2,283 research outputs found
ACCRETION DISK STRUCTURE AND KINEMATICS OF THE BROAD LINE REGIONS IN SELECTED AGN
No full textBroad emission line regions in AGN are connected with the outer layers of accretion disks. This has been shown by means of line variability studies of individual AGN as well as line profile studies of AGN samples. We could model the broad-line profiles in AGN in a simple way only through rotational broadening of Lorentzian profiles. To individual emission lines belongs one typical Lorentz profile only with a fixed turbulence velocity: e.g., 500 km/s for H beta, 3000 km/s for C IV lambda 1550. The rotation velocities in the broad line regions of the AGN range from 1000 to 7000 km/s
ACCRETION DISK STRUCTURE AND KINEMATICS OF THE BROAD LINE REGIONS IN SELECTED AGN
No full textBroad emission line regions in AGN are connected with the outer layers of accretion disks. This has been shown by means of line variability studies of individual AGN as well as line profile studies of AGN samples. We could model the broad-line profiles in AGN in a simple way only through rotational broadening of Lorentzian profiles. To individual emission lines belongs one typical Lorentz profile only with a fixed turbulence velocity: e.g., 500 km/s for H beta, 3000 km/s for C IV lambda 1550. The rotation velocities in the broad line regions of the AGN range from 1000 to 7000 km/s
Broad-line active galactic nuclei rotate faster than narrow-line ones
No full textThe super-massive black holes of 10(6)M(circle dot) to 10(9)M(circle dot) that reside in the nuclei of active galaxies(1) (AGN) are surrounded by a region emitting broad lines, probably associated with an accretion disk. The diameters of the broad-line regions range from a few light-days to more than a hundred light-days(1), and cannot be resolved spatially. The relative significance of inflow, outflow, rotational or turbulent motions in the broad-line regions as well as their structure (spherical, thin or thick accretion disk) are unknown despite intensive studies over more than thirty years(2,3). Here we report a fundamental relation between the observed emission linewidth full-width at half-maximum (FWHM) and the emission line shape FWHM/sigma(line) in AGN spectra. From this relation we infer that the predominant motion in the broad-line regions is Keplerian rotation in combination with turbulence. The geometry of the inner region varies systematically with the rotation velocity: it is flattest for the fast-rotating broad-line objects, whereas slow-rotating narrow-line AGN have a more spherical structure. Superimposed is the trend that the line-emitting region becomes geometrically thicker towards the centre within individual galaxies. Knowing the rotational velocities, we can derive the central black-hole masses more accurately; they are two to ten times smaller than has been estimated previously.Niedersachsen-Israel Research Cooperation Program [ZN2318
QSO/AGN environments at different redshifts
No full textWith the availability of large data sets like the Sloan Digital Sky Survey (SDSS) is it now possible to study a huge amount of galaxy spectra in a statistical manner The spectroscopical data set of the seventh SDSS data release covers 9380 deg(2) (approximate to 23% of the whole sky) We selected nearly 100 000 objects from this SDSS data release 7 that were spectroscopically classified as quasars to investigate their environment. We developed a dedicated software-pipeline to process this enormous amount of data. We classified all galaxies within the Quasar/AGN-neighbourhood of 1 Mpc according to Kauffmann (2003) and Kewley et al (2006) by mean of a diagnostic BPT diagram For doing this we had to measure the narrow Balmer-line components manually. Furthermore. we studied the distribution of these objects in the QSO/AGN environment as well as their spectroscopical properties and the absolute magnitudes. (C) 2009 Elsevier B.V. All rights reserved
Line profile and continuum variability in the very broad-line Seyfert galaxy Mrk 926
No full textAims. We present results of an intensive spectroscopic variability
campaign of the very broad-line Seyfert 1 galaxy Mrk 926. Our aim is to investigate the
broad-line region (BLR) by studying the intensity and line profile variations of this
galaxy on short timescales.
Methods. High signal-to-noise ratio (S/N) spectra were taken with the
9.2 m Hobby-Eberly Telescope (HET) in identical conditions during two observing campaigns
in 2004 and 2005. After the spectral reduction and internal calibration we achieved a
relative flux accuracy of better than 1%.
Results. The rms profiles of the very broad Balmer lines have shapes
that differ from their mean line profiles, consisting of two inner
(v ≲ ± 6000 km s-1) and two outer
(v ≳ ± 6000 km s-1) line components in addition to a
central component (v ≲ ± 600 km s-1). These outer and inner
line segments varied with different amplitudes during our campaign. The radius of the BLR
is very small with an upper limit of 2 light-days for the Hβ BLR size. We
derived an upper limit to the central black hole mass of
M = 11.2 × 107M⊙. The 2-D
cross-correlation functions CCF(τ, v) of
Hβ and Hα are flat within the error limits. The
response of the Balmer line segments with respect to continuum variations is different in
the outer and inner wings of Hα and Hβ. This double
structure in the response curves – of two separate inner and outer components – has also
been seen in the rms line profiles. We conclude that the outer and inner line segments
originate in different regions and/or under different physical conditions
Vertical broad-line region structure in nearby active galactic nuclei
No full textContext. Broad emission lines are emitted in the surroundings of supermassive black holes in the centers of active galactic nuclei (AGN). This region is spatially not resolved.
