347 research outputs found
Near-infrared morphologies of the host galaxies of narrow-line Seyfert 1 galaxies
We present J-band near-infrared (NIR) imaging of the host galaxies of nine narrow-line Seyfert 1 galaxies (NLS1). Based on highfrequency radio observations at 37 GHz, seven of them could host powerful jets that are most likely relativistic. Host galaxy morphology studies of NLS1 galaxies are scarce, but exceedingly important for understanding the seemingly heterogeneous nature of the NLS1 population as well as their evolution and place in the active galactic nuclei (AGN) scheme. Increasing the sample size is essential for achieving statistically significant results. We determine the morphological types of the host galaxies by performing photometric decomposition of NIR images using a 2D image decomposition algorithm GALFIT. We were able to sufficiently model five of the nine host galaxies. Based on the fitting parameters, mainly the Sersic index, all five are disk-like galaxies. Sources with clearly distinguishable bulge components all have pseudo-bulges, and four out of five sources show a component resembling a bar. A surprisingly large fraction, three out of five, show signs of interaction or disturbed morphology. Our results suggest that spiral galaxies with pseudo-bulges are able to launch and maintain powerful jets. They also imply that interaction - mainly minor mergers - may have a role in initially triggering higher levels of nuclear activity in NLS1 galaxies. Furthermore, our results support the heterogeneous nature of the NLS1 class and indicate that this diversity is caused by different evolutionary stages, possibly due to mergers
Temporal profiles of age-dependent changes in cytokine mRNA expression and glial cell activation after status epilepticus in postnatal rat hippocampus
<p>Abstract</p> <p>Background</p> <p>Status epilepticus (SE) is proposed to lead to an age-dependent acute activation of a repertoire of inflammatory processes, which may contribute to neuronal damage in the hippocampus. The extent and temporal profiles of activation of these processes are well known in the adult brain, but less so in the developing brain. We have now further elucidated to what extent inflammation is activated by SE by investigating the acute expression of several cytokines and subacute glial reactivity in the postnatal rat hippocampus.</p> <p>Methods</p> <p>SE was induced by an intraperitoneal (i.p.) injection of kainic acid (KA) in 9- and 21-day-old (P9 and P21) rats. The mRNA expression of interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-ι), interleukin-10 (IL-10), matrix metalloproteinase-9 (MMP-9), glial-derived neurotrophic factor (GDNF), interferon gamma (IFN-γ), and transforming growth factor-beta 1 (TGF-β1) were measured from 4 h up to 3 days after KA injection with real-time quantitative PCR (qPCR). IL-1β protein expression was studied with ELISA, GFAP expression with western blotting, and microglial and astrocyte morphology with immunohistochemistry 3 days after SE.</p> <p>Results</p> <p>SE increased mRNA expression of IL-1β, TNF-ι and IL-10 mRNA in hippocampus of both P9 and P21 rats, their induction being more rapid and pronounced in P21 than in P9 rats. MMP-9 expression was augmented similarly in both age groups and GDNF expression augmented only in P21 rats, whereas neither IFN-γ nor TGF-β1 expression was induced in either age group. Microglia and astrocytes exhibited activated morphology in the hippocampus of P21 rats, but not in P9 rats 3 d after SE. Microglial activation was most pronounced in the CA1 region and also detected in the basomedial amygdala.</p> <p>Conclusion</p> <p>Our results suggest that SE provokes an age-specific cytokine expression in the acute phase, and age-specific glial cell activation in the subacute phase as verified now in the postnatal rat hippocampus. In the juvenile hippocampus, transient increases in cytokine mRNA expression after SE, in contrast to prolonged glial reactivity and region-specific microglial activity after SE, suggest that the inflammatory response is changed from a fulminant and general initial phase to a more moderate and specific subacute response.</p
Radio jets and gamma-ray emission in radio-silent narrow-line Seyfert 1 galaxies
We have detected six narrow-line Seyfert 1 (NLS1) galaxies at 37 GHz that
were previously classified as radio silent and two that were classified as
radio quiet. These detections reveal the presumption that NLS1 galaxies
labelled radio quiet or radio silent and hosted by spiral galaxies are unable
