arXiv subjects

I. Georgantopoulos

Publications and source records attributed to I. Georgantopoulos.

At least 37 records · Page 2Linked to original sources

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

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arXiv2022

A search for X-ray absorbed sources in the 3XMM catalogue, using photometric redshifts and Bayesian spectral fits

Since its launch in 1999, the XMM-\textit{Newton} mission has compiled the largest catalogue of serendipitous X-ray sources, with the 3XMM being the third version of this catalogue. This is because of the combination of a large effective area (5000 $\rm cm^2$ at 1 keV) and a wide field of view (30 arcmin). The 3XMM-DR6 catalogue contains about 470,000 unique X-ray sources over an area of 982 $\rm deg^2$. A significant fraction of these (100,178 sources) have reliable optical, near/mid-IR counterparts in the SDSS, PANSTARRS, VIDEO, UKIDSS and WISE surveys. In a previous paper we have presented photometric redshifts for these sources using the TPZ machine learning algorithm. About one fourth of these (22,677) have adequate photon statistics so that a reliable X-ray spectrum can be extracted. Obviously, owing to both the X-ray counts selection and the optical counterpart constraint, the sample above is biased towards the bright sources. Here, we present XMMFITCAT-Z: a spectral fit catalogue for these sources using the Bayesian X-ray Analysis (BXA) technique. As a science demonstration of the potential of the present catalogue, we comment on the optical and mid-IR colours of the 765 X-ray absorbed sources with $N_\mathrm{H} > 10^{22}\,\mathrm{cm}^{-2}$. We show that a considerable fraction of X-ray selected AGN would not be classified as AGN following the mid-IR W1-W2 vs. W2 selection criterion. These are AGN with lower luminosities, where the contribution of the host galaxy to the MIR emission is non-negligible. Only one third of obscured AGN in X-rays present red colours or r-W2 > 6. Then it appears that the r-W2 criterion, often used in the literature for the selection of obscured AGN, produces very different X-ray absorbed AGN samples compared to the standard X-ray selection criteria.

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arXiv2021

XXL-HSC: An updated catalogue of high-redshift ($z\geqslant3.5$) X-ray AGN in the XMM-XXL northern field. Constraints on the bright end of the soft logN-logS

X-rays offer a reliable method to identify Active Galactic Nuclei (AGN). However, in the high-redshift Universe X-ray AGN are poorly sampled due to their relatively low space density and the small areas covered by X-ray surveys. In addition to wide-area X-ray surveys, it is important to have deep optical data in order to locate the optical counterparts and determine their redshifts. In this work, we build a high-redshift ($z\geqslant3.5$) X-ray selected AGN sample in the XMM-XXL northern field using the most updated [0.5-2 keV] catalogue along with a plethora of new spectroscopic and multi-wavelength catalogues, including the deep optical Subaru Hyper Suprime-Cam (HSC) data reaching magnitude limits i$\sim$26 mag. We select all the spectroscopically confirmed AGN and complement this sample with high-redshift candidates that are HSC g- and r-band dropouts. To confirm the dropouts, we derive their photometric redshifts using spectral energy distribution techniques. We end up with a sample of 54 high-z sources (28 with spec-z), the largest in this field so far (almost three times larger than in previous studies), and we estimate the possible contamination and completeness. We calculate the number counts (logN-logS) in different redshift bins and compare our results with previous studies and models. We provide the strongest high-redshift AGN constraints yet at bright fluxes ($\rm f_{0.5-2~keV} > 10^{-15} erg~s^{-1}~cm^{-2}$). The samples of $z\geqslant3.5$, $z\geqslant4$ and $z\geqslant5$ are in agreement with an exponential decline model similar to that witnessed at optical wavelengths. Our work emphasizes the importance of using wide area X-ray surveys with deep optical data to uncover high redshift AGN.

