arXiv subjects

I. Georgantopoulos

Publications and source records attributed to I. Georgantopoulos.

At least 19 recordsLinked to original sources

arXiv2025

Harnessing the XMM-Newton data: X-ray spectral modelling of 4XMM-DR11 detections and 4XMM-DR11s sources

The XMM-Newton X-ray observatory has played a prominent role in astrophysics, conducting precise and thorough observations of the X-ray sky for the past two decades. The most recent iteration of the 4XMM catalogue and one of its latest data releases DR11 mark significant improvements over previous XMM-Newton catalogues, serving as a cornerstone for comprehending the diverse inhabitants of the X-ray sky. We employ detections and spectra extracted from the 4XMM-DR11 catalogue, subjecting them to fitting procedures using simple models. Our study operates within the framework of the XMM2ATHENA project, which focuses on developing state-of-the-art methods that exploit existing XMM-Newton data. We introduce and publicly release four catalogues containing measurements derived from X-ray spectral modelling of sources. The first catalogue encompasses outcomes obtained by fitting an absorbed power law model to all the extracted spectra for individual detections within the 4XMM-DR11 dataset. The second catalogue presents results obtained by fitting both an absorbed power law and an absorbed blackbody model to all unique physical sources listed in the 4XMM-DR11s catalogue, which documents source detection results from overlapping XMM-Newton observations. For the third catalogue we use the five band count rates derived from the pipe line detection of X-ray sources to mimic low resolution spectra to get a rough estimate of the spectral shape (absorbed power-law) of all 4XMM-DR11 detections. In the fourth catalogue, we conduct spectral analyses for the subset of identified sources with extracted spectra, employing various models based on their classification into categories such as AGN, stars, X-ray binaries, and cataclysmic variables. The scientific potential of these catalogues is highlighted by discussing the capabilities of optical and mid-infrared colours for selecting absorbed AGN. (abridged)

astro-ph.HE↗

arXiv2025

The incidence of X-ray AGN and non-AGN galaxies in the far-infrared: insights into host galaxy properties and AGN obscuration

We investigate the far-infrared (far-IR) incidence of X-ray-selected active galactic nuclei (AGN) and non-AGN galaxies as a function of stellar mass (M$_*$), star formation rate (SFR), and specific black hole accretion rate ($\lambda_{\text{sBHAR}}$), using data from five extragalactic fields (COSMOS, XMM-LSS, Stripe82, ELAIS-S1, and CDFS-SWIRE). We construct spectral energy distributions (SEDs) from optical-to-far-IR photometry to derive host galaxy properties and assess AGN obscuration. X-ray absorption is quantified using the 4XMM-DR11s catalog. Our final sample includes 172,697 non-AGN galaxies (53% Herschel-detected) and 2,417 X-ray AGN (73% Herschel-detected), with $10 < log\,[M_*/M_\sun] < 12$ and $0 < z < 2$. X-ray AGN exhibit a relatively flat far-IR detection rate across stellar mass and specific SFR ($sSFR = SFR / M_*$), unlike non-AGN galaxies, where detection correlates strongly with SFR. Among AGN, far-IR detection declines with increasing $\lambda_{\text{sBHAR}}$, despite rising SFR. Our results suggest X-ray AGN are preferentially found in gas-rich environments, where star formation and black hole accretion coexist. Far-IR incidence remains high across all sSFR bins, supporting a scenario in which AGN feedback regulates, rather than abruptly quenches, star formation. Comparing AGN and non-AGN SFRs without separating Herschel-detected from non-detected sources introduces biases. Obscured AGN show ~10% higher far-IR detection rates than unobscured ones, yet at similar $\lambda_{\text{sBHAR}}$, unobscured AGN tend to have higher SFR. This may suggest obscured AGN inhabit dustier systems with moderate star formation contributing to the far-IR. Our findings support a regulatory AGN feedback mode operating over extended timescales in gas-rich galaxies.