to launch jets to be incorrect. The detections are a plausible indicator of the
presence of a powerful, most likely relativistic jet because this intensity of
emission at 37 GHz cannot be explained by, for example, radiation from
supernova remnants. Additionally, one of the detected NLS1 galaxies is a newly
discovered source of gamma rays and three others are candidates for future
detections.Comment: 5 pages, 1 figure, 37 GHz data available in electronic form at the
CDS. Accepted in A&
37 GHz observations of narrow-line Seyfert 1 galaxies
Observations at 37 GHz, performed at Mets\"ahovi Radio Observatory, are
presented for a sample of 78 radio-loud and radio-quiet narrow-line Seyfert 1
(NLS1) galaxies, together with additional lower and higher frequency radio data
from RATAN-600, Owens Valley Radio Observatory, and the Planck satellite. Most
of the data have been gathered between February 2012 and April 2015 but for
some sources even longer lightcurves exist. The detection rate at 37 GHz is
around 19%, comparable to other populations of active galactic nuclei presumed
to be faint at radio frequencies, such as BL Lac objects. Variability and
spectral indices are determined for sources with enough detections. Based on
the radio data, many NLS1 galaxies show a blazar-like radio spectra exhibiting
significant variability. The spectra at a given time are often inverted or
convex. The source of the high-frequency radio emission in NLS1 galaxies,
detected at 37 GHz, is most probably a relativistic jet rather than star
formation. Jets in NLS1 galaxies are therefore expected to be a much more
common phenomenon than earlier assumed.Comment: Accepted for publication in A&A. Table of 37 GHz data will be
available at the CDS soo
SDSS J211852.96-073227.5: The first non-local, interacting, late-type intermediate Seyfert galaxy with relativistic jets
It has been often suggested that a tangible relation exists between relativistic jets in active galactic nuclei (AGN) and the morphology of their host galaxies. In particular, relativistic jets may commonly be related to merging events. Here we present for the first time a detailed spectroscopic and morphological analysis of a Seyfert galaxy, SDSS J211852.96-073227.5, at z=0.26. This source has previously been classified as a gamma-ray emitting narrow-line Seyfert 1 galaxy. We re-observed it with the 6.5 m Clay Telescope and these new, high-quality spectroscopic data have revealed that it is actually an intermediate-type Seyfert galaxy. Furthermore, the results of modelling the Ks-band near-infrared images obtained with the 6.5 m Baade Telescope indicate that the AGN is hosted by a late-type galaxy in an interacting system, strengthening the suggested connection between galaxy interactions and relativistic jets
Large-scale environments of narrow-line Seyfert 1 galaxies
Studying large-scale environments of narrow-line Seyfert 1 (NLS1) galaxies gives a new perspective on their properties, particularly their radio loudness. The large-scale environment is believed to have an impact on the evolution and intrinsic properties of galaxies, however, NLS1 sources have not been studied in this context before. We have a large and diverse sample of 1341 NLS1 galaxies and three separate environment data sets constructed using Sloan Digital Sky Survey. We use various statistical methods to investigate how the properties of NLS1 galaxies are connected to the large-scale environment, and compare the large-scale environments of NLS1 galaxies with other active galactic nuclei (AGN) classes, for example, other jetted AGN and broad-line Seyfert 1 (BLS1) galaxies, to study how they are related. NLS1 galaxies reside in less dense environments than any of the comparison samples, thus confirming their young age. The average large-scale environment density and environmental distribution of NLS1 sources is clearly different compared to BLS1 galaxies, thus it is improbable that they could be the parent population of NLS1 galaxies and unified by orientation. Within the NLS1 class there is a trend of increasing radio loudness with increasing large-scale environment density, indicating that the large-scale environment affects their intrinsic properties. Our results suggest that the NLS1 class of sources is not homogeneous, and furthermore, that a considerable fraction of them are misclassified. We further support a published proposal to replace the traditional classification to radio-loud, and radio-quiet or radio-silent sources with a division into jetted and non-jetted sources
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