771 research outputs found
The flux ratio of the [OIII] 5007,4959 lines in AGN: Comparison with theoretical calculations
By taking into account relativistic corrections to the magnetic dipole
operator, the theoretical [OIII] 5006.843/4958.511 line intensity ratio of 2.98
is obtained. In order to check this new value using AGN spectra we present the
measurements of the flux ratio of the [OIII] 4959,5007 emission lines for a
sample of 62 AGN, obtained from the Sloan Digital Sky Survey (SDSS) Database
and from published observations. We select only high signal-to-noise ratio
spectra for which the line shapes of the [OIII] 4959,5007 lines are the same.
We obtained an averaged flux ratio of 2.993 +/- 0.014, which is in a good
agreement with the theoretical one.Comment: Accepted for publication in the MNRA
Spectral monitoring of AGNs: Preliminary results for Ark 564 and Arp 102B
We present preliminary results of the long term spectral monitoring of two
active galactic nuclei with different broad line shapes: Ark 564 and Arp 102B.
Ark 564 is a bright nearby narrow line Syfert 1 (NLS1) galaxy with relatively
narrow permitted optical emission lines and a high FeII/H ratio, while
Arp 102B is a nearby broad-line radio galaxy with broad double-peaked Balmer
emission lines. The spectra of Ark 564 were observed during 11-year period
(1999-2009) and the spectra of Arp 102B in the 12-year period (1998-2009), with
SAO 6-m and 1-m telescopes (Russia) and the GHAO 2.1-m telescope (Cananea,
Mexico).Comment: Presented on "8th Serbian Conference on Spectral Line Shapes in
Astrophysics". In revised version minor changes in the tex
Long-term variability of the optical spectra of NGC 4151: II. Evolution of the broad Ha and Hb emission-line profiles
Results of the long-term (11 years, from 1996 to 2006) H and H
line variations of the active galactic nucleus of NGC 4151 are presented. High
quality spectra (S/N>50 and R~8A) of H and H were investigated.
We analyzed line profile variations during monitoring period. Comparing the
line profiles of H and H, we studied different details (bumps,
absorption features) in the line profiles. The variations of the different
H and H line profile segments have been investigated. Also, we
analyzed the Balmer decrement for whole line and for line segments. We found
that the line profiles were strongly changing during the monitoring period,
showing blue and red asymmetries. This indicates a complex BLR geometry of NGC
4151 with, at least, three kinematically distinct regions: one that contributes
to the blue line wing, one to the line core and one to the red line wing. Such
variation can be caused by an accelerating outflow starting very close to the
black hole, where the red part may come from the region {closer to the black
hole than the blue part, which is coming} from the region having the highest
outflow velocities. Taking into account the fact that the BLR of NGC 4151 has a
complex geometry (probably affected by an outflow) and that a portion of the
broad line emission seems to have not a pure photoionization origin, one can
ask the question whether the study of the BLR by reverberation mapping may be
valid in the case of this galaxy.Comment: 24 pages, 18 figures, accepted for publications in A&
Spectral optical monitoring of the double peaked emission line AGN Arp 102B: II. Variability of the broad line properties
We investigate a long-term (26 years, from 1987 to 2013) variability in the
broad spectral line properties of the radio galaxy Arp 102B, an active galaxy
with broad double-peaked emission lines. We use observations presented in Paper
I (Shapovalova et al. 2013) in the period from 1987 to 2011, and a new set of
observations performed in 2012--2013. To explore the BLR geometry, and clarify
some contradictions about the nature of the BLR in Arp 102B we explore
variations in the H and H line parameters during the monitored
period. We fit the broad lines with three broad Gaussian functions finding the
positions and intensities of the blue and red peaks in H and H.
Additionally we fit averaged line profiles with the disc model. We find that
the broad line profiles are double-peaked and have not been changed
significantly in shapes, beside an additional small peak that, from time to
time can be seen in the blue part of the H line. The positions of the
blue and red peaks { have not changed significantly during the monitored
period. The H line is broader than H line in the monitored
period. The disc model is able to reproduce the H and H broad
line profiles, however, observed variability in the line parameters are not in
a good agreement with the emission disc hypothesis. It seems that the BLR of
Arp 102B has a disc-like geometry, but the role of an outflow can also play an
important role in observed variation of the broad line properties.Comment: 17 pages, Accepted for publication in A&
Spectroscopy and spectropolarimetry of AGN: from observations to modelling
Active galactic nuclei (AGN) are one of the most luminous objects in the
Universe, emitting powerful continuum and line emission across all wavelength
bands. They represent an important link in the investigations of the galaxy
evolution and cosmology. The resolving of the AGN inner structure is still a
difficult task with current instruments, therefore the spectroscopy and
spectropolarimetry are crucial tools to investigate these objects and their
components, such as the properties of the supermassive black hole, the broad
line region, and the dusty torus. In this review, we present the results of the
project "Astrophysical spectroscopy of extragalactic objects", from the
observations, data processing and analysis, to the modelling of different
regions in AGN.Comment: Proceedings of the Serbian Astronomical Conference 201
The LSST AGN Data Challenge: Selection methods
Development of the Rubin Observatory Legacy Survey of Space and Time (LSST)
includes a series of Data Challenges (DC) arranged by various LSST Scientific
Collaborations (SC) that are taking place during the projects preoperational
phase. The AGN Science Collaboration Data Challenge (AGNSCDC) is a partial
prototype of the expected LSST AGN data, aimed at validating machine learning
approaches for AGN selection and characterization in large surveys like LSST.
The AGNSC-DC took part in 2021 focusing on accuracy, robustness, and
scalability. The training and the blinded datasets were constructed to mimic
the future LSST release catalogs using the data from the Sloan Digital Sky
Survey Stripe 82 region and the XMM-Newton Large Scale Structure Survey region.
Data features were divided into astrometry, photometry, color, morphology,
redshift and class label with the addition of variability features and images.
We present the results of four DC submitted solutions using both classical and
machine learning methods. We systematically test the performance of supervised
(support vector machine, random forest, extreme gradient boosting, artificial
neural network, convolutional neural network) and unsupervised (deep embedding
clustering) models when applied to the problem of classifying/clustering
sources as stars, galaxies or AGNs. We obtained classification accuracy 97.5%
for supervised and clustering accuracy 96.0% for unsupervised models and 95.0%
with a classic approach for a blinded dataset. We find that variability
features significantly improve the accuracy of the trained models and
correlation analysis among different bands enables a fast and inexpensive first
order selection of quasar candidatesComment: Accepted by ApJ. 21 pages, 14 figures, 5 table
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