T. L. Aldcroft

The Astronomical Observatory of Brera, Merate, Lombardy, Italy

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Publications (134)385.36 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We describe progress in the development of adjustable grazing incidence X-ray optics for 0.5 arcsec resolution cosmic X-ray imaging. To date, no optics technology is available to blend high resolution imaging like the Chandra X-ray Observatory, with square meter collecting area. Our approach to achieve these goals simultaneously is to directly deposit thin film piezoelectric actuators on the back surface of thin, lightweight Wolter-I or Wolter- Schwarschild mirror segments. The actuators are used to correct mirror figure errors due to fabrication, mounting and alignment, using calibration and a one-time figure adjustment on the ground. If necessary, it will also be possible to correct for residual gravity release and thermal effects on-orbit. In this paper we discuss our most recent results in operating multiple adjusters, and extending the process from flat test mirrors to cylindrical and conical test mirror segments. A comparison of modeled and measured influence functions is shown. We also present simulation results showing the process is consistent with the achievement of half arcsec imaging.
    Proc SPIE 09/2013;
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    ABSTRACT: The formation of stars in massive clusters is one of the main modes of the star formation process. However, the study of massive star forming regions is hampered by their typically large distances to the Sun. One exception to this is the massive star forming region Cygnus OB2 in the Cygnus X region, at the distance of about 1400 pc. Cygnus OB2 hosts very rich populations of massive and low-mass stars, being the best target in our Galaxy to study the formation of stars, circumstellar disks, and planets in presence of massive stars. In this paper we combine a wide and deep set of photometric data, from the r band to 24 micron, in order to select the disk bearing population of stars in Cygnus OB2 and identify the class I, class II, and stars with transition and pre-transition disks. We selected 1843 sources with infrared excesses in an area of 1 degree x 1 degree centered on Cyg OB2 in several evolutionary stages: 8.4% class I, 13.1% flat-spectrum sources, 72.9% class II, 2.3% pre-transition disks, and 3.3% transition disks. The spatial distribution of these sources shows a central cluster surrounded by a annular overdensity and some clumps of recent star formation in the outer region. Several candidate subclusters are identified, both along the overdensity and in the rest of the association.
    The Astrophysical Journal 06/2013; 773(2). · 6.73 Impact Factor
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    ABSTRACT: The young massive cluster Cyg OB2 is the closest massive star forming region to the Sun, with hundreds of OB members, and then the best target in the Milky Way to study the feedback of massive stars on the star formation process. To study in detail the stellar population of such a unique target, Cyg OB2 has been observed with GTC/OSIRIS and Chandra/ACIS-I. We present the OSIRIS observations, the catalog and the preliminary scientific results.
    05/2013;
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    ABSTRACT: We present the X-ray spectral analysis of the 390 brightest extragalactic sources in the Chandra-COSMOS catalog, showing at least 70 net counts in the 0.5-7 keV band. This sample has a 100% completeness in optical-IR identification, with 75% of the sample having a spectroscopic redshift and 25% a photometric redshift. Our analysis allows us to accurately determine the intrinsic absorption, the broad band continuum shape ({\Gamma}) and intrinsic L(2-10) distributions, with an accuracy better than 30% on the spectral parameters for 95% of the sample. The sample is equally divided in type-1 (49.7%) and type-2 AGN (48.7%) plus few passive galaxies at low z. We found a significant difference in the distribution of {\Gamma} of type-1 and type-2, with small intrinsic dispersion, a weak correlation of {\Gamma} with L(2-10) and a large population (15% of the sample) of high luminosity, highly obscured (QSO2) sources. The distribution of the X ray/Optical flux ratio (Log(FX /Fi)) for type-1 is narrow (0 < X/O < 1), while type-2 are spread up to X/O = 2. The X/O correlates well with the amount of X-ray obscuration. Finally, a small sample of Compton thick candidates and peculiar sources is presented. In the appendix we discuss the comparison between Chandra and XMM-Newton spectra for 280 sources in common. We found a small systematic difference, with XMM-Newton spectra that tend to have softer power-laws and lower obscuration.