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arXiv2021

Host galaxy properties of X-ray AGN in the Local Universe

We study the host galaxy properties of active galactic nuclei (AGN) that have been detected in X-rays in the nearby Universe ($\rm z<0.2$). For that purpose, we use the catalogue provided by the ROSAT-2RXS in the 0.1-2.4\,keV energy band, one of the largest X-ray datasets with spectroscopic observations. Our sample consists of $\sim 900$ X-ray AGN. The catalogue provides classification of the sources into type 1 and 2, based on optical spectra. $\sim 25\%$ of the AGN are type 2. We use the available optical, near-IR and mid-IR photometry to construct SEDs. We measure the stellar mass ($M_*$) and star formation rate (SFR) of the AGN, by fitting these SEDs with the X-CIGALE code. We compare the $M_*$ and SFR of the two AGN populations, taking into account their different redshift and luminosity distributions. Based on our results, type 2 AGN tend to live in more massive galaxies compared to their type 1 counterparts ($\rm log\,[M_*(M_\odot)]=10.49^{+0.16}_{-0.10}$ vs. $10.23^{+0.05}_{-0.08}$), in agreement with previous studies at higher redshifts. In terms of SFR, our analysis shows, that in the nearby Universe, the number of X-ray AGN that live in quiescent systems is increased compared to that at higher redshifts, in accordance with previous studies in the local universe. However, the majority of AGN ($\sim 75\%$) live inside or above the main sequence.

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arXiv2021

The distribution of the coronal temperature in Seyfert 1 galaxies

The Active Galactic Nuclei (AGN) produce copious amounts of X-rays through the corona that is the hot gas that lies close to the accretion disk. The temperature of the corona can be accurately determined by the cut-off signature in the X-ray spectrum. Owing to the large temperatures of the corona, observations well above 10 keV are necessary. Here, we explore the NuSTAR observations of 118 Gehrels/Swift selected Seyfert 1 AGN. We model the spectrum using a single power-law with an exponential cut-off modified by neutral and ionised absorption as well as a reflection component. We find secure spectral cut-off estimates in 62 sources while for the remaining ones we derive only lower limits. The mean value is 103 keV with a skewed distribution towards large energies with large dispersion. When we consider the lower limits using survival analysis techniques, the mean cut-off energy becomes significantly larger, about 200 keV. Because of various limitations (e.g. limited spectral passband, photon statistics, model degeneracies) we perform extensive simulations to explore the underlying spectral cut-off distribution. We find that an intrinsic spectral cut-off distribution which has a Maxwell-Boltzmann shape with a mean value in the range of 160 - 200 keV can reproduce sufficiently well the observations. Finally, our spectral analysis places very stringent constraints on both the photon index (Gamma=1.77+/-0.01) as well as on the reflection component (R=0.69+/-0.04) of the Seyfert 1 population. From the values of the spectral cut-off and the photon-index we deduce that the mean optical depth of the AGN corona is approximately tau=1.82+/-0.14 and its mean temperature approximately kT=65+/-10 keV.

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arXiv2021

Galaxy properties of type 1 and 2 X-ray selected AGN and comparison among different classification criteria

We present analyses of host galaxy properties of type 1 and type 2 X-ray selected AGNs in the XMM-XXL field, which have available optical spectroscopic classification. We model their optical to far-infrared spectral energy distributions (SEDs) using the X-CIGALE code. X-CIGALE allows the fitting of X-ray flux and accounts for the viewing angle of dusty torus and the attenuation from polar dust. By selecting matched type 1 and 2 subsamples in the X-ray luminosity and redshift parameter space, we find that both types live in galaxies with similar star formation. However, type 2 AGN tend to reside in more massive systems ($10.87^{+0.06}_{-0.12}\,\rm M_\odot$) compared to their type 1 counterparts ($10.57^{+0.20}_{-0.12}\,\rm M_\odot$). In the second part of our analysis, we compare the spectroscopic classification with that from the SED fitting. X-CIGALE successfully identifies all spectroscopic type 2 sources either by estimating an inclination angle that corresponds to edge on viewing of the source or by measuring increased polar dust in these systems. $\sim 85\%$ of spectroscopic type 1 AGN are also identified as such, based on the SED fitting analysis. There is a small number of sources ($\sim 15\%$ of the sample), that present broad lines in their spectra, but show strong indications of obscuration, based on SED analysis. These, could be systems that are viewed face on and have an extended dust component along the polar direction. The performance of X-CIGALE in classifying AGN is similar at low and high redshifts, under the condition that there is sufficient photometric coverage. Finally, usage of optical/mid-IR colour criteria to identify optical red AGN (${\it{u}}-\rm W3$), suggests that these criteria are better suited for IR selected AGN and their efficiency drops for the low to moderate luminosity sources included in X-ray samples.

