ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    facet.materialart.
    Unknown
    Star-forming galactic contrails as a source of metal enrichment and ionizing radiation at high redshift (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-25
    Description: A spectroscopically detected Lyman α emitting halo at redshift 3.216 in the GOODS-N field is found to reside at the convergence of several line-emitting filaments. Spatially extended emission apparently by He ii 1640 Å and several metal transitions is seen within several arcseconds from the position of the central galaxy. The V = 24.9 galaxy mainly responsible for the continuum emission at the centre of the halo has broad-band colours and spectral features consistent with a z = 3.216 star-forming galaxy. Hubble Space Telescope images show that some of the filaments coincide, in projection, with several, mostly blue galaxies, with pronounced head–tail structures partly aligned with each other. These objects, for which we cannot rule that they are foreground, chance projections in front of the high-redshift halo, are seen over an area with a linear extent of at least 12 arcsec. The broad-band images of some galaxies suggest the presence of ram-pressure stripping, including possible evidence for recent star formation in the stripped contrails. Spatial gradients in the appearance of several galaxies may represent a stream of galaxies passing from a colder to a hotter intergalactic medium. The release of the enriched interstellar medium from galaxies and the occurrence of star formation and stellar feedback in the galactic contrails suggest a mechanism for the metal enrichment of the high-redshift intergalactic medium that does not require long-range galactic winds. If these galaxies are at the same redshift as the Lyα halo, their very blue colours may be a consequence of the stripping of gas. A stripped stellar population and star formation in galactic contrails suggest promising sites for the escape of ionizing radiation from high-redshift galaxies.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 2
    facet.materialart.
    Unknown
    The Giant Gemini GMOS survey of zem 〉 4.4 quasars - I. Measuring the mean free path across cosmic time (2014)
    Oxford University Press
    Details
    Publication Date: 2014-10-16
    Description: We have obtained spectra of 163 quasars at z em  〉 4.4 with the Gemini Multi Object Spectrometers, the largest publicly available sample of high-quality, low-resolution spectra at these redshifts. From this data set, we generated stacked quasar spectra in three redshift intervals at z  ~ 5 to model the average rest-frame Lyman continuum flux and to assess the mean free path $\lambda _{\rm mfp}^{912}$ of the intergalactic medium to H  i -ionizing radiation. At mean redshifts z q = (4.56, 4.86, 5.16), we measure $\lambda _{\rm mfp}^{912}=\left(22.2 \pm 2.3, 15.1 \pm 1.8, 10.3 \pm 1.6\right)h_{70}^{-1}$ proper Mpc with uncertainties dominated by sample variance. Combining our results with measurements from lower redshifts, the data are well modelled by a power law $\lambda _{\rm mfp}^{912}=A\left[\left(1+z\right)/5\right]^\eta$ with $A=\left(37 \pm 2\right)h_{70}^{-1}$  Mpc and = –5.4 ± 0.4 at 2.3 〈  z  〈 5.5. This rapid evolution requires a physical mechanism – beyond cosmological expansion – which reduces the effective Lyman limit opacity. We speculate that the majority of H  i Lyman limit opacity manifests in gas outside galactic dark matter haloes, tracing large-scale structures (e.g. filaments) whose average density and neutral fraction decreases with cosmic time. Our measurements of the mean free path shortly after H  i reionization serve as a valuable boundary condition for numerical models thereof. Our measured $\lambda _{\rm mfp}^{912}\approx 10$  Mpc at z = 5.2 confirms that the intergalactic medium is highly ionized without evidence for a break that would indicate a recent end to H  i reionization.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 3
    facet.materialart.
    Unknown
    ReportingTools: an automated result processing and presentation toolkit for high-throughput genomic analyses (2013)
    Oxford University Press
    Details
    Publication Date: 2013-11-29
    Description: : It is common for computational analyses to generate large amounts of complex data that are difficult to process and share with collaborators. Standard methods are needed to transform such data into a more useful and intuitive format. We present ReportingTools, a Bioconductor package, that automatically recognizes and transforms the output of many common Bioconductor packages into rich, interactive, HTML-based reports. Reports are not generic, but have been individually designed to reflect content specific to the result type detected. Tabular output included in reports is sortable, filterable and searchable and contains context-relevant hyperlinks to external databases. Additionally, in-line graphics have been developed for specific analysis types and are embedded by default within table rows, providing a useful visual summary of underlying raw data. ReportingTools is highly flexible and reports can be easily customized for specific applications using the well-defined API. Availability : The ReportingTools package is implemented in R and available from Bioconductor (version ≥ 2.11) at the URL: http://bioconductor.org/packages/release/bioc/html/ReportingTools.html . Installation instructions and usage documentation can also be found at the above URL. Contact : hackney.jason@gene.com or kaminker.josh@gene.com
    Print ISSN: 1367-4803
    Electronic ISSN: 1460-2059
    Topics: Biology , Computer Science , Medicine
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 4
    facet.materialart.
