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  • 1
    Electronic Resource
    Electronic Resource
    The unusual afterglow of the γ-ray burst of 26 March 1998 as evidence for a supernova connection (1999)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 401 (1999), S. 453-456 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Cosmic γ-ray bursts have now been firmly established as one of the most powerful phenomena in the Universe, releasing almost the rest-mass energy of a neutron star within the space of a few seconds (ref. 1). The two most popular models to explain γ-ray bursts are ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/46744
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Ultra-relativistic electrons in Jupiter's radiation belts (2002)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 415 (2002), S. 987-991 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Ground-based observations have shown that Jupiter is a two-component source of microwave radio emission: thermal atmospheric emission and synchrotron emission from energetic electrons spiralling in Jupiter's magnetic field. Later in situ measurements confirmed the existence of Jupiter's ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/415987a
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  • 3
    Electronic Resource
    Electronic Resource
    High process gain opto-electronic matched filters for communications applications (1971)
    Springer
    Optical and quantum electronics 3 (1971), S. 77-91 
    Details
    ISSN: 1572-817X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract This paper is concerned with the application of opto-electronic signal processing to a certain class of interference-resistant communications techniques. The processing techniques are applicable to spread spectrum digital transmissions which are processed by a matched filter at the receiver. The analysis of optical delay line matched filters of the diffraction type is discussed. The analysis considers the basic ultrasonic light modulator, that is, the modulation of a light source by a sonic wave. The sonic wave may represent a received spread spectrum signal or received noise or a combination of both. Two ultrasonic modulators in cascade perform the desired correlation or matched filter function. The analysis considers the effects of intermodulation of signal and noise and also the effects of the beamspreading and attenuation of the sonic signal in the delay lines. Finally, the design of a matched filter having 40 dB process gain is presented together with an estimate of its communications performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01424085
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  • 4
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    The photometric properties of galaxies in the early Universe (2016)
    Oxford University Press
    Details
    Publication Date: 2016-06-19
    Description: We use the large cosmological hydro-dynamic simulation B lue T ides to predict the photometric properties of galaxies during the epoch of reionization ( z = 8–15). These properties include the rest-frame UV to near-IR broad-band spectral energy distributions, the Lyman continuum (LyC) photon production, the UV star formation rate calibration, and intrinsic UV continuum slope. In particular we focus on exploring the effect of various modelling assumptions, including the assumed choice of stellar population synthesis (SPS) model, initial mass function, and the escape fraction of LyC photons, upon these quantities. We find that these modelling assumptions can have a dramatic effect on photometric properties leading to consequences for the accurate determination of physical properties from observations. For example, at z = 8 we predict that nebular emission can account for up to 50 per cent of the rest-frame R -band luminosity, while the choice of SPS model can change the LyC production rate up to a factor of x 2.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    The KMOS AGN Survey at High redshift (KASHz): the prevalence and drivers of ionized outflows in the host galaxies of X-ray AGN (2015)
    Oxford University Press
    Details
    Publication Date: 2015-12-25
    Description: We present the first results from the KMOS ( K -band Multi-Object Spectrograph) AGN (active galactic nuclei) Survey at High redshift (KASH z ), a VLT/KMOS integral-field spectroscopic (IFS) survey of z 0.6 AGN. We present galaxy-integrated spectra of 89 X-ray AGN ( L 2–10 keV = 10 42 –10 45  erg s –1 ), for which we observed [O iii ] ( z 1.1–1.7) or Hα emission ( z 0.6–1.1). The targets have X-ray luminosities representative of the parent AGN population and we explore the emission-line luminosities as a function of X-ray luminosity. For the [O iii ] targets, 50 per cent have ionized gas velocities indicative of gas that is dominated by outflows and/or highly turbulent material (i.e. overall line widths 600 km s –1 ). The most luminous half (i.e. L X 〉 6 x 10 43  erg s –1 ) have a 2 times higher incidence of such velocities. On the basis of our results, we find no evidence that X-ray obscured AGN are more likely to host extreme kinematics than unobscured AGN. Our KASH z sample has a distribution of gas velocities that is consistent with a luminosity-matched sample of z 〈 0.4 AGN. This implies little evolution in the prevalence of ionized outflows, for a fixed AGN luminosity, despite an order-of-magnitude decrease in average star formation rates over this redshift range. Furthermore, we compare our Hα targets to a redshift-matched sample of star-forming galaxies and despite a similar distribution of Hα luminosities and likely star formation rates, we find extreme ionized gas velocities are up to 10 times more prevalent in the AGN-host galaxies. Our results reveal a high prevalence of extreme ionized gas velocities in high-luminosity X-ray AGN and imply that the most powerful ionized outflows in high-redshift galaxies are driven by AGN activity.