AGN) can significantly impact the gas reservoirs of their host galaxies. However, it is still unclear how these outflows can propagate from the very central regions of galaxies to their outskirts, and whether nuclear winds can be driven by and/or be responsible for drastic spectral transitions. In this work we test feedback propagation models on the case test of 2MASS 0918+2117 (2M0918), a z=0.149 X-ray variable AGN, which showed tentative evidence for nuclear ultra-fast outflows (UFOs) in a 2005 XMM-Newton observation. We also investigate whether UFOs can be related to the observed X-ray variability. We observed 2M0918 with XMM-Newton and NuSTAR in 2020 to confirm the presence and characterize the UFOs. We perform a kinematic analysis of the 2005 SDSS optical spectrum to reveal and measure the properties of galaxy-scale ionized outflows. Furthermore, we construct 20-year-long lightcurves of observed flux, line-of-sight column density, and intrinsic accretion rate from the spectra of the first 4 SRG/eROSITA all-sky surveys and archival observations from Chandra and XMM-Newton.We significantly detect UFOs with v$\sim$0.16c and galaxy-scale ionized outflows with velocities of $\sim$ 700 km/s. We also find that the drastic X-ray variability (factors >10) can be explained both in terms of variable obscuration and variable intrinsic luminosity.Comparing the energetics of the two outflow phases, 2M0918 is consistent with momentum-driven wind propagation. 2M0918 expands the sample of AGN with both UFOs and ionized gas winds from 5 to 6, and brings the sample of AGN hosting multiscale outflows to 19, contributing to a clearer picture of feedback physics. From the variations in accretion rate, column density, and ionization level of the obscurer, we propose a scenario that connects obscurers, an accretion enhancement, and the emergence of UFOs

astro-ph.HE↗

arXiv2024

AGN X-ray luminosity function and absorption function in the Early Universe ($3\leq z \leq 6$)

The XLF of AGN offers a robust tool to study the evolution and the growth of SMBHs over cosmic time. Owing to the limited area probed by X-ray surveys, optical surveys are routinely used to probe the accretion in the high redshift Universe $z\geq 3$. However, optical surveys may be incomplete because they are strongly affected by dust redenning. In this work, we derive the XLF and its evolution at high redshifts using a large sample of AGNs selected in different fields with various areas and depths covering a wide range of luminosities. Additionally, we put the tightest yet constraints on the absorption function in this redshift regime. In particular, we use more than 600 soft X-ray selected high-z sources in the Chandra Deep fields, the Chandra COSMOS Legacy survey and the XMM-XXL northern field. We derive the X-ray spectral properties for all sources via spectral fitting, using a consistent technique and model. For modeling the parametric form of the XLF and the absorption function, we use a Bayesian methodology allowing us to correctly propagate the uncertainties for the observed X-ray properties of our sources and also the absorption effects. The evolution of XLF is in agreement with a pure density evolution model similar to what is witnessed at optical wavelengths, although a luminosity dependent density evolution model cannot be securely ruled out. A large fraction ($60\%)$ of our sources are absorbed by column densities of $\rm N_H \geq 10^{23} cm^{-2} $, while $17$\% of the sources are CTK. Our results favor a scenario where both the ISM of the host and the AGN torus contribute to the obscuration. The derived BHAD is in agreement with the simulations, if one takes into account that the X-ray AGN are hosted by massive galaxies, while it differs from the one derived using JWST data. The latter could be due to the differences in the AGN and host-galaxy properties.

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arXiv2023

The High Energy X-ray Probe (HEX-P): The Circum-nuclear Environment of Growing Supermassive Black Holes

Ever since the discovery of the first Active Galactic Nuclei (AGN), substantial observational and theoretical effort has been invested into understanding how massive black holes have evolved across cosmic time. Circum-nuclear obscuration is now established as a crucial component, with almost every AGN observed known to display signatures of some level of obscuration in their X-ray spectra. But despite more than six decades of effort, substantial open questions remain: How does the accretion power impact the structure of the circum-nuclear obscurer? What are the dynamical properties of the obscurer? Can dense circum-nuclear obscuration exist around intrinsically weak AGN? How many intermediate mass black holes occupy the centers of dwarf galaxies? In this paper, we showcase a number of next-generation prospects attainable with the High Energy X-ray Probe (https://hexp.org) to contribute towards solving these questions in the 2030s. The uniquely broad (0.2--80 keV) and strictly simultaneous X-ray passband of HEX-P makes it ideally suited for studying the temporal co-evolution between the central engine and circum-nuclear obscurer. Improved sensitivities and reduced background will enable the development of spectroscopic models complemented by current and future multi-wavelength observations. We show that the angular resolution of HEX-P both below and above 10 keV will enable the discovery and confirmation of accreting massive black holes at both low accretion power and low black hole masses even when concealed by thick obscuration. In combination with other next-generation observations of the dusty hearts of nearby galaxies, HEX-P will hence be pivotal in paving the way towards a complete picture of black hole growth and galaxy co-evolution.

