186 research outputs found
What produces the extended LINER-type emission in the NUGA galaxy NGC 5850?
(Abridged) The role of low ionization nuclear emission region (LINER)
galaxies within the picture of active galactic nuclei (AGN) has been
controversial. It is still not clear whether they host an AGN in a low
accretion mode, or whether they are not active at all but dominated by
alternative ionization mechanisms, namely shocks, winds/outflows, or
photoionization by a post asymptotic giant branch (p-AGB) stellar population.
The detection of extended LINER-like emission was often taken as evidence of
ionization by stellar components but this has not been undisputed. We performed
optical integral field spectroscopic observations on the central approx. 4 kpc
of NGC 5850 using VIMOS at the VLT, which provides spatially-resolved spectra
for the gas emission and the stellar continuum. We derive and analyse emission
line and kinematic maps. We find the central few kpc of NGC 5850 to be
dominated by extended LINER-like emission. The emission-line ratios that are
sensitive to the ionization parameter increase with radial distance to the
nucleus. Therefore, the extended LINER-like emission in NGC 5850 is dominated
by ionization from distributed ionization sources, probably by stars on the
p-AGB. The LINER-like region is surrounded by emission that is classed as
'composite', likely due to a mixture of a LINER-like ionization pattern and
photoionization by low-level star formation. Two star-forming regions are
present in the 21"x19" field of view. One of them is located approximately in
the ring surrounding the kinematically decoupled core. The second one is close
to the nucleus and is the origin of a region of decreased emission line ratios
oriented radially outwards. We find the interstellar gas to have areas of steep
velocity gradients and a complex kinematic morphology, probably caused by the
lopsided (m=1) distribution of the gas. The inflow of gas toward the center
appears possible.Comment: 18 pages, 17 figures, 2 tables, accepted by 'Astronomy and
Astrophysics
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
Rapidly assessing the risks of infectious diseases to wildlife species
Predicting the likelihood of rare events is increasingly demanded by risk managers. A key challenge is dealing with different types of uncertainty, including epistemic uncertainties (lack of knowledge), stochasticity (inherent randomness) and natural variation. One potentially catastrophic event which is impacted by high levels of all three of these uncertainty types is the transmission of livestock pathogens to wildlife, particularly for endangered species. There is often a lack of basic information, e.g. about a given pathogen's presence in local livestock populations or the susceptibility of a given wildlife species to infection by the pathogen. We adapted the OIE (World Organisation for Animal Health) risk assessment framework to rapidly assess and prioritize the risks of livestock pathogens for wildlife, taking account of epistemic uncertainties, stochasticity, seasonal movement of animals and interaction between different species at different spatial and temporal scales. We demonstrate the approach using the endangered saiga antelope (Saiga tatarica tatarica) as a case study. We conclude that, in general, transmission events are likely to be rare and limited to small geographical areas; however, their impact could be high. Brucella spp. and foot-and-mouth disease virus are among those most likely to be transmitted from livestock to the Betpak-Dala saiga population
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