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arXiv2025

XXL-HSC: Host properties of X-ray detected AGNs in XXL clusters

There is compelling evidence that AGNs are strongly influenced by their environment. Therefore, studying the AGN population of clusters is essential, as both large-scale structures and AGN play key roles in galaxy evolution, though the interactions between these elements are still not well understood. The primary objective of this study is to unravel the different factors that may significantly affect the triggering of AGN activity in cluster galaxies, including galaxy merging and interactions with other galaxies, and ram pressure from the hot intracluster medium. For our purposes, we used 82 X-ray detected AGN found within a $4r_{500}$ radius of 164 X-ray detected and spectroscopically confirmed galaxy clusters of the XXL survey, up to a redshift of $z\sim$1. This field is covered by deep optical observations of the Hyper Suprime-Cam, which allows for a reliable morphological classification of galaxies. Furthermore, using the X-ray hardness ratio, the optical spectra and the SEDs of the X-ray sources, we have studied the obscuration and other AGN properties and the SFR of the hosts as further indicators of interactions. We found a moderately significant higher fraction of X-ray AGN in galaxy clusters hosted by merging or disturbed galaxies, compared to non-active cluster galaxies or X-ray AGN in the field. This excess is primarily localised in the cluster outskirts. Also, we discovered a higher number of X-ray-hard AGN (hence, possibly obscured) in clusters than in the field particularly in the outskirts. These findings further support the idea that galaxy mergers and interactions may serve as mechanisms for the triggering and obscuration of AGN activity. The relatively high number of disturbed, merging, and possibly obscured AGN hosts in cluster outskirts suggests that galaxy merging and interactions are key drivers in triggering AGN activity in these outer regions of clusters.

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arXiv2025

Identification of high-redshift X-ray active galactic nuclei in the 4XMM-DR11 serendipitous catalogue using DES data: Comparative analysis with optically-selected QSOs

X-rays provide a robust method in identifying AGN. However, in the high-redshift Universe, their space density is relatively low, and, in combination with the small areas covered by X-ray surveys, the selected AGN are poorly sampled. Deep optical/infrared data are essential for locating counterparts and determining redshifts. In this work, we leverage the XMM-Newton 4XMM-DR11 serendipitous catalogue alongside the extensive optical Dark Energy Survey and the near-infrared VISTA Hemisphere Survey (VHS) to select one of the largest high-z X-ray AGN samples to date. Our analysis focuses on the overlapping area of these surveys, covering about 185 $deg^2$. In addition, we aspire to compare the properties of the X-ray AGN with the optically-selected QSOs. For sources without spectroscopic data (80%), we estimated the photometric redshifts using both SED fitting and machine-learning algorithms. Among the 65,000 X-ray sources in the 4XMM-DES-VHS area, we ended up with 833 z>3.5 AGN (11% having spec-z information) with high reliability and a fraction of outliers {\eta}<10%. The sample completeness is 90%, driven by the depth of DES data. Only 10% of the X-ray selected AGN are also optical QSOs and vice versa. Our findings indicate an observed absorbed fraction ($\log N_H~[cm^{-2}] \geq 23$) of 20-40% for the X-ray AGN, significantly higher than that of optical QSOs. X-ray AGN exhibit fainter observed optical magnitudes and brighter mid-IR magnitudes than optical QSOs. Their median rest-frame SED shapes differ notably with optical QSOs being dominated by AGN emission in the UV-optical wavelengths. While the median SEDs of X-ray AGN suggest extinction in the UV-optical range, individual sources exhibit a wide range of spectral shapes, indicating significant diversity within the population. This analysis supports that X-ray and optically-selected AGN represent distinct and complementary populations.

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arXiv2024

The Compton-thick AGN luminosity function in the local Universe: A robust estimate combining BAT detections and NuSTAR spectra

The Compton-thick Active Galactic Nuclei (AGN) arguably constitute the most elusive class of sources as they are absorbed by large column densities above logN_H(cm^-2)=24. These extreme absorptions hamper the detection of the central source even in hard X-ray energies. In this work, we use both SWIFT and NuSTAR observations in order to derive the most accurate yet Compton-thick AGN luminosity function. We, first, compile a sample of candidate Compton-thick AGN (logN_H(cm^-2)= 24-25) detected in the Swift BAT all-sky survey in the 14-195 keV band. We confirm that they are Compton-thick sources by using the follow-up NuSTAR observations already presented in the literature. Our sample is composed of 44 sources, consistent with a column density of logN_H(cm^-2)=24-25 at the 90% confidence level. These have intrinsic luminosities higher than L(10-50 keV) ~ 3x10^41 erg/s and are found up to a redshift of z=0.05 (200 Mpc). We derive the luminosity function of Compton-thick AGN using a Bayesian methodology where both the full column density and the luminosity distributions are taken into account. The faint end of the luminosity function is flat, having a slope of 0.01(+0.51,-0.74), rather arguing against a numerous population of low luminosity Compton-thick AGN. Based on our luminosity function, we estimate that the fraction of Compton-thick AGN relative to the total number of AGN is of the order of 24 (+5,-5) % in agreement with previous estimates in the local Universe based on BAT samples.

