89 research outputs found
Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, which is a
complete, distance-limited (6000 km/s) and magnitude-limited
(B14) sample of 7000 optical galaxies. The sample covers 2/3 (8.27
sr) of the sky () and appears to have a good completeness in
redshift (98%). We select the sample on the basis of homogenized corrected
total blue magnitudes in order to minimize systematic effects in galaxy
sampling.
We identify the groups in this sample by means of both the hierarchical and
the percolation {\it friends of friends} methods. The resulting catalogs of
loose groups appear to be similar and are among the largest catalogs of groups
presently available. Most of the NOG galaxies (60%) are found to be
members of galaxy pairs (580 pairs for a total of 15% of objects)
or groups with at least three members (500 groups for a total of
45% of objects). About 40% of galaxies are left ungrouped (field
galaxies). We illustrate the main features of the NOG galaxy distribution.
Compared to previous optical and IRAS galaxy samples, the NOG provides a denser
sampling of the galaxy distribution in the nearby universe. Given its large sky
coverage, the identification of groups, and its high-density sampling, the NOG
is suited for the analysis of the galaxy density field of the nearby universe,
especially on small scales.Comment: 47 pages including 6 figures. Accepted for publication in Ap
Galaxy Distances in the Nearby Universe: Corrections For Peculiar Motions
By correcting the redshift--dependent distances for peculiar motions through
a number of peculiar velocity field models, we recover the true distances of a
wide, all-sky sample of nearby galaxies (~ 6400 galaxies with velocities
cz<5500 km/s), which is complete up to the blue magnitude B=14 mag. Relying on
catalogs of galaxy groups, we treat ~2700 objects as members of galaxy groups
and the remaining objects as field galaxies.
We model the peculiar velocity field using: i) a cluster dipole
reconstruction scheme; ii) a multi--attractor model fitted to the Mark II and
Mark III catalogs of galaxy peculiar velocities. According to Mark III data the
Great Attractor has a smaller influence on local dynamics than previously
believed, whereas the Perseus-Pisces and Shapley superclusters acquire a
specific dynamical role. Remarkably, the Shapley structure, which is found to
account for nearly half the peculiar motion of the Local Group, is placed by
Mark III data closer to the zone of avoidance with respect to its optical
position.
Our multi--attractor model based on Mark III data favors a cosmological
density parameter Omega ~ 0.5 (irrespective of a biasing factor of order
unity). Differences among distance estimates are less pronounced in the ~ 2000
- 4000 km/s distance range than at larger or smaller distances. In the last
regions these differences have a serious impact on the 3D maps of the galaxy
distribution and on the local galaxy density --- on small scales.Comment: 24 pages including (9 eps figures and 7 tables). Figures 1,2,3,4 are
available only upon request. Accepted by Ap
Merging Binary Clusters
We study three prominent bi-modal X-ray clusters: A3528, A1750 and A3395.
Using observations taken with ROSAT and ASCA, we analyze the temperature and
surface brightness distributions. We also analyze the velocity distributions of
the three clusters using new measurements supplemented with previously
published data. We examine both the overall cluster properties, as well as the
two sub-cluster elements in each. These results are then applied to the
determination of the overall cluster masses, and demonstrate excellent
consistency between the various methods used. While the characteristic
parameters of the sub-clusters are typical of isolated objects, our temperature
results for the regions between the two sub-clusters clearly confirm the
presence of merger activity. These three clusters represent a progression of
equal-sized sub-cluster mergers, starting from initial contact to immediately
before first core passage.Comment: 12 pages, 3 full page figures in color, accepted for publication in
the Astrophysical Journa
The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined UZC and SSRS2
redshift surveys to construct a catalog of 1168 groups of galaxies; 411 of
these groups have 5 or more members within the redshift survey. The group
catalog covers 4.69 steradians and all groups exceed a number density contrast
threshold of 80. We demonstrate that the groups catalog is homogeneous across
the two underlying redshift surveys; the catalog of groups and their members
thus provides a basis for other statistical studies of the large-scale
distribution of groups and their physical properties. The median physical
properties of the groups are similar to those for groups derived from