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arXiv2021

The physical properties of local (U)LIRGs: a comparison with nearby early- and late-type galaxies

In order to pinpoint the place of the (U)LIRGs in the local Universe we examine the properties of a sample of 67 such systems and compare them with those of 268 ETGs and 542 LTGs from the DustPedia database. We make use of multi-wavelength photometric data and the CIGALE SED fitting code to extract their physical parameters. The median SEDs as well as the values of the derived parameters were compared to those of the local ETGs and LTGs. In addition to that, (U)LIRGs were divided into seven classes, according to the merging stage of each system, and variations in the derived parameters were investigated. (U)LIRGs occupy the `high-end' on the dust and stellar mass, and SFR in the local Universe with median values of 5.2$\times10^7~M_{\odot}$, 6.3$\times10^{10}~M_{\odot}$ and 52$~M_{\odot}$yr$^{-1}$, respectively. The PDR-dust emission in (U)LIRGs is 11.7% of the total dust luminosity, significantly higher than ETGs (1.6%) and the LTGs (5.2%). The median value of the dust temperature in (U)LIRGs is 32 K, which is higher compared to both the ETGs (28 K) and the LTGs (22 K). Small differences, in the derived parameters, are seen for the seven merging classes of our sample of (U)LIRGs with the most evident one being on the star-formation rate, where in systems in late merging stages the median SFR reaches up to 99 M$_{\odot}$ yr$^{-1}$ compared to 26 M$_{\odot}$ yr$^{-1}$ for the isolated ones. In contrast to the local normal galaxies where old stars dominate the stellar emission, the young stars in (U)LIRGs contribute with 64% of their luminosity to the total stellar luminosity. The fraction of the dust-absorbed stellar luminosity is extremely high in (U)LIRGs (78%) compared to 7% and 25% in ETGs and ETGs, respectively. The fraction of the stellar luminosity used to heat up the dust grains is very high in (U)LIRGs, while 74% of the dust emission comes from the young stars.

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arXiv2021

The relation between AGN type and host galaxy properties

We use 3,213 Active Galactic Nuclei (AGNs) from the $\it{XMM}$-XXL northern field to investigate the relation of AGN type with host galaxy properties. Applying a Bayesian method, we derive the hardness ratios (HRs) and through these the hydrogen column density ($\rm N_H$) for each source. We consider as absorbed sources (type-2) those with $\rm N_H > 10^{21.5}\, \rm{cm^{-2}}$. We examine the star formation rate (SFR) as well the stellar mass (M$_*$) distributions for both absorbed and unabsorbed sources. Our work indicates that there is no significant link between the AGN type and these host galaxy properties. Next, we investigate whether the AGN power, as represented by its X-ray luminosity, $\rm L_X$, correlates with any deviation of the host galaxy's place from the so-called Main Sequence of galaxies, and we examine this separately for the obscured and the unobscured AGN populations. To take into account the effect of M$_*$ and redshift on SFR, we use the normalised SFR (SFR$_{norm}$). We find that the correlation between $\rm L_X$ and SFR$_{norm}$, follows approximately the same trend for both absorbed and unabsorbed sources, a result that favours the standard AGN unification models. Finally, we explore the connection between the obscuration, $\rm N_H$, and the SFR. We find that there is no relation between these, suggesting that the obscuration is not related to the large scale SFR in the galaxy.

