Bi-based superconducting multilayers, consisting of Bi2Sr2CuO6+δ (2201) layers alternately stacke... more Bi-based superconducting multilayers, consisting of Bi2Sr2CuO6+δ (2201) layers alternately stacked with CaCuO2 or SrCuO2 layers, have been deposited by Molecular Beam Epitaxy (MBE) using co-deposition and growth interruption techniques. In situ Reflection High Energy Electron Diffraction (RHEED) has been used to monitor the surface of the different layers giving evidence of a two-dimensional growth mode. The layered structure of the samples has been confirmed by X-ray diffraction analyses. Resistive measurements have shown superconducting 2201/CaCuO2 samples with critical temperatures strongly depending on the thickness of the CaCuO2. The 2201/SrCuO2 multilayers do not show a zero electrical resistance above 4.2 K, but the resistance vs. temperature curves present a sharp decrease around 60 K indicative of a superconducting onset.
Monthly Notices of the Royal Astronomical Society, 2014
We present the results from an X-ray spectral analysis of active galactic nuclei (AGN) in the Cha... more We present the results from an X-ray spectral analysis of active galactic nuclei (AGN) in the Chandra Deep Field-South, AEGIS-XD and Chandra-COSMOS surveys, focussing on the identification and characterisation of the most heavily obscured, Compton thick (CT, N H > 10 24 cm −2 ) sources. Our sample is comprised of 3184 X-ray selected extragalactic sources, which has a high rate of redshift completeness ( 97.6%), and includes improved photometric redshifts over previous studies. We use spectral models designed for heavily obscured AGN which self consistently include all major spectral signatures of heavy absorption. We identify CT sources not selected through our spectral fitting method using X-ray colours, validate our spectral fitting method through simulations, and take considerations for the constraints on N H given the low count nature of many of our sources. After these considerations we identify a total of 100 CT AGN with best-fit N H > 10 24 cm −2 and N H constrained to be above 10 23.5 cm −2 at 90% confidence. These sources cover an intrinsic 2-10 keV X-ray luminosity range of 10 42 − 3 × 10 45 erg s −1 and a redshift range of z=0.1-4. This sample will enable characterisation of these heavily obscured AGN across cosmic time and to ascertain their cosmological significance. These survey fields are sites of extensive multi-wavelength coverage, including near-infrared CANDELS data and far-infrared Herschel data, enabling forthcoming investigations into the host properties of CT AGN. Furthermore, by using the torus models to test different covering factor scenarios, and by investigating the inclusion of the soft scattered emission, we find evidence that the covering factor of the obscuring material decreases with L X for all redshifts, consistent with the receding torus model, and that this factor increases with redshift, consistent with an increase in the obscured fraction towards higher redshifts. The strong relationship between the parameters of obscuration and L X points towards an origin intrinsic to the AGN, however the increase of the covering factor with redshift may point towards contributions to the obscuration by the host galaxy. We make N H , Γ (with uncertainties), observed X-ray fluxes and intrinsic 2-10 keV luminosities for all sources analysed in this work publicly available in an online catalogue.
We have investigated Al/Al2O3/Al Superconducting Tunnel Junctions (STJs) for their use as X-ray d... more We have investigated Al/Al2O3/Al Superconducting Tunnel Junctions (STJs) for their use as X-ray detector. The junctions have been fabricated on sapphire substrates both with and without a SiO buffer layer. It was found that the presence of the SiO significantly changes the Al2O3 tunnel barrier properties. Experiments under X-ray irradiation from 55Fe X-ray source are reported. The spectra show that the SiO buffer layer succeeds in reducing the events coming from the phonons generated into the substrate. Besides, the charge yield is about 85% for STJs with the SiO buffer layer, quite high in comparison with the 5% of STJs without the buffer layer. .
High-quality, c-axis-oriented thin films of the intermetallic superconductor YNi2B2C were obtaine... more High-quality, c-axis-oriented thin films of the intermetallic superconductor YNi2B2C were obtained in situ by magnetron sputtering on MgO and other substrates held at about T 800 C. The best films showed a maximum of Tc 15.1 K with Tc 0.1 K. We report on structural and electrical film characterization including dc resistivity measurements up to 450 K as well as critical-field and critical-current measurements. Scanning tunnel microscope tunneling measurements were also performed, giving further evidence of the overall BCS nature of ...
Eddy currents non-destructive evaluation (NDE) consists in the use of electromagnetic techniques ... more Eddy currents non-destructive evaluation (NDE) consists in the use of electromagnetic techniques through which the inspection is carried out by detecting magnetic anomalies in the material under examination. The exploitation of the very high sensitivity of SQUID superconducting magnetometers to magnetic flux variations makes it an interesting and promising candidate for magnetic field detection. SQUID (superconducting quantum interference device) magnetometry can allow to overcome the traditional limits due to the lack of sensitivity in conventional electromagnetic NDE techniques. In this paper we present a new project concerning the design of a prototype of a high-temperature SQUID-based NDE instrumentation and its mains applications.
