17,483 research outputs found
The Galaxy Population of Low-Redshift Abell Clusters
We present a study of the luminosity and color properties of galaxies
selected from a sample of 57 low-redshift Abell clusters. We utilize the
non-parametric dwarf-to-giant ratio (DGR) and the blue galaxy fraction (fb) to
investigate the clustercentric radial-dependent changes in the cluster galaxy
population. Composite cluster samples are combined by scaling the counting
radius by r200 to minimize radius selection bias. The separation of galaxies
into a red and blue population was achieved by selecting galaxies relative to
the cluster color-magnitude relation. The DGR of the red and blue galaxies is
found to be independent of cluster richness (Bgc), although the DGR is larger
for the blue population at all measured radii. A decrease in the DGR for the
red and red+blue galaxies is detected in the cluster core region, while the
blue galaxy DGR is nearly independent of radius. The fb is found not to
correlate with Bgc; however, a steady decline toward the inner-cluster region
is observed for the giant galaxies. The dwarf galaxy fb is approximately
constant with clustercentric radius except for the inner cluster core region
where fb decreases. The clustercentric radial dependence of the DGR and the
galaxy blue fraction, indicates that it is unlikely that a simple scenario
based on either pure disruption or pure fading/reddening can describe the
evolution of infalling dwarf galaxies; both outcomes are produced by the
cluster environment.Comment: 28 pages, 6 figures, accepted for publication in Ap
Luminosity Distributions within Rich Clusters - III: A comparative study of seven Abell/ACO clusters
We recover the luminosity distributions over a wide range of absolute
magnitude (-24.5 < M_{R} < -16.5) for a sample of seven rich southern galaxy
clusters. We find a large variation in the ratio of dwarf to giant galaxies,
DGR: 0.8\le \le 3.1. This variation is shown to be inconsistent with a
ubiquitous cluster luminosity function. The DGR shows a smaller variation from
cluster to cluster in the inner regions (r \ls 0.56 Mpc). Outside these regions
we find the DGR to be strongly anti-correlated with the mean local projected
galaxy density with the DGR increasing towards lower densities. In addition the
DGR in the outer regions shows some correlation with Bautz-Morgan type. Radial
analysis of the clusters indicate that the dwarf galaxies are less centrally
clustered than the giants and form a significant halo around clusters. We
conclude that measurements of the total cluster luminosity distribution based
on the inner core alone are likely to be severe underestimates of the dwarf
component, the integrated cluster luminosity and the contribution of galaxy
masses to the cluster's total mass. Further work is required to quantify this.
The observational evidence that the unrelaxed, lower density outer regions of
clusters are dwarf-rich, adds credence to the recent evidence and conjecture
that the field is a predominantly dwarf rich environment and that the dwarf
galaxies are under-represented in measures of the local field luminosity
function.Comment: 31 pages including 11 figures. Also available from
http://star-www.st-and.ac.uk/~spd3/bib.htm
Tracking Down a Critical Halo Mass for Killing Galaxies through the Growth of the Red-Sequence
Red-sequence galaxies record the history of terminated star-formation in the
Universe and can thus provide important clues to the mechanisms responsible for
this termination. We construct composite samples of published cluster and field
galaxy photometry in order to study the build-up of galaxies on the
red-sequence, as parameterised by the dwarf-to-giant ratio (DGR). We find that
the DGR in clusters is higher than that of the field at all redshifts, implying
that the faint end of the red-sequence was established first in clusters. We
find that the DGR evolves with redshift for both samples, consistent with the
``down-sizing'' picture of star formation. We examine the predictions of
semi-analytic models for the DGR and find that neither the magnitude of its
environmental dependence nor its evolution is correctly predicted in the
models. Red-sequence DGRs are consistently too high in the models, the most
likely explanation being that the strangulation mechanism used to remove hot
gas from satellite galaxies is too efficient. Finally we present a simple toy
model including a threshold mass, below which galaxies are not strangled, and
show that this can predict the observed evolution of the field DGR.Comment: MNRAS letters accepted. 5 pages, 1 figur
Dust origin in late-type dwarf galaxies: ISM growth vs. type II supernovae
We re-evaluate the roles of different dust sources in dust production as a
function of metallicity in late-type dwarf galaxies, with the goal of
understanding the relation between dust content and metallicity. The dust
content of late-type dwarf galaxies with episodic star formation is studied
with a multicomponent model of dust evolution, which includes dust input from
AGB stars, type II SNe and dust mass growth by accretion of gas species in the
ISM. Dust growth in the ISM becomes an important dust source in dwarf galaxies,
on the timescale of 0.1 - few Gyrs. It increases the dust-to-gas ratio (DGR)
during post-burst evolution, unlike type II SNe, which eject grains into the
ISM only during starbursts. Before the dust growth in the ISM overtakes the
dust production, AGB stars can be major sources of dust in metal-poor dwarf
galaxies. Our models reproduce the relation between the DGR and oxygen
abundance, derived from observations of a large sample of dwarf galaxies. The
