arXiv subjects

Guenther Hasinger

Publications and source records attributed to Guenther Hasinger.

At least 55 records · Page 3Linked to original sources

arXiv2003

Formation and Evolution of Supermassive Black Holes in Galactic Centers: Observational Constraints

Deep X-ray surveys have shown that the cosmic X-ray background (XRB) is largely due to the accretion onto supermassive black holes, integrated over the cosmic time. These surveys have resolved more than 80% of the 0.1-10 keV X-ray background into discrete sources. Optical spectroscopic identifications show that the sources producing the bulk of the X-ray background are a mixture of obscured (type-1) and unobscured (type-2) AGNs, as predicted by the XRB population synthesis models. A class of highly luminous type-2 AGN, so called QSO-2s, has been detected in the deepest Chandra and XMM-Newton surveys. The new Chandra AGN redshift distribution peaks at much lower redshifts (z~0.7) than that based on ROSAT data, indicating that Seyfert galaxies peak at significantly lower redshifts than QSOs.

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arXiv2003

Studying the Evolving Universe with XMM-Newton and Chandra

First indications of the warm/hot intergalactic medium, tracing out the large scale structure of the universe, have been obtained in sensitive Chandra and XMM-Newton high resolution absorption line spectroscopy of bright blazars. High resolution X-ray spectroscopy and imaging also provides important new constraints on the physical condition of the cooling matter in the centers of clusters, requiring major modifications to the standard cooling flow models. XMM-Newton and Chandra low resolution spectroscopy detected significant Fe K_alpha absorption features in the spectrum of the ultraluminous, high redshift lensed broad absorption line QSO APM 08279+5255, yielding new insights in the outflow geometry indicating a supersolar Fe/O ratio. Chandra high resolution imaging spectroscopy of the nearby ULIRG/obscured QSO NGC 6240 for the first time gave evidence of two active supermassive black holes in the same galaxy, likely bound to coalesce in the course of the ongoing major merger in this galaxy. Deep X-ray surveys have shown that the cosmic X-ray background (XRB) is largely due to the accretion onto supermassive black holes, integrated over the cosmic time. These surveys have resolved more than 80% of the X-ray background into discrete sources. Optical spectroscopic identifications show that the sources producing the bulk of the X-ray background are a mixture of obscured (type-2) and unobscured (type-1) AGNs, as predicted by the XRB population synthesis models. A class of highly luminous type-2 AGN, so called QSO-2s, has been detected in the deepest Chandra and XMM-Newton surveys. The new Chandra AGN redshift distribution peaks at much lower redshifts (z~0.7) than that based on ROSAT data, indicating that the evolution of Seyfert galaxies occurs at significantly later cosmic time than that of QSOs.

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arXiv2002

Discovery of a binary AGN in the ultraluminous infrared galaxy NGC 6240 using Chandra

Ultraluminous infrared galaxies (ULIRGs) are outstanding due to their huge luminosity output in the infrared, which is predominantly powered by super starbursts and/or hidden active galactic nuclei (AGN). NGC 6240 is one of the nearest ULIRGs and is considered a key representative of its class. Here, we report the first high-resolution imaging spectroscopy of NGC 6240 in X-rays. The observation, performed with the ACIS-S detector aboard the Chandra X-ray observatory, led to the discovery of two hard nuclei, coincident with the optical-IR nuclei of NGC 6240. The AGN character of both nuclei is revealed by the detection of absorbed hard, luminous X-ray emission and two strong neutral Fe_K_alpha lines. In addition, extended X-ray emission components are present, changing their rich structure in dependence of energy. The close correlation of the extended emission with the optical Halpha emission of NGC 6240, in combination with the softness of its spectrum, clearly indicates its relation to starburst-driven superwind activity.

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arXiv2002

The X-ray evolving universe: (ionized) absorption and dust, from nearby Seyfert galaxies to high-redshift quasars

(Abridged) Cold and warm absorbers have beeen detected in all types of active galaxies (AGN) from low to high redshift. This gas, located in the black hole region of AGN, is thought to play an important role in AGN unification scenarios, in explaining the X-ray background, in black hole growth and AGN evolution. We provide a review of the observations of dusty and dust-free warm and cold absorbers at low and high redshift, including most recent results and exciting questions still open. Emphasis is on the science issues that we will be able to address with XEUS for the first time, particularly at high redshift, including: (i) determination of metal abundances of X-ray (cold) absorbers by detection of metal absorption edges, (ii) analysis of the composition of dust mixed with cold and ionized gas (K-edges of metals in cold dust and cold gas will be resolvable from each other for the first time), (iii) measurement of the velocity field of the gas, (iv) utilization of these results to investigate the evolution of gas and dust in AGN from high to low redshift: the evolution of abundances, dust content, ionization state, amount and velocity of gas, and its role in feeding the black hole. We emphasize the importance of iron absorption measurements with XEUS at high redshift for two key issues of cosmology: the early star formation history of the universe, and the measurement of cosmological parameters. As an example, we discuss recent XMM-Newton observations of the high-redshift BAL quasar APM 08279+5255.