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arXiv2020

The XMM deep survey in the CDFS XI. X-ray properties of 185 bright sources

We present X-ray spectra of 185 bright sources detected in the XMM-Newton deep survey of the Chandra Deep Field South, combining the three EPIC cameras. The 2-10 keV flux limit of the sample is 2e-15 erg/s/cm2. The sources are distributed over a redshift range of z=0.1-3.8. Eleven new X-ray redshift measurements are included. A spectral analysis was performed using a simple model to obtain absorbing column densities, rest-frame 2-10 keV luminosities and Fe K line properties of 180 sources at z>0.4. Obscured AGN are found to be more abundant toward higher redshifts. Using the XMM-Newton data alone, seven Compton-thick AGN candidates are identified, which makes the Compton-thick AGN fraction to be ~4%. An exploratory spectral inspection method with two rest-frame X-ray colours and an Fe line strength indicator is introduced and tested against the results from spectral fitting. This method works reasonably well to characterise a spectral shape and can be useful for a pre-selection of Compton-thick AGN candidates. We found six objects exhibiting broad Fe K lines out of 21 unobscured AGN of best data quality, implying a detection rate of ~30%. Five redshift spikes, each of which has more than six sources, are identified in the redshift distribution of the X-ray sources. Contrary to the overall trend, the sources at the two higher-redshift spikes at z=1.61 and z=2.57 have puzzlingly low obscuration.

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arXiv2020

An obscured AGN population hidden in the VIPERS galaxies: identification through spectral energy distribution decomposition

The detection of X-ray emission constitutes a reliable and efficient tool for the selection of Active Galactic Nuclei (AGNs), although it may be biased against the most heavily absorbed AGNs. Simple mid-IR broad-band selection criteria identify a large number of luminous and absorbed AGNs, yet again host contamination could lead to non-uniform and incomplete samples. Spectral Energy Distribution (SED) decomposition is able to decouple the emission from the AGN versus that from star-forming regions, revealing weaker AGN components. We aim to identify the obscured AGN population in the VIPERS survey in the CFHTLS W1 field through SED modelling. We construct SEDs for 6,860 sources and identify 160 AGNs at a high confidence level using a Bayesian approach. Using optical spectroscopy, we confirm the nature of ~85% of the AGNs. Our AGN sample is highly complete (~92%) compared to mid-IR colour selected AGNs, including a significant number of galaxy-dominated systems with lower luminosities. In addition to the lack of X-ray emission (80%), the SED fitting results suggest that the majority of the sources are obscured. We use a number of diagnostic criteria in the optical, infrared and X-ray regime to verify these results. Interestingly, only 35% of the most luminous mid-IR selected AGNs have X-ray counterparts suggesting strong absorption. Our work emphasizes the importance of using SED decomposition techniques to select a population of type II AGNs, which may remain undetected by either X-ray or IR colour surveys.