steep decrease in the DGR at low O values is explained by the relatively low
efficiency of dust condensation in stars. The scatter observed at higher O
values is determined mainly by different critical metallicities for the
transition from stardust- to ISM-growth dominated dust production, depending on
the star formation history. In galaxies with episodic star formation,
additional dispersion in the DGR is introduced by grain destruction during
starbursts, followed by an increase of the dust mass due to dust growth in the
ISM during post-burst evolution. We find that the carbon-to-silicate ratio
changes dramatically, when the ISM growth becomes the dominant dust source,
therefore this ratio can be used as an indicator of the transition. The
observed DGR-O relation in dwarf galaxies favours low condensation efficiencies
in type II SNe, together with an increase in the total dust mass by means of
dust growth in the ISM.Comment: 11 pages, 10 figures, language and minor errors correcte
On finite-density QCD at large Nc
Deryagin, Grigoriev, and Rubakov (DGR) have shown that in finite-density QCD
at infinite Nc the Fermi surface is unstable with respect to the formation of
chiral waves with wavenumber twice the Fermi momentum, while the BCS
instability is suppressed. We show here that at large, but finite Nc, the DGR
instability only occurs in a finite window of chemical potentials from above
Lambda_QCD to mu_critical = exp(gamma ln^2 Nc + O(ln Nc ln ln Nc))Lambda_QCD,
where gamma = 0.02173. Our analysis shows that, at least in the perturbative
regime, the instability occurs only at extremely large Nc, Nc > 1000 Nf, where
Nf is the number of flavors. We conclude that the DGR instability is not likely
to occur in QCD with three colors, where the ground state is expected to be a
color superconductor. We speculate on possible structure of the ground state of
finite-density QCD with very large Nc.Comment: 13 pages, 5 figures, 3 figures drawn using PicTe
Homological thickness and stability of torus knots
In this paper we show that the non-alternating torus knots are homologically
thick, i.e. that their Khovanov homology occupies at least three diagonals.
Furthermore, we show that we can reduce the number of full twists of the torus
knot without changing certain part of its homology, and consequently, we show
that there exists stable homology of torus knots conjectured by Dunfield, Gukov
and Rasmussen in \cite{dgr}. Since our main tool is the long exact sequence in
homology, we have applied our approach in the case of the Khovanov-Rozansky
() homology, and thus obtained analogous stability properties of
homology of torus knots, also conjectured in \cite{dgr}.Comment: 24 pages, expanded Section
Development of canopy vigour maps using UAV for site-specific management during vineyard spraying process
Site-specific management of crops represents an important improvement in terms of efficiency and efficacy of the different labours, and its implementation has experienced a large development in the last decades, especially for field crops. The particular case of the spray application process for what are called “specialty crops” (vineyard, orchard fruits, citrus, olive trees, etc.)FI-DGR grant from Generalitat de Catalunya (2018 FI_B1 00083).
Research and improvement of Dosaviña have been developed under LIFE PERFECT project: Pesticide Reduction using Friendly and Environmentally Controlled Technologies (LIFE17 ENV/ES/000205)This research was partially funded by the “Ajuts a les activitats de demostració (operació 01.02.01 de Transferència Tecnològica del Programa de desenvolupament rural de Catalunya 2014-2020)” and an FI-DGR grant from Generalitat de Catalunya (2018 FI_B1 00083). Research and improvement of Dosaviña have been developed under the LIFE PERFECT project: Pesticide Reduction using Friendly and Environmentally Controlled Technologies (LIFE17 ENV/ES/000205).This research was partially funded by the “Ajuts a les activitats de demostració (operació 01.02.01 de Transferència Tecnològica del Programa de desenvolupament rural de Catalunya 2014-2020)” and an FI-DGR grant from Generalitat de Catalunya (2018 FI_B1 00083). Research and improvement of Dosaviña have been developed under LIFE PERFECT project: Pesticide Reduction using Friendly and Environmentally Controlled Technologies (LIFE17 ENV/ES/000205)Postprint (updated version
Computation of Minimal Homogeneous Generating Sets and Minimal Standard Bases for Ideals of Free Algebras
Let \KX =K\langle X_1,\ldots ,X_n\rangle be the free algebra generated by
over a field . It is shown that with respect to any
weighted -gradation attached to \KX, minimal homogeneous
generating sets for finitely generated graded (two-sided) ideals of \KX can
be algorithmically computed, and that if an ungraded (two-sided) ideal of
\KX has a finite Gr\"obner basis \G with respect to a graded monomial
ordering on \KX, then a minimal standard basis for can be computed via
computing a minimal homogeneous generating set of the associated graded ideal
\langle\LH (I)\rangle.Comment: 13 pages. Algorithm1, Algorithm 2, and Algorithm 3 are revise
A'Campo curvature bumps and the Dirac phenomenon near a singular point
The level curves of an analytic function germ almost always have bumps at
unexpected points near the singularity. This profound discovery of N. A'Campo
is fully explored in this paper for f(z,w)\in \C\{z,w\}, using the
Newton-Puiseux infinitesimals and the notion of gradient canyon. Equally
unexpected is the Dirac phenomenon: as c\ra 0, the total Gaussian curvature
of accumulates in the gradient canyons
- …