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arXiv2023

Optical and mid-infrared line emission in nearby Seyfert galaxies

Line ratio diagnostics provide valuable clues on the source of ionizing radiation in galaxies with intense black hole accretion and starbursting events, such as local Seyfert or galaxies at the peak of the star formation history. We aim to provide a reference joint optical and mid-IR analysis for studying AGN identification via line ratios and testing predictions from photoionization models. We obtained homogenous optical spectra with the Southern Africa Large Telescope for 42 Seyfert galaxies with Spitzer/IRS spectroscopy and X-ray to mid-IR multiband data available. After confirming the power of the main optical ([OIII]) and mid-IR ([NeV], [OIV], [NeIII]) emission lines in tracing AGN activity, we explore diagrams based on ratios of optical and mid-IR lines by exploiting photoionization models of different ionizing sources (AGN, star formation and shocks). We find that pure AGN photoionization models are good at reproducing observations of Seyfert galaxies with an AGN fractional contribution to the mid-IR (5-40 micron) emission larger than 50 per cent. For targets with a lower AGN contribution these same models do not fully reproduce the observed mid-IR line ratios. Mid-IR ratios like [NeV]/[NeII], [OIV]/[NeII] and [NeIII]/[NeII] show a dependence on the AGN fractional contribution to the mid-IR unlike optical line ratios. An additional source of ionization, either from star formation or radiative shocks, can help explain the observations in the mid-IR. Among combinations of optical and mid-IR diagnostics in line ratio diagrams, only those involving the [OI]/Halpha ratio are promising diagnostics for simultaneously unraveling the relative role of AGN, star formation and, shocks. A proper identification of the dominant ionizing source would require the exploitation of analysis tools based on advanced statistical techniques as well as spatially resolved data.

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arXiv2023

AGN feedback in an infant galaxy cluster: the LOFAR-Chandra view of the giant FRII radio galaxy J103025+052430 at z=1.7

In the nearby universe jets from AGN are observed to have a dramatic impact on their surrounding extragalactic environment. Their effect at the `cosmic noon' (z>1.5), the epoch when star formation and AGN activity peak, is instead much less constrained. Here we present a study of the giant (750 kpc) radio galaxy 103025+052430 located at the centre of a protocluster at redshift z=1.7, with a focus on its interaction with the external medium. We present new LOFAR observations at 144 MHz, which we combine with VLA 1.4 GHz and 0.5-7 keV Chandra archival data. The new map at 144 MHz confirms that the source has a complex morphology, possibly consistent with the `hybrid morphology' classification. The large size of the source gave us the possibility to perform a resolved radio spectral index analysis, a very unique opportunity for a source at such high redshift. This reveals a tentative flattening of the radio spectral index at the edge of the backflow in the Western lobe, which might be indicating plasma compression. The spatial coincidence between this region and the thermal X-ray bubble C suggests a causal connection between the two. Contrary to previous estimates for the bright X-ray component A, we find that inverse Compton scattering between the radio-emitting plasma of the Eastern lobe and the CMB photons can account for a large fraction (~45%-80%) of its total 0.5-7 keV measured flux. Finally, the X-ray bubble C, which is consistent with a thermal origin, is found to be significantly overpressurised with respect to the ambient medium. This suggests that it will tend to expand and release its energy in the surroundings, contributing to the overall intracluster medium heating. Overall, 103025+052430 gives us the chance to investigate the interaction between AGN jets and the surrounding gas in a system that is likely the predecessor of the rich galaxy clusters we all well know at z=0.