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arXiv2020

The $\it{XXL}$ survey: XL. Obscuration properties of red AGN in $\it{XXL-N}$

The combination of optical and mid-infrared (MIR) photometry has been extensively used to select red active galactic nuclei (AGNs). Our aim is to explore the obscuration properties of these red AGNs with both X-ray spectroscopy and spectral energy distributions (SEDs). In this study, we re-visit the relation between optical/MIR extinction and X-ray absorption. We use IR selection criteria, specifically the $W1$ and $W2$ WISE bands, to identify 4798 AGNs in the $\it{XMM-XXL}$ area ($\sim 25$deg$^2$). Application of optical/MIR colours ($r- W2 > 6$) reveals 561 red AGNs (14$\%$). Of these, 47 have available X-ray spectra with at least 50 net (background-subtracted) counts per detector. For these sources, we construct SEDs from the optical to the MIR using the CIGALE code. The SED fitting shows that 44 of these latter 47 sources present clear signs of obscuration based on the AGN emission and the estimated inclination angle. Fitting the SED also reveals ten systems ($\sim20\%$) which are dominated by the galaxy. In these cases, the red colours are attributed to the host galaxy rather than AGN absorption. Excluding these ten systems from our sample and applying X-ray spectral fitting analysis shows that up to $76\%$ (28/37) of the IR red AGNs present signs of X-ray absorption. Thus, there are nine sources ($\sim20\%$ of the sample) that although optically red, are not substantially X-ray absorbed. Approximately $50\%$ of these sources present broad emission lines in their optical spectra. We suggest that the reason for this apparent discrepancy is that the r-W2 criterion is sensitive to smaller amounts of obscuration relative to the X-ray spectroscopy. In conclusion, it appears that the majority of red AGNs present considerable obscuration levels as shown by their SEDs. Their X-ray absorption is moderate with a mean of $\rm N_H \sim 10^{22}\, \rm{cm^{-2}}$.

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arXiv2019

Obscuration properties of mid-IR selected AGN

The goal of this work is to study the obscuration properties of mid-infrared (mid-IR) selected AGN. For that purpose, we use {\it{WISE}} sources in the Stripe 82-XMM area to identify mid-IR AGN candidates, applying the Assef et al. criteria. Stripe 82 has optical photometry $\approx$\,2 times deeper than any single-epoch SDSS region. XMM-Newton observations cover $\sim$26\,deg$^2$. Applying the aforementioned criteria, 1946 IR AGN are selected. $\sim 78\%$ have SDSS detection, while 1/3 of them is detected in X-rays, at a flux limit of $\rm \sim 5 \times 10^{-15}\,erg\,s^{-1}\,cm^{-2}$. Our final sample consists of 507 IR AGN with X-ray detection and optical spectra. Applying a $\rm r-W2>6$ colour criterion, we find that the fraction of optically red AGN drops from 43\% for those sources with SDSS detection to $23\%$ for sources that also have X-ray detection. X-ray spectral fitting reveals 40 ($\sim8\%$) X-ray absorbed AGN ($\rm N_H>10^{22}~cm^{-2}$). Among the X-ray unabsorbed AGN, there are 70 red systems. To further investigate the absorption of these sources, we construct Spectral Energy Distributions (SEDs) for the total IR AGN sample. SED fitting reveals that $\sim20\%$ of the optically red sources have such colours because the galaxy emission is a primary component in the optical part of the SED, even though the AGN emission is not absorbed at these wavelengths. SED fitting also confirms that $12\%$ of the X-ray unabsorbed, IR AGN are optically obscured.

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arXiv2019

The Hubble Catalog of Variables (HCV)

The Hubble Space Telescope (HST) has obtained multi-epoch observations providing the opportunity for a comprehensive variability search aiming to uncover new variables. We have therefore undertaken the task of creating a catalog of variable sources based on version 3 of the Hubble Source Catalog (HSC), which relies on publicly available images obtained with the WFPC2, ACS, and WFC3 instruments onboard the HST. We adopted magnitude-dependent thresholding in median absolute deviation (a robust measure of light curve scatter) combined with sophisticated preprocessing techniques and visual quality control to identify and validate variable sources observed by Hubble with the same instrument and filter combination five or more times. The Hubble Catalog of Variables (HCV) includes 84,428 candidate variable sources (out of 3.7 million HSC sources that were searched for variability) with $V \leq 27$ mag; for 11,115 of them the variability is detected in more than one filter. The data points in the light curves of the variables in the HCV catalog range from five to 120 points (typically having less than ten points); the time baseline ranges from under a day to over 15 years; while $\sim$8% of all variables have amplitudes in excess of 1 mag. Visual inspection performed on a subset of the candidate variables suggests that at least 80% of the candidate variables that passed our automated quality control are true variable sources rather than spurious detections resulting from blending, residual cosmic rays, and calibration errors. The HCV is the first, homogeneous catalog of variable sources created from archival HST data and currently is the deepest catalog of variables available. The catalog includes variable stars in our Galaxy and nearby galaxies, as well as transients and variable active galactic nuclei. (abbreviated)

astro-ph.SR↗

arXiv2019

Compton-thick active galactic nuclei from the 7 Ms observation in the Chandra Deep Field South

