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  • 1
    Electronic Resource
    Electronic Resource
    The cosmic microwave background radiation temperature at a redshift of 2.34 (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 408 (2000), S. 931-935 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The existence of the cosmic microwave background radiation is a fundamental prediction of hot Big Bang cosmology, and its temperature should increase with increasing redshift. At the present time (redshift 〉z = 0), the temperature has been determined with high precision to be ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35050020
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    Paper (German National Licenses)
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  • 2
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    Srianandet al.Reply: (2007)
    American Physical Society
    Details
    Publication Date: 2007-12-06
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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  • 3
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    Editorial Note: Srianandet al.Reply [Phys. Rev. Lett.99, 239002 (2007)] (2008)
    American Physical Society
    Details
    Publication Date: 2008-01-17
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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  • 4
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    Detection of emission lines from z ~ 3 DLAs towards the QSO J2358+0149 (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-27
    Description: Using VLT/X-shooter, we searched for emission line galaxies associated with four damped Lyman α systems (DLAs) and one sub-DLA at 2.73 ≤ z ≤3.25 towards QSO J2358+0149. We detect [O iii ] emission from a ‘low-cool’ DLA at z abs = 2.9791 (having log N (H i ) = 21.69 ± 0.10, [Zn/H] = –1.83 ± 0.18) at an impact parameter of, ~ 12 kpc. The associated galaxy is compact with a dynamical mass of (1–6) x 10 9 M , very high excitation ([O iii ]/[O ii ] and [O iii ]/[Hβ] both greater than 10), 12+[O/H]≤8.5 and moderate star formation rate (SFR ≤2 M  yr –1 ). Such properties are typically seen in the low- z extreme blue compact dwarf galaxies. The kinematics of the gas is inconsistent with that of an extended disc and the gas is part of either a large scale wind or cold accretion. We detect Lyα emission from the z abs = 3.2477 DLA [having log N (H i ) = 21.12 ± 0.10 and [Zn/H] = –0.97 ± 0.13]. The Lyα emission is redshifted with respect to the metal absorption lines by 320 km s –1 , consistent with the location of the red hump expected in radiative transport models. We derive SFR ~0.2–1.7 M  yr –1 and Lyα escape fraction of ≥10 per cent. No other emission line is detected from this system. Because the DLA has a small velocity separation from the quasar (~500 km s –1 ) and the DLA emission is located within a small projected distance ( 〈 5 kpc), we also explore the possibility that the Lyα emission is being induced by the QSO itself. QSO-induced Lyα fluorescence is possible if the DLA is within a physical separation of 340 kpc to the QSO. Detection of stellar continuum light and/or the oxygen emission lines would disfavour this possibility. We do not detect any emission line from the remaining three systems.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Extended Ly{alpha} emission around quasars with eclipsing damped Ly{alpha} systems (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-09
    Description: We present spectroscopic observations of six high redshift ( z em  〉 2) quasars, which have been selected for their Lyman α (Lyα) emission region being only partially covered by a strong proximate ( z abs  ~  z em ) coronagraphic damped Lyα system (DLA). We detected spatially extended Lyα emission envelopes surrounding these six quasars, with projected spatial extent in the range 26 ≤ d Lyα ≤ 51 kpc. No correlation is found between the quasar ionizing luminosity and the Lyα luminosity of their extended envelopes. This could be related to the limited covering factor of the extended gas and/or due to the AGN being obscured in other directions than towards the observer. Indeed, we find a strong correlation between the luminosity of the envelope and its spatial extent, which suggests that the envelopes are probably ionized by the AGN. The metallicity of the coronagraphic DLAs is low and varies in the range –1.75 〈 [Si/H] 〈 –0.63. Highly ionized gas is observed to be associated with most of these DLAs, probably indicating ionization by the central AGN. One of these DLAs has the highest Al iii /Si ii ratio ever reported for any intervening and/or proximate DLA. Most of these DLAs are redshifted with respect to the quasar, implying that they might represent infalling gas probably accreted on to the quasar host galaxies through filaments.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 6
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    Clustering at high redshift: the connection between Lyman {alpha} emitters and Lyman break galaxies (2013)
    Oxford University Press
    Details
    Publication Date: 2013-09-17
    Description: We present a physically motivated semi-analytic model to understand the clustering of high-redshift Lyman α emitters (LAEs). We show that the model parameters constrained by the observed luminosity functions can be used to predict large-scale bias and angular correlation function of LAEs. These predictions are shown to reproduce the observations remarkably well. We find that average masses of dark matter haloes hosting LAEs brighter than the threshold narrow-band magnitude ~25 are ~10 11 M . These are smaller than that of typical Lyman break galaxies (LBGs) brighter than a similar threshold continuum magnitude by a factor of ~10. This results in a smaller clustering strength of LAEs compared to LBGs. However, using the observed relationship between the UV continuum and Lyman α luminosity of LAEs, we show that both LAEs and LBGs belong to the same parent galaxy population with narrow-band techniques having greater efficiency in picking up galaxies with low UV luminosity. We also show that the lack of evidence for the presence of the one-halo term in the observed LAE angular correlation functions can be attributed to a sub-Poisson distribution of LAEs in dark matter haloes as a result of their low halo occupations.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 7