    Unknown
    Testing metallicity indicators at z ~ 1.4 with the gravitationally lensed galaxy CASSOWARY 20 (2014)
    Oxford University Press
    Details
    Publication Date: 2014-04-15
    Description: We present X-shooter observations of CASSOWARY 20 (CSWA 20), a star-forming (SFR ~ 6 M yr –1 ) galaxy at z  = 1.433, magnified by a factor of 11.5 by the gravitational lensing produced by a massive foreground galaxy at z  = 0.741. We analysed the integrated physical properties of the H ii regions of CSWA 20 using temperature- and density-sensitive emission lines. We find the abundance of oxygen to be ~1/7 of solar, while carbon is ~50 times less abundant than in the Sun. The unusually low C/O ratio may be an indication of a particularly rapid time-scale of chemical enrichment. The wide wavelength coverage of X-shooter gives us access to five different methods for determining the metallicity of CSWA 20, three based on emission lines from H ii regions and two on absorption features formed in the atmospheres of massive stars. All five estimates are in agreement, within the factor of ~2 uncertainty of each method. The interstellar medium (ISM) of CSWA 20 only partially covers the star-forming region as viewed from our direction; in particular, absorption lines from neutrals and first ions are exceptionally weak. We find evidence for large-scale outflows of the ISM with speeds of up 750 km s –1 , similar to the values measured in other high- z galaxies sustaining much higher rates of star formation.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 5
    facet.materialart.
    Unknown
    A refined measurement of the mean transmitted flux in the Ly{alpha} forest over 2 〈 z 〈 5 using composite quasar spectra (2013)
    Oxford University Press
    Details
    Publication Date: 2013-03-16
    Description: We present new measurements of the mean transmitted flux in the Lyα forest over 2 〈 z  〈 5 made using 6065 quasar spectra from the Sloan Digital Sky Survey data release 7 (SDSS DR7). We exploit the general lack of evolution in the mean quasar continuum to avoid the bias introduced by continuum fitting over the Lyα forest at high redshifts, which has been the primary systematic uncertainty in previous measurements of the mean Lyα transmission. The individual spectra are first combined into 26 composites with mean redshifts spanning 2.25 ≤ z comp  ≤ 5.08. The flux ratios of separate composites at the same rest wavelength are then used, without continuum fitting, to infer the mean transmitted flux, F ( z ), as a fraction of its value at z  ~ 2. Absolute values for F ( z ) are found by scaling our relative values to measurements made from high-resolution data by Faucher-Giguère et al. at z  ≤ 2.5, where continuum uncertainties are minimal. We find that F ( z ) evolves smoothly with redshift, with no evidence of a previously reported feature at z ~= 3.2. This trend is consistent with a gradual evolution of the ionization and thermal state of the intergalactic medium over 2 〈 z  〈 5. Our results generally agree with the most careful measurements to date made from high-resolution data, but offer much greater precision and extend to higher redshifts. This work also improves upon previous efforts using SDSS spectra by significantly reducing the level of systematic errors.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 6
    facet.materialart.
    Unknown
    Acoustic emissions document stress changes over many seismic cycles in stick-slip experiments (2013)
    Wiley
    Details
    Publication Date: 2013-05-01
    Description: [1]  The statistics of large earthquakes commonly involve large uncertainties due to the lack of long-term, robust earthquake recordings. Small-scale seismic events are abundant and can be used to examine variations in fault structure and stress. We report on the connection between stress and micro-seismic event statistics prior to the possibly smallest earthquakes: those generated in the laboratory. We investigate variations in seismic b value of acoustic emission events during the stress build-up and release on laboratory-created fault zones. We show that b values mirror periodic stress changes that occur during series of stick-slip events, and are correlated with stress over many seismic cycles. Moreover, the amount of b value increase associated with slip events indicates the extent of the corresponding stress drop. Consequently, b value variations can be used to approximate the stress state on a fault: a possible tool for the advancement of time-dependent seismic hazard assessment.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 7
    facet.materialart.
    Unknown
    The thermal history of the intergalactic medium down to redshift z = 1.5: a new curvature measurement (2014)
    Oxford University Press
    Details
    Publication Date: 2014-05-17
    Description: According to the photoheating model of the intergalactic medium (IGM), He ii reionization is expected to affect its thermal evolution. Evidence for additional energy injection into the IGM has been found at 3   z   4, though the evidence for the subsequent fall-off below z  ~ 2.8 is weaker and depends on the slope of the temperature–density relation, . Here we present, for the first time, an extension of the IGM temperature measurements down to the atmospheric cut-off of the H i Lyman-α (Lyα) forest at z ~= 1.5. Applying the curvature method on a sample of 60 Ultraviolet and Visual Echelle Spectrograph (UVES) spectra we investigated the thermal history of the IGM at z  〈 3 with precision comparable to the higher redshift results. We find that the temperature of the cosmic gas traced by the Lyα forest [ $T(\bar{\Delta })]$ increases for increasing overdensity from $T(\bar{\Delta })\sim 22670$ to 33740 K in the redshift range z  ~ 2.8–1.6. Under the assumption of two reasonable values for , the temperature at the mean density ( T 0 ) shows a tendency to flatten at z   2.8. In the case of  ~ 1.5, our results are consistent with previous ones which indicate a falling T 0 for redshifts z   2.8. Finally, our $T(\bar{\Delta })$ values show reasonable agreement with moderate blazar heating models.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 8
    facet.materialart.