astro-ph.GA↗

arXiv2024

Towards a complete census of luminous Compton-thick Active Galactic Nuclei in the local Universe

X-ray surveys provide the most efficient means for the detection of Active Galactic Nuclei (AGN). However, they face difficulties in detecting the most heavily obscured Compton-thick AGN. The BAT detector on board the Gehrels/Swift mission, operating in the very hard 14-195 keV band, has provided the largest samples of Compton-thick AGN in the local Universe. However, even these flux limited samples can miss the most obscured sources among the Compton-thick AGN population. A robust way to find these local sources is to systematically study volume-limited AGN samples detected in the IR or the optical part of the spectrum. Here, we utilize a local sample (<100 Mpc) of mid-IR selected AGN, unbiased against obscuration, to determine the fraction of Compton-thick sources in the local universe. When available we acquire X-ray spectral information for the sources in our sample from previously published studies. Additionally, to maximize the X-ray spectral information for the sources in our sample, we analyse, for the first time, eleven unexplored XMM-Newton and NuSTAR observations, identifying four new Compton-thick sources. Our results reveal an increased fraction of Compton-thick AGN among the sources that have not been detected by BAT of 44 %. Overall we estimate a fraction of Compton thick sources in the local universe of 25-30% among mid-IR selected AGN. We find no evidence for evolution of the AGN Compton-thick fraction with luminosity.

astro-ph.GA↗

arXiv2024

STONKS: Quasi-real time XMM-Newton transient detection system

Over recent decades, astronomy has entered the era of massive data and real-time surveys. This is improving the study of transient objects - although they still contain some of the most poorly understood phenomena in astrophysics, as it is inherently more difficult to obtain data on them. In order to help detect these objects in their brightest state, we have built a quasi-real time transient detection system for the XMM-Newton pipeline: the Search for Transient Objects in New detections using Known Sources (STONKS) pipeline. STONKS detects long-term X-ray transients by automatically comparing new XMM-Newton detections to any available archival X-ray data at this position, sending out an alert if the amplitude of variability between observations is over 5. This required an initial careful cross-correlation and flux calibration of various X-ray catalogs from different observatories (XMM-Newton, Chandra, Swift, ROSAT, and eROSITA). We also systematically computed the XMM-Newton upper limits at the position of any X-ray source covered by the XMM-Newton observational footprint, even without any XMM-Newton counterpart. The behavior of STONKS was then tested on all 483 observations performed with imaging mode in 2021. Over the 2021 testing run, STONKS provided $0.7^{+0.7}_{-0.5}$ alerts per day, about 80% of them being serendipitous. STONKS also detected targeted tidal disruption events, ensuring its ability to detect other serendipitous events. As a byproduct of our method, the archival multi-instrument catalog contains about one million X-ray sources, with 15% of them involving several catalogs and 60% of them having XMM-Newton upper limits. STONKS demonstrates a great potential for revealing future serendipitous transient X-ray sources, providing the community with the ability to follow-up on these objects a few days after their detection.

astro-ph.HE↗

arXiv2024

AGN populations in the local universe: their alignment with the main-sequence, characteristics of their stellar populations, accretion efficiency, and the impact of AGN feedback

In this study, we utilize a sample of 338 galaxies within the redshift range of $\rm 0.02<z<0.1$, drawn from the Sloan Digital Sky Survey (SDSS), for which there are available classifications, based on their emission line ratios. We, further, identify and select Compton-thick (CT) AGN through the use of X-ray and infrared luminosities at $12\,\mu m$. We construct the spectral energy distributions (SEDs) for all sources and fit them using the CIGALE code to derive properties related to both the AGN and host galaxies. Employing stringent criteria to ensure the reliability of SED measurements, our final sample comprises 14 CT AGN, 118 Seyfert 2 (Sy2), 82 composite, and 124 LINER galaxies. Our analysis reveals that, irrespective of their classification, the majority of the sources lie below the star-forming main-sequence (MS). Additionally, a lower level of AGN activity is associated with a closer positioning to the MS. Utilizing the D$_n$4000 spectral index as a proxy for the age of stellar populations, we observe that LINERs exhibit the oldest stellar populations compared to other AGN classes. Conversely, CT sources are situated in galaxies with the youngest stellar populations. Furthermore, LINER and composite galaxies tend to show the lowest accretion efficiency, while CT AGN, on average, display the most efficient accretion among the four AGN populations. Our findings are consistent with a scenario in which the different AGN populations might not originate from the same AGN activity burst. Early triggers in gas rich environments can create high accretion rate SMBHs leading to a progression from CT to Sy2, while later triggers in gas poor stages result in low accretion rate SMBHs like those found in LINERs.

