179 research outputs found
The nuclear radio structure of X-ray bright AGN
The physical nature of the X-ray/radio correlation of AGN is still an
unsolved question. High angular resolution observations are necessary to
disentangle the associated energy dynamics into nuclear and stellar components.
We present MERLIN/EVN 18cm observations of 13 X-raying AGN. The sample consists
of Seyfert 1, Narrow Line Seyfert 1, and LINER-like galaxies. We find that for
all objects the radio emission is unresolved and that the radio luminosities
and brightness temperatures are too high for star formation to play an
important role. This indicates that the radio emission in these sources is
closely connected to processes that occur in the vicinity of the central
massive black hole, also where the X-ray emission is believed to originate in.Comment: 5 pages, 3 figures, submitted to "The Universe under the Microscope -
Astrophysics at High Angular Resolution", Bad Honnef, German
The nuclear radio structure of X-ray bright AGN
The physical nature of the X-ray/radio correlation of AGN is still an
unsolved question. High angular resolution observations are necessary to
disentangle the associated energy dynamics into nuclear and stellar components.
We present MERLIN/EVN 18cm observations of 13 X-raying AGN. The sample consists
of Seyfert 1, Narrow Line Seyfert 1, and LINER-like galaxies. We find that for
all objects the radio emission is unresolved and that the radio luminosities
and brightness temperatures are too high for star formation to play an
important role. This indicates that the radio emission in these sources is
closely connected to processes that occur in the vicinity of the central
massive black hole, also where the X-ray emission is believed to originate in.Comment: 5 pages, 3 figures, submitted to "The Universe under the Microscope -
Astrophysics at High Angular Resolution", Bad Honnef, German
The nuclear radio structure of X-ray bright AGN
The physical nature of the X-ray/radio correlation of AGN is still an
unsolved question. High angular resolution observations are necessary to
disentangle the associated energy dynamics into nuclear and stellar components.
We present MERLIN/EVN 18cm observations of 13 X-raying AGN. The sample consists
of Seyfert 1, Narrow Line Seyfert 1, and LINER-like galaxies. We find that for
all objects the radio emission is unresolved and that the radio luminosities
and brightness temperatures are too high for star formation to play an
important role. This indicates that the radio emission in these sources is
closely connected to processes that occur in the vicinity of the central
massive black hole, also where the X-ray emission is believed to originate in.Comment: 5 pages, 3 figures, submitted to "The Universe under the Microscope -
Astrophysics at High Angular Resolution", Bad Honnef, German
Galaxy evolution across the optical emission-line diagnostic diagrams?
The discovery of the M-sigma relation, the local galaxy bimodality, and the
link between black-hole and host-galaxy properties, have raised the question
whether AGN play a role in galaxy evolution. Several theoretical models
implement AGN feedback to explain the observed galaxy luminosity function, and
possibly the color and morphological transformation of spiral galaxies into
passive ellipticals. To understand the importance of AGN feedback, a study of
the AGN populations in the radio-optical domain is crucial. A mass sequence
linking star-forming galaxies and AGN has been already noted in previous works,
and it is now investigated as possible evolutionary sequence. We observed a
sample of 119 intermediate-redshift (0.04<z<0.4) SDSS-FIRST radio emitters with
the Effelsberg 100-m telescope at 4.85 and 10.45 GHz and obtained spectral
indices. We find indications of spectral index flattening in high-metallicity
star-forming galaxies, composite galaxies, and Seyferts. This "flattening
sequence" along the [NII]-based emission-line diagnostic diagram is consistent
with the hardening of galaxy ionizing field, due to nuclear activity. After
combining our data with FIRST measurements at 1.4 GHz, we find that the
three-point radio spectra of Seyferts and LINERs show substantial differences,
attributable to small radio core components and larger (arcsecond sized)
jet/lobe components, respectively. A visual inspection of FIRST images seems to
confirm this hypothesis. Galaxies along this sequence are hypothesized to be
transitioning from the active star-forming galaxies (blue cloud) to the passive
elliptical galaxies (red sequence). This supports the suggestion that AGN play
a role in shutting down star-formation, and allow the transition from one
galaxy class to the other.Comment: 20 pages, 19 figures, accepted for publication in A&
A low-luminosity type-1 QSO sample; III. Optical spectroscopic properties and activity classification
We report on the optical spectroscopic analysis of a sample of 99
low-luminosity quasi-stellar objects (LLQSOs) at base the
Hamburg/ESO QSO survey (HES). The LLQSOs presented here offer the possibility
of studying the faint end of the QSO population at smaller cosmological
distances and, therefore, in greater detail. A small number of our LLQSO
present no broad component. Two sources show double broad components, whereas
six comply with the classic NLS1 requirements. As expected in NLR of broad line
AGNs, the [S{\sc{ii}}]based electron density values range between 100 and
1000 N/cm. Using the optical characteristics of Populations A and
B, we find that 50\% of our sources with H broad emission are consistent
with the radio-quiet sources definition. The remaining sources could be
interpreted as low-luminosity radio-loud quasar. The BPT-based classification
renders an AGN/Seyfert activity between 50 to 60\%. For the remaining sources,
the possible star burst contribution might control the LINER and HII
classification. Finally, we discuss the aperture effect as responsible for the
differences found between data sets, although variability in the BLR could play
a significant role as well.Comment: 22 pages; 5 tables; 17 figures; in press with A&
Line and Continuum Variability in Active Galaxies
We compared optical spectroscopic and photometric data for 18 AGN galaxies
over 2 to 3 epochs, with time intervals of typically 5 to 10 years. We used the
Multi-Object Double Spectrograph (MODS) at the Large Binocular Telescope (LBT)
and compared the spectra to data taken from the SDSS database and the
literature. We find variations in the forbidden oxygen lines as well as in the
hydrogen recombination lines of these sources. For 4 of the sources we find
that, within the calibration uncertainties, the variations in continuum and
line spectra of the sources are very small. We argue that it is mainly the
difference in black hole mass between the samples that is responsible for the
different degree of continuum variability. In addition we find that for an
otherwise constant accretion rate the total line variability (dominated by the
narrow line contributions) reverberates the continuum variability with a
dependency . Since
this dependency is prominently expressed in the narrow line emission it implies
that the luminosity dominating part of the narrow line region must be very
compact with a size of the order of at least 10 light years. A comparison to
literature data shows that these findings describe the variability
characteristics of a total of 61 broad and narrow line sources.Comment: 30 pages including the appendix, 18 figures including the appendix.
Accepted 2015 September 3. Received 2015 August 24; in original form 2015
July 3 in Monthly Notices of the Royal Astronomical Societ
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