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arXiv2002

The X-ray Spectrum of Supernova Remnant 1987A

We discuss the X-ray emission observed from Supernova Remnant 1987A with the Chandra X-ray Observatory. We analyze a high resolution spectrum obtained in 1999 October with the high energy transmission grating (HETG). From this spectrum we measure the strengths and an average profile of the observed X-ray lines. We also analyze a high signal-to-noise ratio CCD spectrum obtained in 2000 December. The good statistics (~ 9250 counts) of this spectrum and the high spatial resolution provided by the telescope allow us to perform spectroscopic analyses of different regions of the remnant. We discuss the relevant shock physics that can explain the observed X-ray emission. The X-ray spectra are well fit by plane parallel shock models with post-shock electron temperatures of ~ 2.6 keV and ionization ages of ~ 6 x 10^10 cm^3/s. The combined X-ray line profile has a FWHM of ~ 5000 km/s, indicating a blast wave speed of ~ 3500 km/s. At this speed, plasma with a mean post-shock temperature of ~ 17 keV is produced. This is direct evidence for incomplete electron-ion temperature equilibration behind the shock. Assuming this shock temperature, we constrain the amount of collisionless electron heating at the shock front at T_e0 / T_s = 0.11 (+0.02,-0.01). We find that the plasma has low metallicity (abundances are ~ 0.1 -- 0.4 solar) and is nitrogen enriched (N/O ~ 0.8 by number), similar to that found for the equatorial ring. Analysis of the spectra from different regions of the remnant reveals slight differences in the parameters of the emitting plasma. The plasma is cooler near the optical Spot 1 (at position angle ~ 30 degrees) and in the eastern half of the remnant, where the bright optical spots are found, than in the western half, consistent with the presence of slower (~ 500 km/s) shocks entering denser ring material.

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arXiv2002

The sources of the X-ray background

Deep X-ray surveys have shown that the cosmic X-ray background (XRB) is largely due to the accretion onto supermassive black holes, integrated over cosmic time. The ROSAT, Chandra and XMM-Newton satellites have resolved more than 80% of the 0.1-10 keV X-ray background into discrete sources. Optical spectroscopic identifications are about 90% and 60% complete for the deepest ROSAT and Chandra/ XMM-Newton surveys, respectively, and show that the sources producing the bulk of the X-ray background are a mixture of obscured (type-2) and unobscured (type-1) AGNs, as predicted by the XRB population synthesis models, following the unified AGN scenarios. The characteristic hard spectrum of the XRB can be explained if most of the AGN are heavily absorbed, and in particular a class of highly luminous type-2 AGN, so called QSO-2s exist. The deep Chandra and XMM-Newton surveys have recently detected several examples of QSO-2s. The space density of the X-ray selected AGN, as determined from ROSAT surveys does not seem to decline as rapidly as that of optically selected QSO, however, the statistics of the high-redshift samples is still rather poor. The new Chandra and XMM-Newton surveys at significantly fainter fluxes are starting to provide additional constraints here, but the preliminary observed redshift distribution peaks at much lower redshifts (z=0.5-0.7) than the predictions based on the ROSAT luminosity function.