    Monthly Notices of the Royal Astronomical Society 02/2013; 431(1). · 5.52 Impact Factor
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    ABSTRACT: The equatorial 2 deg2 COSMOS area is the only large field for which a complete, deep, pan-chromatic data set exists, from an outstanding survey effort, and that all large telescopes can observe. Now, this pioneering and ambitious COSMOS survey is undergoing major extension, pushing its frontiers via the newly approved Chandra COSMOS Legacy Survey, the second largest Chandra proposal ever approved.'COSMOS-Legacy' will uniformly cover the 1.7 deg2 COSMOS/HST field with 2.8 Ms of Chandra ACIS-I imaging at ~160 ksec depth. This project expands the current deep C-COSMOS area by a factor of ~3 at ~3e-16 (1.45 vs 0.44 deg2). This will be achieved with 56x50 ks tiles covering a total area of 2.2 deg2, which will be observed during Chandra Cycle 14. The area and depth of COSMOS Legacy are designed to detect ~{40 zgt4, and ~}4 zgt5 Large Scale Structures on gt15 arcmin scales. These structures have proven to connect luminous AGN (over 200 at zgt3 will be detected) and sub-mm galaxies. COSMOS Legacy will also probe mini-quasars at zgt7, using anistotropies of the unresolved X-ray Background, and the masses of the Dark Matter halos hosting X-ray AGN up to 3, via autocorrelation functions on ~30arcmin scales. To fully achieve these goals, COSMOS Legacy is complemented by spectroscopic follow-up with DEIMOS and MOSFIRE at Keck and KMOS at the VLT and FMOS at Subaru, just approved observations with Spitzer and JVLA, and with harder (5-80 keV) X-ray imaging with NuSTAR. In the near future, observations with Subaru HyperSuprimeCam (grizY) to r(AB)=28.2 are planned.
    American Astronomical Society Meeting Abstracts; 01/2013
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    ABSTRACT: Studies of quasar mass outflows are rapidly reshaping our understanding of physics near the supermassive black hole (SMBH). The ~parsec scale emitting/absorbing regions near SMBHs will remain spatially unresolved for the foreseeable future (milliarcsec at z ~ 0.01). Spectroscopic variability timescale information can, however, constrain the structure, stability, location, and dynamics of the emitting and absorbing gas near the SMBH. Though outflows likely accompany all luminous accretion disks, broad absorption line (BAL) quasars provide the most dramatic examples — their massive outflows display P-Cygni profiles that span velocities to ~0.3c. We present multi-epoch spectroscopy of seventeen BAL QSOs using the Fred Lawrence Whipple Observatory's 1.5m telescope's FAST Spectrograph. These objects were identified as BALs in SDSS, observed with Chandra, and then monitored with FAST at observed-frame cadences of 1, 3, 9, 27, and 81 days, as well as 1 and 2 years. We also monitor a set of non-BAL quasars with matched redshift and luminosity as controls. We identify significant variability in the BALs, particularly at the 1 and 2 year cadences, and use its magnitude and frequency to constrain the outflows impacting the broad absorption line region.
    American Astronomical Society, AAS Meeting #221, Long Beach, CA; 01/2013
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    ABSTRACT: Optical catalog in riz bands in a 30'x30' area around CygnusOB2. (1 data file).
    VizieR Online Data Catalog. 11/2012;
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    ABSTRACT: We describe an X-ray Observatory mission with 0.5" angular resolution, comparable to the Chandra X-ray Observatory, but with 30 times more effective collecting area. The concept is based on developing the new technology of adjustable X-ray optics for ultra thin (0.4 mm), highly nested grazing incidence X-ray mirrors. Simulations to date indicate that the corrections for manufacturing and mounting can be determined on the ground and the effects of gravity release can be calculated to sufficient accuracy, so that all adjustments are applied only once on-orbit, without the need of any on-orbit determination of the required corrections. The mission concept is based on the Chandra Observatory, and takes advantage of the technology studies which have taken place over the past fifteen years developing large area, light weight mirrors.
