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Sökning: WFRF:(van Groningen E.)

  • Resultat 21-25 av 25
  • Föregående 12[3]
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  • van Groningen, E., et al. (författare)
  • Broad emission line profiles in Seyfert-1 galaxies : [O III]-wings from a transition zone
  • 1989
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 211:2, s. 293-309309
  • Tidskriftsartikel (refereegranskat)abstract
    • The authors demonstrate that broad wings are present under the strong [O III] lambda 5007 line in 10 out of 12 observed Seyfert-1 galaxies. The question is addressed whether the wing is due to broad [O III] emission or to some other ion. The alternatives considered are Fe II (42) lambda 5018, He I lambda 5016 and Si II lambdalambda 5041, 5056 or even Hbeta. The authors have searched for a counterpart of the wing in other forbidden and permitted lines. The observations yield a crude estimate of the density in the wing-emitting region. The authors derive a lower limit to the region's size. Because the [O III] emitting gas holds an intermediate position between the broad line region (BRL) and the narrow line region (NLR), both in density and distance, the authors denominate it the transition line region (TLR). They surmise that the outflowing part of the BLR provides the material of the TLR, before slowing down to NLR velocities
  • van Groningen, E. (författare)
  • Broad emission line profiles in Seyfert-1 galaxies. I. Evidence for a disk and a wind in Mkn 335
  • 1987
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 186:1-2, s. 103-113113
  • Tidskriftsartikel (refereegranskat)abstract
    • High resolution spectroscopic observations of the Seyfert-1 galaxy Mkn 335 are presented. This galaxy is exceptional in the sense that its broad emission lines display a strong blue asymmetry. It is shown that the Halpha/Hbeta intensity ratio changes drastically with velocity shift. It is also found that the Hdelta/Hbeta ratio varies only by a small amount from line core to the wings, and is close to the theoretical case B recombination value. It is proposed that these Balmer line ratios are produced by a medium with very high densities and a temperature of about 10 4 K. These observations are interpreted by a model with two dynamically and spatially separate components: a disk which contains the very high density material and emits ~80% of the Balmer lines in a symmetric profile and an outflowing component of much lower density which emits the blue wing and most of Ly alpha and the higher excitation lines (such as C IV lambda1549)
  • Van Groningen, E., et al. (författare)
  • One-sided jets in extragalactic radiosources
  • 1980
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 90:1-2, s. L7-L9L9
  • Tidskriftsartikel (refereegranskat)abstract
    • Some explanations for the existence of one-sided jets in symmetrical extended radio sources are discussed. It is shown that in the case of the quasar 4C32.69, a relativistic Doppler interpretation is improbable. Observational constraints on a model involving anisotropic radiation are also examined. This model cannot be ruled out, although non-relativistic interpretations of one-sided jets are most likely
  • Wanders, I., et al. (författare)
  • Seeing and aperture effects on [O III]-based flux calibration of AGN spectra. NGC 3516 : a case study
  • 1992
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 266:1, s. 72-7676
  • Tidskriftsartikel (refereegranskat)abstract
    • In variability studies of the broad emission lines in the spectra of active galactic nuclei, the narrow emission lines are generally used to flux calibrate spectra taken at different epochs to each other. In objects where the narrow-line region is resolved, seeing affects the ratio of narrow-line flux to broad-line and continuum flux entering the aperture since the broad-line region and the continuum source are unresolved. Thus observing under different seeing conditions introduces artificial correlated variations of the continuum and broad-line fluxes if one assumes the narrow lines to be constant in flux. The authors show that one can correct for this effect by simulating seeing variations using a narrow-band [O III] image, taken in good seeing conditions, of the nearby Seyfert 1 galaxy NGC 3516, in which the narrow-line region is clearly resolved and extends over more than 20". They also show that centring the aperture on the object consistently is very important and miscentring is also a source of artificial variability of the broad-line and continuum fluxes
  • Örndahl, E., et al. (författare)
  • An optical imaging study of 0.4 <= z <= 0.8 quasar host galaxies. I. Observations and reduction
  • 2003
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 404, s. 883-899
  • Tidskriftsartikel (refereegranskat)abstract
    • We have conducted an optical imaging study aimed at resolving the host galaxies of 79 radio-loud and radio-quiet quasars at z=0.4-0.8, extending the number of investigated objects in this redshift range by ~ 45%. Observations were performed mainly in the R band but also in V and I band using the Nordic Optical Telescope on La Palma. In this paper we discuss the sample composition and observations and the reduction techniques used. The quasars were selected in pairs of radio-loud and radio-quiet objects matched in the z-V plane in order to facilitate a statistical comparison. The radio-loud part of the sample contains comparable numbers of flat and steep radio spectrum sources which also are matched in redshift and V magnitude. Point spread function subtraction was performed using one-dimensional luminosity profiles both on the quasar image and on a field star, and subtracted images and luminosity profiles are shown for each quasar field. The detection rate is 60% for the radio-quiet host galaxies and 80% for radio-loud hosts. The host galaxies have magnitudes which make them brighter than an L* galaxy by a factor of 1.5-4 at the low end of the redshift range, which increases by 2-3 times towards the higher end of the redshift range. Both radio-quiet and radio-loud hosts follow the radio galaxy R-z Hubble relation well. Analysis and discussion of colours and morphology is presented in \citet{orn}. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.
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  • Resultat 21-25 av 25
  • Föregående 12[3]

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