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Sökning: WFRF:(Durret F.)

  • Resultat 1-7 av 7
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1.
  • Pierre, M., et al. (författare)
  • The XXL survey : First results and future
  • 2017
  • Ingår i: Astronomical Notes - Astronomische Nachrichten. - : Wiley-VCH Verlagsgesellschaft. - 0004-6337 .- 1521-3994. ; 338:2-3, s. 334-341
  • Tidskriftsartikel (refereegranskat)abstract
    • The XXL survey currently covers two 25 deg(2) patches with XMM observations of similar to 10 ks. We summarize the scientific results associated with the first release of the XXL dataset, which occurred in mid-2016. We review several arguments for increasing the survey depth to 40 ks during the next decade of XMM operations. X-ray (z < 2) cluster, (z < 4) active galactic nuclei (AGN), and cosmic background survey science will then benefit from an extraordinary data reservoir. This, combined with deep multi-lambda observations, will lead to solid standalone cosmological constraints and provide a wealth of information on the formation and evolution of AGN, clusters, and the X-ray background. In particular, it will offer a unique opportunity to pinpoint the z > 1 cluster density. It will eventually constitute a reference study and an ideal calibration field for the upcoming eROSITA and Euclid missions.
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2.
  • Micheva, Genoveva, et al. (författare)
  • Deep multiband surface photometry on a sample of 24 blue compact galaxies II. A volume-limited sample of 21 emission line galaxies
  • 2013
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 556, s. A10-
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. We present deep surface photometry of a volume-limited sample of 21 UM emission line galaxies in broadband optical UBVRI and near infrared (NIR) HKs filters. The sample comprises 19 blue compact galaxies (BCGs) and two spirals. Methods. We separated the burst and host populations for each galaxy and compared them to stellar evolutionary models with and without nebular emission contribution. We measured and analyzed the A(180) asymmetry in all filters, the concentration index C, the scale length, and the central surface brightness of the host galaxy. Results. A shift in the average A180 asymmetry is detected from optical to NIR. This shift seems correlated with the morphological class of the BCGs. Using the color-asymmetry relation, we identify five BCGs in the sample as mergers, which is confirmed by their morphological class. Though clearly separated from normal galaxies in the concentration-asymmetry parameter space, we find that it is not possible to distinguish luminous starbursting BCGs from the merely star forming low luminosity BCGs.
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3.
  • Micheva, G., et al. (författare)
  • Deep multiband surface photometry on a sample of 24 blue compact galaxies II. A volumelimited sample of 21 emission line galaxies.
  • 2013
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 556, s. 10-
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. We present deep surface photometry of a volume-limited sample of 21 UM emission line galaxies in broadband optical UBVRI and near infrared (NIR) HKs filters. The sample comprises 19 blue compact galaxies (BCGs) and two spirals.Methods. We separated the burst and host populations for each galaxy and compared them to stellar evolutionary models with and without nebular emission contribution. We measured and analyzed the A180 asymmetry in all filters, the concentration index C, the scale length, and the central surface brightness of the host galaxy.Results. A shift in the average A180 asymmetry is detected from optical to NIR. This shift seems correlated with the morphological class of the BCGs. Using the color-asymmetry relation, we identify five BCGs in the sample as mergers, which is confirmed by their morphological class. Though clearly separated from normal galaxies in the concentration-asymmetry parameter space, we find that it is not possible to distinguish luminous starbursting BCGs from the merely star forming low luminosity BCGs.
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4.
  • Micheva, G., et al. (författare)
  • Deep multiband surface photometry on star forming galaxies : I. A sample of 24 blue compact galaxies
  • 2012
  • Ingår i: ArXiv e-prints.