    Proc SPIE 10/2012;
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    ABSTRACT: The next generation of large X-ray telescopes with sub-arcsecond resolution will require very thin, highly nested grazing incidence optics. To correct the low order figure errors resulting from initial manufacture, the mounting process, and the effects of going from 1 g during ground alignment to zero g on-orbit, we plan to adjust the shapes via piezoelectric "cells" deposited on the backs of the reflecting surfaces. This presentation investigates how well the corrections might be made. We take a benchmark conical glass element, 410×205 mm, with a 20×20 array of piezoelectric cells 19×9 mm in size. We use finite element analysis to calculate the influence function of each cell. We then simulate the correction via pseudo matrix inversion to calculate the stress to be applied by each cell, considering distortion due to gravity as calculated by finite element analysis, and by putative low order manufacturing distortions described by Legendre polynomials. We describe our algorithm and its performance, and the implications for the sensitivity of the resulting slope errors to the optimization strategy.
    Proc SPIE 10/2012;
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    ABSTRACT: The coalescence of two SMBHs in galaxy major merger gives rise to the strongest Gravitational Wave (GW) events in the universe. Typically, the GW emission is asymmetric and causes the newly merged single SMBH to displace from the galaxy center of few parsecs. Under particular condition of BH spin and mass ratio, the SMBH can gain a significant velocity (up to ~5000km/s) and it may be displaced by several kpc. If the SMBH is ejected from the galaxy, or even if wanders through the halo for several Gyrs, it will continue to shine for 10^6-10^7 yr, until it exhausts the fuel and is no longer recognizable as an active SMBH. The partial or total absence of the SMBH from the galaxy center has strong implications on the SF history of the galaxy. Despite predicted by theoretical models of structure formation, GW recoiling SMBHs are very hard to detect. The recoils with high probability have a very small velocity resulting in undetectable offsets, those with low probability can escape easily from the galaxy and not been recognized as such. We discovered in the COSMOS survey CID-42 (z=0.359), the best candidate recoiling SMBH to date, just caught when still active. CID-42 clearly shows both the presence of two compact sources, ~2.5 kpc embedded in the same galaxy in HST imaging, and a ~1100km/s velocity offset between the narrow and broad components of Hα, in 3 optical spectra. High resolution Chandra data were crucial to resolve the X-ray emission from the two optical sources and determines the AGN activity level of each. The results clearly favor the recoiling scenario for this source. Models & simulations have been developed to explain the observed properties of CID-42.
    09/2012;
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    ABSTRACT: We report on technical progress made over the past year developing thin film piezoelectric adjustable grazing incidence optics. We believe such mirror technology represents a solution to the problem of developing lightweight, sub-arc second imaging resolution X-ray optics. Such optics will be critical to the development next decade of astronomical X-ray observatories such as SMART-X, the Square Meter Arc Second Resolution X-ray Telescope. SMART-X is the logical heir to Chandra, with 30 times the collecting area and Chandra-like imaging resolution, and will greatly expand the discovery space opened by Chandra’s exquisite imaging resolution. In this paper we discuss deposition of thin film piezoelectric material on flat glass mirrors. For the first time, we measured the local figure change produced by energizing a piezo cell - the influence function, and showed it is in good agreement with finite element modeled predictions. We determined that at least one mirror substrate material is suitably resistant to piezoelectric deposition processing temperatures, meaning the amplitude of the deformations introduced is significantly smaller than the adjuster correction dynamic range. Also, using modeled influence functions and IXO-based mirror figure errors, the residual figure error was predicted post-correction. The impact of the residual figure error on imaging performance, including any mid-frequency ripple introduced by the corrections, was modeled. These, and other, results are discussed, as well as future technology development plans.