Ground-based and Airborne Instrumentation for Astronomy IV, 2012
The 4MOST consortium is currently halfway through a Conceptual Design study for ESO with the aim ... more The 4MOST consortium is currently halfway through a Conceptual Design study for ESO with the aim to develop a wide-field (>3 square degree, goal >5 square degree), high-multiplex (>1500 fibres, goal 3000 fibres) spectroscopic survey facility for an ESO 4m-class telescope (VISTA). 4MOST will run permanently on the telescope to perform a 5 year public survey yielding more than 20 million spectra at resolution R∼5000 (λ=390-1000 nm) and more than 2 million spectra at R~20,000 (395-456.5 nm & 587-673 nm). The 4MOST design is especially intended to complement three key all-sky, space-based observatories of prime European interest: Gaia, eROSITA and Euclid. Initial design and performance estimates for the wide-field corrector concepts are presented. Two fibre positioner concepts are being considered for 4MOST. The first one is a Phi-Theta system similar to ones used on existing and planned facilities. The second one is a new R-Theta concept with large patrol area. Both positioner concepts effectively address the issues of fibre focus and pupil pointing. The 4MOST spectrographs are fixed configuration two-arm spectrographs, with dedicated spectrographs for the high-and low-resolution fibres. A full facility simulator is being developed to guide trade-off decisions regarding the optimal field-of-view, number of fibres needed, and the relative fraction of high-to-low resolution fibres. The simulator takes mock catalogues with template spectra from Design Reference Surveys as starting point, calculates the output spectra based on a throughput simulator, assigns targets to fibres based on the capabilities of the fibre positioner designs, and calculates the required survey time by tiling the fields on the sky. The 4MOST consortium aims to deliver the full 4MOST facility by the end of 2018 and start delivering high-level data products for both consortium and ESO community targets a year later with yearly increments.
We report the discovery of superstrong, fading, high-ionization iron line emission in the galaxy ... more We report the discovery of superstrong, fading, high-ionization iron line emission in the galaxy SDSSJ095209.56+214313.3 (SDSSJ0952+2143 hereafter), which must have been caused by an X-ray outburst of large amplitude. SDSSJ0952+2143 is unique in its strong multiwavelength variability; such a broadband emission-line and continuum response has not been observed before. The strong iron line emission is accompanied by unusual Balmer line emission with a broad base, narrow core and doublepeaked narrow horns, and strong HeII emission. These lines, while strong in the SDSS spectrum taken in 2005, have faded away significantly in new spectra taken in December 2007. Comparison of SDSS, 2MASS, GALEX and follow-up GROND photometry reveals variability in the NUV, optical and NIR band. Taken together, these unusual observations can be explained by a giant outburst in the EUV-X-ray band, detected even in the optical and NIR. The intense and variable iron, Helium and Balmer lines represent the "light echo" of the flare, as it traveled through circumnuclear material. The outburst may have been caused by the tidal disruption of a star by a supermassive black hole. Spectroscopic surveys such as SDSS are well suited to detect emission-line light echoes of such rare flare events. Reverberation-mapping of these light echoes can then be used as a new and efficient probe of the physical conditions in the circumnuclear material in non-active or active galaxies.
In this concluding part of the series of three papers dedicated to the Swift BAT hard X-ray surve... more In this concluding part of the series of three papers dedicated to the Swift BAT hard X-ray survey ( BXS), we focus on the X-ray spectral analysis and statistical properties of the source sample. Using a dedicated method to extract time-averaged spectra of BAT sources, we show that Galactic sources have, generally, softer spectra than extragalactic objects and that Seyfert 2 galaxies are harder than Seyfert 1s. The averaged spectrum of all Seyfert galaxies is consistent with a power-law with a photon index of 2:00 AE 0:07. The cumulative flux-number relation for the extragalactic sources in the 14Y170 keV band is best described by a power-law with a slope ¼ 1:55 AE 0:20 and a normalization of 9:6 AE 1:9 ; 10 À3 AGNs deg À2 (or 396 AE 80 AGNs all-sky) above a flux level of 2 ; 10 À11 ergs cm À2 s À1 ($0.85 mcrab). The integration of the cumulative flux per unit area indicates that BAT resolves 1%Y2% of the X-ray background emission in the 14Y170 keV band. A subsample of 24 extragalactic sources above the 4.5 detection limit is used to study the statistical properties of AGNs. This sample is composed of local Seyfert galaxies (z ¼ 0:026, median value) and $10% blazars. We find that 55% of the Seyfert galaxies are absorbed by column densities of N H > 10 22 H atoms cm À2 but that none is genuinely bona fide Compton thick. This study shows the capabilities of BAT to probe the hard X-ray sky to the millicrab level.