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    The UVES large program for testing fundamental physics - II. Constraints on a change in {mu} towards quasar HE 0027-1836 (2013)
    Oxford University Press
    Details
    Publication Date: 2013-09-17
    Description: We present an accurate analysis of the H 2 absorption lines from the z abs  ~ 2.4018 damped Lyα system towards HE 0027–1836 observed with the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT/UVES) as a part of the European Southern Observatory Large Programme ‘The UVES large programme for testing fundamental physics’ to constrain the variation of proton-to-electron mass ratio, μ   m p / m e . We perform cross-correlation analysis between 19 individual exposures taken over three years and the combined spectrum to check the wavelength calibration stability. We notice the presence of a possible wavelength-dependent velocity drift especially in the data taken in 2012. We use available asteroids spectra taken with UVES close to our observations to confirm and quantify this effect. We consider single- and two-component Voigt profiles to model the observed H 2 absorption profiles. We use both linear regression analysis and Voigt profile fitting where μ/μ is explicitly considered as an additional fitting parameter. The two-component model is marginally favoured by the statistical indicators and we get μ/μ = –2.5 ± 8.1 stat  ± 6.2 sys ppm. When we apply the correction to the wavelength-dependent velocity drift, we find μ/μ = –7.6 ± 8.1 stat  ± 6.3 sys ppm. It will be important to check the extent to which the velocity drift we notice in this study is present in UVES data used for previous μ/μ measurements.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    An investigation of the line of sight towards QSO PKS 0237-233 (2013)
    Oxford University Press
    Details
    Publication Date: 2013-09-26
    Description: We present a detailed analysis of absorption systems along the line of sight towards QSO PKS 0237–233 using a high-resolution spectrum of signal-to-noise ratio ~60–80 obtained with the Ultraviolet and Visual Echelle Spectrograph mounted on the Very Large Telescope (VLT/UVES). This line of sight is known to show a remarkable overdensity of C iv systems that has been interpreted as revealing the presence of a supercluster of galaxies. A detailed analysis of each of these absorption systems is presented. In particular, for the z abs  = 1.6359 (with two components of log N H I [cm –2 ] = 18.45, 19.05) and z abs  = 1.6720 (log N H I  = 19.78) sub-damped Lyα systems (sub-DLAs), we measure accurate abundances (resp. [O/H] = –1.63 ± 0.07 and [Zn/H] = –0.57 ± 0.05 relative to solar). While the depletion of refractory elements on to dust grains in both sub-DLAs is not noteworthy, photoionization models show that ionization effects are important in a part of the absorbing gas of the sub-DLA at z abs  = 1.6359 (H i is 95 per cent ionized) and in a part of the gas of the sub-DLA at z abs  = 1.6720. The C iv clustering properties along the line of sight is studied in order to investigate the nature of the observed overdensity. We conclude that despite the unusually high number of C iv systems detected along the line of sight, there is no compelling evidence for the presence of a single unusual overdensity and that the situation is consistent with chance coincidence.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 9
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    Photon underproduction crisis: Are QSOs sufficient to resolve it? (2015)
    Oxford University Press
    Details
    Publication Date: 2015-05-15
    Description: We investigate the recent claim of ‘photon underproduction crisis’ by Kollmeier et al. which suggests that the known sources of ultraviolet (UV) radiation may not be sufficient to generate the inferred H i photoionization rate ( $\Gamma _{\rm H\,\small {i}}$ ) in the low-redshift intergalactic medium. Using the updated QSO emissivities from the recent studies and our cosmological radiative transfer code developed to estimate the UV background, we show that the QSO contributions to $\Gamma _{\rm H\,\small {i}}$ is higher by a factor ~2 as compared to the previous estimates. Using self-consistently computed combinations of star formation rate density and dust attenuation, we show that a typical UV escape fraction of 4 per cent from star-forming galaxies should be sufficient to explain the inferred $\Gamma _{\rm H\,\small {i}}$ by Kollmeier et al. Interestingly, we find that the contribution from QSOs alone can explain the recently inferred $\Gamma _{\rm H\,\small {i}}$ by Shull et al. which used the same observational data but different simulation. Therefore, we conclude that the crisis is not as severe as it was perceived before and there seems no need to look for alternate explanations such as low luminosity hidden QSOs or decaying dark matter particles.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 10
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    Physical conditions in three high-z H2-bearing DLAs: implications for grain size (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-12
    Description: We present results of our numerical simulation of three H 2 -bearing damped Lyman α absorbers (DLAs) in the redshift interval ~ 2–3. The systems we have modelled are the DLAs at z abs = 2.3377 towards the quasar LBQS 1232 + 0815, at z abs = 2.418 37 towards SDSS J143912.04 + 111740.5 and at z abs = 2.6265 towards FBQS J081240.6 + 320808. We have used the spectral synthesis code cloudy to simulate the physical environment of these DLAs, and constrain the density, radiation field, geometry and dust-grain properties of the DLAs self-consistently based on the observed column densities of various atomic and molecular species such as H i , fine structure lines of C i and the rotational level population of H 2 . In our models, we explore the effect of grain size distribution on the predicted column densities of different species. Within the allowed uncertainties in the inferred dust-to-gas ratio, both models with standard interstellar medium grains and smaller sized grains reproduce the observations equally well. Improved constraints on dust-to-gas ratio and line-of-sight extinction are important for probing the grain size distribution in high- z DLAs. We find the H 2 -bearing clouds to have line-of-sight thickness in the range 1–6 pc, consistent with what has been found using partial coverage or 21-cm observations in some high- z DLAs.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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