348 research outputs found
Regression games
The solution of a TU cooperative game can be a distribution of the value of the grand coalition, i.e. it can be a distribution of the payo (utility) all the players together achieve. In a regression model, the evaluation of the explanatory variables can be a distribution of the overall t, i.e. the t of the model every regressor variable is involved. Furthermore, we can take regression models as TU cooperative games where the explanatory (regressor) variables are the players. In this paper we introduce the class of regression games, characterize it and apply the Shapley value to evaluating the explanatory variables in regression models. In order to support our approach we consider Young (1985)'s axiomatization of the Shapley value, and conclude that the Shapley value is a reasonable tool to evaluate the explanatory variables of regression models
Environment status of blue compact galaxies and trigger of star formation
(abridged) The work studies active star formation (SF) and a possible trigger
of SF bursts due to gravitational interaction. Following the study by Taylor et
al. we extend the search for possible disturbing galaxies of various masses to
a much larger sample of 86 BCGs from the sky region of Second Byurakan survey.
The sample under study is separated by the criteria: EW([O III]5007 > 45 A and
V < 6,000 km/s and should be representative of all low-mass galaxies which
experience SF bursts. We argue that the moderate tidal disturbers should be
taken into account, and incorporate the respective range of distances in the
search for disturbing neighbours. The majority of the neighbours in the
vicinity of the studied BCGs are found through the study of their environment
among UZC galaxies, and the follow-up careful search of the fainter galaxies in
the NED database. For the remaining BCGs, the neighbouring galaxies are found
based on the results of the 6-m telescope spectroscopy. By studing the data on
the radial velocities of galaxies in the vicinity of BCGs we found: 1) 33 of
the studied BCGs (38.5 %) are associated with significantly brighter galaxies
(DB > 1.5 mag); 2) 23 BCGs (26.5%) have neighbours either of comparable or
significantly lower brightness; 3) 14 of the studied BCGs (16%) with no evident
associated galaxy are either certain, or probable, mergers. We conclude that in
\~80% (or more) BCGs from the studied sample, the SF bursts are triggered
either by tidal action of various strengths from other galaxies, or due to
mergers of low-mass galaxies. We briefly discuss the implications of our main
conclusion for evolutionary links of BCGs to other types of low-mass galaxies.
Among the ``isolated'' BCGs (without a bright neighbour) 43+-10% are probably
disturbed by dwarf galaxies and 26+-8% have a merger morphology.Comment: 22 pages, 7 figures, accepted to A&A on March 26, 200
Sampling, Intervention, Prediction, Aggregation: A Generalized Framework for Model-Agnostic Interpretations
Model-agnostic interpretation techniques allow us to explain the behavior of
any predictive model. Due to different notations and terminology, it is
difficult to see how they are related. A unified view on these methods has been
missing. We present the generalized SIPA (sampling, intervention, prediction,
aggregation) framework of work stages for model-agnostic interpretations and
demonstrate how several prominent methods for feature effects can be embedded
into the proposed framework. Furthermore, we extend the framework to feature
importance computations by pointing out how variance-based and
performance-based importance measures are based on the same work stages. The
SIPA framework reduces the diverse set of model-agnostic techniques to a single
methodology and establishes a common terminology to discuss them in future
work
SBS 0335-052W - an Extremely Low Metallicity Dwarf Galaxy
We present Multiple Mirror Telescope (MMT) and Keck II telescope
spectrophotometry and 3.5m Calar Alto telescope R, I photometry of the western
component of the extremely low-metallicity blue compact galaxy SBS 0335-052.
The components, separated by 22 kpc, appear to be members of a unique,
physically connected system. It is shown that SBS 0335-052W consists of at
least three stellar clusters and has the same redshift as SBS 0335-052. The
oxygen abundance in its two brightest knots is extremely low, 12+log(O/H)=
7.22+/-0.03 and 7.13+/-0.08, respectively. These values are lower than in SBS
0335-052 and are nearly the same as those in I Zw 18. The (R-I) color profiles
are very blue in both galaxies due to the combined effects of ionized gas and a
young stellar population emission. We argue that SBS 0335-052W is likely to be
a nearby, young dwarf galaxy.Comment: 18 pages, 4 EPS figures, to appear in ApJ, 1 July 199
The Hamburg/SAO Survey for Emission-Line Galaxies. III. The Third List of 81 Galaxies
We present the third list with results {Tables 2 to 6 are available only in
electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html. Figures A1 to
A9 will be made available only in the electronic version of the journal.} of
the Hamburg/SAO Survey for Emission-Line Galaxies (HSS therein, SAO - Special
Astrophysical Observatory, Russia). This survey is based on the digitized
objective-prism photoplate database of the Hamburg Quasar Survey (HQS).