independent surveys including the ESO Key Programme and the Las Campanas
Redshift Survey. We include tables of groups and their members.Comment: Accepted for publication on A
Three-Dimensional Identification and Reconstruction of Galaxy Systems within Deep Redshift Surveys
We have developed a new geometrical method for identifying and reconstructing
a homogeneous and highly complete set of galaxy groups in the next generation
of deep, flux-limited redshift surveys. Our method combines information from
the three-dimensional Voronoi diagram and its dual, the Delaunay triangulation,
to obtain group and cluster catalogs that are remarkably robust over wide
ranges in redshift and degree of density enhancement. Using the mock DEEP2
catalogs, we demonstrate that the VDM algorithm can be used to identify a
homogeneous set of groups in a magnitude-limited sample (I\sbr{AB}\le23.5)
throughout the survey redshift window . The actual group
membership can be effectively reconstructed even in the distorted redshift
space environment for systems with line of sight velocity dispersion
greater than \kms. By comparing the galaxy cluster
catalog derived from the mock DEEP2 observations to the underlying distribution
of clusters found in real space with much fainter galaxies included (which
should more closely trace mass in the cluster), we can assess completeness in
velocity dispersion directly. We conclude that the recovered DEEP2 group and
cluster sample should be statistically complete for
\kms. Finally, we argue that the reconstructed bivariate distribution of
systems as a function of redshift and velocity dispersion reproduces with high
fidelity the underlying real space distribution and can thus be used robustly
to constrain cosmological parametersComment: Latex, 21 pages, ApJ submitte
Substructures in WINGS clusters
We search for and characterize substructures in the projected distribution of
galaxies observed in the wide field CCD images of the 77 nearby clusters of the
WIde-field Nearby Galaxy-cluster Survey (WINGS). This sample is complete in
X-ray flux in the redshift range 0.04<z<0.07. We search for substructures in
WINGS clusters with DEDICA, an adaptive-kernel procedure. We test the procedure
on Monte-Carlo simulations of the observed frames and determine the reliability
for the detected structures. DEDICA identifies at least one reliable structure
in the field of 55 clusters. 40 of these clusters have a total of 69
substructures at the same redshift of the cluster (redshift estimates of
substructures are from color-magnitude diagrams). The fraction of clusters with
subclusters (73%) is higher than in most studies. The presence of subclusters
affects the relative luminosities of the brightest cluster galaxies (BCGs).
Down to L ~ 10^11.2 L_Sun, our observed differential distribution of subcluster
luminosities is consistent with the theoretical prediction of the differential
mass function of substructures in cosmological simulations.Comment: A&A accepted - figure 6 is available from
http://adlibitum.oats.inaf.it/ramella/WINGSfig
Distances to Nearby Galaxies in Sculptor
We present an analysis of Hubble Space Telescope/WFPC2 images of nine nearby
galaxies in Sculptor. We derive their distances from the luminosity of the tip
of the red giant branch stars with a typical accuracy of ~ 12%. Their distances
are 4.21 Mpc (Sc22), 4.92 Mpc (DDO226), 3.94 Mpc (NGC253), 3.40 Mpc (KDG2),
3.34 Mpc (DDO6), 3.42 Mpc (ESO540-030), 4.43 Mpc (ESO245-05), 4.27 Mpc
(UGCA442), and 3.91 Mpc (NGC7793). The galaxies are concentrated in several
spatially separated loose groups around NGC300, NGC253, and NGC7793. The
Sculptor galaxy complex together with the CVn I cloud and the Local Group form
a 10 Mpc amorphous filament, apparently driven by the free Hubble flow.Comment: 20 pages, 6 figures, A&A accepted. Figure 2 (5444k) is available at
http://luna.sao.ru/~sme/fig2Sculptor.tar.g
The VIMOS VLT Deep Survey: the group catalogue
[Abridged] We present a homogeneous and complete catalogue of optical groups
identified in the purely flux limited (17.5<=I<=24.0) VIMOS-VLT Deep Survey
(VVDS). We use mock catalogues extracted from the MILLENNIUM simulation, to
correct for potential systematics that might affect the overall distribution as
well as the individual properties of the identified systems. Simulated samples
allow us to forecast the number and properties of groups that can be
potentially found in a survey with VVDS-like selection functions. We use them
to correct for the expected incompleteness and also to asses how well galaxy
redshifts trace the line-of-sight velocity dispersion of the underlying mass
overdensity. In particular, we train on these mock catalogues the adopted
group-finding technique (the Voronoi-Delaunay Method, VDM). The goal is to
