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  • 1
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    Investigating evidence for different black hole accretion modes since redshift z ~ 1 (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-02
    Description: Chandra data in the COSMOS, AEGIS-XD and 4 Ms Chandra Deep Field South are combined with multiwavelength photometry available in those fields to determine the rest-frame U  –  V versus V  –  J colours of X-ray AGN hosts in the redshift intervals 0.1 〈  z  〈 0.6 (mean $\overline{z}=0.40$ ) and 0.6 〈  z  〈 1.2 (mean $\overline{z}=0.85$ ). This combination of colours provides an effective and least model-dependent means of separating quiescent from star-forming, including dust reddened, galaxies. Morphological information emphasizes differences between AGN populations split by their U  –  V versus V  –  J colours. AGN in quiescent galaxies consist almost exclusively of bulges, while star-forming hosts are equally split between early- and late-type hosts. The position of AGN hosts on the U  –  V versus V  –  J diagram is then used to set limits on the accretion density of the Universe associated with evolved and star-forming systems independent of dust induced biases. It is found that most of the black hole growth at z 0.40 and 0.85 is associated with star-forming hosts. Nevertheless, a non-negligible fraction of the X-ray luminosity density, about 15–20 per cent, at both $\overline{z}=0.40$ and 0.85, is taking place in galaxies in the quiescent region of the U  –  V versus V  –  J diagram. For the low-redshift sub-sample, 0.1 〈  z  〈 0.6, we also find tentative evidence, significant at the 2 level, that AGN split by their U  –  V and V  –  J colours have different Eddington ratio distributions. AGN in blue star-forming hosts dominate at relatively high Eddington ratios. In contrast, AGN in red quiescent hosts become increasingly important as a fraction of the total population towards low Eddington ratios. At higher redshift, z  〉 0.6, such differences are significant at the 2 level only for sources with Eddington ratios 10 – 3 . These findings are consistent with scenarios in which diverse accretion modes are responsible for the build-up of supermassive black holes at the centres of galaxies. We compare these results with the predictions of the galform semi-analytic model for the cosmological evolution of AGN and galaxies. This model postulates two black hole fuelling modes, the first is linked to star formation events and the second takes place in passive galaxies. galform predicts that a substantial fraction of the black hole growth at z  〈 1 is associated with quiescent galaxies, in apparent conflict with the observations. Relaxing the strong assumption of the model that passive AGN hosts have zero star formation rate could bring those predictions in better agreement with the data.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Selection of AGN candidates in the GOODS-South Field through Spitzer/MIPS 24 {mu}m variability (2014)
    Oxford University Press
    Details
    Publication Date: 2014-12-07
    Description: We present a study of galaxies showing mid-infrared variability in data taken in the deepest Spitzer /MIPS 24 μm surveys in the Great Observatory Origins Deep Survey South field. We divide the data set in epochs and subepochs to study the long-term (months–years) and the short-term (days) variability. We use a 2 -statistics method to select active galactic nucleus (AGN) candidates with a probability ≤1 per cent that the observed variability is due to statistical errors alone. We find 39 (1.7 per cent of the parent sample) sources that show long-term variability and 55 (2.2 per cent of the parent sample) showing short-term variability. That is, 0.03 sources arcmin –2 for both, long-term and short-term variable sources. After removing the expected number of false positives inherent to the method, the estimated percentages are 1.0 and 1.4 per cent of the parent sample for the long term and short term, respectively. We compare our candidates with AGN selected in the X-ray and radio bands, and AGN candidates selected by their IR emission. Approximately, 50 per cent of the MIPS (Multiband Imaging Photometer for Spitzer ) 24 μm variable sources would be identified as AGN with these other methods. Therefore, MIPS 24 μm variability is a new method to identify AGN candidates, possibly dust obscured and low-luminosity AGN, that might be missed by other methods. However, the contribution of the MIPS 24 μm variable identified AGN to the general AGN population is small (≤13 per cent) in GOODS-South.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Higher prevalence of X-ray selected AGN in intermediate-age galaxies up to z ~ 1 (2014)
    Oxford University Press
    Details
    Publication Date: 2014-08-13