We report on oscillations of a Josephson-junction system revealing a close analogy with fundament... more We report on oscillations of a Josephson-junction system revealing a close analogy with fundamental effects known in laser physics. The experiments are performed on series arrays of junctions whose IV curves show evidence of a mode in which all the junctions oscillate in synchronism on resonances appearing, in zero external magnetic field, at multiples of the first cavity mode. Evidence is provided that the mode is generated by collective oscillations which develop spontaneously because the frequencies of the modes are equal within a 1 ...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007
The EURopean Illicit TRAfficing Countermeasures Kit (EURITRACK) project is part of the 6th Europe... more The EURopean Illicit TRAfficing Countermeasures Kit (EURITRACK) project is part of the 6th European Union Framework Program. It aims at developing a Tagged Neutron Inspection System (TNIS) to detect illicit materials, such as explosives and narcotics, in cargo containers. Fast neutron induced reactions produce specific gamma-rays used to determine the chemical composition of the inspected material. The associated particle technique is employed to precisely locate the interaction points of the neutrons. A new deuterium-tritium neutron generator has been developed, including a pixelized alpha particle detector. The TNIS also comprises high-efficiency fast neutron and gamma-ray detectors, a dedicated front-end electronics and an integrated software to entirely drive the system and automatically process the data. Most components have been integrated during last months at Institute Ruder Boskovic, in Zagreb, Croatia. An overview of the TNIS and of its preliminary performances is presented.
Resistivity vs. temperature measurements on La0.7Ca0.3MnO3/YBa2Cu3O 7−δ /La0.7Ca0.3MnO3 (LCMO/YBC... more Resistivity vs. temperature measurements on La0.7Ca0.3MnO3/YBa2Cu3O 7−δ /La0.7Ca0.3MnO3 (LCMO/YBCO/LCMO) trilayers with different YBCO thickness, were performed in external magnetic field H up to 8 T. By evaluating the activation energy U from the slope of the resistivity Arrhenius plot, a strong depression of U has been observed when decreasing the YBCO layer thickness and the absolute U values appear to be reduced with respect to the values reported in literature in the case of YBCO thin films and YBCO/insulating multilayers. Moreover, a logarithmic U vs. H dependence is shown both in the case of thick and thin YBCO layers indicating the formation of a two dimensional vortex lattice. The experimental data are discussed considering the strong influence of the ferromagnetic LCMO on the superconducting YBCO properties which reduces the effective YBCO thickness more than predicted by the conventional theories.
A summary of the Chandra ACIS-I C-COSMOS observations as carried out is given in Table 3. The obs... more A summary of the Chandra ACIS-I C-COSMOS observations as carried out is given in Table 3. The observations took place in two main blocks: 2006 December-2007 January and 2007 April-June. (2 data files).
We combine HST /WFC3 imaging and G141 grism observations from the CANDELS and 3D-HST surveys to p... more We combine HST /WFC3 imaging and G141 grism observations from the CANDELS and 3D-HST surveys to produce a catalog of grism spectroscopic redshifts for galaxies in the CANDELS/GOODS-South field. The WFC3/G141 grism spectra cover a wavelength range of 1.1 ≤ λ ≤ 1.7µm with a resolving power of R ∼ 130 for point sources, thus providing rest-frame optical spectra for galaxies out to z ∼ 3.5. The catalog is selected in the H -band (F160W) and includes both galaxies with and without previously published spectroscopic redshifts. Grism spectra are extracted for all H -band detected galaxies with H≤24 and a CANDELS photometric redshift z phot ≥ 0.6. The resulting spectra are visually inspected to identify emission lines and redshifts are determined using cross-correlation with empirical spectral templates. To establish the accuracy of our redshifts, we compare our results against high-quality spectroscopic redshifts from the literature. Using a sample of 411 control galaxies, this analysis yields a precision of σ N MAD = 0.0028 for the grism-derived redshifts, which is consistent with the accuracy reported by the 3D-HST team. Our final catalog covers an area of 153 arcmin 2 and contains 1019 redshifts for galaxies in GOODS-S. Roughly 60% (608/1019) of these redshifts are for galaxies with no previously published spectroscopic redshift. These new redshifts span a range of 0.677 ≤ z ≤ 3.456 and have a median redshift of z = 1.282. The catalog contains a total of 234 new redshifts for galaxies at z > 1.5. In addition, we present 20 galaxy pair candidates identified for the first time using the grism redshifts in our catalog, including four new galaxy pairs at z ∼ 2, nearly doubling the number of such pairs previously identified.