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    The KMOS Redshift One Spectroscopic Survey (KROSS): dynamical properties, gas and dark matter fractions of typical z ~ 1 star-forming galaxies (2016)
    Oxford University Press
    Details
    Publication Date: 2016-02-06
    Description: The KMOS Redshift One Spectroscopic Survey (KROSS) is an ESO-guaranteed time survey of 795 typical star-forming galaxies in the redshift range z = 0.8–1.0 with the KMOS instrument on the Very Large Telescope. In this paper, we present resolved kinematics and star formation rates for 584 z ~ 1 galaxies. This constitutes the largest near-infrared Integral Field Unit survey of galaxies at z ~ 1 to date. We demonstrate the success of our selection criteria with 90 per cent of our targets found to be H α emitters, of which 81 per cent are spatially resolved. The fraction of the resolved KROSS sample with dynamics dominated by ordered rotation is found to be 83 ± 5 per cent. However, when compared with local samples these are turbulent discs with high gas to baryonic mass fractions, ~35 per cent, and the majority are consistent with being marginally unstable (Toomre Q ~ 1). There is no strong correlation between galaxy averaged velocity dispersion and the total star formation rate, suggesting that feedback from star formation is not the origin of the elevated turbulence. We postulate that it is the ubiquity of high (likely molecular) gas fractions and the associated gravitational instabilities that drive the elevated star formation rates in these typical z ~ 1 galaxies, leading to the 10-fold enhanced star formation rate density. Finally, by comparing the gas masses obtained from inverting the star formation law with the dynamical and stellar masses, we infer an average dark matter to total mass fraction within 2.2 r e (9.5 kpc) of 65 ± 12 per cent, in agreement with the results from hydrodynamic simulations of galaxy formation.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    KROSS: mapping the H{alpha} emission across the star formation sequence at z {approx} 1 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-01-24
    Description: We present first results from the KMOS ( K -band Multi-Object Spectrograph) Redshift One Spectroscopic Survey, an ongoing large kinematical survey of a thousand, z ~ 1 star-forming galaxies, with VLT KMOS. Out of the targeted galaxies (~500 so far), we detect and spatially resolve Hα emission in ~90 and 77 per cent of the sample, respectively. Based on the integrated Hα flux measurements and the spatially resolved maps, we derive a median star formation rate (SFR) of ~7.0 M  yr –1 and a median physical size of 〈 $r^{\prime }_{\rm 1/2}$ 〉 = 5.1 kpc. We combine the inferred SFRs and effective radii measurements to derive the star formation surface densities ( SFR ) and present a ‘resolved’ version of the star formation main sequence (MS) that appears to hold at subgalactic scales, with similar slope and scatter as the one inferred from galaxy-integrated properties. Our data also yield a trend between SFR and (sSFR) (distance from the MS) suggesting that galaxies with higher sSFR are characterized by denser star formation activity. Similarly, we find evidence for an anticorrelation between the gas phase metallicity ( Z ) and the (sSFR), suggesting a 0.2 dex variation in the metal content of galaxies within the MS and significantly lower metallicities for galaxies above it. The origin of the observed trends between SFR –(sSFR) and Z –(sSFR) could be driven by an interplay between variations of the gas fraction or the star formation efficiency of the galaxies along and off the MS. To address this, follow-up observations of our sample that will allow gas mass estimates are necessary.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Theoretical predictions for the effect of nebular emission on the broad-band photometry of high-redshift galaxies (2013)
    Oxford University Press
    Details
    Publication Date: 2013-10-12
