243,978 research outputs found
The Iron K Line Profile of IRAS 18325-5926
IRAS 18325-5926 is an X-ray bright, Compton-thin, type-2 Seyfert galaxy and
it was the first Seyfert 2 in which the presence of a broad Fe K-alpha emission
line was claimed. However, although the structure of the Fe line appears broad,
there is tentative evidence that it may comprise multiple lines. Nevertheless,
previous analyses have only consisted of fitting standalone broad components to
the Fe K band. Here, we have analyzed all available X-ray CCD data from Suzaku,
XMM-Newton and ASCA to fully investigate the nature of the emission complex by
testing broad-band physical models and alternative hypotheses. We find that
both a model consisting of broad, blurred reflection from an ionized accretion
disc and a model consisting of cold, neutral reflection plus narrow emission
lines from highly-ionized photoionized gas (log \xi = 3.5) offer statistically
comparable fits to the data although the true reality of the Fe line cannot
currently be determined with existing data. However, it is hoped that better
quality data and improved photon statistics in the Fe K band will allow a more
robust distinction between models to be made.Comment: Accepted by MNRAS; 13 pages; 10 figures; 2 table
Fitting an Equation to Data Impartially
© 2023 by the author. Licensee MDPI, Basel, Switzerland. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/We consider the problem of fitting a relationship (e.g., a potential scientific law) to data involving multiple variables. Ordinary (least squares) regression is not suitable for this because the estimated relationship will differ according to which variable is chosen as being dependent, and the dependent variable is unrealistically assumed to be the only variable which has any measurement error (noise). We present a very general method for estimating a linear functional relationship between multiple noisy variables, which are treated impartially, i.e., no distinction between dependent and independent variables. The data are not assumed to follow any distribution, but all variables are treated as being equally reliable. Our approach extends the geometric mean functional relationship to multiple dimensions. This is especially useful with variables measured in different units, as it is naturally scale invariant, whereas orthogonal regression is not. This is because our approach is not based on minimizing distances, but on the symmetric concept of correlation. The estimated coefficients are easily obtained from the covariances or correlations, and correspond to geometric means of associated least squares coefficients. The ease of calculation will hopefully allow widespread application of impartial fitting to estimate relationships in a neutral way.Peer reviewe
The Gaia-ESO Survey: dynamics of ionized and neutral gas in the Lagoon nebula (M8)
We present a spectroscopic study of the dynamics of the ionized and neutral
gas throughout the Lagoon nebula (M8), using VLT/FLAMES data from the Gaia-ESO
Survey. We explore the connections between the nebular gas and the stellar
population of the associated star cluster NGC6530. We characterize through
spectral fitting emission lines of H-alpha, [N II] and [S II] doublets, [O
III], and absorption lines of sodium D doublet, using data from the
FLAMES/Giraffe and UVES spectrographs, on more than 1000 sightlines towards the
entire face of the Lagoon nebula. Gas temperatures are derived from line-width
comparisons, densities from the [S II] doublet ratio, and ionization parameter
from H-alpha/[N II] ratio. Although doubly-peaked emission profiles are rarely
found, line asymmetries often imply multiple velocity components along the line
of sight. This is especially true for the sodium absorption, and for the [O
III] lines. Spatial maps for density and ionization are derived, and compared
to other known properties of the nebula and of its massive stars 9 Sgr,
Herschel 36 and HD 165052 which are confirmed to provide most of the ionizing
flux. The detailed velocity fields across the nebula show several expanding
shells, related to the cluster NGC6530, the O stars 9 Sgr and Herschel 36, and
the massive protostar M8East-IR. The origins of kinematical expansion and
ionization of the NGC6530 shell appear to be different. We are able to put
constrains on the line-of-sight (relative or absolute) distances between some
of these objects and the molecular cloud. The large obscuring band running
through the middle of the nebula is being compressed by both sides, which might
explain its enhanced density. We also find an unexplained large-scale velocity
gradient across the entire nebula. At larger distances, the transition from
ionized to neutral gas is studied using the sodium lines.Comment: 26 pages, 31 figures, accepted on Astronomy and Astrophysics journa
Clustering Students Based on Gamification User Types and Learning Styles
The aim of this study is clustering students according to their gamification
user types and learning styles with the purpose of providing instructors with a
new perspective of grouping students in case of clustering which cannot be done
by hand when there are multiple scales in data. The data used consists of 251
students who were enrolled at a Turkish state university. When grouping
students, K-means algorithm has been utilized as clustering algorithm. As for
determining the gamification user types and learning styles of students,
Gamification User Type Hexad Scale and Grasha-Riechmann Student Learning Style
Scale have been used respectively. Silhouette coefficient is utilized as
clustering quality measure. After fitting the algorithm in several ways,
highest Silhouette coefficient obtained was 0.12 meaning that results are
neutral but not satisfactory. All the statistical operations and data
visualizations were made using Python programming language.Comment: 9 pages, 3 figure
Nuclear gas dynamics in Arp 220 - sub-kiloparsec scale atomic hydrogen disks
We present new, high angular resolution (~0.22") MERLIN observations of
neutral hydrogen (HI) absorption and 21-cm radio continuum emission across the
central ~900 parsecs of the ultraluminous infrared galaxy, Arp220. Spatially
resolved HI absorption is detected against the morphologically complex and
extended 21-cm radio continuum emission, consistent with two counterrotating
disks of neutral hydrogen, with a small bridge of gas connecting the two.