astro-ph.GA↗

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 link among X-ray spectral properties, AGN structure and the host galaxy

In this work, we compare the SMBH and host galaxy properties of X-ray obscured and unobscured AGN. For that purpose, we use $\sim 35 000$ X-ray detected AGN in the 4XMM-DR11 catalogue for which there are available measurements for their X-ray spectral parameters, from the XMM2Athena Horizon 2020 European project. We calculate the host galaxy properties via SED fitting analysis. Our final sample consists of 1 443 AGN. In the first part of our analysis, we use different N$_H$ thresholds (10$^{23}$ cm$^{-2}$ or 10$^{22}$ cm$^{-2}$), taking also into account the uncertainties associated with the N$_H$ measurements, to classify these sources into obscured and unobscured. We find that obscured AGN tend to live in more massive systems that have lower SFR compared to their unobscured counterparts. However, only the difference in stellar mass, M$_*$, appears statistically significant ($>2σ$). The results do not depend on the N$_H$ threshold used to classify AGN. The differences in M$_*$ and SFR are not statistically significant for luminous AGN ($\rm log (L_{X,2-10 KeV}/erg s^{-1})> 44$). Our findings also show that unobscured AGN have, on average, higher specific black hole accretion rates compared to their obscured counterparts. In the second part of our analysis, we cross-match the 1 443 X-ray AGN with the SDSS DR16 quasar catalogue to obtain information on the SMBH properties of our sources. This results in 271 type 1 AGN, at $\rm z<1.9$. Our findings show that type 1 AGN with increased N$_H$ ($>10^{22}$ cm$^{-2}$) tend to have higher M$_{BH}$ compared to AGN with lower N$_H$ values, at similar M$_*$. The M$_{BH}$/M$_*$ ratio remains consistent for N$_H$ values below 10$^{22}$ cm$^{-2}$, but it exhibits signs of an increase at higher N$_H$ values. Finally, we detect a correlation between $Γ$ and Eddington ratio, but only for type 1 sources with N$_H<10^{22}$ cm$^{-2}$.

astro-ph.GA↗

arXiv2023

The properties of supermassive black holes and their host galaxies for type 1 and 2 AGN in the eFEDS and COSMOS fields

In this study, our primary objective is to compare the properties of SMBH and their host galaxies between type 1 and type 2 AGN. In our analysis, we use X-ray detected sources in two fields, namely the eFEDS and the COSMOS-Legacy. To classify the X-ray sources, we perform SED fitting analysis, using the CIGALE code. Ensuring the robustness of our analysis is paramount, and to achieve this, we impose stringent selection criteria. Thus, only sources with extensive photometric data across the optical, near- and mid-infrared part of the spectrum and reliable host galaxy properties and classifications were included. The final sample consists of 3,312 AGN, of which 3\,049 are classified as type 1 and 263 as type 2. The sources span a redshift range of $\rm 0.5 2$ and $\rm log,[L_{X,2-10keV}(ergs^{-1})]>44$. Similar patterns emerge when we categorize AGN based on their X-ray obscuration levels ($N_H$). However, in this case, the observed differences are pronounced only for low-to-intermediate L$_X$ AGN and are also sensitive to the $\rm N_H$ threshold applied for the AGN classification. These comprehensive findings enhance our understanding of the intricate relationships governing AGN types and their host galaxy properties across diverse cosmic epochs and luminosity regimes.

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arXiv2023

The STATiX pipeline for the detection of X-ray transients in three dimensions

The recent serendipitous discovery of a new population of short duration X-ray transients, thought to be associated with collisions of compact objects or stellar explosions in distant galaxies, has motivated efforts to build up statistical samples by mining X-ray telescope archives. Most searches to date however, do not fully exploit recent developments in the signal and imaging processing research domains to optimise searches for short X-ray flashes. This paper addresses this issue by presenting a new source detection pipeline, STATiX (Space and Time Algorithm for Transients in X-rays), which directly operates on 3-dimensional X-ray data cubes consisting of two spatial and one temporal dimension. The algorithm leverages wavelet transforms and the principles of sparsity to denoise X-ray observations and then detect source candidates on the denoised data cubes. The light curves of the detected sources are then characterised using the Bayesian blocks algorithm to identify flaring periods. We describe the implementation of STATiX in the case of XMM-Newton data, present extensive validation and performance verification tests based on simulations and also apply the pipeline to a small subset of seven XMM-Newton observations, which are known to contain transients sources. In addition to known flares in the selected fields we report a previously unknown short duration transient found by our algorithm that is likely associated with a flaring Galactic star. This discovery demonstrates the potential of applying STATiX to the full XMM-Newton archive.

