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
Filter
  • Oxford University Press  (30)
  • Springer  (2)
  • 1
    Electronic Resource
    Electronic Resource
    New views through the gravitational telescope (1990)
    Springer
    Astrophysics and space science 170 (1990), S. 389-393 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract New improvements in extragalactic research have recently increased the number of sources at high redshift, i.e., QSOs and especially galaxies. Gravitational lensing/magnification events are more common among them, particularly because gravitationally magnified sources are preferentially selected in the flux-limited catalogues used to find distant sources. They offer a means of investigating the matter distribution from small scales (microlensing) to large scales (macrolensing). Recent observations and realistic mass distribution models of the arc-like structures (in A370 and CI 2244-02) allow us to describe the observations well and to set new and independent conditions on the material content of the deflecting clusters; they also allow detailed studies of sources which are at the ends of the gravitational telescopes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00652699
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    facet.materialart.
    Unknown
    The NGC 4013 tale: a pseudo-bulged, late-type spiral shaped by a major merger (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-08
    Description: Many spiral galaxy haloes show stellar streams with various morphologies when observed with deep images. The origin of these tidal features is discussed, either coming from a satellite infall or caused by residuals of an ancient, gas-rich major merger. By modelling the formation of the peculiar features observed in the NGC 4013 halo, we investigate their origin. By using gadget -2 with implemented gas cooling, star formation, and feedback, we have modelled the overall NGC 4013 galaxy and its associated halo features. A gas-rich major merger occurring 2.7–4.6 Gyr ago succeeds in reproducing the NGC 4013 galaxy properties, including all the faint stellar features, strong gas warp, boxy-shaped halo and vertical 3.6 μm luminosity distribution. High gas fractions in the progenitors are sufficient to reproduce the observed thin and thick discs, with a small bulge fraction, as observed. A major merger is able to reproduce the overall NGC 4013 system, including the warp strength, the red colour and the high stellar mass density of the loop, while a minor merger model cannot. Because the gas-rich model suffices to create a pseudo-bulge with a small fraction of the light, NGC 4013 is perhaps the archetype of a late-type galaxy formed by a relatively recent merger. Then late type, pseudo-bulge spirals are not mandatorily made through secular evolution, and the NGC 4013 properties also illustrate that strong warps in isolated galaxies may well occur at a late phase of a gas-rich major merger.
    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
    GRB host galaxies with VLT/X-Shooter: properties at 0.8 〈 z 〈 1.3 (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-06
    Description: Long gamma-ray bursts (LGRBs) are associated with the death of massive stars. Their host galaxies therefore represent a unique class of objects tracing star formation across the observable Universe. Indeed, recently accumulated evidence shows that GRB hosts do not differ substantially from general population of galaxies at high ( z  〉 2) redshifts. However, it has been long recognized that the properties of z  〈 1.5 hosts, compared to general star-forming population, are unusual. To better understand the reasons for the supposed difference in LGRB hosts properties at z  〈 1.5, we obtained Very Large Telescope (VLT)/X-Shooter spectra of six hosts lying in the redshift range of 0.8 〈  z  〈 1.3. Some of these hosts have been observed before, yet we still lack well-constrained information on their characteristics such as metallicity, dust extinction and star formation rate (SFR). We search for emission lines in the VLT/X-Shooter spectra of the hosts and measure their fluxes. We perform a detailed analysis, estimating host average extinction, SFRs, metallicities and electron densities where possible. Measured quantities of our hosts are compared to a larger sample of previously observed GRB hosts at z  〈 2. SFRs and metallicities are measured for all the hosts analysed in this paper and metallicities are well determined for four hosts. The mass–metallicity relation, the fundamental metallicity relation and SFRs derived from our hosts occupy similar parameter space as other host galaxies investigated so far at the same redshift. We therefore conclude that GRB hosts in our sample support the found discrepancy between the properties of low-redshift GRB hosts and the general population of star-forming 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
  • 4
    facet.materialart.
    Unknown
    The main sequence of star-forming galaxies at z ~ 0.6: reinstating major mergers (2014)
    Oxford University Press
    Details
    Publication Date: 2014-07-03
    Description: The relation between the star formation rate (SFR) and the stellar mass of star-forming galaxies has been used to argue that major mergers cannot be the main driver of star formation. Here, we re-examine these arguments using the representative IMAGES-CDFS sample of star-forming galaxies at z = 0.4–0.75, taking advantage of their previously established classification into pre-fusion, fusion, and relaxing galaxy mergers. Contrary to previous claims, we show there is no tension between the main-sequence scatter and the average duration of the fusion SFR peak. We confirm previous estimates of the fraction of SFR due to morphologically selected galaxies (~23 per cent) or the SFR enhancement due to major merger during the fusion phase (~10 per cent). However, galaxy mergers are not instantaneous processes, which implies that the total fraction of the SFR associated with galaxies undergoing major mergers must account for the three merger phases. When doing so, galaxies involved in major mergers are found to represent 53–88 per cent of the total SFR at z ~ 0.6. The fraction of luminous infrared galaxies (LIRGs) in the fusion phase is found to be in agreement with the observed morphological fraction of LIRGs without discs and with the observed and expected major merger rates at z ≤ 1.5.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 5
    facet.materialart.