Here, we present new spectroscopic results of candidates which were obtained
in 1998 with the 2.1 m KPNO and the 2.2 m Calar Alto telescopes. All candidates
are selected in the declination band +35 to +40.
The follow-up spectroscopy with the 2 m class telescopes confirmed 85
emission-line objects out of 113 observed candidates and allowed their
quantitative spectral classification. For 80 of them, the redshifts are
determined for the first time. For 5 previously known ELGs, line ratios are
presented for the first time. We could classify 55 out of the 85 emission-line
objects as BCG/H{\sc ii} galaxies or probable BCGs, 4 - as QSOs, 6 - as Seyfert
galaxies, 1 - as super-association in a subluminous spiral galaxy, and 11 are
low-excitation objects - either starburst nuclear (SBN), or dwarf amorphous
nuclear starburst galaxies (DANS). We could not classify 8 ELGs. Further, for 8
more galaxies we did not detect any significant emission lines.Comment: A&A latex file with 8 tables and one figure. Astron. Astrophys.
Suppl. accepted 200
Wide Field Imaging. I. Applications of Neural Networks to object detection and star/galaxy classification
[Abriged] Astronomical Wide Field Imaging performed with new large format CCD
detectors poses data reduction problems of unprecedented scale which are
difficult to deal with traditional interactive tools. We present here NExt
(Neural Extractor): a new Neural Network (NN) based package capable to detect
objects and to perform both deblending and star/galaxy classification in an
automatic way. Traditionally, in astronomical images, objects are first
discriminated from the noisy background by searching for sets of connected
pixels having brightnesses above a given threshold and then they are classified
as stars or as galaxies through diagnostic diagrams having variables choosen
accordingly to the astronomer's taste and experience. In the extraction step,
assuming that images are well sampled, NExt requires only the simplest a priori
definition of "what an object is" (id est, it keeps all structures composed by
more than one pixels) and performs the detection via an unsupervised NN
approaching detection as a clustering problem which has been thoroughly studied
in the artificial intelligence literature. In order to obtain an objective and
reliable classification, instead of using an arbitrarily defined set of
features, we use a NN to select the most significant features among the large
number of measured ones, and then we use their selected features to perform the
classification task. In order to optimise the performances of the system we
implemented and tested several different models of NN. The comparison of the
NExt performances with those of the best detection and classification package
known to the authors (SExtractor) shows that NExt is at least as effective as
the best traditional packages.Comment: MNRAS, in press. Paper with higher resolution images is available at
http://www.na.astro.it/~andreon/listapub.htm
The Close Environment of Seyfert Galaxies and Its Implication for Unification Models
This paper presents a statistical analysis of the circumgalactic environment
of nearby Seyfert galaxies based on a computer-aided search of companion
galaxies on the Digitized Sky Survey (DSS). An intrinsic difference between the
environment of Seyfert 1 and Seyfert 2 galaxies, suggested by previous work, is
confirmed as statistically significant. For Seyfert 2 galaxies we find a
significant excess of large companions (diameter of companion >= 10 Kpc) within
a search radius <= 100 Kpc of projected linear distance, as well as within a
search radius equal to three times the diameter \ds of each Seyfert galaxy. For
Seyfert 1 galaxies there is no clear evidence of any excess of companion
galaxies neither within 100 Kpc, nor within 3\ds. For all samples the number of
companions suggests a markedly non-Poissonian distribution for galaxies on
scales <= 100 Kpc. This difference in environment is not compatible with the
simplest formulation of the Unification Model for Seyferts: both types 1 and 2
should be intrinsicaly alike, the only difference being due to orientation of
an obscuring torus. We propose an alternative formulation.Comment: 1 figure, accepted for publication in Astrophysical Journal Letter
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