    Description: We analyse the stellar populations in the host galaxies of 53 X-ray selected optically dull active galactic nuclei (AGN) at 0.34 〈 z 〈 1.07 with ultradeep ( m AB = 26.5, 3) optical medium-band ( R ~ 50) photometry from the Survey for High-z Absorption Red and Dead Sources (SHARDS). The spectral resolution of SHARDS allows us to consistently measure the strength of the 4000 Å break, D n (4000), a reliable age indicator for stellar populations. We confirm that most X-ray selected moderate-luminosity AGN ( L X 〈 10 44  erg s –1 ) are hosted by massive galaxies (typically M * 〉10 10.5 M ) and that the observed fraction of galaxies hosting an AGN increases with the stellar mass. A careful selection of random control samples of inactive galaxies allows us to remove the stellar mass and redshift dependences of the AGN fraction to explore trends with several stellar age indicators. We find no significant differences in the distribution of the rest-frame U – V colour for AGN hosts and inactive galaxies, in agreement with previous results. However, we find significantly shallower 4000 Å breaks in AGN hosts, indicative of younger stellar populations. With the help of a model-independent determination of the extinction, we obtain extinction-corrected U – V colours and light-weighted average stellar ages. We find that AGN hosts have younger stellar populations and higher extinction compared to inactive galaxies with the same stellar mass and at the same redshift. We find a highly significant excess of AGN hosts with D n (4000) ~ 1.4 and light-weighted average stellar ages of 300–500 Myr, as well as a deficit of AGN in intrinsic red galaxies. We interpret failure in recognizing these trends in previous studies as a consequence of the balancing effect in observed colours of the age–extinction degeneracy.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    The first hominin of Europe (2008)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2008-03-28
    Description: The earliest hominin occupation of Europe is one of the most debated topics in palaeoanthropology. However, the purportedly oldest of the Early Pleistocene sites in Eurasia lack precise age control and contain stone tools rather than human fossil remains. Here we report the discovery of a human mandible associated with an assemblage of Mode 1 lithic tools and faunal remains bearing traces of hominin processing, in stratigraphic level TE9 at the site of the Sima del Elefante, Atapuerca, Spain. Level TE9 has been dated to the Early Pleistocene (approximately 1.2-1.1 Myr), based on a combination of palaeomagnetism, cosmogenic nuclides and biostratigraphy. The Sima del Elefante site thus emerges as the oldest, most accurately dated record of human occupation in Europe, to our knowledge. The study of the human mandible suggests that the first settlement of Western Europe could be related to an early demographic expansion out of Africa. The new evidence, with previous findings in other Atapuerca sites (level TD6 from Gran Dolina), also suggests that a speciation event occurred in this extreme area of the Eurasian continent during the Early Pleistocene, initiating the hominin lineage represented by the TE9 and TD6 hominins.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Carbonell, Eudald -- Bermudez de Castro, Jose M -- Pares, Josep M -- Perez-Gonzalez, Alfredo -- Cuenca-Bescos, Gloria -- Olle, Andreu -- Mosquera, Marina -- Huguet, Rosa -- van der Made, Jan -- Rosas, Antonio -- Sala, Robert -- Vallverdu, Josep -- Garcia, Nuria -- Granger, Darryl E -- Martinon-Torres, Maria -- Rodriguez, Xose P -- Stock, Greg M -- Verges, Josep M -- Allue, Ethel -- Burjachs, Francesc -- Caceres, Isabel -- Canals, Antoni -- Benito, Alfonso -- Diez, Carlos -- Lozano, Marina -- Mateos, Ana -- Navazo, Marta -- Rodriguez, Jesus -- Rosell, Jordi -- Arsuaga, Juan L -- England -- Nature. 2008 Mar 27;452(7186):465-9. doi: 10.1038/nature06815.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institut Catala de Paleoecologia Humana i Evolucio Social, Area de Prehistoria, Universitat Rovira i Virgili, Placa Imperial Tarraco 1, 43005 Tarragona, Spain. eudald.carbonell@urv.cat〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18368116" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Fossils ; Genetic Speciation ; Geologic Sediments ; History, Ancient ; Hominidae/anatomy & histology/*classification ; Mammals/anatomy & histology ; *Mandible/anatomy & histology ; Spain ; Technology
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 5
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    Paleomagnetic age for hominid fossils at Atapuerca archaeological site, Spain (1995)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1995-08-11
    Description: A paleomagnetic investigation at the Gran Dolina site excavation (Atapuerca, Spain) shows that the sediments containing the recently discovered human occupation were deposited more than 780,000 years ago, near the time of the Matuyama-Brunhes boundary. Forty-one oriented samples were obtained from 22 sites along an 18-meter section of the Gran Dolina karst filling. The lower 16 sites displayed reversed-polarity magnetizations whereas the upper six sites were normal. The reversal spans the hominid finds at stratigraphic level TD6 (the Aurora stratum), and these hominid fossils are therefore the oldest in southern Europe.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pares, J M -- Perez-Gonzalez, A -- New York, N.Y. -- Science. 1995 Aug 11;269(5225):830-2.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institut de Ciencias de la Terra Juame Almera, Consejo de Investigaciones Cientificas (CSIC), Barcelona, Spain.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/7638599" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Fossils ; History, Ancient ; *Hominidae ; Humans ; Magnetics ; Spain