    Proc SPIE 09/2012;
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    ABSTRACT: In order to fully understand the gravitational collapse of molecular clouds, the star formation process and the evolution of circumstellar disks, these phenomena must be studied in different Galactic environments with a range of stellar contents and positions in the Galaxy. The young massive association Cygnus OB2, in the Cygnus-X region, is an unique target to study how star formation and the evolution of circumstellar disks proceed in the presence of a large number of massive stars. We present a catalog obtained with recent optical observations in r,i,z filters with OSIRIS, mounted on the $10.4\,m$ GTC telescope, which is the deepest optical catalog of Cyg OB2 to date. The catalog consist of 64157 sources down to M=0.15 solar masses at the adopted distance and age of Cyg OB2. A total of 38300 sources have good photometry in all three bands. We combined the optical catalog with existing X-ray data of this region, in order to define the cluster locus in the optical diagrams. The cluster locus in the r-i vs. i-z diagram is compatible with an extinction of the optically selected cluster members in the 2.64<AV<5.57 range. We derive an extinction map of the region, finding a median value of AV=4.33 in the center of the association, decreasing toward the north-west. In the color-magnitude diagrams, the shape of the distribution of main sequence stars is compatible with the presence of an obscuring cloud in the foreground at about 850+/-25 pc from the Sun.
    The Astrophysical Journal Supplement Series 08/2012; 202(2). · 16.24 Impact Factor
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    ABSTRACT: We present Chandra High Resolution Camera observations of CID-42, a candidate recoiling supermassive black hole (SMBH) at z = 0.359 in the COSMOS survey. CID-42 shows two optical compact sources resolved in the HST/ACS image embedded in the same galaxy structure and a velocity offset of ~1300 km s–1 between the Hβ broad and narrow emission line, as presented by Civano et al. Two scenarios have been proposed to explain the properties of CID-42: a gravitational wave (GW) recoiling SMBH and a double Type 1/Type 2 active galactic nucleus (AGN) system, where one of the two is recoiling because of slingshot effect. In both scenarios, one of the optical nuclei hosts an unobscured AGN, while the other one, either an obscured AGN or a star-forming compact region. The X-ray Chandra data allow us to unambiguously resolve the X-ray emission and unveil the nature of the two optical sources in CID-42. We find that only one of the optical nuclei is responsible for the whole X-ray unobscured emission observed and a 3σ upper limit on the flux of the second optical nucleus is measured. The upper limit on the X-ray luminosity plus the analysis of the multiwavelength spectral energy distribution indicate the presence of a star-forming region in the second source rather than an obscured SMBH, thus favoring the GW recoil scenario. However, the presence of a very obscured SMBH cannot be fully ruled out. A new X-ray feature, in a SW direction with respect to the main source, is discovered and discussed.
    The Astrophysical Journal 05/2012; 752(1):49. · 6.73 Impact Factor
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    ABSTRACT: The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that has imaged the central 0.9 deg^2 of the COSMOS field down to limiting depths of 1.9 10^-16 erg cm^-2 s-1 in the 0.5-2 keV band, 7.3 10^-16 erg cm^-2 s^-1 in the 2-10 keV band, and 5.7 10^-16 erg cm^-2 s-1 in the 0.5-10 keV band. In this paper we report the i, K and 3.6micron identifications of the 1761 X-ray point sources. We use the likelihood ratio technique to derive the association of optical/infrared counterparts for 97% of the X-ray sources. For most of the remaining 3%, the presence of multiple counterparts or the faintness of the possible counterpart prevented a unique association. For only 10 X-ray sources we were not able to associate a counterpart, mostly due to the presence of a very bright field source close by. Only 2 sources are truly empty fields. Making use of the large number of X-ray sources, we update the "classic locus" of AGN and define a new locus containing 90% of the AGN in the survey with full band luminosity >10^42 erg/s. We present the linear fit between the total i band magnitude and the X-ray flux in the soft and hard band, drawn over 2 orders of magnitude in X-ray flux, obtained using the combined C-COSMOS and XMM-COSMOS samples. We focus on the X-ray to optical flux ratio (X/O) and we test its known correlation with redshift and luminosity, and a recently introduced anti-correlation with the concentration index (C). We find a strong anti-correlation (though the dispersion is of the order of 0.5 dex) between C and X/O, computed in the hard band, and that 90% of the obscured AGN in the sample with morphological information live in galaxies with regular morphology (bulgy and disky/spiral), suggesting that secular processes govern a significant fraction of the BH growth at X-ray luminosities of 10^43- 10^44.5 erg/s.
