332 research outputs found
A Population of Compact Elliptical Galaxies Detected with the Virtual Observatory
Compact elliptical galaxies are characterized by small sizes and high stellar
densities. They are thought to form through tidal stripping of massive
progenitors. However, only a handful of them were known, preventing us from
understanding the role played by this mechanism in galaxy evolution. We present
a population of 21 compact elliptical galaxies gathered with the Virtual
Observatory. Follow-up spectroscopy and data mining, using high-resolution
images and large databases, show that all the galaxies exhibit old metal-rich
stellar populations different from those of dwarf elliptical galaxies of
similar masses but similar to those of more massive early-type galaxies,
supporting the tidal stripping scenario. Their internal properties are
reproduced by numerical simulations, which result in compact dynamically hot
remnants resembling the galaxies in our sample.Comment: 26 pages, 5 figures, 2 tables. Science in press, published in Science
Express on 1/Oct/2009. Full resolution figures in the supplementary online
material are available from the Science Magazine web-sit
\u3cem\u3eiac\u3c/em\u3e Gene Expression in the Indole-3-Acetic Acid-Degrading Soil Bacterium \u3cem\u3eEnterobacter soli\u3c/em\u3e LF7
We show for soil bacterium Enterobacter soli LF7 that the possession of an indole-3-acetic acid catabolic (iac) gene cluster is causatively linked to the ability to utilize the plant hormone indole-3-acetic acid (IAA) as a carbon and energy source. Genome-wide transcriptional profiling by mRNA sequencing revealed that these iac genes, chromosomally arranged as iacHABICDEFG and coding for the transformation of IAA to catechol, were the most highly induced (\u3e29-fold) among the relatively few (iac cluster were genes for a major facilitator superfamily protein (mfs) and enzymes of the ÎČ-ketoadipate pathway (pcaIJD-catBCA), which channels catechol into central metabolism. This entire iacHABICDEFG-mfs-pcaIJD-catBCA gene set was constitutively expressed in an iacR deletion mutant, confirming the role of iacR, annotated as coding for a MarR-type regulator and located upstream of iacH, as a repressor of iac gene expression. In E. soli LF7 carrying the DNA region upstream of iacH fused to a promoterless gfp gene, green fluorescence accumulated in response to IAA at concentrations as low as 1.6 ÎŒM. The iacH promoter region also responded to chlorinated IAA, but not other aromatics tested, indicating a narrow substrate specificity. In an iacR deletion mutant, gfp expression from the iacH promoter region was constitutive, consistent with the predicted role of iacR as a repressor. A deletion analysis revealed putative â35/â10 promoter sequences upstream of iacH, as well as a possible binding site for the IacR repressor
The rich cluster of galaxies ABCG 85.I. X-ray analysis
We present an X-ray analysis of the rich cluster ABCG 85 based on ROSAT PSPC
data. By applying an improved wavelet analysis, we show that our view of this
cluster is notably changed from what was previously believed (a main region and
a south blob). The main emission comes from the central part of the main body
of the cluster on which is superimposed that of a foreground group of galaxies.
The foreground group and the main cluster are separated (if redshifts are
cosmological) by 46 1/h_50 Mpc. The southern blob is clearly not a group: it is
resolved into X-ray emitting galaxies (in particular the second more luminous
galaxy of the main cluster). Several X-ray features are identified with bright
galaxies. We performed a spectral analysis and derived the temperature (T),
metallicity (Z) and hydrogen column density NH. The global quantities are:
T=4keV (in agreement with the velocity dispersion of 760km/s) and
. We cannot derive accurate gradients for these quantities with
our data, but there is strong evidence that the temperature is lower () and the metallicity much higher (Z ) in the very centre
(within about 50 1/h_50 kpc). We present a pixel by pixel method to model the
physical properties of the X-ray gas and derive its density distribution. We
apply classical methods to estimate the dynamical, gas and stellar masses, as
well as the cooling time and cooling flow characteristics. At the limiting
radius of the image (1.4 1/h_50 Mpc), we find _{\odot}M_{gas}/M_{Dyn}\sim 0.18 h_{50}^{-1.5}6.7\ 10^{12}M_{\odot}M/L_{V}\sim 300$.
