The XMM deep survey in the CDF-S

Publications of The Astronomical Society of Japan - PUBL ASTRON SOC JPN, 2006

Two nearby clusters of galaxies, A194 (z=0.018) and A1060 (z=0.0114), have been analyzed for their X-ray point-source properties with XMM-Newton EPIC-PN data. A multi-band source detection technique was applied to both of the clusters, resulting in 46 sources from the A194 field and 32 sources from the A1060 field, respectively. The cumulative log(N)-log(S) for a flux limit of FX >= 1 × 10-14erg cm-2 s-1 was calculated and compared with that of the Lockman Hole. A ˜ 3sigma excess of X-ray sources was found for the cluster regions. Considering the higher fraction observed in optical studies from the clusters, we estimate that the cluster source density is 6-times higher than the blank-field source density, and 15-times higher than the local group. Our X-ray selected sources have luminosity values of 1039.6 <= LX <= 1041.4 erg s-1, in which X-ray emission from LMXBs, hot halos and starburst galaxies becomes noticeable. The significance of the source-density excess gradually v...

The Astrophysical Journal, 2012

The Swift Burst Alert Telescope (BAT) is discovering interesting new objects while monitoring the sky in the 14-195 keV band. Here we present the X-ray properties and spectral energy distributions (SEDs) for two unusual active galactic nucleus sources. Both NVSS 193013+341047 and IRAS 05218−1212 are absorbed, Compton-thin, but heavily obscured (N H ∼ 10 23 cm −2 ), X-ray sources at redshifts <0.1. The SEDs reveal these galaxies to be very red, with high extinction in the optical and UV. A similar SED is seen for the extremely red objects (EROs) detected in the higher redshift universe. This suggests that these unusual BAT-detected sources are a low-redshift (z 1) analog to EROs, which recent evidence suggests are a class of the elusive type II quasars. Studying the multi-wavelength properties of these sources may reveal the properties of their high-redshift counterparts.

The Astrophysical Journal, 2010

We report the final optical identifications of the medium-depth (∼60 ks), contiguous (2 deg 2 ) XMM-Newton survey of the COSMOS field. XMM-Newton has detected ∼1800 X-ray sources down to limiting fluxes of ∼5 × 10 −16 , ∼3 × 10 −15 , and ∼7 × 10 −15 erg cm −2 s −1 in the 0.5-2 keV, 2-10 keV, and 5-10 keV bands, respectively (∼1 × 10 −15 , ∼6 × 10 −15 , and ∼1 × 10 −14 erg cm −2 s −1 , in the three bands, respectively, over 50% of the area). The work is complemented by an extensive collection of multiwavelength data from 24 μm to UV, available from the COSMOS survey, for each of the X-ray sources, including spectroscopic redshifts for 50% of the sample, and high-quality photometric redshifts for the rest. The XMM and multiwavelength flux limits are well matched: 1760 (98%) of the X-ray sources have optical counterparts, 1711 (∼95%) have IRAC counterparts, and 1394 (∼78%) have MIPS 24 μm detections. Thanks to the redshift completeness (almost 100%) we were able to constrain the high-luminosity tail of the X-ray luminosity function confirming that the peak of the number density of log L X > 44.5 active galactic nuclei (AGNs) is at z ∼ 2. Spectroscopically identified obscured and unobscured AGNs, as well as normal and star-forming galaxies, present well-defined optical and infrared properties. We devised a robust method to identify a sample of ∼150 high-redshift (z > 1), obscured AGN candidates for which optical spectroscopy is not available. We were able to determine that the fraction of the obscured AGN population at the highest (L X > 10 44 erg s −1 ) X-ray luminosity is ∼15%-30% when selection effects are taken into account, providing an important observational constraint for X-ray background synthesis. We studied in detail the optical spectrum and the overall spectral energy 348 No. 1, 2010 THE XMM-NEWTON WIDE-FIELD SURVEY IN THE COSMOS FIELD 349

AIP Conference Proceedings, 2001

We present a study of the sample of luminous infrared galaxies (LIGs, LIR > 10 11 L⊙) observed in the hard (2-10 keV) X rays. The main results are: 1) most LIGs are powered both by AGN and starburst activity; 2) the AGNs in our sample are absorbed in the infrared by a lower NH than in the X-rays or, alternatively, the dust-togas ratio is lower than galactic; 3) the study of a subsample of sources observed in the 20-200 keV band indicates that most of the AGNs hosted by the LIGs are heavily obscured up to 100 keV and, therefore, their contribution to the X-ray background must be small.