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    SHARDS: stellar populations and star formation histories of a mass-selected sample of 0.65 〈 z 〈 1.1 galaxies (2013)
    Oxford University Press
    Details
    Publication Date: 2013-08-22
    Description: We report on results from the analysis of a stellar mass-selected (log ( M * /M ) ≥ 9.0) sample of 1644 galaxies at 0.65 〈 z  〈 1.1 with ultradeep (m AB  〈 26.5) optical medium-band ( R ~ 50) photometry from the Survey for High-z Absorption Red and Dead Sources (SHARDS). The spectral resolution of SHARDS allows us to consistently measure the strength of the 4000 Å spectral break [ D n (4000), an excellent age indicator for the stellar populations of quiescent galaxies] for all galaxies at z ~ 0.9 down to log ( M * /M ) ~ 9. The D n (4000) index cannot be resolved from broad-band photometry, and measurements from optical spectroscopic surveys are typically limited to galaxies at least 10 times more massive. When combined with the rest-frame U  – V colour, ( U  – V ) r , D n (4000) provides a powerful diagnostic of the extinction affecting the stellar population that is relatively insensitive to degeneracies with age, metallicity or star formation history. We use this novel approach to estimate de-reddened colours and light-weighted stellar ages for individual sources. We explore the relationships linking stellar mass, ( U  – V ) r , and D n (4000) for the sources in the sample, and compare them to those found in local galaxies. The main results are: (a) both D n (4000) and ( U  – V ) r correlate with M * . The dispersion in D n (4000) values at a given M * increases with M * , while the dispersion for ( U  – V ) r decreases due to the higher average extinction prevalent in massive star-forming galaxies. (b) For massive galaxies, we find a smooth transition between the blue cloud and red sequence in the intrinsic U  – V colour, in contrast with other recent results. (c) At a fixed stellar age, we find a positive correlation between extinction and stellar mass. (d) The fraction of sources with declining or halted star formation increases steeply with the stellar mass, from ~5 per cent at log ( M * /M ) = 9.0–9.5 to ~80 per cent at log ( M * /M ) 〉 11, in agreement with downsizing scenarios.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
    Electronic Resource
    Electronic Resource
    Magnetic response of hard superconductors subjected to parallel rotating magnetic fields (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 3455-3461 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The manifestation of flux-line cutting in the magnetic behavior of a type-II superconductor, either (i) subjected to a rotating magnetic field, or (ii) undergoing slow oscillations in a static magnetic field, is investigated theoretically. We have applied both the generalized double critical-state model and the two-velocity hydrodynamic one to interpret available experimental results for oscillating disks of Nb. The hydrodynamic model generates only closed hysteresis loops, after the first full oscillation, in accordance with the experimental hysteresis loops observed at a relatively small amplitude of oscillation, θmax=45°. However, at larger amplitudes of oscillation, several measured loops are evidently open. This behavior as well as their asymmetric form could be reproduced only by the generalized double critical-state model. The limits of applicability of both models are discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1400094
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  • 8
    Electronic Resource
    Electronic Resource
    Modulation of the reflectivity in amorphous semiconductors
    Amsterdam : Elsevier
    Solid State Communications 86 (1993), S. 417-420 
    Details
    ISSN: 0038-1098
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0038-1098(93)90457-X
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  • 9
    Electronic Resource
    Electronic Resource
    Upper critical field and isotope effect in the oxide superconductors (1992)
    Springer
    Journal of low temperature physics 87 (1992), S. 63-72 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In a model for which the pairing is due mainly to an electronic mechanism supplemented by a small phonon contribution, we study the isotope effect exhibited by the upper critical magnetic field H c2 and compare with the critical temperature. When paramagnetic impurities are added, we find very different behaviours from that predicted in a pure phonon model. The alignment of the paramagnetic spin by the external magnetic field as well as Pauli limiting is neglected in our calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00141567
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  • 10
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    Modification of the isotope effect due to pair breaking (1991)
    American Physical Society
    Details
    Publication Date: 1991-04-01
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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