We present some early results from a deep KECK-DEIMOS spectroscopic survey of 2000 z >... more We present some early results from a deep KECK-DEIMOS spectroscopic survey of 2000 z > 3.5 galaxies in the Cosmic Evolution Survey (COSMOS) field. The extensive COSMOS photometric data set has provided us with one of the largest samples of galaxies at 3.5 < z < 6, identified using photometric redshifts as well as Lyman Break Galaxies (LBG), Lyman Alpha
shown along with model fits . Error bars are 1σ including standard measurement error and systemat... more shown along with model fits . Error bars are 1σ including standard measurement error and systematic flux calibration error. The optical, near and mid-infrared, and radio data are taken from the COSMOS survey , with newly acquired warm IRAC data used at 3.6 and 4.5μm. The 0.87 and 1.1mm fluxes are taken from the sub-mm imaging survey 14,15 , wile the 2mm data point presented here was acquired with the GISMO camera on the IRAM 30m telescope. The 2.7, 3.3, and 8.2mm flux limits are from the CO 6-5, 5-4, and 2-1 measurements 8 . The best-fit stellar mass is 1.0±0.3 x10 10 solar masses with A v =0.8 and an age of 10Myr. The best fit Far-Infrared (60-120μm) luminosity ranges from 0.9-3.2 x10 13 solar luminosities depending on the model assumptions. However, the 3mm upper limits, the radio flux limit, and the CO luminosity favor lower luminosities.
We investigate the (large-scale) bar fraction in a mass-complete sample of M > 10^10.5 Msun di... more We investigate the (large-scale) bar fraction in a mass-complete sample of M > 10^10.5 Msun disk galaxies at 0.2 < z < 0.6 in the COSMOS field. The fraction of barred disks strongly depends on mass, disk morphology, and specific star formation rate (SSFR). At intermediate stellar mass (10^10.5 < M < 10^11 Msun) the bar fraction in early-type disks
There is one large area - the South Ecliptic Pole (SEP) - that has excellent MIPS coverage but ha... more There is one large area - the South Ecliptic Pole (SEP) - that has excellent MIPS coverage but has no accompanying IRAC data. This field is a primary target of far-infrared, sub-millimeter and millimeter telescopes, both from the ground and from space. What makes SEP unique among other fields with comparable area and data coverage is its highly elongated geometry
A large population of heavily obscured, Compton-thick AGN is predicted by AGN synthesis models fo... more A large population of heavily obscured, Compton-thick AGN is predicted by AGN synthesis models for the cosmic X-ray background and by the "relic" super-massive black-hole mass function measured from local bulges. However, even the deepest X-ray surveys are inefficient to search for these elusive AGN. Alternative selection criteria, combining mid-infrared with near-infrared and optical photometry, have instead been successful to pin-point a large population of Compton thick AGN. We take advantage of the deep Chandra and Spitzer coverage of a large area (more than 10 times the area covered by the Chandra deep fields, CDFs) in the COSMOS field, to extend the search of highly obscured, Compton-thick active nuclei to higher luminosity. These sources have low surface density and large samples can be provided only through large area surveys, like the COSMOS survey. We analyze the X-ray properties of COSMOS MIPS sources with 24µm fluxes higher than 550µJy. For the MIPS sources not directly detected in the Chandra images we produce stacked images in soft and hard X-rays bands. To estimate the fraction of Compton-thick AGN in the MIPS source population we compare the observed stacked count rates and hardness ratios to those predicted by detailed Monte Carlo simulations including both obscured AGN and star-forming galaxies. The volume density of Compton thick QSOs (logL(2-10keV)=44-45 ergs s −1 , or logλL λ (5.8µm)=44.79-46.18 ergs s −1 for a typical infrared to X-ray luminosity ratio) evaluated in this way is (4.8 ± 1.1) × 10 −6 Mpc −3 in the redshift bin 1.2-2.2. This density is ∼ 44% of that of all X-ray selected QSOs in the same redshift and luminosity bin, and it is consistent with the expectation of most up-to-date AGN synthesis models for the Cosmic X-ray background ). The density of lower luminosity Compton-thick AGN (logL(2-10keV)=43.5-44) at z=0.7-1.2 is (3.7 ± 1.1) × 10 −5 Mpc −3 , corresponding to ∼ 67% of that of X-ray selected AGN. The comparison between the fraction of infrared selected, Compton thick AGN to the X-ray selected, unobscured and moderately obscured AGN at high and low luminosity suggests that Compton-thick AGN follow a luminosity dependence similar to that discovered for Compton-thin AGN, becoming relatively rarer at high luminosities. We estimate that the fraction of AGN (unobscured, moderately obscured and Compton thick) to the total MIPS source population is 49 ± 10%, a value significantly higher than that previously estimated at similar 24µm fluxes. We discuss how our findings can constrain AGN feedback models.