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arXiv2001

The AGN contribution to mid-infrared surveys

We provide constraints on the AGN contribution to the mid-IR extragalactic background light from a correlation analysis of deep X-ray and mid-IR observations in two regions centred on the Lockman Hole (LH) and Hubble Deep Field North (HDFN). Among the 76 galaxies detected by XMM in the LH area (200 square arcminutes), 24 show mid-IR emission, but the relative percentage of X-ray sources with mid-IR counterparts increases with the band energy: from 30% of the 0.5-2 keV sources up to 63% of the 5-10 keV sources. In contrast, only a small fraction of the mid-IR sources (around 10%) show X-ray emission. In the region centred on the HDFN (24 square arcminutes), 25% of the mid-IR sources are detected in the X-ray, while 30-40% of the X-ray sources show mid-IR emission. Under the conservative assumption that all XMM sources are AGN-dominated, AGNs contribute 15% of the total mid-IR flux in the LH. For the HDFN we have assumed that AGN-dominated sources are luminous X-ray sources with radio to X-ray SEDs typical of local AGNs, in which case we find that 18% of the mid-IR flux are due to AGN emission. If we put together all the existing information from the deepest HDFN data to the shallow large-area BeppoSAX observations in the ELAIS S1 region using the median mid-IR to X-ray spectral indices as a function of the X-ray flux, we find an AGN contribution to the 15um background of 17%. We conclude that the population of IR luminous galaxies detected in the ISOCAM deep surveys are mainly constituted by dust-obscured starbursts.

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arXiv2001

XMM-Newton Observation of a Distant X-ray Selected Cluster of Galaxies at z=1.26 with Possible Cluster Interaction

We report on the XMM-Newton (XMM) observation of RXJ1053.7+5735, one of the most distant (z = 1.26) X-ray selected clusters of galaxies, which also shows an unusual double-lobed X-ray morphology, indicative of possible cluster-cluster interaction. The cluster was discovered during our ROSAT deep pointings in the direction of the Lockman Hole. The XMM observations were performed with the European Photon Imaging Camera (EPIC) during the performance verification phase. Total effective exposure time was ~ 100 ksec. The best fit temperature based on a simultaneous fit of spectra from the all EPIC cameras is 4.9(+1.5/-0.9) keV. Metallicity is poorly constrained even using the joint fit of all spectra, with an upper limit on the iron abundance of 0.62 solar. Using the best fit model parameters, we derived a bolometric luminosity of L(bol) = 3.4x10^44 h_{50}^-2 erg /s. Despite the fact that it was observed at fairly large off-axis angle, the temperature errors are much smaller compared with those of typical measurements based on ASCA or Beppo-Sax observations of z > 0.6 clusters, demonstrating the power of the XMM for determining the X-ray temperature for high-z clusters. The measured temperature and luminosity show that one can easily reach the intrinsically X-ray faint and cool cluster regime comparable with those of z ~ 0.4 clusters observed by past satellites. The new cluster temperature and L(bol) we have measured for RXJ1053.7+5735 is consistent with a weak/no evolution of the L(bol) - Tx relation out to z ~ 1.3, which lends support to a low Omega universe, although more data-points of z > 1 clusters are required for a more definitive statement. The caution has to be also exercised in interpreting the result, because of the uncertainty associated with the dynamical status of this cluster.

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arXiv2001

Multiple Components of the Luminous Compact X-ray Source at the Edge of Holmberg II observed by ASCA and ROSAT

We report the results of the analysis of ASCA/ROSAT observations of the compact luminous X-ray source found at the edge of the nearby star-forming dwarf galaxy Holmberg II (UGC 4305).Our ASCA spectrum revealed that the X-ray emission extends to the hard band and can be best described by a power-law with a photon spectral index of 1.9. The ASCA spectrum does not fit with a multi-color disk blackbody. The joint ASCA-ROSAT spectrum suggests two components to the spectrum: the hard power-law component and a warm thermal plasma kT~0.3[keV]. An additional absorption over that of our galaxy is required. The wobble correction of the ROSAT HRI image has clearly unveiled the existence of an extended component which amounts to 27+/-5% of the total X-ray emission. These observations indicate that there are more than one component in the X-ray emission. The properties of the point-like component is indicative of an accretion onto an intermediate mass blackhole, unless a beaming is taking place. We argue that the extended component does not come from electron scattering and/or reflection by scattered optically-thick clouds of the central radiation. Possible explanations of this X-ray source include multiple supernova remnants feeding an intermediate-mass blackhole. (abridged)

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arXiv2001

Soft X-ray AGN Luminosity Function from ROSAT Surveys II. Table of the binned Soft X-ray Luminosity Function

This is the second paper of our investigation of the 0.5-2 keV soft X-ray luminosity function (SXLF) of active galactic nuclei (AGN) using results from ROSAT surveys of various depth. The large dynamic range of the combined sample, from shallow large-area ROSAT All-Sky Survey (RASS)-based samples to the satellite's deepest pointed observation on the Lockman Hole, enabled us to trace the behavior of the SXLF. While the first paper (Miyaji, Hasinger, Schmidt 2000, hereafter paper I) emphasized the global behavior of the SXLF, cosmological evolution and contribution to the soft X-ray background, this paper presents actual numerical values for practical use of our results. To present the binned SXLF, we have used an improved estimator, which is free from biases associated with the conventional 1/Va estimator.