astro-ph.HE↗

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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arXiv2022

Star-forming early- and quiescent late-type galaxies in the local Universe

The general consensus is that LTGs undergo intense star-formation activity, while ETGs are mostly inactive. We question this general rule and investigate the existence of star-forming ETGs and quiescent LTGs in the local Universe. By computing the physical properties of 2,209 such galaxies in the GAMA survey being morphologically classified and using information on their structural properties as well as the density of their local environment, we seek for understanding the differences from their 'typical' counterparts. We separate galaxies into subsets based on their dominant ionising process, making use of criteria based on the WH$_α$ width and the [NII/H$_α$] ratio. Taking advantage of the SED fitting code CIGALE we derive galaxy properties, such as the $M_\text{star}$, $M_\text{dust}$, and SFR and also estimate the unattenuated and the dust-absorbed stellar emission, for both the young and old stellar populations. Ongoing star-formation activity is found in 47% of ETGs and 8% of LTGs are quiescent. The star-forming E galaxies, together with the LBSs, constitute a population that follows very well the SFMS of spiral galaxies. The fraction of the luminosity originating from young stars in the star-forming ETGs is quite substantial ($\sim$ 25%) and similar to that of the star-forming LTGs. Investigating possible differences between star-forming and quiescent galaxies we find that the intrinsic shape of the SED of the star-forming galaxies is, on average, very similar for all morphological types. Concerning their structural parameters, quiescent galaxies tend to show larger values of the Sérsic index and larger $R_\text{eff}$ (compared to star-forming galaxies). Finally, we find that star-forming galaxies preferably reside in lower-density environments compared to the quiescent ones, which exhibit a higher percentage of sources being members of groups.

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arXiv2022

Comparison of star formation histories of AGN and non-AGN galaxies

We use AGN with $\rm L_{X} \sim 10^{42.5-44}\,erg\,s^{-1}$, from the COSMOS-Legacy survey that lie within the UltraVISTA region and cross match them with the LEGA-C catalogue. The latter provides measurements of the calcium break, D$_n$4000, and H$_δ$ Balmer line that allow us to study the stellar populations of AGN and compare them with a galaxy reference catalogue. Our samples consist of 69 AGN and 2176 non-AGN systems, within $\rm 0.6<z<1.3$, that satisfy the same photometric selection criteria. We construct the SEDs of both population and use the CIGALE code to investigate the effect of the two indices in the SED fitting process. Our analysis shows that the inclusion of D$_n$4000 and H$_δ$ allows CIGALE to constrain better the ages of the stellar populations. Furthermore, we find an increase of the estimated stellar masses by, on average, $\sim 0.2$ dex, in particular for systems with young stars (D$_n$4000$\,<1.5$), when the two indices are included in the SED fitting. We then compare the D$_n$4000 and H$_δ$ of AGN with sources in the reference catalogue, accounting for the different stellar mass of the two populations. Low to moderate L$_X$ AGN tend to reside in galaxies with older stellar populations and are less likely to have experienced a recent star formation burst, compared to galaxies in the control sample. We, also, compare the two populations as a function of their morphology (bulge-dominated, BD, vs. non-BD) and compactness. A similar fraction of AGN and non-AGN systems are classified as non-BD ($\sim 70\%$). Our analysis shows that BD AGN tend to have younger stellar populations compared to BD, non-AGN systems. On the other hand, non-BD AGN have, on average, older stellar populations and are less likely to have experienced a burst compared to non-BD sources in the reference sample. Furthermore, AGN tend to prefer more compact systems compared to non-AGN.