Bi-based superconducting multilayers, consisting of Bi2Sr2CuO6+δ (2201) layers alternately stacke... more Bi-based superconducting multilayers, consisting of Bi2Sr2CuO6+δ (2201) layers alternately stacked with CaCuO2 or SrCuO2 layers, have been deposited by Molecular Beam Epitaxy (MBE) using co-deposition and growth interruption techniques. In situ Reflection High Energy Electron Diffraction (RHEED) has been used to monitor the surface of the different layers giving evidence of a two-dimensional growth mode. The layered structure of the samples has been confirmed by X-ray diffraction analyses. Resistive measurements have shown superconducting 2201/CaCuO2 samples with critical temperatures strongly depending on the thickness of the CaCuO2. The 2201/SrCuO2 multilayers do not show a zero electrical resistance above 4.2 K, but the resistance vs. temperature curves present a sharp decrease around 60 K indicative of a superconducting onset.
Monthly Notices of the Royal Astronomical Society, 2014
We present the results from an X-ray spectral analysis of active galactic nuclei (AGN) in the Cha... more We present the results from an X-ray spectral analysis of active galactic nuclei (AGN) in the Chandra Deep Field-South, AEGIS-XD and Chandra-COSMOS surveys, focussing on the identification and characterisation of the most heavily obscured, Compton thick (CT, N H > 10 24 cm −2 ) sources. Our sample is comprised of 3184 X-ray selected extragalactic sources, which has a high rate of redshift completeness ( 97.6%), and includes improved photometric redshifts over previous studies. We use spectral models designed for heavily obscured AGN which self consistently include all major spectral signatures of heavy absorption. We identify CT sources not selected through our spectral fitting method using X-ray colours, validate our spectral fitting method through simulations, and take considerations for the constraints on N H given the low count nature of many of our sources. After these considerations we identify a total of 100 CT AGN with best-fit N H > 10 24 cm −2 and N H constrained to be above 10 23.5 cm −2 at 90% confidence. These sources cover an intrinsic 2-10 keV X-ray luminosity range of 10 42 − 3 × 10 45 erg s −1 and a redshift range of z=0.1-4. This sample will enable characterisation of these heavily obscured AGN across cosmic time and to ascertain their cosmological significance. These survey fields are sites of extensive multi-wavelength coverage, including near-infrared CANDELS data and far-infrared Herschel data, enabling forthcoming investigations into the host properties of CT AGN. Furthermore, by using the torus models to test different covering factor scenarios, and by investigating the inclusion of the soft scattered emission, we find evidence that the covering factor of the obscuring material decreases with L X for all redshifts, consistent with the receding torus model, and that this factor increases with redshift, consistent with an increase in the obscured fraction towards higher redshifts. The strong relationship between the parameters of obscuration and L X points towards an origin intrinsic to the AGN, however the increase of the covering factor with redshift may point towards contributions to the obscuration by the host galaxy. We make N H , Γ (with uncertainties), observed X-ray fluxes and intrinsic 2-10 keV luminosities for all sources analysed in this work publicly available in an online catalogue.
We have investigated Al/Al2O3/Al Superconducting Tunnel Junctions (STJs) for their use as X-ray d... more We have investigated Al/Al2O3/Al Superconducting Tunnel Junctions (STJs) for their use as X-ray detector. The junctions have been fabricated on sapphire substrates both with and without a SiO buffer layer. It was found that the presence of the SiO significantly changes the Al2O3 tunnel barrier properties. Experiments under X-ray irradiation from 55Fe X-ray source are reported. The spectra show that the SiO buffer layer succeeds in reducing the events coming from the phonons generated into the substrate. Besides, the charge yield is about 85% for STJs with the SiO buffer layer, quite high in comparison with the 5% of STJs without the buffer layer. .
High-quality, c-axis-oriented thin films of the intermetallic superconductor YNi2B2C were obtaine... more High-quality, c-axis-oriented thin films of the intermetallic superconductor YNi2B2C were obtained in situ by magnetron sputtering on MgO and other substrates held at about T 800 C. The best films showed a maximum of Tc 15.1 K with Tc 0.1 K. We report on structural and electrical film characterization including dc resistivity measurements up to 450 K as well as critical-field and critical-current measurements. Scanning tunnel microscope tunneling measurements were also performed, giving further evidence of the overall BCS nature of ...
Eddy currents non-destructive evaluation (NDE) consists in the use of electromagnetic techniques ... more Eddy currents non-destructive evaluation (NDE) consists in the use of electromagnetic techniques through which the inspection is carried out by detecting magnetic anomalies in the material under examination. The exploitation of the very high sensitivity of SQUID superconducting magnetometers to magnetic flux variations makes it an interesting and promising candidate for magnetic field detection. SQUID (superconducting quantum interference device) magnetometry can allow to overcome the traditional limits due to the lack of sensitivity in conventional electromagnetic NDE techniques. In this paper we present a new project concerning the design of a prototype of a high-temperature SQUID-based NDE instrumentation and its mains applications.