The Astrophysical Journal, 2005

We present the first results from the Calán-Yale Deep Extragalactic Research (CYDER) survey. The main goal of this survey is to study serendipitous X-ray sources detected by Chandra in an intermediate flux range (10 −15 − 10 −12 ergs s −1) that comprises most of the X-ray background. 267 X-ray sources spread over 5 archived fields were detected. The log N − log S distribution obtained for this sample is consistent with the results of other surveys. Deep V and I images were taken of these fields in order to calculate X-ray-to-optical flux ratios. Identifications and redshifts were obtained for 106 sources using optical spectroscopy from 8-m class telescopes to reach the optically faintest sources, to the same level as deeper X-ray fields like the Chandra Deep Fields, showing that the nature of sources detected depends mostly on the optical limit for spectroscopy. In general, sources optically classified as obscured Active Galactic Nuclei (AGNs) have redder optical colors than unobscured AGN. A rough correlation between f X /f opt and hard X-ray luminosity was found for obscured

Monthly Notices of the Royal Astronomical Society, 2015

We combine deep X-ray survey data from the Chandra observatory and the wide-area/shallow XMM-XXL field to estimate the active galactic nuclei (AGN) X-ray luminosity function in the redshift range z = 3-5. The sample consists of nearly 340 sources with either photometric (212) or spectroscopic (128) redshift in the above range. The combination of deep and shallow survey fields also provides a luminosity baseline of three orders of magnitude, L X (2-10 keV) ≈ 10 43-10 46 erg s −1 at z > 3. We follow a Bayesian approach to determine the binned AGN space density and explore their evolution in a model-independent way. Our methodology properly accounts for Poisson errors in the determination of X-ray fluxes and uncertainties in photometric redshift estimates. We demonstrate that the latter is essential for unbiased measurement of space densities. We find that the AGN X-ray luminosity function evolves strongly between the redshift intervals z = 3-4 and z = 4-5. There is also suggestive evidence that the amplitude of this evolution is luminosity dependent. The space density of AGN with L X (2-10 keV) < 10 45 erg s −1 drops by a factor of 5 between the redshift intervals above, while the evolution of brighter AGN appears to be milder. Comparison of our X-ray luminosity function with that of ultraviolet (UV)/optical selected quasi-stellar objects at similar redshifts shows broad agreement at bright luminosities, L X (2-10 keV) > 10 45 erg s −1. At fainter luminosities X-ray surveys measure higher AGN space densities. The faint-end slope of UV/optical luminosity functions, however, is steeper than for X-ray selected AGN. This implies that the Type I AGN fraction increases with decreasing luminosity at z > 3, opposite to trends established at lower redshift. We also assess the significance of AGN in keeping the hydrogen ionized at high redshift. Our X-ray luminosity function yields ionizing photon rate densities that are insufficient to keep the Universe ionized at redshift z > 4. A source of uncertainty in this calculation is the escape fraction of UV photons for X-ray selected AGN.

New Journal of Physics, 2011

We present the largest sample of spectroscopically confirmed X-ray luminous high-redshift galaxy clusters to date comprising 22 systems in the range 0.9 < z < ∼ 1.6 as part of the XMM-Newton Distant Cluster Project (XDCP). All systems were initially selected as extended X-ray sources over 76.1 deg 2 of non-contiguous deep archival XMM-Newton coverage, of which 49.4 deg 2 are part of the core survey with a quantifiable selection function and 17.7 deg 2 are classified as 'gold' coverage as starting point for upcoming cosmological applications. Distant cluster candidates were followed-up with moderately deep optical and near-infrared imaging in at least two bands to photometrically identify the cluster galaxy populations and obtain redshift estimates based on colors of simple stellar population models. We test and calibrate the most promising redshift estimation techniques based on the R−z and z−H colors for efficient distant cluster identifications and find a good redshift accuracy performance of the z−H color out to at least z∼1.5, while the redshift evolution of the R−z color leads to increasingly large uncertainties at z > ∼ 0.9. Photometrically identified high-z systems are spectroscopically confirmed with VLT/FORS 2 with a minimum of three concordant cluster member redshifts. We present first details of two newly identified clusters, ‡ Based on observations under program IDs 079.A-0634 and 085.A-0647 collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, and observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