The cooling time is estimated for different models, leading to a cooling radius
of 30-80 kpc depending on theComment: 14 pages incl 16 postscript figures available, 4 tables, corrected
stellar mass. Accepted for publication in Astronomy & Astrophysic
The rich cluster of galaxies ABCG 85. II. X-ray analysis using the ROSAT HRI
We present a new X-ray analysis mainly based on ROSAT HRI data. The HRI
spatial resolution combined with an improved wavelet analysis method and with
complementary radio and optical data provides new results compared to a
previous paper based on ROSAT PSPC data (Pislar et al. 1997). We use also
redshift data in order to identify galaxies dynamically belonging to the main
body of the cluster and/or to superimposed substructures. Various kinds of
emission are superimposed on a mean thermal X-ray emission due to the
intra-cluster gas: a) an X-ray flux excess in the centre; b) a south blob,
partially generated by individual galaxies. The mean velocity and velocity
dispersion of the galaxies located in this region are the same as those of the
cluster as a whole: it therefore does not seem to be a bound subgroup; c) West
emission due to a foreground group with self-emission from a Seyfert galaxy
located at the north-west; d) emission in the south-west due to inverse Compton
emission associated to a very steep radio source (the remnant of an active
galactic nucleus). We have examined the possibility for the central peak to be
an "unusual" galaxy, as assumed for the central galaxy of J2310-43 (Tananbaum
et al. 1997). We conclude on the existence of a cooling flow region, in which
the presence of at least three small features certainly related to cooler blobs
is revealed by the wavelet analysis. We have performed a pixel-to-pixel
modelling of the double X-ray emission. The large scale emission component is
comparable to those derived from by the PSPC data and the small scale one is
interpreted as a cooling-flow. A multiphase gas model analysis leads to a mass
deposit of 50-150 M_\odot/yr.Comment: 11 pages, 6 figures, 3 tables, LaTeX Accepted for publication in
Astronomy & Astrophysics main journa
(R1504) Second-order Modified Nonstandard Runge-Kutta and Theta Methods for One-dimensional Autonomous Differential Equations
Nonstandard finite difference methods (NSFD) are used in physical sciences to approximate solutions of ordinary differential equations whose analytical solution cannot be computed. Traditional NSFD methods are elementary stable but usually only have first order accuracy. In this paper, we introduce two new classes of numerical methods that are of second order accuracy and elementary stable. The methods are modified versions of the nonstandard two-stage explicit Runge-Kutta methods and the nonstandard one-stage theta methods with a specific form of the nonstandard denominator function. Theoretical analysis of the stability and accuracy of both modified NSFD methods is presented. Numerical simulations that concur with the theoretical findings are also presented, which demonstrate the computational advantages of the proposed new modified nonstandard finite difference methods
Universal asymptotic behavior in flow equations of dissipative systems
Based on two dissipative models, universal asymptotic behavior of flow
equations for Hamiltonians is found and discussed. Universal asymptotic
behavior only depends on fundamental bath properties but not on initial system
parameters, and the integro-differential equations possess an universal
attractor. The asymptotic flow of the Hamiltonian can be characterized by a
non-local differential equation which only depends on one parameter -
independent of the dissipative system or truncation scheme. Since the fixed
point Hamiltonian is trivial, the physical information is completely
transferred to the transformation of the observables. This yields a more stable
flow which is crucial for the numerical evaluation of correlation functions.
Furthermore, the low energy behavior of correlation functions is determined
analytically. The presented procedure can also be applied if relevant
perturbations are present as is demonstrated by evaluating dynamical
correlation functions for sub-Ohmic environments. It can further be generalized
to other dissipative systems.Comment: 15 pages, 9 figures; to appear in Phys. Rev.