    Description: By combining optical and near-IR observations from the Hubble Space Telescope with near-IR photometry from the Spitzer Space Telescope , it is possible to measure the rest-frame UV–optical colours of galaxies at z  = 4–8. The UV–optical spectral energy distribution of star formation dominated galaxies is the result of several different factors. These include the joint distribution of stellar masses, ages and metallicities (solely responsible for the pure stellar spectral energy distribution), and the subsequent reprocessing by dust and gas in the interstellar medium. Using a large cosmological hydrodynamical simulation ( MassiveBlack-II ), we investigate the predicted spectral energy distributions of galaxies at high redshift with a particular emphasis on assessing the potential contribution of nebular emission. We find that the average (median) pure stellar UV–optical colour correlates with both luminosity and redshift such that galaxies at lower redshift and higher luminosity are typically redder. Assuming that the escape fraction of ionizing photons is close to zero, the effect of nebular emission is to redden the UV–optical 1500 – V w colour by, on average, 0.4 mag at z  = 8 declining to 0.25 mag at z  = 4. Young and low-metallicity stellar populations, which typically have bluer pure stellar UV–optical colours, produce larger ionizing luminosities and are thus more strongly affected by the reddening effects of nebular emission. This causes the distribution of 1500 – V w colours to narrow and the trends with luminosity and redshift to weaken. The strong effect of nebular emission leaves observed-frame colours critically sensitive to the redshift of the source. For example, increasing the redshift by 0.1 can result in observed-frame colours changing by up to ~0.6. These predictions reinforce the need to include nebular emission when modelling the spectral energy distributions of galaxies at high redshift and also highlight the difficultly in interpreting the observed colours of individual galaxies without precise redshift information.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Spectroscopy of z ~ 7 candidate galaxies: using Lyman {alpha} to constrain the neutral fraction of hydrogen in the high-redshift universe (2014)
    Oxford University Press
    Details
    Publication Date: 2014-08-07
    Description: Following our previous spectroscopic observations of z 〉 7 galaxies with Gemini/Gemini Near Infra-Red Spectrograph (GNIRS) and Very Large Telescope (VLT)/XSHOOTER, which targeted a total of eight objects, we present here our results from a deeper and larger VLT/FOcal Reducer and Spectrograph (FORS2) spectroscopic sample of Wide Field Camera 3 selected z 〉 7 candidate galaxies. With our FORS2 setup we cover the 737–1070 nm wavelength range, enabling a search for Lyman α in the redshift range spanning 5.06–7.80. We target 22 z -band dropouts and find no evidence of Lyman α emission, with the exception of a tentative detection (〈5, which is our adopted criterion for a secure detection) for one object. The upper limits on Lyman α flux and the broad-band magnitudes are used to constrain the rest-frame equivalent widths for this line emission. We analyse our FORS2 observations in combination with our previous GNIRS and XSHOOTER observations, and suggest that a simple model where the fraction of high rest-frame equivalent width emitters follows the trend seen at z = 3-6.5 is inconsistent with our non-detections at z ~ 7.8 at the 96 per cent confidence level. This may indicate that a significant neutral H i fraction in the intergalactic medium suppresses Lyman α, with an estimated neutral fraction $\chi _{\rm H\,\small {I}}\sim 0.5$ , in agreement with other estimates.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    The KMOS Redshift One Spectroscopic Survey (KROSS): the Tully-Fisher relation at z ~ 1 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-22
    Description: We present the stellar mass ( M * ), and K-corrected K -band absolute magnitude ( M K ) Tully–Fisher relations (TFRs) for subsamples of the 584 galaxies spatially resolved in H α emission by the KMOS Redshift One Spectroscopic Survey (KROSS). We model the velocity field of each of the KROSS galaxies and extract a rotation velocity, V 80 at a radius equal to the major axis of an ellipse containing 80 per cent of the total integrated H α flux. The large sample size of KROSS allowed us to select 210 galaxies with well-measured rotation speeds. We extract from this sample a further 56 galaxies that are rotationally supported, using the stringent criterion V 80 / 〉 3, where is the flux weighted average velocity dispersion. We find the M K and M * TFRs for this subsample to be $M_{K} / \rm {mag}= (-7.3 \pm 0.9) \times [(\log (V_{80}/\rm {km\ s^{-1}})-2.25]- 23.4 \pm 0.2$ , and $\log (M_{{\ast }} / \mathrm{M}_{{\odot }})= (4.7 \pm 0.4) \times [(\log (V_{80}/\rm {km\ s^{-1}}) - 2.25] + 10.0 \pm 0.3$ , respectively. We find an evolution of the M * TFR zero-point of –0.41 ± 0.08 dex over the last ~8 billion years. However, we measure no evolution in the M K TFR zero-point over the same period. We conclude that rotationally supported galaxies of a given dynamical mass had less stellar mass at z ~ 1 than the present day, yet emitted the same amounts of K -band light. The ability of KROSS to differentiate, using integral field spectroscopy with KMOS, between those galaxies that are rotationally supported and those that are not explains why our findings are at odds with previous studies without the same capabilities.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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