    Unknown
    Morpho-kinematics of z ~ 1 galaxies probe the hierarchical scenario (2016)
    Oxford University Press
    Details
    Publication Date: 2016-12-14
    Description: We have studied a representative sample of intermediate-mass galaxies at z ~ 1, observed by the kinematic survey KMOS 3D . We have re-estimated the kinematical parameters from the published kinematic maps and analysed photometric data from Hubble Space Telescope ( HST ) to measure optical disc inclinations and Position Angle. We find that only half of the z ~ 1 galaxies show kinematic properties consistent with rotating discs using the same classification scheme than that adopted by the KMOS 3D team. Because merger orbital motions can also brought rotation, we have also analysed galaxy morphologies from the available HST imagery. Combining these results to those from kinematics, it leads to a full morpho-kinematic classification. To test the robustness of the latter for disentangling isolated discs from mergers, we confronted the results with an analysis of pairs from the open grism redshift survey 3D-HST. All galaxies found in pairs are affected by either kinematic and/or morphological perturbations. Conversely, all galaxies classified as virialized spirals are found to be isolated. A significant fraction (one-fourth) of rotating discs classified from kinematics by the KMOS 3D team are found in pairs, which further supports the need for a morpho-kinematic classification. It results that only one-third of z ~ 1 galaxies are isolated and virialized spirals, while 58 per cent of them are likely involved in a merger sequence, from first approach to disc rebuilding. The latter fraction is in good agreement with the results of semi-empirical cold dark matter models, supporting a merger-dominated hierarchical scenario as being the main driver of galaxy formation at least during the last 8 billion years.
    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
    Reproducing properties of MW dSphs as descendants of DM-free TDGs (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-26
    Description: The Milky Way (MW) dwarf spheroidal (dSph) satellites are known to be the most dark-matter (DM) dominated galaxies with estimates of dark-to-baryonic matter reaching even above 100. It comes from the assumption that dwarfs are dynamically supported by their observed velocity dispersions. However, their spatial distributions around the MW are not at random and this could challenge their origin, previously assumed to be residues of primordial galaxies accreted by the MW potential. Here, we show that, alternatively, dSphs could be the residue of tidal dwarf galaxies (TDGs), which would have interacted with the Galactic hot gaseous halo and disc. TDGs are gas rich and have been formed in a tidal tail produced during an ancient merger event at the M31 location, and expelled towards the MW. Our simulations show that low-mass TDGs are fragile to an interaction with the MW disc and halo hot gas. During the interaction, their stellar content is progressively driven out of equilibrium and strongly expands, leading to low surface brightness feature and mimicking high dynamical M / L ratios. Our modelling can reproduce the properties, including the kinematics, of classical MW dwarfs within the mass range of the Magellanic Clouds to Draco. An ancient gas-rich merger at the M31 location could then challenge the currently assumed high content of DM in dwarf galaxies. We propose a simple observational test with the coming GAIA mission, to follow their expected stellar expansion, which should not be observed within the current theoretical framework.
    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
  • 7
    facet.materialart.
    Unknown
    Co-orbiting satellite galaxy structures are still in conflict with the distribution of primordial dwarf galaxies (2014)
    Oxford University Press
    Details
    Publication Date: 2014-06-21
    Description: Both major galaxies in the Local Group host planar distributions of co-orbiting satellite galaxies, the Vast Polar Structure (VPOS) of the Milky Way and the Great Plane of Andromeda (GPoA). The cold dark matter (CDM) cosmological model did not predict these features. However, according to three recent studies the properties of the GPoA and the flattening of the VPOS are common features among subhalo based CDM satellite systems, and the GPoA can be naturally explained by satellites being acquired along cold gas streams. We point out some methodological issues in these studies: either the selection of model satellites is different from that of the observed ones, or an incomplete set of observational constraints has been considered, or the observed satellite distribution is inconsistent with basic assumptions. Once these issues have been addressed, the conclusions are different: features like the VPOS and GPoA are very rare (each with probability 10 –3 , and combined probability 〈10 –5 ) if satellites are selected from a CDM simulation combined with semi-analytic modelling, and accretion along cold streams is no natural explanation of the GPoA. The origin of planar dwarf galaxy structures remains unexplained in the standard paradigm of galaxy 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
  • 8
    facet.materialart.