We propose a merger model in which the two nuclei represent the galaxy cores
which have survived the initial encounter and are now in the final stages of
merging, similar to conclusions drawn from previous CO studies (Sakamoto,
Scoville & Yun 1999). However, we suggest that instead of being coplanar with
the main CO disk (in which the eastern nucleus is embedded), the western
nucleus lies above it and, as suggested by bridge of HI connecting the two
nuclei, will soon complete its final merger with the main disk. We suggest that
the collection of radio supernovae (RSN) detected in VLBA studies in the more
compact western nucleus represent the second burst of star formation associated
with this final merger stage and that free-free absorption due to ionised gas
in the bulge-like component can account for the observed RSN distribution.
(Abridged)Comment: 26 pages including 8 figures and 1 table; accepted for publication in
Ap
Interstellar abundances in the neutral and ionized gas of NGC604
We present FUSE spectra of the giant HII region NGC604 in the spiral galaxy
M33. Chemical abundances are derived from far-UV absorption lines and are
compared to those derived from optical emission lines. We derived the column
densities of HI, NI, OI, SiII, PII, ArI, and FeII, fitting the line profiles
with either a single component or several components. Our net results, assuming
a single component, show that N, O, Si, and Ar are apparently underabundant in
the neutral phase by a factor of 10 or more with respect to the ionized phase,
while Fe is the same. However, we discuss the possibility that the absorption
lines are made of individual unresolved components, and find that only PII,
ArI, and FeII lines should not be affected by the presence of hidden saturated
components, while NI, OI, and SiII might be much more affected. If N, O, and Si
are actually underabundant in the neutral gas of NGC604 with respect to the
ionized gas, this would confirm earlier results obtained for the blue compact
dwarfs. However, a deeper analysis focused on P, Ar, and Fe mitigates the above
conclusion and indicates that the neutral gas and ionized gas could have
similar abundances.Comment: Accepted for publication in A&
Dense 3D Face Correspondence
We present an algorithm that automatically establishes dense correspondences
between a large number of 3D faces. Starting from automatically detected sparse
correspondences on the outer boundary of 3D faces, the algorithm triangulates
existing correspondences and expands them iteratively by matching points of
distinctive surface curvature along the triangle edges. After exhausting
keypoint matches, further correspondences are established by generating evenly
distributed points within triangles by evolving level set geodesic curves from
the centroids of large triangles. A deformable model (K3DM) is constructed from
the dense corresponded faces and an algorithm is proposed for morphing the K3DM
to fit unseen faces. This algorithm iterates between rigid alignment of an
unseen face followed by regularized morphing of the deformable model. We have
extensively evaluated the proposed algorithms on synthetic data and real 3D
faces from the FRGCv2, Bosphorus, BU3DFE and UND Ear databases using
quantitative and qualitative benchmarks. Our algorithm achieved dense
correspondences with a mean localisation error of 1.28mm on synthetic faces and
detected anthropometric landmarks on unseen real faces from the FRGCv2
database with 3mm precision. Furthermore, our deformable model fitting
algorithm achieved 98.5% face recognition accuracy on the FRGCv2 and 98.6% on
Bosphorus database. Our dense model is also able to generalize to unseen
datasets.Comment: 24 Pages, 12 Figures, 6 Tables and 3 Algorithm
The Hard X-Ray View of Reflection, Absorption, and the Disk-Jet Connection in the Radio-Loud AGN 3C 33
We present results from Suzaku and Swift observations of the nearby radio
galaxy 3C 33, and investigate the nature of absorption, reflection, and jet
production in this source. We model the 0.5-100 keV nuclear continuum with a
power law that is transmitted either through one or more layers of pc-scale
neutral material, or through a modestly ionized pc-scale obscurer. The standard
signatures of reflection from a neutral accretion disk are absent in 3C 33:
there is no evidence of a relativistically blurred Fe K emission line,
and no Compton reflection hump above 10 keV. We find the upper limit to the
neutral reflection fraction is R<0.41 for an e-folding energy of 1 GeV. We
observe a narrow, neutral Fe K line, which is likely to originate at
least 2,000 R_s from the black hole. We show that the weakness of reflection
features in 3C 33 is consistent with two interpretations: either the inner
accretion flow is highly ionized, or the black-hole spin configuration is
retrograde with respect to the accreting material.Comment: 12 pages, 11 figures, 4 tables. Accepted for publication in Ap
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