The Astrophysical Journal, 1999

The infrared-luminous galaxy NGC 3256 is a classic example of a merger-induced nuclear starburst system. We find here that it is the most X-ray-luminous star-forming galaxy yet detected (L 0.5−10 keV = 1.6 × 10 42 ergs s −1 ). Long-slit optical spectroscopy and a deep, high-resolution ROSAT X-ray image show that the starburst is driving a "superwind" which accounts for ∼ 20% of the observed soft X-ray emission. Analysis of X-ray spectral data from ASCA indicates this gas has a characteristic temperature of kT ≈ 0.3 keV. Our model for the broadband X-ray emission of NGC 3256 contains two additional components: a warm thermal plasma (kT ≈ 0.8 keV) associated with the central starburst, and a hard power-law component with an energy index of α X ≈ 0.7. We discuss the energy budget for the two thermal plasmas and find that the input of mechanical energy from the starburst is more than sufficient to sustain the observed level of emission. We also examine possible origins for the power-law component, concluding that neither a buried AGN nor the expected population of high-mass X-ray binaries can account for this emission. Inverse-Compton scattering, involving the galaxy's copious flux of infrared photons and the relativistic electrons produced by supernovae, is likely to make a substantial contribution to the hard X-ray flux. Such a model is consistent with the observed radio and IR fluxes and the radio and X-ray spectral indices. We explore the role of X-ray-luminous starbursts in the production of the cosmic X-ray background radiation. The number counts and spectral index distribution of the faint radio source population, thought to be dominated by star-forming galaxies, suggest that a significant fraction of the hard X-ray background could arise from starbursts at moderate redshift.

The Astrophysical Journal, 2019

We present a search for nuclear X-ray emission in the Brightest Cluster Galaxies (BCGs) of a sample of groups and clusters of galaxies extracted from the Chandra archive. The exquisite angular resolution of Chandra allows us to obtain robust photometry at the position of the BCG, and to firmly identify unresolved X-ray emission when present, thanks to an accurate characterization of the extended emission at the BCG position. We consider two redshift bins (0.2<z<0.3 and 0.55<z<0.75) and analyze all the clusters observed by Chandra with exposure time larger than 20 ks. Our samples have 81 BCGs in 73 clusters and 51 BCGs in 49 clusters in the low- and high-redshift bin, respectively. X-ray emission in the soft (0.5-2 keV) or hard (2-7 keV) band is detected only in 14 and 9 BCGs (∼18% of the total samples), respectively. The X-ray photometry shows that at least half of the BCGs have a high hardness ratio, compatible with significant intrinsic absorption. This is confirmed by the spectral analysis with a power law model plus intrinsic absorption. We compute the fraction of X-ray bright BCGs above a given hard X-ray luminosity, considering only sources with positive photometry in the hard band (12/5 sources in the low/high-z sample). In the 0.2<z<0.3 interval the hard X-ray luminosity ranges from 10^42 to 7×10^43 erg s−1, with most sources found below 10^43 erg s−1. In the 0.55<z<0.75 range, we find a similar distribution of luminosities below ∼10^44 erg s−1, plus two very bright sources of a few 10^45 erg s−1 associated to two radio galaxies. We also find that X-ray luminous BCGs tend to be hosted by cool core clusters, despite the majority of cool cores do not host nuclear X-ray emission.