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arXiv2023

Comparing the host galaxy ages of X-ray selected AGN in COSMOS: Obscured AGN are associated with older galaxies

We explore the properties of the host galaxies of X-ray selected AGN in the COSMOS field using the Chandra Legacy sample and the LEGA-C survey VLT optical spectra. Our main goal is to compare the relative ages of the host galaxies of the obscured and unobscured AGN by means of the calcium break Dn(4000) and the Hdelta Balmer line. The host galaxy ages are examined in conjunction with other properties such as the galaxy stellar mass, and star-formation rate as well as the AGN Eddington ratio. Our sample consists of 50 unobscured or mildly obscured (logN_H (cm-2) < 23) and 23 heavily obscured AGN (log N_H (cm-2) >23) in the redshift range z=0.6-1. We take specific caution to create control samples in order to match the exact luminosity and redshift distributions for the obscured and unobscured AGN. The majority of unobscured AGN appear to live in young galaxies in contrast to the obscured AGN which appear to live in galaxies located between the young and old galaxy populations. This finding may be in contrast to those evolutionary AGN unification models which postulate that the AGN begin their life in a heavy obscuration phase. The host galaxies of the obscured AGN have significantly lower levels of specific star-formation. At the same time the obscured AGN have lower Eddington ratios indicating a link between the star-formation and the black hole accretion. We find that the distribution of the stellar masses of the host galaxies of obscured AGN is skewed towards higher stellar masses in agreement with previous findings. Our results on the relative age of obscured AGN are valid when we match our obscured and unobscured AGN samples according to the stellar mass of their host galaxies. All the above results become less conspicuous when a lower column density (log N_H(cm-2)= 21.5 or 22) is used to separate the obscured and unobscured AGN populations.

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arXiv2023

Hydrogen Column Density Variability in a Sample of Local Compton-Thin AGN

We present the analysis of multiepoch observations of a set of 12 variable, Compton-thin, local (z<0.1) active galactic nuclei (AGN) selected from the 100-month BAT catalog. We analyze all available X-ray data from \chandra, \xmm, and \nustar, adding up to a total of 53 individual observations. This corresponds to between 3 and 7 observations per source, probing variability timescales between a few days and $\sim 20$~yr. All sources have at least one \nustar observation, ensuring high-energy coverage, which allows us to disentangle the line-of-sight and reflection components in the X-ray spectra. For each source, we model all available spectra simultaneously, using the physical torus models \myt, \bor, and \uxc. The simultaneous fitting, along with the high-energy coverage, allows us to place tight constraints on torus parameters such as the torus covering factor, inclination angle, and average column density. We also estimate the line-of-sight column density ($N_{\rm H}$) for each individual observation. Within the 12 sources, we detect clear line-of-sight $N_{\rm H}$ variability in 5, non-variability in 5, and for 2 of them it is not possible to fully disentangle intrinsic-luminosity and $N_{\rm H}$ variability. We observe large differences between the average values of line-of-sight $N_{\rm H}$ (or $N_{\rm H}$ of the obscurer) and the average $N_{\rm H}$ of the torus (or $N_{\rm H}$ of the reflector), for each source, by a factor between $\sim2$ to $>100$. This behavior, which suggests a physical disconnect between the absorber and the reflector, is more extreme in sources that present $N_{\rm H}$ variability. $N_{\rm H}$-variable AGN also tend to present larger obscuration and broader cloud distributions than their non-variable counterparts. We observe that large changes in obscuration only occur at long timescales, and use this to place tentative lower limits on torus cloud sizes.

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arXiv2022

Identifying the 3FHL catalog: VI. Results of the 2019 Gemini optical spectroscopy campaign

Active galactic Nuclei (AGNs) with their relativistic jets pointed toward the observer, are a class of luminous gamma-ray sources commonly known as blazars. The study of this source class is essential to unveil the physical processes powering these extreme jets, to understand their cosmic evolution, as well as to indirectly probe the extragalactic background light. To do so, however, one needs to correctly classify and measure a redshift for a large sample of these sources. The Third Fermi-LAT Catalog of High-Energy Sources (3FHL) contains $1212$ blazars detected at energies greater than 10 GeV. However, $\sim$25% of these sources are unclassified and $\sim$56% lack redshift information. To increase the optical completeness of blazars in the 3FHL catalog, we devised an optical spectroscopic follow-up campaign using 4 $m$ and 8 $m$ telescopes. In this paper, we present the results of the last part of this campaign, where we observed 5 blazars using the 8 $m$ Gemini-S telescope in Chile. We report all 5 sources to be classified as BL Lacs, a redshift lower limit for 2 sources, and featureless spectra for the remaining 3 sources. We also performed a one-zone leptonic fit to the two sources with the redshift lower limits.

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