We present the X-ray spectroscopic study of the Compton-thick (CT) active galactic nuclei (AGN) population within the $\textit{Chandra}$ Deep Field South (CDF-S) by using the deepest X-ray observation to date, the $\textit{Chandra}$ 7 Ms observation of the CDF-S. We combined an opimized version of our automated selection technique and a Bayesian Monte Carlo Markov Chains (MCMC) spectral fitting procedure, to develop a method to pinpoint and then characterize candidate CT AGN as less model dependent and/or data-quality dependent as possible. To obtain reliable automated spectral fits, we only considered the sources detected in the hard (2-8 keV) band from the CDF-S 2 Ms catalog with either spectroscopic or photometric redshifts available for 259 sources. Instead of using our spectral analysis to decide if an AGN is CT, we derived the posterior probability for the column density, and then we used it to assign a probability of a source being CT. We also tested how the model-dependence of the spectral analysis, and the spectral data quality, could affect our results by using simulations. We finally derived the number density of CT AGN by taking into account the probabilities of our sources being CT and the results from the simulations. Our results are in agreement with X-ray background synthesis models, which postulate a moderate fraction (25%) of CT objects among the obscured AGN population.

astro-ph.HE↗

arXiv2019

Robust Identification of Active Galactic Nuclei through HST Optical Variability in GOODS-S: Comparison with the X-ray and mid-IR Selected Samples

Identifying Active Galactic Nuclei (AGNs) through their X-ray emission is efficient, but necessarily biased against X-ray-faint objects. We aim to characterize this bias by comparing X-ray-selected AGNs to the ones identified through optical variability and mid-IR colours. We present a catalogue of AGNs selected through optical variability using all publicly available z-band Hubble Space Telescope images in the GOODS-South field. For all objects in the catalogue, we compute X-ray upper limits or discuss detections in the deepest available 7 Ms Chandra Deep Field South images and present the Spitzer/IRAC mid-IR colours. For the variability study, we consider only sources observed over at least five epochs and over a time baseline of up to ten years. We adopt the elevated median absolute deviation as a variability indicator robust against individual outlier measurements and identify 113 variability-selected AGN candidates. Among these, 26 have an X-ray counterpart and lie within the conventional AGN area in the FX/Fopt diagram. The candidates with X-ray upper limits are on average optically fainter, have higher redshifts compared to the X-ray detected ones and are consistent with low luminosity AGNs. Out of 41 variable optical sources with IR detections, 13 fulfill the IR AGN colour selection criteria. Our work emphasizes the importance of optical variability surveys for constructing complete samples of AGNs including the ones that remain undetected even by the deepest X-ray and IR surveys.