    Unknown
    New measurements of the ionizing ultraviolet background over 2 〈 z 〈 5 and implications for hydrogen reionization (2013)
    Oxford University Press
    Details
    Publication Date: 2013-11-14
    Description: We present new measurements of the intensity of the ionizing ultraviolet background and the global emissivity of ionizing photons over 2 〈  z  〈 5. Our results are based on a suite of updated measurements of physical properties of the high-redshift intergalactic medium (IGM), including gas temperatures and the opacity of the IGM to Lyα and ionizing photons. Consistent with previous works, we find a relatively flat hydrogen photoionization rate over 2 〈  z  〈 5, although our measurements are roughly a factor of 2 higher than the 2008 values of Faucher-Giguère et al., due primarily to our lower gas temperatures. The ionizing emissivity we derive is also generally higher than other recent estimates due to a combination of lower gas temperatures, higher ionizing opacity and an accounting of cosmological radiative transfer effects. We find evidence that the emissivity increases from z  ~ 3 to 5, reaching ~5 ionizing photons per atom per Gyr at z  = 4.75 for realistic galaxy spectra. We further find that galaxies must dominate the emissivity near 1 Ryd at z  ≥ 4, and possibly at all redshifts z  ≥ 2.4. Our results suggest that the globally averaged ionizing ‘efficiency’ of star-forming galaxies increases substantially with redshift over 3.2 ≤  z  ≤ 4.75. This trend is consistent with the conclusion often drawn from reionization models that the ionizing efficiency of galaxies must be higher during reionization in order for galaxies to reionize the IGM by z  = 6. Our emissivity values at z  ~ 5 suggest that ionizing photons may have been a factor of 2 more abundant during the final stages of reionization than previously indicated. The evolution of the ionizing emissivity over 2 〈  z  〈 5 suggests, moreover, that the steep decline in the photoionization rate from z  ~ 5 to 6 may indicate a rapid evolution in the mean free path at z  〉 5.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 9
    facet.materialart.
    Unknown
    Probing the metallicity and ionization state of the circumgalactic medium at z ~ 6 and beyond with O I absorption (2014)
    Oxford University Press
    Details
    Publication Date: 2014-01-29
    Description: Low-ionization metal absorption due to O i has been identified as an important probe of the physical state of the intergalactic/circumgalactic medium at the tail end of reionization. We use here high-resolution hydrodynamic simulations to interpret the incidence rate of O i absorbers at z  ~ 6 as observed by Becker et al. We infer weak O i absorbers (EW 0.1 Å) to have typical H i column densities in the range of sub-damped Lyman α systems, densities of 80 times the mean baryonic density and metallicities of about 1/500th solar. This is similar to the metallicity inferred at similar overdensities at z  ~ 3, suggesting that the metal enrichment of the circumgalactic medium around low-mass galaxies has already progressed considerably by z  ~ 6. The apparently rapid evolution of the incidence rates for O i absorption over the redshift range 5 z 6 mirrors that of self-shielded Lyman-limit systems at lower redshift and is mainly due to the rapid decrease of the metagalactic photoionization rate at z 5. We predict the incidence rate of O i absorbers to continue to rise rapidly with increasing redshift as the IGM becomes more neutral. If the distribution of metals extends to lower density regions, O i absorbers will allow the metal enrichment of the increasingly neutral filamentary structures of the cosmic web to be probed.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 10
    facet.materialart.
    Unknown
    A consistent determination of the temperature of the intergalactic medium at redshift = 2.4 (2014)
    Oxford University Press
    Details
    Publication Date: 2014-02-15
    Description: We present new measurements of the thermal state of the intergalactic medium (IGM) at z  ~ 2.4 derived from absorption line profiles in the Lyα forest. We use a large set of high-resolution hydrodynamical simulations to calibrate the relationship between the temperature–density ( T –) relation in the IGM and the distribution of H i column densities, N H I , and velocity widths, N H I , of discrete Lyα forest absorbers. This calibration is then applied to the measurement of the lower cut-off of the N H I – N H I distribution recently presented by Rudie et al. We infer a power-law T – relation, T  =  T 0  – 1 , with a temperature at mean density, $T_{0} = [1.00^{+0.32}_{-0.21}]\times 10^{4}\rm \,K$ and slope ( – 1) = 0.54 ± 0.11. The slope is fully consistent with that advocated by the analysis of Rudie et al.; however, the temperature at mean density is lower by almost a factor of 2, primarily due to an adjustment in the relationship between column density and physical density assumed by these authors. These new results are in excellent agreement with the recent temperature measurements of Becker et al., based on the curvature of the transmitted flux in the Lyα forest. This suggests that the thermal state of the IGM at this redshift is reasonably well characterized over the range of densities probed by these methods.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...