    Unknown
    GRB 100219A with X-shooter - abundances in a galaxy at z =4.7 (2013)
    Oxford University Press
    Details
    Publication Date: 2013-01-03
    Description: Abundances of galaxies at redshifts z  〉 4 are difficult to obtain from damped Lyα (DLA) systems in the sightlines of quasars (QSOs) due to the Lyα forest blanketing and the low number of high-redshift QSOs known to date. Gamma-ray bursts (GRBs) with their higher luminosity are well suited to study galaxies out to the formation of the first stars at z  〉 10. The large wavelength coverage of the X-shooter spectrograph makes it an excellent tool to study the interstellar medium of high-redshift galaxies, in particular if the redshift is not known beforehand. In this paper, we determine the properties of a GRB host at z  = 4.667 23 from absorption lines combined with X-ray and optical imaging data. This is one of the highest redshifts where a detailed analysis with medium-resolution data is possible. We measure a relatively high metallicity of [S/H] = –1.1 ± 0.2 for a galaxy at this redshift. Assuming ultraviolet pumping as origin for the fine-structure lines, the material observed is between 0.3 and 1.0 kpc from the GRB. The extinction determined by the spectral slope from X-rays to the infrared shows a moderate value of A V  = 0.13 ± 0.05 mag and relative abundances point to a warm disc extinction pattern. Low- and high-ionization as well as fine-structure lines show a complicated kinematic structure probably pointing to a merger in progress. We also detect one intervening system at z  = 2.18. GRB-DLAs have a shallower evolution of metallicity with redshift than QSO absorbers and no evolution in their H i column density or ionization fraction. GRB hosts at high redshifts seem to continue the trend of the metallicity–luminosity relation towards lower metallicities but the sample is still too small to draw a definite conclusion. While the detection of GRBs at z  〉 4 with current satellites is still difficult, they are very important for our understanding of the early epochs of star and galaxy 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
  • 9
    facet.materialart.
    Unknown
    The vast thin plane of M31 corotating dwarfs: an additional fossil signature of the M31 merger and of its considerable impact in the whole Local Group (2013)
    Oxford University Press
    Details
    Publication Date: 2013-05-08
    Description: The recent discovery by Ibata et al. of a vast thin disc of satellites (VTDS) around M31 offers a new challenge for the understanding of the Local Group properties. This comes in addition to the unexpected proximity of the Magellanic Clouds (MCs) to the Milky Way (MW), and to another vast polar structure (VPOS), which is almost perpendicular to our Galaxy disc. We find that the VTDS plane is coinciding with several stellar, tidally induced streams in the outskirts of M31, and, that its velocity distribution is consistent with that of the giant stream (GS). This is suggestive of a common physical mechanism, likely linked to merger tidal interactions, knowing that a similar argument may apply to the VPOS at the MW location. Furthermore, the VTDS is pointing towards the MW, being almost perpendicular to the MW disc, as the VPOS is. We compare these properties to the modelling of M31 as an ancient, gas-rich major merger, which has been successfully used to predict the M31 substructures and the GS origin. We find that without fine tuning, the induced tidal tails are lying in the VTDS plane, providing a single and common origin for many stellar streams and for the vast stellar structures surrounding both the MW and M31. The model also reproduces quite accurately positions and velocities of the VTDS spheroidal dwarfs. Our conjecture leads to a novel interpretation of the Local Group past history, as a gigantic tidal tail due to the M31 ancient merger is expected to send material towards the MW, including the MCs. Such a link between M31 and the MW is expected to be quite exceptional, though it may be in qualitative agreement with the reported rareness of MW–MCs systems in nearby 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
  • 10
    facet.materialart.
    Unknown
    Modelling the narrow-line regions of active galaxies in the Sloan Digital Sky Survey - I. Sample selection and physical conditions (2013)
    Oxford University Press
    Details
    Publication Date: 2013-03-23
    Description: Using spectroscopy from the Sloan Digital Sky Survey Data Release Seven, we systematically determine the electron density n e and electron temperature T e of active galaxies and star-forming galaxies, while mainly focusing on the narrow-line regions (NLRs). Herein, active galaxies refer to composites, low-ionization narrow emission-line regions (LINERs) and Seyfert galaxies, following the Baldwin–Phillips–Terlevich diagram classifications afforded by the SDSS data. The plasma diagnostics of n e and T e are determined through the I [S ii ] 6716/6731 and I [O iii ] 5007/4363 ratios, respectively. By simultaneously determining n e from [S ii ] and T e from [O iii ] in our [O iii ] 4363 emission sample of 15 019 galaxies, we find two clear sequences: T LINER T composite 〉 T Seyfert 〉 T star-forming and n LINER n Seyfert 〉 n composite 〉 n star-forming . The typical range of n e in the NLRs of active galactic nuclei (AGNs) is 10 2 – 3 cm –3 . The temperatures in the NLRs range from 1.0 to 2.0  x 10 4 K for Seyferts, and the ranges are even higher and wider for LINERs and composites. The transitions of n e and T e from the NLRs to the discs are revealed. We also present a comparative study, including stellar mass ( M * ), specific star formation rate (SFR/ M * ) and plasma diagnostic results. We propose that Y L Y SY 〉 Y C 〉 Y SF , where Y is the characteristic present-day star-formation time-scale. One remarkable feature of the Seyferts shown on an M * –SFR/ M * diagram, which we call the evolutionary pattern of AGNs with high ionization potential, is that the strong [O iii ] 4363 Seyferts distribute uniformly with the weak Seyferts, definitely a reverse of the situation for star-forming galaxies. It is a natural and well-known consensus that strong [O iii ] 4363 emissions in star-forming galaxies imply young stellar populations and thus low stellar masses. However, in the AGN case, several strong lines of evidence suggest that some supplementary energy source(s) should be responsible for high ionization potential.
    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...