    The Astrophysical Journal Supplement Series 05/2012; 201(2). · 16.24 Impact Factor
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    ABSTRACT: We present Chandra High Resolution Camera observations of CID-42, a candidate recoiling supermassive black hole (SMBH) at z=0.359 in the COSMOS survey. CID-42 shows two optical compact sources resolved in the HST/ACS image embedded in the same galaxy structure and a velocity offset of ~1300 km/s between the H\beta\ broad and narrow emission line, as presented by Civano et al. (2010). Two scenarios have been proposed to explain the properties of CID-42: a GW recoiling SMBH and a double Type 1/ Type 2 AGN system, where one of the two is recoiling because of slingshot effect. In both scenario, one of the optical nuclei hosts an unobscured AGN, while the other one, either an obscured AGN or a star forming compact region. The X-ray Chandra data allow to unambiguously resolve the X-ray emission, and unveil the nature, of the two optical sources in CID-42. We find that only one of the optical nuclei is responsible for the whole X-ray unobscured emission observed and a 3sigma upper limit on the flux of the second optical nucleus is measured. The upper limit on the X-ray luminosity plus the analysis of the multiwavelength spectral energy distribution indicate the presence of a starforming region in the second source rather than an obscured SMBH, thus favoring the GW recoil scenario. However the presence of a very obscured SMBH cannot be fully ruled-out. A new X-ray feature, in a SW direction with respect to the main source, is discovered and discussed.
    05/2012;
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    ABSTRACT: Kinetic energy carried by AGN winds and jets may rival radiation as the dominant feedback mechanism regulating galaxy-SMBH co-evolution. Though outflows likely accompany all luminous accretion disks, broad absorption line quasars (BALQSOs) provide the most dramatic astrophysical examples; their massive outflows display P-Cygni profiles that span velocities up to 0.3c and are visible in the spectra of 15-40% of optically-selected quasars. Spectroscopic variability studies of BALQSOs probe the structure, stability, location, and dynamics of the emitting and absorbing gas near the SMBH and can provide insight into connections between AGN feedback and host galaxy formation and evolution. We report on a multi-year spectroscopic campaign that monitors seventeen BALQSOs (identified originally in the SDSS) using the Fred Lawrence Whipple Observatory's 1.5m telescope's FAST spectrograph. These targets have Chandra X-ray data and have been repeatedly observed with FAST, in regular cadences from one day to two years -- a 6 year cadence is planned for spring 2012. We identify variability in the broad absorption line region, assess its significance, magnitude, and frequency and discuss the constraints these investigations can place on QSO outflows.
    American Astronomical Society, AAS Meeting #219, Austin, TX; 01/2012
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    ABSTRACT: Black hole and galaxy co-evolution models predict a phase in which multiple galaxies with active black holes interact, with visible signatures of interaction, and that their activity may be stimulated by tidal disruptions of their ISM. Several studies have been recently conducted to prove the existence of this phase. However, a proper multiwavelength characterization of galaxy pairs is still missing. We present analysis of X-ray emitting galaxy pairs selected in the Chandra COSMOS survey. The sources in each pair are within a redshift difference of 0.2 and a projected separation of 10 arcseconds, corresponding to projected physical separations ranging from 27 kpc to 82 kpc. In order to characterize the pairs in the context of the black hole/galaxy co-evolution scenario, we i) fit spectral energy distributions to determine the relative AGN and galaxy contributions, ii) calculated X-ray luminosities and hardness ratios to check the active nature of the black holes and to get a sense of the obscuration levels, iii) examined the morphologies for signatures of mergers, and iv) determined relative velocities from available spectra. Active black holes are present in all of the galaxies, as they are very luminous in the X-ray band, though mildly obscured. In most of the sources, the host galaxy out shines the nuclear light in the optical band. In several lower redshift pairs, where morphological features are more easily observed, we see disturbed morphology and tidal structures, signatures of a first close passage. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.
