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  • 1
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    New insights on the recoiling/binary black hole candidate J0927+2943 via molecular gas observations (2014)
    Oxford University Press
    Details
    Publication Date: 2014-10-12
    Description: The peculiar QSO J0927+2943 shows multiple sets of emission lines in its optical spectrum. This signature has been interpreted as the relative motion between a black hole, either recoiling or bound in a binary system, and its host galaxy, or as a superposition of two galaxies along the line of sight. In order to test these scenarios, we have collected 2 mm CO(2–1) observations using the IRAM Plateau de Bure Interferometer, and optical images and spectroscopy at the Calar Alto observatory. Together with archival HST images, these data provide unique insights on the nature of this system. The recoiling/binary black hole scenarios are ruled out by the clear detection of a galactic–scale molecular gas reservoir at the same redshift of the QSO broad lines. The observations presented here also disfavour the superposition model, although with less constraints. Thus, the origin of the second, bright set of narrow emission lines in J0927+2943 is still unknown.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Mantle structure in the Central Mediterranean region from P and S receiver functions (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract We investigate the upper mantle discontinuities in the Central Mediterranean region by applying the P and S receiver function techniques on waveforms recorded at broadband stations located around the Tyrrhenian basin. P and S‐wave velocity profiles (down to 300km depth) are calculated with joint inversion of P and S receiver functions. We could identify the Moho, Lithosphere‐Asthenosphere Boundary and an underlying low‐velocity layer between ~60 and ~200km depth. The low‐velocity layer is interpreted as asthenospheric material, and its lower boundary is identified below the western Ionian and Tyrrhenian basins as a sharp Lehmann discontinuity. Although the stations are located on different lithospheric domains we find a strong correlation between Moho and the Lithosphere‐Asthenosphere Boundary depths, which suggests ubiquitous coupling of the crust and lithospheric mantle, consistently with the southward opening of the Tyrrhenian basin. The Tyrrhenian and western Ionian basins present thinning of the transition zone of ~14km, as inferred from a reduced P660s‐P410s differential time. Below the southern Apennines we observe a standard differential time that implies an average mantle transition zone thickness. We explain these mantle transition zone thickness variations as due to temperature heterogeneity linked to the area's subduction history. Finally, under central Europe (the location of the deep S‐to‐p conversion points) two strong signals from non‐standard discontinuities within the mantle transition zone are observed. These signals can be explained as being generated at the boundaries of high seismic velocity layers that are spatially correlated with stagnant slabs in the transition zone detected by seismic tomography.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    The locations of magma chambers at Mt Etna, Italy, mapped by b-values (1999)
    In:  Geophys. Res. Lett., Reston, VA, U. S. Geological Survey, vol. 26, no. 16, pp. 2553-2556, pp. B09407, (ISSN: 1340-4202)
    Details
    Publication Date: 1999
    Keywords: Statistical investigations ; Seismicity ; Volcanology ; GRL
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    BIBLIOGRAPHY SEISMOLOGY
  • 4
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    European seafloor observatory offers new possibilities for deep-sea studies (2000)
    In:  Eos, Trans., Am. Geophys. Un., San Francisco, Pergamon, vol. 81, no. 5, pp. 45, 48, 49, pp. 1246
    Details
    Publication Date: 2000
    Keywords: Seismology ; OBS ; GEOSTAR ; EU ; CEC ; Geomagnetics ; Oceanography ; GeodesyY ; climate ; abyssal
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    BIBLIOGRAPHY SEISMOLOGY
  • 5
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    New insights from seismic tomography on the complex geodynamic evolution of two adjacent domains: Gulf of Cadiz and Alboran Sea (2013)
    Wiley
    Details
    Publication Date: 2013-04-30