Ground-based and Airborne Instrumentation for Astronomy IV, 2012
The 4MOST consortium is currently halfway through a Conceptual Design study for ESO with the aim ... more The 4MOST consortium is currently halfway through a Conceptual Design study for ESO with the aim to develop a wide-field (>3 square degree, goal >5 square degree), high-multiplex (>1500 fibres, goal 3000 fibres) spectroscopic survey facility for an ESO 4m-class telescope (VISTA). 4MOST will run permanently on the telescope to perform a 5 year public survey yielding more than 20 million spectra at resolution R∼5000 (λ=390-1000 nm) and more than 2 million spectra at R~20,000 (395-456.5 nm & 587-673 nm). The 4MOST design is especially intended to complement three key all-sky, space-based observatories of prime European interest: Gaia, eROSITA and Euclid. Initial design and performance estimates for the wide-field corrector concepts are presented. Two fibre positioner concepts are being considered for 4MOST. The first one is a Phi-Theta system similar to ones used on existing and planned facilities. The second one is a new R-Theta concept with large patrol area. Both positioner concepts effectively address the issues of fibre focus and pupil pointing. The 4MOST spectrographs are fixed configuration two-arm spectrographs, with dedicated spectrographs for the high-and low-resolution fibres. A full facility simulator is being developed to guide trade-off decisions regarding the optimal field-of-view, number of fibres needed, and the relative fraction of high-to-low resolution fibres. The simulator takes mock catalogues with template spectra from Design Reference Surveys as starting point, calculates the output spectra based on a throughput simulator, assigns targets to fibres based on the capabilities of the fibre positioner designs, and calculates the required survey time by tiling the fields on the sky. The 4MOST consortium aims to deliver the full 4MOST facility by the end of 2018 and start delivering high-level data products for both consortium and ESO community targets a year later with yearly increments.
We report the discovery of superstrong, fading, high-ionization iron line emission in the galaxy ... more We report the discovery of superstrong, fading, high-ionization iron line emission in the galaxy SDSSJ095209.56+214313.3 (SDSSJ0952+2143 hereafter), which must have been caused by an X-ray outburst of large amplitude. SDSSJ0952+2143 is unique in its strong multiwavelength variability; such a broadband emission-line and continuum response has not been observed before. The strong iron line emission is accompanied by unusual Balmer line emission with a broad base, narrow core and doublepeaked narrow horns, and strong HeII emission. These lines, while strong in the SDSS spectrum taken in 2005, have faded away significantly in new spectra taken in December 2007. Comparison of SDSS, 2MASS, GALEX and follow-up GROND photometry reveals variability in the NUV, optical and NIR band. Taken together, these unusual observations can be explained by a giant outburst in the EUV-X-ray band, detected even in the optical and NIR. The intense and variable iron, Helium and Balmer lines represent the "light echo" of the flare, as it traveled through circumnuclear material. The outburst may have been caused by the tidal disruption of a star by a supermassive black hole. Spectroscopic surveys such as SDSS are well suited to detect emission-line light echoes of such rare flare events. Reverberation-mapping of these light echoes can then be used as a new and efficient probe of the physical conditions in the circumnuclear material in non-active or active galaxies.
In this concluding part of the series of three papers dedicated to the Swift BAT hard X-ray surve... more In this concluding part of the series of three papers dedicated to the Swift BAT hard X-ray survey ( BXS), we focus on the X-ray spectral analysis and statistical properties of the source sample. Using a dedicated method to extract time-averaged spectra of BAT sources, we show that Galactic sources have, generally, softer spectra than extragalactic objects and that Seyfert 2 galaxies are harder than Seyfert 1s. The averaged spectrum of all Seyfert galaxies is consistent with a power-law with a photon index of 2:00 AE 0:07. The cumulative flux-number relation for the extragalactic sources in the 14Y170 keV band is best described by a power-law with a slope ¼ 1:55 AE 0:20 and a normalization of 9:6 AE 1:9 ; 10 À3 AGNs deg À2 (or 396 AE 80 AGNs all-sky) above a flux level of 2 ; 10 À11 ergs cm À2 s À1 ($0.85 mcrab). The integration of the cumulative flux per unit area indicates that BAT resolves 1%Y2% of the X-ray background emission in the 14Y170 keV band. A subsample of 24 extragalactic sources above the 4.5 detection limit is used to study the statistical properties of AGNs. This sample is composed of local Seyfert galaxies (z ¼ 0:026, median value) and $10% blazars. We find that 55% of the Seyfert galaxies are absorbed by column densities of N H > 10 22 H atoms cm À2 but that none is genuinely bona fide Compton thick. This study shows the capabilities of BAT to probe the hard X-ray sky to the millicrab level.