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arXiv2022

XXL-HSC: The link between AGN activity and star formation in the Early Universe ($z\geqslant3.5$)

In this work, we aimed at investigating the star formation rate of active galactic nuclei host galaxies in the early Universe. To this end, we constructed a sample of 149 luminous ($\rm L_{2-10keV} > 10^{44}\,erg\,s^{-1}$) X-ray AGNs at $\rm z \geq3.5$ selected in three fields with different depths and observed areas (Chandra COSMOS Legacy survey, XMM-XXL North and eFEDS). We built their spectral energy distributions (SED) using available multi-wavelength photometry from X-rays up to far-IR. Then, we estimated the stellar mass, M$_{*}$, and the SFR of the AGNs using the X-CIGALE SED fitting algorithm. After applying several quality criteria, we ended up with 89 high-z sources. More than half (55\%) of the X-ray sample have spectroscopic redshifts. Based on our analysis, our high-z X-ray AGNs live in galaxies with median $\rm M_{*}=5.6 \times10^{10}~M_\odot$ and $\rm SFR_{*}\approx240\,M_\odot yr^{-1}$. The majority of the high-z sources ($\sim89$\%) were found inside or above the main sequence (MS) of star-forming galaxies. Estimation of the normalised SFR, $\rm SFR_{NORM}$, defined as the ratio of the SFR of AGNs to the SFR of MS galaxies, showed that the SFR of AGNs is enhanched by a factor of $\sim 1.8$ compared to non-AGN star-forming systems. Combining our results with previous studies at lower redshifts, we confirmed that $\rm SFR_{NORM}$ does not evolve with redshift. Using the specific BHAR (i.e., $\rm L_X$ divided by $\rm M_{*}$), $\rm λ_{BHAR}$, that can be used as a tracer of the Eddington ratio, we found that the bulk of AGNs that lie inside or above the MS have higher specific accretion rates compared to sources below the MS. Finally, we found indications that the SFR of the most massive AGN host galaxies ($\rm log\,(M_{*}/ M_\odot) >10^{11.5-12}$) remains roughly constant as a function of M$_*$, in agreement with the SFR of MS star-forming galaxies.

astro-ph.GA↗

arXiv2022

Star formation of X-ray AGN in COSMOS: The role of AGN activity and galaxy stellar mass

We use $\sim 1,000$ X-ray sources in the COSMOS-Legacy survey and study the position of the AGN relative to the star forming main sequence (MS). We also construct a galaxy (non-AGN) reference sample that includes $\sim 90,000$ sources. We apply the same photometric selection criteria on both datasets and construct their spectral energy distributions (SEDs) using optical to far-infrared photometry compiled by the HELP project. We perform SED fitting, using the X-CIGALE algorithm and the same parametric grid for both datasets, to measure the star formation rate (SFR) and stellar mass of the sources. The mass completeness of the data is calculated at different redshift intervals and is applied on both samples. We define our own main sequence, based on the distributions of the specific SFR at different redshift ranges and exclude quiescent galaxies from our analysis. These allow us to compare the SFR of the two populations in a uniform manner, minimizing systematics and selection effects. Our results show that at low to moderate X-ray luminosities, AGN tend to have lower or, at most, equal star formation rates compared to non-AGN systems with similar stellar mass and redshift. At higher ($\rm L_{X,2-10keV} > 2-3\times 10^{44}\,erg\,s^{-1}$), we observe an increase of the SFR of AGN, for systems that have $\rm 10.5 < log\,[M_*(M_\odot)] < 11.5$.

astro-ph.GA↗

arXiv2022

The RapidXMM Upper Limit Server: X-ray aperture photometry of the XMM-Newton archival observations

This paper presents the construction of the RapidXMM database that is available through the XMM-Newton Science Archive and offers access to upper limits and aperture photometry across the field of view of the XMM-Newton Pointed and Slew Survey observations. The feature of RapidXMM is speed. It enables the fast retrieval of X-ray upper limits and photometry products in three energy bands (0.2-2, 2-12, 0.2-12 keV) for large numbers of input sky positions. This is accomplished using the Hierarchical Equal Area Iso Latitude pixelation of the sphere (HEALPix). The pre-calculated upper-limits and associated X-ray photometry products are reprojected into the HEALPix grid of cells before being ingested into the RapidXMM database. This results in tables of upper limits and aperture photometry within HEALPix cells of size ~3 arcsec (Pointed Observations) and ~6 arcsec (Slew Survey). The database tables are indexed by the unique integer number of the HEALPix cells. This reduces spatial nearest-neighbor queries by sky position to an integer-matching exercise and significantly accelerates the retrieval of results. We describe in detail the processing steps that lead from the science products available in the XMM-Newton archive to a database optimised for sky queries. We also present two simple show-case applications of RapidXMM for scientific studies: searching for variable X-ray sources, and stacking analysis of X-ray faint populations

astro-ph.HE↗