XMMPZCAT: A catalogue of photometric redshifts for X-ray sources

The third version of the XMM-Newton serendipitous catalogue (3XMM), containing almost half million sources, is now the largest X-ray catalogue. However, its full scientific potential remains untapped due to the lack of distance information (i.e. redshifts) for the majority of its sources. Here we present XMMPZCAT, a catalogue of photometric redshifts (photo-z) for 3XMM sources. We searched for optical counterparts of 3XMM-DR6 sources outside the Galactic plane in the SDSS and Pan-STARRS surveys, with the addition of near- (NIR) and mid-infrared (MIR) data whenever possible (2MASS, UKIDSS, VISTA-VHS, and AllWISE). We used this photometry data set in combination with a training sample of 5157 X-ray selected sources and the MLZ-TPZ package, a supervised machine learning algorithm based on decision trees and random forests for the calculation of photo-z. We have estimated photo-z for 100,178 X-ray sources, about 50% of the total number of 3XMM sources (205,380) in the XMM-Newton fields selected to build this catalogue (4208 out of 9159). The accuracy of our results highly depends on the available photometric data, with a rate of outliers ranging from 4% for sources with data in the optical+NIR+MIR, up to $\sim$40% for sources with only optical data. We also addressed the reliability level of our results by studying the shape of the photo-z probability density distributions.Comment: 16 pages, 14 figures, A&A accepte

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 $\rm 0.5<z<3.5$ and encompass a wide range of L$_X$, falling within $\rm 42<log,[L_{X,2-10keV}(ergs^{-1})]<46$. Our results show that type 2 AGN exhibit a tendency to inhabit more massive galaxies, by $0.2-0.3$\,dex, compared to type 1 sources. Type 2 AGN also display, on average, lower specific black hole accretion rates, a proxy of the Eddington ratio, compared to type 1 AGN. These differences persist across all redshifts and L$_X$ considered within our dataset. Moreover, our analysis uncovers, that type 2 sources tend to have lower star-formation rates compared to 1 AGN, at $\rm z<1$. This picture reverses at $\rm z>2$ 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.Comment: A&A accepted, 10 pages, 5 figures, 5 table

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.Comment: Accepted for publication in MNRAS in May 4, 2020. 18 figures, 3 tables

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.Comment: MNRAS accepted, 10 pages, 8 figure

Estimating Photometric Redshifts for X-ray sources in the X-ATLAS field, using machine-learning techniques

We present photometric redshifts for 1,031 X-ray sources in the X-ATLAS field, using the machine learning technique TPZ (Carrasco Kind & Brunner 2013). X-ATLAS covers 7.1 deg2 observed with the XMM-Newton within the Science Demonstration Phase (SDP) of the H-ATLAS field, making it one of the largest contiguous areas of the sky with both XMMNewton and Herschel coverage. All of the sources have available SDSS photometry while 810 have additionally mid-IR and/or near-IR photometry. A spectroscopic sample of 5,157 sources primarily in the XMM/XXL field, but also from several X-ray surveys and the SDSS DR13 redshift catalogue, is used for the training of the algorithm. Our analysis reveals that the algorithm performs best when the sources are split, based on their optical morphology, into point-like and extended sources. Optical photometry alone is not enough for the estimation of accurate photometric redshifts, but the results greatly improve when, at least, mid-IR photometry is added in the training process. In particular, our measurements show that the estimated photometric redshifts for the X-ray sources of the training sample, have a normalized absolute median deviation, n_mad=0.06, and the percentage of outliers, eta=10-14 percent, depending on whether the sources are extended or point-like. Our final catalogue contains photometric redshifts for 933 out of the 1,031 X-ray sources with a median redshift of 0.9.Comment: 10 pages, 13 figures, A&A accepte

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.Comment: A&A Accepted 10 pages, 8 figures, 2 table

Searching for highly obscured AGN in the XMM-Newton serendipitous source catalog

The majority of active galactic nuclei (AGN) are obscured by large amounts of absorbing material that makes them invisible at many wavelengths. X-rays, given their penetrating power, provide the most secure way for finding these AGN. The XMM-Newton serendipitous source catalog is the largest catalog of X-ray sources ever produced; it contains about half a million detections. These sources are mostly AGN. We have derived X-ray spectral fits for very many 3XMM-DR4 sources ($\gtrsim$ 114 000 observations, corresponding to $\sim$ 77 000 unique sources), which contain more than 50 source photons per detector. Here, we use a subsample of $\simeq$ 1000 AGN in the footprint of the SDSS area (covering 120 deg$^2$) with available spectroscopic redshifts. We searched for highly obscured AGN by applying an automated selection technique based on X-ray spectral analysis that is capable of efficiently selecting AGN. The selection is based on the presence of either a) flat rest-frame spectra; b) flat observed spectra; c) an absorption turnover, indicative of a high rest-frame column density; or d) an Fe K$\alpha$ line with an equivalent width > 500 eV. We found 81 highly obscured candidate sources. Subsequent detailed manual spectral fits revealed that 28 of them are heavily absorbed by column densities higher than 10$^{23}$ cm$^{-2}$. Of these 28 AGN, 15 are candidate Compton-thick AGN on the basis of either a high column density, consistent within the 90% confidence level with N$_{\rm H}$ $>$10$^{24}$ cm$^{-2}$, or a large equivalent width (>500 eV) of the Fe K$\alpha$ line. Another six are associated with near-Compton-thick AGN with column densities of $\sim$ 5$\times$10$^{23}$ cm$^{-2}$. A combination of selection criteria a) and c) for low-quality spectra, and a) and d) for medium- to high-quality spectra, pinpoint highly absorbed AGN with an efficiency of 80%.Comment: 18 pages, 10 figures, accepted for publication in A&

Clustering of 2PIGG galaxy groups with 2dFGRS galaxies

Prompted by indications from QSO lensing that there may be more mass associated with galaxy groups than expected, we have made new dynamical infall estimates of the masses associated with 2PIGG groups and clusters. We have analysed the redshift distortions in the cluster-galaxy cross-correlation function as a function of cluster membership, cross-correlating z<0.12 2PIGG clusters and groups with the full 2dF galaxy catalogue. We have made estimates of the dynamical infall parameter beta and new estimates of the group velocity dispersions. We first find that the amplitude of the full 3-D redshift space cross-correlation function, xi_{cg}, rises monotonically with group membership. We use a simple linear-theory infall model to fit xi(sigma, pi) in the range 5<s<40h^{-1}Mpc. We find that the beta versus membership relation for the data shows a minimum at intermediate group membership n~20 or L~2x10^11h^-2Lsun, implying that the bias and hence M/L ratios rise by a significant factor (~5x) both for small groups and rich clusters. However, the mocks show a systematic shift between the location of the beta minimum and the M/L minimum at L~10^10h^-2Lsun given by direct calculation using the known DM distribution. Our overall conclusion is that bias estimates from dynamical infall appear to support the minimum in star-formation efficiency at intermediate halo masses. Nevertheless, there may still be significant systematic problems arising from measuring beta~1/b using large-scale infall rather than M/L using small-scale velocity dispersions.Comment: 20 pages, 32 figures, 9 table