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arXiv2000

X-ray Surveys of the obscured Universe

Deep X-ray surveys have shown that the cosmic X-ray background (XRB) is largely due to accretion onto supermassive black holes, integrated over cosmic time. However, the characteristic hard spectrum of the XRB can only be explained if most AGN spectra are heavily absorbed. The absorbed AGN will suffer severe extinction and therefore, unlike classical QSOs, will not be prominent at optical wavelengths. Most of the accretion power is being absorbed by gas and dust and will have to be reradiated in the FIR/sub-mm band. AGN could therefore contribute a substantial fraction to the recently discovered cosmic FIR/sub-mm background. Here it is shown that a number of high-redshift absorbed X-ray sources selected in the ROSAT Deep Survey of the Lockman Hole have broad-band spectral energy distributions very similar to the local ULIRG NGC6240, lending additional support to the background models for the obscured universe.

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arXiv1999

Soft X-ray AGN Luminosity Function from ROSAT Surveys I. Cosmological Evolution and Contribution to the Soft X-ray Background

We investigate the evolution of the 0.5-2 keV soft X-ray luminosity function (SXLF) of active galactic nuclei (AGN) using results from ROSAT surveys of various depth, ranging from shallow large-area ROSAT All-Sky Survey -based samples to the deepest pointed observation on the Lockman Hole. As previously found, the SXLF evolves rapidly as a function of redshift up to z\sim 1.5 and is consistent with remaining constant beyond this redshift. We found that a form of the Luminosity-Dependent Density Evolution (LDDE) gives an excellent fit to the data. Extrapolating one form of the LDDE model (LDDE1) explains \approx 60% of the estimated soft extragalactic Cosmic X-ray Background (CXRB). We have also found another representation (LDDE2), which produces \approx 90% of the CXRB and still gives an excellent fit to the sample AGNs. These two versions of the LDDE models can be considered two extremes of the possible extrapolations of the SXLF below the flux limit. We have also investigated the evolution of the number density of luminous QSOs. Unlike these QSOs, the ROSAT-selected QSOs do not show evidence for the decrease of the number density in z>3. The statistical significance of the difference is, however, marginal.

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arXiv1999

The ROSAT All-Sky Survey Bright Source Catalogue

We present the ROSAT All-Sky Survey Bright Source Catalogue (RASS-BSC, revision 1RXS) derived from the all-sky survey performed during the first half year (1990/91) of the ROSAT mission. 18,811 sources are catalogued (i) down to a limiting ROSAT PSPC count-rate of 0.05 cts/s in the 0.1-2.4 keV energy band, (ii) with a detection likelihood of at least 15 and (iii) at least 15 source counts. The 18,811 sources underwent both an automatic validation and an interactive visual verification process in which for 94% of the sources the results of the standard processing were confirmed. The remaining 6% have been analyzed using interactive methods and these sources have been flagged. Flags are given for (i) nearby sources; (ii) sources with positional errors; (iii) extended sources; (iv) sources showing complex emission structures; and (v) sources which are missed by the standard analysis software. Broad band (0.1-2.4 keV) images are available for sources flagged by (ii), (iii) and (iv). For each source the ROSAT name, position in equatorial coordinates, positional error, source count-rate and error, background count-rate, exposure time, two hardness-ratios and errors, extent and likelihood of extent, likelihood of detection, and the source extraction radius are provided. At a brightness limit of 0.1 cts/s (8,547 sources) the catalogue represents a sky coverage of 92%. The RASS-BSC, the table of possible identification candidates, and the broad band images are available in electronic form (Voges et al. 1996a) via http://wave.xray.mpe.mpg.de/rosat/catalogues/rass-bsc .

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arXiv1999

On the Relationship between Galaxy Formation and Quasar Evolution

We compare the evolution with cosmic time of the star-formation rate per comoving volume in galaxies and of the volume emissivity by Active Galactic Nuclei, as a clue to understand the relationship between black hole accretion and the formation of the surrounding structure. We find an interesting similarity between the evolution rates for the total populations of galaxies and AGNs, which indicates that, on average, the history of BH accretion tracks that of stellar formation in the hosting galaxies. Similarly, the evolution of luminous quasars parallels that of the stellar populations in massive spheroidal galaxies, in keeping with the locally established association of supermassive BHs and galactic bulges. We finally comment on our finding that high-luminosity, high-mass systems evolve on a faster cosmic timescale than the lower mass ones: to explain this, the theories of structure formation based on the gravitational collapse of dark matter halos have to be complemented with a detailed description of the dynamical processes in the baryonic component, which dominate the formation and evolution in high-density environments.