fine-tune its free parameters, recover in a robust and unbiased way the
redshift and velocity dispersion distributions of groups and maximize the level
of completeness (C) and purity (P) of the group catalogue. We identify 318 VVDS
groups with at least 2 members within 0.2<=z<=1.0, among which 144 (/30) with
at least 3 (/5) members. The sample has globally C=60% and P=50%. Nearly 45% of
the groups with at least 3 members are still recovered if we run the algorithm
with a parameter set which maximizes P (75%). We exploit the group sample to
study the redshift evolution of the fraction f_b of blue galaxies (U-B<=1)
within 0.2<=z<=1. We find that f_b is significantly lower in groups than in the
whole ensemble of galaxies irrespectively of their environment. These
quantities increase with redshift, with f_b in groups showing a marginally
significant steeper increase. We also confirm that, at any explored redshift,
f_b decreases for increasing group richness, and we extend towards fainter
luminosities the magnitude range over which this result holds.Comment: Submitted to A&A, revised version after referee comments, Table 5
adde
Computational modelling of meiotic entry and commitment
In response to developmental and environmental conditions, cells exit the mitotic cell cycle and enter the meiosis program to generate haploid gametes from diploid germ cells. Once cells decide to enter the meiosis program they become irreversibly committed to the completion of meiosis irrespective of the presence of cue signals. How meiotic entry and commitment occur due to the dynamics of the regulatory network is not well understood. Therefore, we constructed a mathematical model of the regulatory network that controls the transition from mitosis to meiosis in Schizosaccharomyces pombe. Upon nitrogen starvation, yeast cells exit mitosis and undergo conjugation and meiotic entry. The model includes the regulation of Mei2, an RNA binding protein required for conjugation and meiotic entry, by multiple feedback loops involving Pat1, a kinase that keeps cells in mitosis, and Ste11, a transcription activator required for the sexual differentiation. The model accounts for various experimental observations and demonstrates that the activation of Mei2 is bistable, which ensures the irreversible commitment to meiosis. Further, we show by integrating the meiosis-specific regulation with a cell cycle model, the dynamics of cell cycle exit, G1 arrest and entry into meiosis under nitrogen starvation. © 2017 The Author(s)
Transcriptome sequencing of lentil based on second-generation technology permits large-scale unigene assembly and SSR marker discovery
<p>Abstract</p> <p>Background</p> <p>Lentil (<it>Lens culinaris </it>Medik.) is a cool-season grain legume which provides a rich source of protein for human consumption. In terms of genomic resources, lentil is relatively underdeveloped, in comparison to other Fabaceae species, with limited available data. There is hence a significant need to enhance such resources in order to identify novel genes and alleles for molecular breeding to increase crop productivity and quality.</p> <p>Results</p> <p>Tissue-specific cDNA samples from six distinct lentil genotypes were sequenced using Roche 454 GS-FLX Titanium technology, generating c. 1.38 × 10<sup>6 </sup>expressed sequence tags (ESTs). <it>De novo </it>assembly generated a total of 15,354 contigs and 68,715 singletons. The complete unigene set was sequence-analysed against genome drafts of the model legume species <it>Medicago truncatula </it>and <it>Arabidopsis thaliana </it>to identify 12,639, and 7,476 unique matches, respectively. When compared to the genome of <it>Glycine max</it>, a total of 20,419 unique hits were observed corresponding to c. 31% of the known gene space. A total of 25,592 lentil unigenes were subsequently annoated from GenBank. Simple sequence repeat (SSR)-containing ESTs were identified from consensus sequences and a total of 2,393 primer pairs were designed. A subset of 192 EST-SSR markers was screened for validation across a panel 12 cultivated lentil genotypes and one wild relative species. A total of 166 primer pairs obtained successful amplification, of which 47.5% detected genetic polymorphism.</p> <p>Conclusions</p> <p>A substantial collection of ESTs has been developed from sequence analysis of lentil genotypes using second-generation technology, permitting unigene definition across a broad range of functional categories. As well as providing resources for functional genomics studies, the unigene set has permitted significant enhancement of the number of publicly-available molecular genetic markers as tools for improvement of this species.</p
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