    01/2012;
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    ABSTRACT: We presentChandra X-ray imaging and spectroscopy for 14 quasars in spatially resolved pairs tar-geted as part of a complete sample of binary quasars with small transverse separations drawn from Sloan Digital Sky Survey (DR6) photometry. We measure the X-ray properties of all 14 QSOs, and study the distribution of X-ray and optical-to-X-ray power-law indices in these binary quasars. We find no significant difference when compared with large control samples of isolated quasars, true even for SDSS J1254+0846, discussed in detail in a companion paper, which clearly inhabits an ongoing, pre-coalescence galaxy merger showing obvious tidal tails. We present infrared photometry from our observations with SWIRC at the MMT, and from the WISE Preliminary Data Release, and fit simple spectral energy distributions to all 14 QSOs. We find preliminary evidence that substantial contri-butions from star formation are required, but possibly no more so than for isolated X-ray-detected QSOs. Sensitive searches of the X-ray images for extended emission, and the optical images for optical galaxy excess show that these binary QSOs — expected to occur in strong peaks of the dark matter distribution — are not preferentially found in rich cluster environments. While larger binary QSO samples with richer far-IR and sub-millimeter multiwavelength data might better reveal signatures of merging and triggering, optical color-selection of QSO pairs may be biased against such signatures. X-ray and/or variability selection of QSO pairs, while challenging, should be attempted. We present in our Appendix a primer on X-ray flux and luminosity calculations.
    The Astrophysical Journal 10/2011; 743(1). · 6.73 Impact Factor
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    ABSTRACT: From optical spectroscopy of X-ray sources observed as part of the Chandra Multiwavelength Project (ChaMP), we present redshifts and classifications for a total of 1569 Chandra sources from our targeted spectroscopic follow-ups using the FLWO 1.5m, WIYN 3.5m, CTIO 4m, Magellan 6.5m, MMT 6.5m and Gemini 8m telescopes, and from archival SDSS spectroscopy. We classify the optical counterparts as 50% broad line AGN, 16% emission line galaxies, 14%s absorption line galaxies, and 20% stars. We detect QSOs out to z 5.5 and galaxies out to z 3. We have compiled extensive photometry, including X-ray (ChaMP), UV (GALEX), Optical (SDSS), NIR (UKIDSS, 2MASS), MIR (WISE) and Radio (FIRST, NVSS) bands. Together with our spectroscopic information, this enables us to derive detailed spectral energy distributions (SEDs) for all our extragalactic sources. We fit a variety of template SEDs to determine bolometric luminosities, and to constrain AGN and starburst components where both present. The latter in combination to the derived X-ray spectral fits for all our sources will provide us with a large sample to be able to study in detail the AGN/Star-formation coevolution and the relationship between nuclear obscuration and star-formation.
    09/2011;
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    ABSTRACT: We present analysis of Chandra X-ray imaging and spectroscopy for a sample of 14 quasars in close pairs, targeted as part of a complete sample of binary quasar candidates with small transverse separations drawn from Sloan Digital Sky Survey (SDSS). One pair, SDSS J1254+0846 at z=0.44 clearly inhabits an ongoing, pre-coalescence galaxy merger showing obvious tidal tails. We measure the X-ray properties of all 14 QSOs, and study the distribution of X-ray and optical-to-X-ray power-law indices in these binary quasars, and find no significant difference with large control samples of isolated quasars. We present near-IR photometry from UKIDDS, 2MASS or the MMT with SWIRC, and fit simple spectral energy distributions to all 14 QSOs, and find preliminary evidence that substantial contributions from star formation are required, but no more so than for isolated X-ray-detected QSOs. Sensitive searches of the X-ray images for extended emission, and the optical images for optical galaxy excess show that these binary QSOs, while likely occurring in strong peaks of the dark matter distribution, are not preferentially found in rich cluster environments.
    05/2011;

Publication Stats

866 Citations
385.36 Total Impact Points

Institutions

  • 2012
    • The Astronomical Observatory of Brera
      Merate, Lombardy, Italy
  • 1996–2012
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2008
    • Johns Hopkins University
      Baltimore, Maryland, United States
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
  • 2005
    • University of Santiago, Chile
      • Departamento de Economía
      CiudadSantiago, Santiago, Chile
  • 1994–2002
    • The University of Arizona
      • Large Binocular Telescope Observatory
      Tucson, Arizona, United States