We report on oscillations of a Josephson-junction system revealing a close analogy with fundament... more We report on oscillations of a Josephson-junction system revealing a close analogy with fundamental effects known in laser physics. The experiments are performed on series arrays of junctions whose IV curves show evidence of a mode in which all the junctions oscillate in synchronism on resonances appearing, in zero external magnetic field, at multiples of the first cavity mode. Evidence is provided that the mode is generated by collective oscillations which develop spontaneously because the frequencies of the modes are equal within a 1 ...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007
The EURopean Illicit TRAfficing Countermeasures Kit (EURITRACK) project is part of the 6th Europe... more The EURopean Illicit TRAfficing Countermeasures Kit (EURITRACK) project is part of the 6th European Union Framework Program. It aims at developing a Tagged Neutron Inspection System (TNIS) to detect illicit materials, such as explosives and narcotics, in cargo containers. Fast neutron induced reactions produce specific gamma-rays used to determine the chemical composition of the inspected material. The associated particle technique is employed to precisely locate the interaction points of the neutrons. A new deuterium-tritium neutron generator has been developed, including a pixelized alpha particle detector. The TNIS also comprises high-efficiency fast neutron and gamma-ray detectors, a dedicated front-end electronics and an integrated software to entirely drive the system and automatically process the data. Most components have been integrated during last months at Institute Ruder Boskovic, in Zagreb, Croatia. An overview of the TNIS and of its preliminary performances is presented.
Resistivity vs. temperature measurements on La0.7Ca0.3MnO3/YBa2Cu3O 7−δ /La0.7Ca0.3MnO3 (LCMO/YBC... more Resistivity vs. temperature measurements on La0.7Ca0.3MnO3/YBa2Cu3O 7−δ /La0.7Ca0.3MnO3 (LCMO/YBCO/LCMO) trilayers with different YBCO thickness, were performed in external magnetic field H up to 8 T. By evaluating the activation energy U from the slope of the resistivity Arrhenius plot, a strong depression of U has been observed when decreasing the YBCO layer thickness and the absolute U values appear to be reduced with respect to the values reported in literature in the case of YBCO thin films and YBCO/insulating multilayers. Moreover, a logarithmic U vs. H dependence is shown both in the case of thick and thin YBCO layers indicating the formation of a two dimensional vortex lattice. The experimental data are discussed considering the strong influence of the ferromagnetic LCMO on the superconducting YBCO properties which reduces the effective YBCO thickness more than predicted by the conventional theories.
A summary of the Chandra ACIS-I C-COSMOS observations as carried out is given in Table 3. The obs... more A summary of the Chandra ACIS-I C-COSMOS observations as carried out is given in Table 3. The observations took place in two main blocks: 2006 December-2007 January and 2007 April-June. (2 data files).
We combine HST /WFC3 imaging and G141 grism observations from the CANDELS and 3D-HST surveys to p... more We combine HST /WFC3 imaging and G141 grism observations from the CANDELS and 3D-HST surveys to produce a catalog of grism spectroscopic redshifts for galaxies in the CANDELS/GOODS-South field. The WFC3/G141 grism spectra cover a wavelength range of 1.1 ≤ λ ≤ 1.7µm with a resolving power of R ∼ 130 for point sources, thus providing rest-frame optical spectra for galaxies out to z ∼ 3.5. The catalog is selected in the H -band (F160W) and includes both galaxies with and without previously published spectroscopic redshifts. Grism spectra are extracted for all H -band detected galaxies with H≤24 and a CANDELS photometric redshift z phot ≥ 0.6. The resulting spectra are visually inspected to identify emission lines and redshifts are determined using cross-correlation with empirical spectral templates. To establish the accuracy of our redshifts, we compare our results against high-quality spectroscopic redshifts from the literature. Using a sample of 411 control galaxies, this analysis yields a precision of σ N MAD = 0.0028 for the grism-derived redshifts, which is consistent with the accuracy reported by the 3D-HST team. Our final catalog covers an area of 153 arcmin 2 and contains 1019 redshifts for galaxies in GOODS-S. Roughly 60% (608/1019) of these redshifts are for galaxies with no previously published spectroscopic redshift. These new redshifts span a range of 0.677 ≤ z ≤ 3.456 and have a median redshift of z = 1.282. The catalog contains a total of 234 new redshifts for galaxies at z > 1.5. In addition, we present 20 galaxy pair candidates identified for the first time using the grism redshifts in our catalog, including four new galaxy pairs at z ∼ 2, nearly doubling the number of such pairs previously identified.