    Description: [1]  In this study, we present a three-dimensional P wave upper-mantle tomography model of the southwest Iberian margin and Alboran Sea based on teleseismic arrival times recorded by Iberian and Moroccan land stations and by a seafloor network deployed for 1 year in the Gulf of Cadiz area during the European Commission Integrated observations from NEAR shore sourcES of Tsunamis: towards an early warning system (EC NEAREST) project. The three-dimensional model was computed down to 600 km depth. The tomographic images exhibit significant velocity contrasts, as large as 3%, confirming the complex evolution of this plate boundary region. Prominent high-velocity anomalies are found beneath Betics-Alboran Sea, off-shore southwest Portugal, and north Portugal, at sublithospheric depths. The transition zones between high- and low-velocity anomalies in southwest and south Iberia are associated to the contact of oceanic and continental lithosphere. The fast structure below the Alboran Sea-Granada area depicts an L-shaped body steeply dipping from the uppermost mantle to the transition zone where it becomes less curved. This anomaly is consistent with the results of previous tomographic investigations and recent geophysical data such as stress distribution, GPS measurements of plate motion, and anisotropy patterns. In the Atlantic domain, under the Horseshoe Abyssal Plain, the main feature is a high-velocity zone found at uppermost mantle depths. This feature appears laterally separated from the positive anomaly recovered in the Alboran domain by the interposition of low-velocity zones which characterize the lithosphere beneath the southwest Iberian peninsula margin, suggesting that there is no continuity between the high-velocity anomalies of the two domains west and east of the Gibraltar Strait.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Electronic Resource
    Electronic Resource
    Statistical assessment of seismicity patterns in Italy: Are they precursors of subsequent events? (2000)
    Springer
    Journal of seismology 4 (2000), S. 435-449 
    Details
    ISSN: 1573-157X
    Keywords: precursors ; quiescence ; seismicity patterns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The variations of seismicity rate in Central Apenninesprior to the sequence started in September, 1997 (at00:33 UTC, M L5.6) has been analysedby statistical methods, with the purpose of pointingup eventual periods of quiescence. The analysis wascarried out on the instrumental catalogue of theIstituto Nazionale di Geofisica (ING), covering theperiod from January 1975 to March 1998. In apreliminary phase, the catalogue was declustered usingthe Reasenberg algorithm. After that, eventualmagnitude shifts due to variations in the modalitiesof observation have been individuated and corrected.The subsequent analysis, carried out making use of theZmap software package, has put in evidence thatthe sequence of September 1997 was preceded bya 2.5 year period characterised by absence of eventsof magnitude larger than 3.2, in an area approximately20 × 40 km wide, including the epicentre of themain shock. The statistical methodology shows thatonly 1/103 of the space-time volumes analysed inthis study, exhibited quiescence of the same level.The study of seismicity rate change correlated toprevious main shocks in a larger area of CentralApennines shows that none of them were preceded by aseismic quiescence, specially close to the epicentreof the main shock, and lasting until the time ofoccurrence of the main shock as in the 1997 case.Actually, we found other patterns of precursoryquiescence with different time or space distribution.We conclude that precursory quiescence is a realfeature of Central Apennines seismicity, but it isdifficult to define a simple hypothesis, which appliesto the generality of cases and can be tested beforeimplementation in a system of earthquake riskmitigation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026540018598
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    Paper (German National Licenses)
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  • 7
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    The nature of massive black hole binary candidates - II. Spectral energy distribution atlas (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-25
    Description: Recoiling supermassive black holes (SMBHs) are considered one plausible physical mechanism to explain high velocity shifts between narrow and broad emission lines sometimes observed in quasar spectra. If the sphere of influence of the recoiling SMBH is such that only the accretion disc is bound, the dusty torus would be left behind, hence the SED should then present distinctive features (i.e. a mid-infrared deficit). Here, we present results from fitting the spectral energy distributions (SEDs) of 32 type-1 AGN with high velocity shifts between broad and narrow lines. The aim is to find peculiar properties in the multiwavelength SEDs of such objects by comparing their physical parameters (torus and disc luminosity, intrinsic reddening, and size of the 12 μm emitter) with those estimated from a control sample of ~1000 typical quasars selected from the Sloan Digital Sky Survey in the same redshift range. We find that all sources, with the possible exception of J1154+0134, analysed here present a significant amount of 12 μm emission. This is in contrast with a scenario of an SMBH displaced from the centre of the galaxy, as expected for an undergoing recoil event.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Linking the fate of massive black hole binaries to the active galactic nuclei luminosity function (2015)