Advances in Space Research, 2006

Today's sensitive, high-resolution Chandra X-ray observations allow the study of many populations of X-ray sources. The traditional astronomical tools of photometric diagrams and luminosity functions are now applied to these populations, and provide the means for classifying the X-ray sources and probing their evolution. While overall stellar mass drives the amount of X-ray binaries in old stellar populations, the amount of sources in star forming galaxies is related to the star formation rate. Short-lived, luminous, high mass binaries (HMXBs) dominate these young X-ray populations. 1. Chandra observations of X-ray binary (XRB) populations It is well known that the Milky Way hosts both old and young X-ray source populations, reflecting its general stellar make up. In 1978, the Einstein Observatory, the first imaging X-ray telescope, opened up the systematic study of the X-ray emission of normal galaxies, and revealed populations of X-ray sources, at least in nearby spiral galaxies (Fabbiano 1989). With Chandra's sub-arcsecond angular resolution, combined with CCD photometric capabilities (Weisskopf et al. 2000), the study of normal galaxies in X-rays has taken a revolutionary leap: populations of individual X-ray sources, with luminosities comparable to those of the Galactic X-ray binaries, can be detected at the distance of the Virgo Cluster and beyond. We can now study these X-ray populations in galaxies of all morphological types, down to typical limiting luminosities in the 10 37 ergs s-1 range. At these luminosities, the old population X-ray sources are accreting neutron star or black-hole binaries with a lowmass stellar companion, the LMXBs (life-times ~10 8-9 yrs). The young population X-ray sources, in the same luminosity range, are dominated by neutron star or black hole binaries with a massive stellar companion, the HMXBs (life-times ~ 10 6-7 yrs; see Verbunt & van den Heuvel 1995 for a review on the formation and evolution of X-ray binaries), although a few young supernova remnants (SNRs) may also be expected. At lower luminosities, reachable with Chandra in Local Group galaxies, Galactic sources include accreting white dwarfs and more evolved SNRs. Fig. 1 shows two typical observations of galaxies with Chandra: the spiral M83 (Soria & Wu 2003) and the elliptical NGC4697 (Sarazin, Irwin & Bregman 2000), both observed with the ACIS CCD detector. The images are color coded to indicate the energy of the detected photons (red 0.3-1 keV, green 1-2 keV and blue 2-8 keV). Populations of point-like sources are easily detected above a generally cooler diffuse emission from the hot interstellar medium. Note that luminous X-ray sources are relatively sparse by comparison with the underlying stellar population, and can be detected individually with the Chandra subarcsecond resolution, with the exception of those in crowded circum-nuclear regions.

Monthly Notices of the Royal Astronomical Society, 2004

In this paper we present the first results from an ongoing serendipitous survey aiming to identify X-ray selected 'normal' galaxies (i.e. not AGN dominated) by combining archival XMM-Newton data with the Sloan Digital Sky Survey. In the first 4.5 deg 2 of this program we have identified a total of 11 'normal' galaxy candidates (8 of them with optical spectroscopy) with fluxes f X (0.5 − 8 keV) ≈ 10 −15 − 10 −13 erg s −1 cm −2. These sources are selected to have low X-ray-to-optical flux ratio (log f X /f opt < ∼ −2), soft X-ray spectral properties and optical spectra, when available, consistent with the presence of a stellar ionising continuum. These sources comprise both early and late type systems at redshifts z < ∼ 0.2 with luminosities L X (0.5 − 8 keV) ≈ 10 39 − 10 42 erg s −1. This dataset provides the first tight constraint on the surface density of X-ray selected 'normal' galaxies at relatively bright fluxes spanning two orders of magnitude (10 −15 −10 −13 erg s −1 cm −2). The slope of the 'normal' galaxy log N −log S in the above flux range is estimated −1.4±0.3 consistent with the euclidean prediction. We also discuss the prospects of 'normal' galaxy studies at X-ray wavelengths using both our continuously expanding survey and future X-ray missions.

Arxiv preprint arXiv: …, 2008

Abstract: Two nearby clusters of galaxies: A194 (z= 0.018) and A1060 (z= 0.0114) have been analyzed for their X-ray point source properties with XMM-Newton EPIC-PN data. A multi-band source detection technique was applied to both of the clusters, resulting in 46 ...