We present some early results from a deep KECK-DEIMOS spectroscopic survey of 2000 z &amp;gt;... more We present some early results from a deep KECK-DEIMOS spectroscopic survey of 2000 z &amp;gt; 3.5 galaxies in the Cosmic Evolution Survey (COSMOS) field. The extensive COSMOS photometric data set has provided us with one of the largest samples of galaxies at 3.5 &amp;lt; z &amp;lt; 6, identified using photometric redshifts as well as Lyman Break Galaxies (LBG), Lyman Alpha
shown along with model fits . Error bars are 1σ including standard measurement error and systemat... more shown along with model fits . Error bars are 1σ including standard measurement error and systematic flux calibration error. The optical, near and mid-infrared, and radio data are taken from the COSMOS survey , with newly acquired warm IRAC data used at 3.6 and 4.5μm. The 0.87 and 1.1mm fluxes are taken from the sub-mm imaging survey 14,15 , wile the 2mm data point presented here was acquired with the GISMO camera on the IRAM 30m telescope. The 2.7, 3.3, and 8.2mm flux limits are from the CO 6-5, 5-4, and 2-1 measurements 8 . The best-fit stellar mass is 1.0±0.3 x10 10 solar masses with A v =0.8 and an age of 10Myr. The best fit Far-Infrared (60-120μm) luminosity ranges from 0.9-3.2 x10 13 solar luminosities depending on the model assumptions. However, the 3mm upper limits, the radio flux limit, and the CO luminosity favor lower luminosities.
We investigate the (large-scale) bar fraction in a mass-complete sample of M > 10^10.5 Msun di... more We investigate the (large-scale) bar fraction in a mass-complete sample of M > 10^10.5 Msun disk galaxies at 0.2 < z < 0.6 in the COSMOS field. The fraction of barred disks strongly depends on mass, disk morphology, and specific star formation rate (SSFR). At intermediate stellar mass (10^10.5 < M < 10^11 Msun) the bar fraction in early-type disks
There is one large area - the South Ecliptic Pole (SEP) - that has excellent MIPS coverage but ha... more There is one large area - the South Ecliptic Pole (SEP) - that has excellent MIPS coverage but has no accompanying IRAC data. This field is a primary target of far-infrared, sub-millimeter and millimeter telescopes, both from the ground and from space. What makes SEP unique among other fields with comparable area and data coverage is its highly elongated geometry
A large population of heavily obscured, Compton-thick AGN is predicted by AGN synthesis models fo... more A large population of heavily obscured, Compton-thick AGN is predicted by AGN synthesis models for the cosmic X-ray background and by the "relic" super-massive black-hole mass function measured from local bulges. However, even the deepest X-ray surveys are inefficient to search for these elusive AGN. Alternative selection criteria, combining mid-infrared with near-infrared and optical photometry, have instead been successful to pin-point a large population of Compton thick AGN. We take advantage of the deep Chandra and Spitzer coverage of a large area (more than 10 times the area covered by the Chandra deep fields, CDFs) in the COSMOS field, to extend the search of highly obscured, Compton-thick active nuclei to higher luminosity. These sources have low surface density and large samples can be provided only through large area surveys, like the COSMOS survey. We analyze the X-ray properties of COSMOS MIPS sources with 24µm fluxes higher than 550µJy. For the MIPS sources not directly detected in the Chandra images we produce stacked images in soft and hard X-rays bands. To estimate the fraction of Compton-thick AGN in the MIPS source population we compare the observed stacked count rates and hardness ratios to those predicted by detailed Monte Carlo simulations including both obscured AGN and star-forming galaxies. The volume density of Compton thick QSOs (logL(2-10keV)=44-45 ergs s −1 , or logλL λ (5.8µm)=44.79-46.18 ergs s −1 for a typical infrared to X-ray luminosity ratio) evaluated in this way is (4.8 ± 1.1) × 10 −6 Mpc −3 in the redshift bin 1.2-2.2. This density is ∼ 44% of that of all X-ray selected QSOs in the same redshift and luminosity bin, and it is consistent with the expectation of most up-to-date AGN synthesis models for the Cosmic X-ray background ). The density of lower luminosity Compton-thick AGN (logL(2-10keV)=43.5-44) at z=0.7-1.2 is (3.7 ± 1.1) × 10 −5 Mpc −3 , corresponding to ∼ 67% of that of X-ray selected AGN. The comparison between the fraction of infrared selected, Compton thick AGN to the X-ray selected, unobscured and moderately obscured AGN at high and low luminosity suggests that Compton-thick AGN follow a luminosity dependence similar to that discovered for Compton-thin AGN, becoming relatively rarer at high luminosities. We estimate that the fraction of AGN (unobscured, moderately obscured and Compton thick) to the total MIPS source population is 49 ± 10%, a value significantly higher than that previously estimated at similar 24µm fluxes. We discuss how our findings can constrain AGN feedback models.
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Papers by Mara Salvato