Aims. We intend to get information on the structure and geometry of this broad emitting line region based on line profile observations.
Methods. We model the rotational and turbulent velocities in the line-emitting regions based on observed full-width at half maximum line values (FWHM) and σline of the variable broad emission lines in four nearby AGN: NGC 3783, NGC 7469, NGC 5548, and 3C 390.3. On the basis of these velocities, we estimate the height of the line-emitting regions above the midplane in context with their distances from the center.
Results. The Hβ lines are emitted in a more flattened configuration above the midplane in comparison to the highly ionized lines. The Hβ lines originate at heights of 0.7 to 1.6 light-days and at distances of 1.4 to 24 light-days with height/distance ratios (H/R) of only 0.07 to 0.5. The highly ionized lines originate at smaller radii than the Hβ lines and/or at greater distances above the midplane with H/R values of 0.2 to 1.7. In total, the emission lines do not originate in a thin atmosphere of an accretion disk but rather at very extended regions above an accretion disk. The observed geometries of the line-emitting regions resemble the geometries of accretion disk wind models. Furthermore, the angle of the central opening cone (generated by the emitting regions of the highly ionized lines) is small for those galaxies with slow rotational velocities and increases with the rotation velocity of the central region.
Conclusions. The derived geometries of the line-emitting regions of all four AGN are consistent with the geometries that are predicted in outflowing disk wind models
The shape of broad-line profiles in active galactic nuclei
No full textAims. We present a study of the broad optical/UV emission line profiles in active galactic nuclei (AGN) to get information on the dominant velocity components (turbulence, rotation, etc.) in the central broad-line region (BLR).
Methods. We introduce line broadening simulations of emission line profiles and compare these results with the largest homogeneous data set of reverberation-mapped AGN.
Results. The underlying broad-line profiles in AGN are Lorentzian profiles caused by turbulence in the line emitting region. The turbulent velocities are different for the different line emitting regions of Hγ, Hα, Lyα, C ii
Accretion disk wind as explanation for the broad-line region structure in NGC 5548
No full textContext. Supermassive black holes in the centers of active galactic nuclei (AGN) are surrounded by broad-line regions (BLRs). The broad emission lines seen in the AGN spectra are emitted in this spatially unresolved region.
Aims. We intend to obtain information on the structure and geometry of this BLR based on observed line profiles.
Methods. We modeled the rotational and turbulent velocities in the line-emitting region on the basis of the line-width FWHM and line dispersion σline of the variable broad emission lines in NGC 5548. Based on these velocities we estimated the height of the line-emitting regions above the midplane in the context of their distances from the center.
Results. The broad emission lines originate at distances of 2 to 27 light days from the center. Higher ionized lines originate in the inner region (≤ 13 light days) in specific filamentary structures 1 to 14 light days above the midplane. In contrast, the Hβ line is emitted in an outer (6−26 light days), more flattened configuration at heights of 0.7 to 4 light days only above the midplane.
Conclusions. The derived geometry of the line-emitting region in NGC 5548 is consistent with an outflowing wind launched from an accretion disk
Spectral line variability amplitudes in active galactic nuclei
No full textWe present the results of a long-term variability campaign of very broad-line
AGNs with line widths broader than FWHM > 5000 km s-1.
The main goal of our investigation was to study whether the widths of the
optical broad emission lines are correlated with the optical intensity
variations on timescales of years. Our AGN sample consisted of 10 objects.
We detected a significant correlation between optical continuum variability
amplitudes and Hβ emission line widths (FWHM) and, to a lesser degree,
between Hβ line intensity variations and Hβ equivalent widths.
We add the spectroscopic data of variable AGNs from the literature to
supplement our sample.
The AGNs from other optical variability campaigns with different line-widths
helped to improve the statistical significance of our very broad-line AGN
sample. After including the data on 35 additional galaxies, the
correlation between
optical continuum variability amplitudes and Hβ emission line widths
becomes even more significant and the probability that this is a random
correlation drops to 0.7 percent
The environment of AGNs and the activity degree of their surrounding galaxies
No full textAims. We present results of a comprehensive spectral study on the large-scale environment of active galactic nuclei (AGNs) based on Sloan Spectroscopic Survey data.
Methods. We analyzed the spectra of galaxies in the environment of AGN and other activity classes up to distances of 1 Mpc.
Results. The mean Hα and [O ii
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