    Oxford University Press
    Details
    Publication Date: 2015-03-13
    Description: Massive black hole binaries are naturally predicted in the context of the hierarchical model of structure formation. The binaries that manage to lose most of their angular momentum can coalesce to form a single remnant. In the last stages of this process, the holes undergo an extremely loud phase of gravitational wave emission, possibly detectable by current and future probes. The theoretical effort towards obtaining a coherent physical picture of the binary path down to coalescence is still underway. In this paper, for the first time, we take advantage of observational studies of active galactic nuclei evolution to constrain the efficiency of gas-driven binary decay. Under conservative assumptions we find that gas accretion towards the nuclear black holes can efficiently lead binaries of any mass forming at high redshift (2) to coalescence within the current time. The observed ‘downsizing’ trend of the accreting black hole luminosity function further implies that the gas inflow is sufficient to drive light black holes down to coalescence, even if they bind in binaries at lower redshifts, down to z   0.5 for binaries of ~10 7 M , and z   0.2 for binaries of ~10 6 M . This has strong implications for the detection rates of coalescing black hole binaries of future space-based gravitational wave experiments.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    The nature of massive black hole binary candidates - I. Spectral properties and evolution (2013)
    Oxford University Press
    Details
    Publication Date: 2013-07-04
    Description: Theoretically, bound binaries of massive black holes are expected as the natural outcome of mergers of massive galaxies. From the observational side, however, massive black hole binaries remain elusive. Velocity shifts between narrow and broad emission lines in quasar spectra are considered a promising observational tool to search for spatially unresolved, dynamically bound binaries. In this series of papers, we investigate the nature of such candidates through analyses of their spectra, images and multiwavelength spectral energy distributions. Here we investigate the properties of the optical spectra, including the evolution of the broad line profiles, of all the sources identified in our previous study. We find a diverse phenomenology of broad and narrow line luminosities, widths, shapes, ionization conditions and time variability, which we can broadly ascribe to four classes based on the shape of the broad line profiles. (1) Objects with bell-shaped broad lines with big velocity shifts (〉1000 km s –1 ) compared to their narrow lines show a variety of broad line widths and luminosities, modest flux variations over a few years, and no significant change in the broad line peak wavelength. (2) Objects with double-peaked broad emission lines tend to show very luminous and broadened lines, and little time variability. (3) Objects with asymmetric broad emission lines show a broad range of broad line luminosities and significant variability of the line profiles. (4) The remaining sources tend to show moderate to low broad line luminosities, and can be ascribed to diverse phenomena. We discuss the implications of our findings in the context of massive black hole binary searches.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Caught in the act: discovery of a physical quasar triplet (2013)
    Oxford University Press
    Details
    Publication Date: 2013-04-13
    Description: We present the discovery of a triplet of quasars at z   1.51. The whole system is well accommodated within 25 arcsec (i.e. 200 kpc in projected distance). The velocity differences among the three objects (as measured through the broad Mg  ii emission line) are 〈1000 km s –1 , suggesting that the quasars belong to the same physical structure. Broad-band near-infrared (NIR) images of the field do not reveal evidence of galaxies or galaxy clusters that could act as a gravitational lens, ruling out the possibility that two or all the three quasars are multiple images of a single, strongly lensed source. QQQ J1519+0627 is the second triplet of quasars known up to date. We estimate that these systems are extremely rare in terms of simple accidental superposition. The lack of strong galaxy overdensity suggests that this peculiar system is harboured in the seeds of a yet-to-be-formed massive structure. Based on observations collected at the La Silla Observatory with the New Technology Telescope of the European Southern Observatory and at the Calar Alto Observatory with the 3.5 m telescope of the Centro Astrónmico Hispano Alemán.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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