  • Tidskriftsartikel (refereegranskat)abstract
    • [Abridged] We present deep optical and near-infrared UBVRIHKs imaging data for 24 blue compact galaxies (BCGs). The sample contains luminous dwarf and intermediate-mass BCGs which are predominantly metal-poor, although a few have near-solar metallicities. We have analyzed isophotal and elliptical integration surface brightness and color profiles, extremely deep (mu_B\lt29 mag arcsec\^$$-2$$) contour maps and RGB images for each galaxy in the sample. The colors are compared to different spectral evolutionary models. We detect extremely extended low surface brightness (LSB) components dominant beyond the Holmberg radius as well as optical bridges between companion galaxies at the mu_V~28th mag arcsec\^$$-2$$ isophotal level. The central surface brightness mu_0 and scale length h_r are derived from two radial ranges typically assumed to be dominated by the underlying host galaxy. We find that mu_0 and h_r of the BCGs host deviate from those of dwarf ellipticals (dE) and dwarf irregulars (dI) solely due to a strong burst contribution to the surface brightness profile almost down to the Holmberg radius. Structural parameters obtained from a fainter region, mu_B=26-28 mag arcsec\^$$-2$$, are consistent with those of true LSB galaxies for the starbursting BCGs in our sample, and with dEs and dIs for the BCGs with less vigorous star formation.
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5.
  • Penston, M. V., et al. (författare)
  • The extended narrow line region of NGC 4151. I. Emission line ratios and their implications
  • 1990
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 236:1, s. 53-6262
  • Tidskriftsartikel (refereegranskat)abstract
    • The paper presents the first results from long-slit spectra of the Seyfert galaxy NGC 4151 which give average diagnostic ratios of weak lines in the extended narrow line region (ENLR) of that galaxy and the first direct density measurement in an ENLR. These data confirm that the ENLR is kinematically undisturbed gas in the disc of the galaxy which is illuminated by an ionizing continuum stronger by a factor of 13 than a power law interpolated between observed ultraviolet and X-ray fluxes. Explanations of this apparent excess include a hot thermal continuum, time variations and an anisotropic radiation field. The authors give reasons for favouring anisotropy which might be caused by shadowing by a thick accretion disc or by relativistic beaming. Shadowing by a molecular torus is unlikely, given the absence of an infrared signal from the reradiated flux absorbed by any torus. Anisotropy would have important implications for the bolometric luminosity and nature of active galactic nuclei
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6.
  • Prokhorov, Dmitry, et al. (författare)
  • An analysis of electron distributions in galaxy clusters by means of the flux ratio of iron lines FeXXV and XXVI
  • 2009
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 496:1, s. 25-30
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims The interpretation of hard X-ray emission from galaxy clusters is still ambiguous and different proposed models can be probed using various observational methods. Here we explore a new method based on Fe-line observations. Methods. Spectral-line emissivities have usually been calculated by assuming a Maxwellian electron distribution. In this paper, a generalized approach to calculating the iron-line flux for a modified Maxwellian distribution is considered. Results. We calculated the flux ratio of iron lines for various possible populations of electrons proposed to account for measurements of hard X-ray excess-emission from the clusters A2199 and Coma. We found that the influence of the suprathermal electron population on the flux ratio is more significant in low temperature clusters (as Abell 2199) than in high temperature clusters (as Coma).
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7.
  • Prokhorov, Dmitry, et al. (författare)
  • An approximate theory for substructure propagation in clusters
  • 2007
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 474:2, s. 375-384
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. The existence of dark matter can be proved in an astrophysical context by the discovery of a system in which the observed baryons and the inferred dark matter are spatially segregated, such as the bullet cluster (1E0657-558). The full descriptions of the dark matter halo and X-ray gas substructure motions are necessary to forecast the location of the dark halo from X-ray maps, which can be confirmed by the detection of a galaxy concentration or by gravitational lensing. Methods. We present an analytical hydrodynamic model to determine the distance between the X-ray and dark-matter components and the Mach number of the merger shock. Results. An approximate solution is given for the problem of the substructure propagation in merging clusters. A new method to predict the position of a dark matter halo in clusters, where there is a separation between the X-ray gas and the dark halo, is proposed and applied to the clusters 1E0657-558 and Abell 1763.
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  • Resultat 1-7 av 7

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