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arXiv1997

The X-ray background and the ROSAT Deep Surveys

In this article we review the measurements and understanding of the X-ray background (XRB), discovered by Giacconi and collaborators 35 years ago. We start from the early history and the debate whether the XRB is due to a single, homogeneous physical process or to the summed emission of discrete sources, which was finally settled by COBE and ROSAT. We then describe in detail the progress from ROSAT deep surveys and optical identifications of the faint X-ray source population. In particular we discuss the role of active galactic nuclei (AGNs) as dominant contributors for the XRB, and argue that so far there is no need to postulate a hypothesized new population of X-ray sources. The recent advances in the understanding of X-ray spectra of AGN is reviewed and a population synthesis model, based on the unified AGN schemes, is presented. This model is so far the most promising to explain all observational constraints. Future sensitive X-ray surveys in the harder X-ray band will be able to unambiguously test this picture.

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arXiv1997

The X-ray background and the AGN X-ray luminosity function

ROSAT deep and shallow surveys have provided an almost complete inventory of the constituents of the soft X-ray background which led to a population synthesis model for the whole X-ray background with interesting cosmological consequences. According to this model the X-ray background is the ``echo'' of mass accretion onto supermassive black holes, integrated over cosmic time. A new determination of the soft X-ray luminosity function of active galactic nuclei (AGN) is inconsistent with pure luminosity evolution. The comoving volume density of AGN at redshift 2-3 approaches that of local normal galaxies. This indicates that many larger galaxies contain black holes and it is likely that the bulk of the black holes was produced before most of the stars in the universe. However, only X-ray surveys in the harder energy bands, where the maximum of the energy density of the X-ray background resides, will provide the acid test of this picture.

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arXiv1997

The ROSAT Deep Survey I. X-ray sources in the Lockman Field

The ROSAT Deep Survey in the Lockman Hole is the most sensitive X-ray survey performed to date, encompassing an exposure time of 207 ksec with the PSPC and a total of 1.32 Msec with the HRI aboard ROSAT. Here we present the complete catalogue of 50 X-ray sources with PSPC fluxes (0.5--2 keV) above $ 5.5 \times 10^{-15} erg cm^{-2} s^{-1}$. The optical identifications are discussed in an accompanying paper (Schmidt et al., 1997). We also derive a new log(N)--log(S) function reaching a source density of $970 \pm 150 deg^{-2}$ at a limiting flux of $10^{-15} erg cm^{-2} s^{-1}$. At this level 70-80% of the 0.5--2 keV X-ray background is resolved into discrete sources. Utilizing extensive simulations of artificial PSPC and HRI fields we discuss in detail the effects of source confusion and incompleteness both on source counts and on optical identifications. Based on these simulations we set conservative limits on flux and on off-axis angles, which guarantee a high reliability of the catalogue. We also present simulations of shallower fields and show that surveys, which are based on PSPC exposures longer than 50 ksec, become severely confusion limited typically a factor of 2 above their $4σ$ detection threshold. This has consequences for recent claims of a possible new source population emerging at the faintest X-ray fluxes. Keywords: surveys -- cosmology: diffuse radiations -- X-rays: galaxies

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arXiv1997

The ROSAT Deep Survey II. Optical identification, photomettry and spectra of sources in the Lockman field

The ROSAT Deep Survey includes a complete sample of 50 X-ray sources with fluxes in the $0.5 - 2$ keV band larger than 5.5 $10^{-15}$ erg cm$^{-2}$ s$^{-1}$ in the Lockman field (Hasinger et al., Paper I). We have obtained deep broad-band CCD images of the field and spectra of many optical objects near the positions of the X-ray sources. We define systematically the process leading to the optical identifications of the X-ray sources. For this purpose, we introduce five identification (ID) classes that characterize the process in each case. Among the 50 X-ray sources, we identify 39 AGNs, 3 groups of galaxies, 1 galaxy and 3 galactic stars. Four X-ray sources remain unidentified so far; two of these objects may have an unusually large ratio of X-ray to optical flux. Keywords: surveys -- galaxies: active -- quasars: emission lines -- galaxies: Seyfert -- X-rays: galaxies

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