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arXiv2019

The source number counts at high energies: SWIFT vs. NuSTAR

The hard X-ray sky at energies above 10 keV, has been extensively explored by the Swift and the NuSTAR missions in the 14-195 keV and the 3-24 keV bands respectively. The major population of the hard X-ray detected sources are AGN. We compare the number count distributions derived from the swift 105-month catalogue with those from the serendipitous NuSTAR source catalogue. In the 14-195 keV band, the Swift/BAT counts follow a Euclidean slope with alpha=1.51+/-0.10 (90% confidence level). The NuSTAR counts in the 8-24 keV band present a steeper slope with alpha = 1.71+/- 0.2$, because of an upturn at fluxes below ~2x10^{-13} erg/cm2/s. The same upturn is observed in the soft (3-8 keV) NuSTAR number counts, which in overall also present a steep slope with alpha = 1.82+/- 0.15. Only the bright part of the NuSTAR 3-8 keV counts agrees with the chandra number counts in the 2-10 keV band while the fainter part (<7x10^{-13} erg/cm2/s ) of the soft NuSTAR counts is in marked disagreement with the chandra counts. Next, we compare the derived number counts in the different bands using our X-ray AGN population synthesis models. The comparison between the Chandra and the Swift/BAT number counts shows a very good agreement for the 'standard' AGN spectrum with a power-law slope Gamma=1.9, a high energy cut-off at ~130 keV and a 2-10 keV reflection component of 3%. On the other hand, using the above standard AGN spectral model, only the bright part of the NuSTAR 8-24 keV and 3-8 keV number counts, agree with the model predictions. Then it is most likely that the disagreement between the X-ray number counts in the different bands is because of the faint NuSTAR number counts. We discuss various possibilities for the origin of this disagreement.

astro-ph.HE↗

arXiv2018

The dependence of the X-ray AGN clustering on the properties of the host galaxy

We study the clustering dependence of X-ray AGN and normal galaxies on the stellar mass (M$_\star$), star-formation rate (SFR) and specific star-formation rate (sSFR) of the (host) galaxy. Towards this end, we use 407 X-ray AGN from the XMM-XXL survey ($\sim$ 25 deg$^2$ in the North) and $\sim45,000$ galaxies in the VIPERS field (W1: $\sim$16 deg$^2$). We match the AGN and galaxy samples to have the same M$_\star$, SFR and redshift distributions. Based on our results, the two populations live in DMHs with similar mass ($\log M / (M_{\odot} \, h^{-1})\approx 12.8$) and have similar dependence on the galaxy properties. Specifically, our measurements show a positive dependence of the AGN and galaxy clustering on M$_\star$ and a negative dependence on SFR and sSFR. We also find that the X-ray clustering is independent of the location of the host galaxy above or below the star-forming main sequence.

astro-ph.GA↗

arXiv2018

Disentangling the AGN and Star-Formation connection using XMM-Newton

There is growing evidence supporting the coeval growth of galaxies and their resident SMBH. Most studies also claim a correlation between the activity of the SMBH and the star-formation of the host galaxy. It is unclear, though, whether this correlation extends to all redz and LX. In this work, we use data from the X-ATLAS and XMM-XXL North fields and compile the largest X-ray sample up to date, to investigate how X-ray AGN affect the star-formation of their host galaxies in a wide redz and luminosity baseline, i.e., 0.03<z<3 and log LX (2-10 keV)= (41-45.5) ergs-1. Our sample consists of 3336 AGN. 1872 X-ray objects have spectroscopic redz. For the remaining sources we calculate photometric redz using TPZ, a machine-learning algorithm. We estimate stellar masses (M*) and Star Formation Rates (SFRs) by applying SED fitting through the CIGALE code, using optical, near-IR and mid-IR photometry. 608 of our sources also have far-IR photometry (Herschel). We use these sources to calibrate the SFR calculations of the rest of our X-ray sample. Our results show a correlation between the LX and the SFR, at all redz and LX spanned by our sample. We also find a dependence of the specific SFR (sSFR) on redz, while there are indications that LX enhances the sSFR even at low redz. We then disentangle the effects of M* and redz on the SFR and study again its dependence on the LX. Towards this end, we use the Schreiber et al. formula to estimate the SFR of main sequence galaxies that have the same stellar mass and redshift as our X-ray AGN. Our analysis reveals that the AGN enhances the star-formation of its host galaxy, when the galaxy lies below the main sequence and quenches the star-formation of the galaxy it lives in, when the host lies above the main sequence. Therefore, the effect of AGN on the SFR of the host galaxy, depends on the location of the galaxy relative to the main sequence.

astro-ph.GA↗