We perform a detailed investigation of moderate-to-high quality X-ray spectra of ten of the most luminous active galactic nuclei (AGNs) known at z > 4 (up to z ∼ 6.28). This study includes five new XMM-Newton observations and five archived X-ray observations (four by XMM-Newton and one by Chandra). We find that the X-ray power-law photon indices of our sample, composed of eight radio-quiet sources and two that are moderately radio loud, are not significantly different from those of lower redshift AGNs. The upper limits obtained on intrinsic neutral hydrogen column densities, N H < ∼ 10 22 -10 23 cm −2 , indicate that these AGNs are not significantly absorbed. A joint fit performed on our eight radio-quiet sources, with a total of ∼7000 photons, constrains the mean photon index of z > 4 radio-quiet AGNs to Γ=1.97 +0.06 −0.04 , with no detectable intrinsic dispersion from source to source. We also obtain a strong constraint on the mean intrinsic column density, N H < ∼ 3×10 21 cm −2 , showing that optically selected radio-quiet AGNs at z > 4 are, on average, not more absorbed than their lower-redshift counterparts. All this suggests that the X-ray production mechanism and the central environment in radio-quiet AGNs have not significantly evolved over cosmic time. The mean equivalent width of a putative neutral narrow Fe Kα line is constrained to be < ∼ 190 eV, and similarly we place constraints on the mean Compton reflection component (R < ∼ 1.2). None of the AGNs varied on short (∼1 hr) timescales, but on longer timescales (months-to-years) strong variability is observed in four of the sources. In particular, the X-ray flux of the z=5.41 radio-quiet AGN SDSS 0231−0728 dropped by a factor of ∼4 over a rest-frame period of 73 d. This is the most extreme X-ray variation observed in a luminous z > 4 radio-quiet AGN.

2002

We investigate the nature of the luminous X-ray source population detected in a (72 ks) Chandra ACIS-S observation of NGC 4038/39, the Antennae galaxies. We derive the average X-ray spectral properties of sources in different luminosity ranges, and we correlate the X-ray positions with radio, IR, and optical (HST) data. The X-ray sources are predominantly associated with young stellar clusters, indicating that they belong to the young stellar population. Based on both their co-added X-ray spectrum, and on the lack of associated radio emission, we conclude that the Ultra Luminous X-ray sources (ULXs), with L X ≥ 10 39 ergs s −1 , are not young compact Supernova Remnants (SNR), but accretion binaries. While their spectrum is consistent with those of ULXs studied in nearby galaxies, and interpreted as the counterparts of intermediate mass black-holes (M> 10 − 1000 M ⊙ ), comparison with the position of star-clusters suggests that some of the ULXs may be runaway binaries, thus suggesting lower-mass binary systems. The co-added spectrum of the sources in the 3 × 10 38 − 10 39 erg s −1 luminosity range is consistent with those of Galactic black-hole candidates. These sources are also on average displaced from neighboring star clusters. The softer spectrum of the less luminous sources suggests the presence of SNRs or of hot interstellar medium (ISM) in the Chandra source extraction area. Comparison with HI and CO observations shows that most sources are detected in the outskirts of large concentrations of gas. The absorbing columns inferred from these observations would indeed absorb X-rays up to 5 keV, so there may be several hidden X-ray sources. Associated with these obscured regions we find 6 sources with heavily absorbed X-ray spectra and absorption-corrected luminosities in the ULX range. We detect the nuclei of both galaxies with luminosities in the 10 39 ergs s −1 range and soft, possibly thermal, X-ray spectra.

The Astrophysical Journal Supplement Series, 2007

We present a detailed spectral analysis of point-like X-ray sources in the XMM-COSMOS field. Our sample of 135 sources only includes those that have more than 100 net counts in the 0.3-10 keV energy band and have been identified through optical spectroscopy. The majority of the sources are well described by a simple power-law model with either no absorption (76%) or a significant intrinsic, absorbing column (20%). The remaining ∼ 4% of the sources require a more complex modeling by incorporating additional components to the power-law. For sources with more than 180 net counts (bright sample), we allowed both the photon spectral index Γ and the equivalent hydrogen column N H to be free parameters. For fainter sources, we fix Γ to the average value and allow N H to vary. The mean spectral index of the 82 sources in the bright sample is < Γ >= 2.06±0.08, with an intrinsic dispersion of ∼ 0.24. Each of these sources have fractional errors on the value of Γ below 20%. As expected, the distribution of intrinsic absorbing column densities is markedly different between AGN with or without broad optical emission lines. We find within our sample four Type-2 QSOs candidates (L X > 10 44 erg s −1 , N H > 10 22 cm −2 ), with a spectral energy distribution well reproduced by a composite Seyfert-2 spectrum, that demonstrates the strength of the wide field XMM/COSMOS survey to detect these rare and underrepresented sources. In addition, we have identified a Compton-thick (N H > 1.5 × 10 24 cm −2 ) AGN at z=0.1248. Its X-ray spectrum is well fitted by a pure reflection model and a significant Fe Kα line at rest-frame energy of 6.4 keV.