A 3-D wavelet analysis of substructure in the Coma cluster: statistics and morphology
Evidence for clustering within the Coma cluster is found by means of a
multiscale analysis of the combined angular-redshift distribution. We have
compiled a catalogue of 798 galaxy redshifts from published surveys from the
region of the Coma cluster. We examine the presence of substructure and of
voids at different scales ranging from Mpc, using
subsamples of the catalogue, ranging from km/s to km/s.
Our substructure detection method is based on the wavelet transform and on the
segmentation analysis. The wavelet transform allows us to find out structures
at different scales and the segmentation method allows us a quantitative
statistical and morphological analysis of the sample. From the whole catalogue
we select a subset of 320 galaxies, with redshifts between cz=5858 km/s and
cz=8168 km/s that we identify as belonging to the central region of Coma and on
which we have performed a deeper analysis, on scales ranging from
kpc to Mpc. Our results are expressed in terms of the number of
structures or voids and their sphericity for different values of the threshold
detection and at all the scales investigated. According to our analysis, there
is strong evidence for multiple hierarchical substructure, on scales ranging
from a few hundreds of kpc to about Mpc. The morphology of these
substructures is rather spherical. On the scale of kpc we find two
main subclusters which where also found before, but our wavelet analysis shows
even more substructures, whose redshift position is approximatively marked by
these bright galaxies: NGC 4934 & 4840, 4889, 4898 & 4864, 4874 & 4839, 4927,
4875.Comment: 24 pages, 6 figures. ApJ (Main Journal), accepted for publication.
Added one section on statistical tests and slightly modified text and
abstrac
Memory-multi-fractional Brownian motion with continuous correlations
We propose a generalization of the widely used fractional Brownian motion
(FBM), memory-multi-FBM (MMFBM), to describe viscoelastic or persistent
anomalous diffusion with time-dependent memory exponent in a
changing environment. In MMFBM the built-in, long-range memory is continuously
modulated by . We derive the essential statistical properties of
MMFBM such as response function, mean-squared displacement (MSD),
autocovariance function, and Gaussian distribution. In contrast to existing
forms of FBM with time-varying memory exponents but reset memory structure, the
instantaneous dynamic of MMFBM is influenced by the process history, e.g., we
show that after a step-like change of the scaling exponent of the
MSD after the -step may be determined by the value of
before the change. MMFBM is a versatile and useful process for correlated
physical systems with non-equilibrium initial conditions in a changing
environment.Comment: 15 pages, 10 figures, RevTe
A Wavelet-Based Algorithm for the Spatial Analysis of Poisson Data
Wavelets are scaleable, oscillatory functions that deviate from zero only
within a limited spatial regime and have average value zero. In addition to
their use as source characterizers, wavelet functions are rapidly gaining
currency within the source detection field. Wavelet-based source detection
involves the correlation of scaled wavelet functions with binned,
two-dimensional image data. If the chosen wavelet function exhibits the
property of vanishing moments, significantly non-zero correlation coefficients
will be observed only where there are high-order variations in the data; e.g.,
they will be observed in the vicinity of sources.
In this paper, we describe the mission-independent, wavelet-based source
detection algorithm WAVDETECT, part of the CIAO software package. Aspects of
our algorithm include: (1) the computation of local, exposure-corrected
normalized (i.e. flat-fielded) background maps; (2) the correction for exposure
variations within the field-of-view; (3) its applicability within the
low-counts regime, as it does not require a minimum number of background counts
per pixel for the accurate computation of source detection thresholds; (4) the
generation of a source list in a manner that does not depend upon a detailed
knowledge of the point spread function (PSF) shape; and (5) error analysis.
These features make our algorithm considerably more general than previous
methods developed for the analysis of X-ray image data, especially in the low
count regime. We demonstrate the algorithm's robustness by applying it to
various images.Comment: Accepted for publication in Ap. J. Supp. (v. 138 Jan. 2002). 61
pages, 23 figures, expands to 3.8 Mb. Abstract abridged for astro-ph
submissio
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