32 research outputs found
2DPHOT: A Multi-purpose Environment for the Two-dimensional Analysis of Wide-field Images
We describe 2DPHOT, a general purpose analysis environment for source
detection and analysis in deep wide-field images. 2DPHOT is an automated tool
to obtain both integrated and surface photometry of galaxies in an image, to
perform reliable star-galaxy separation with accurate estimates of
contamination at faint flux levels, and to estimate completeness of the image
catalog. We describe the analysis strategy on which 2DPHOT is based, and
provide a detailed description of the different algorithms implemented in the
package. This new environment is intended as a dedicated tool to process the
wealth of data from wide-field imaging surveys. To this end, the package is
complemented by 2DGUI, an environment that allows multiple processing of data
using a range of computing architectures.Comment: Accepted to PAS
A Catalog of Distant Compact Groups Using DPOSS
In this paper we present an objectively defined catalog of 459 small, high
density groups of galaxies out to z~0.2 in a region of 6260 square degrees in
the northern sky derived from the Digitized Second Palomar Observatory Sky
Survey. Our catalog extends down to r = 19.0 and has a median redshift of z_med
= 0.12, making it complementary to Hickson's catalog for the nearby universe
(z_med = 0.03). The depth and angular coverage of this catalog makes it
valuable for studies of the general characteristics of small groups of galaxies
and how galaxies evolve in and around them. We also examine the relationship
between compact groups and large scale structure.Comment: accepted to A
On the Nature of Fossil Galaxy Groups: Are they really fossils ?
We use SDSS-DR4 photometric and spectroscopic data out to redshift z~0.1
combined with ROSAT All Sky Survey X-ray data to produce a sample of
twenty-five fossil groups (FGs), defined as bound systems dominated by a
single, luminous elliptical galaxy with extended X-ray emission. We examine
possible biases introduced by varying the parameters used to define the sample
and the main pitfalls are discussed. The spatial density of FGs, estimated via
the V/V_ MAX} test, is 2.83 x 10^{-6} h_{75}^3 Mpc^{-3} for L_x > 0.89 x 10^42
h_{75}^-2 erg/s consistent with Vikhlinin et al. (1999), who examined an X-ray
overluminous elliptical galaxy sample (OLEG). We compare the general properties
of FGs identified here with a sample of bright field ellipticals generated from
the same dataset. These two samples show no differences in the distribution of
neighboring faint galaxy density excess, distance from the red sequence in the
color-magnitude diagram, and structural parameters such as a and internal
color gradients. Furthermore, examination of stellar populations shows that our
twenty-five FGs have similar ages, metallicities, and -enhancement as
the bright field ellipticals, undermining the idea that these systems represent
fossils of a physical mechanism that occurred at high redshift. Our study
reveals no difference between FGs and field ellipticals, suggesting that FGs
might not be a distinct family of true fossils, but rather the final stage of
mass assembly in the Universe.Comment: 18 pages, Accepted to A
NoSOCS in SDSS. II. Mass Calibration of Low Redshift Galaxy Clusters with Optical and X-ray Properties
We use SDSS data to investigate the scaling relations of 127 NoSOCS and 56
CIRS galaxy clusters at low redshift (). We show that richness and
both optical and X-ray luminosities are reliable mass proxies. The scatter in
mass at fixed observable is 40%, depending on the aperture, sample and
observable considered. For example, for the massive CIRS systems
= 0.33 0.05 and = 0.48
0.06. For the full sample = 0.43 0.03 and
= 0.56 0.06. We estimate substructure using two and
three dimensional optical data, verifying that substructure has no significant
effect on the cluster scaling relations (intercepts and slopes), independent of
which substructure test we use. For a subset of twenty-one clusters, we
estimate masses from the M-T relation using temperature measures from BAX.
The scaling relations derived from the optical and X-ray masses are indeed very
similar, indicating that our method consistently estimates the cluster mass and
yields equivalent results regardless of the wavelength from which we measure
mass. For massive systems, we represent the mass-richness relation by a
function with the form , with
M being expressed in units of 10 M. Using the virial
mass, for CIRS clusters, we find A = (1.39 0.07) and B = (1.00
0.11). The relations based on the virial mass have a scatter of
= 0.37 0.05, while = 0.77
0.22 for the caustic mass and = 0.34 0.08
for the temperature based mass (abridged).Comment: 27 pages, 22 figures, 12 tables, Accepted to MNRA
Basal Body Positioning Is Controlled by Flagellum Formation in Trypanosoma brucei
To perform their multiple functions, cilia and flagella are precisely positioned at the cell surface by mechanisms that remain poorly understood. The protist Trypanosoma brucei possesses a single flagellum that adheres to the cell body where a specific cytoskeletal structure is localised, the flagellum attachment zone (FAZ). Trypanosomes build a new flagellum whose distal tip is connected to the side of the old flagellum by a discrete structure, the flagella connector. During this process, the basal body of the new flagellum migrates towards the posterior end of the cell. We show that separate inhibition of flagellum assembly, base-to-tip motility or flagella connection leads to reduced basal body migration, demonstrating that the flagellum contributes to its own positioning. We propose a model where pressure applied by movements of the growing new flagellum on the flagella connector leads to a reacting force that in turn contributes to migration of the basal body at the proximal end of the flagellum
NoSOCS in SDSS. I. Sample Definition and Comparison of Mass Estimates
We use Sloan Digital Sky Survey (SDSS) data to investigate galaxy cluster
properties of systems first detected within DPOSS. With the high quality
photometry of SDSS we derived new photometric redshifts and estimated richness
and optical luminosity. For a subset of low redshift () clusters, we
have used SDSS spectroscopic data to identify groups in redshift space in the
region of each cluster, complemented with massive systems from the literature
to assure the continuous mass sampling. A method to remove interlopers is
applied, and a virial analysis is performed resulting in estimates of velocity
dispersion, mass, and a physical radius for each low- system. We discuss the
choice of maximum radius and luminosity range in the dynamical analysis,
showing that a spectroscopic survey must be complete to at least M if one
wishes to obtain accurate and unbiased estimates of velocity dispersion and
mass. We have measured X-ray luminosity for all clusters using archival data
from RASS. For a smaller subset (twenty-one clusters) we selected temperature
measures from the literature and estimated mass from the M-T relation,
finding that they show good agreement with the virial estimate. However, these
two mass estimates tend to disagree with the caustic results. We measured the
presence of substructure in all clusters of the sample and found that clusters
with substructure have virial masses higher than those derived from T. This
trend is not seen when comparing the caustic and X-ray masses. That happens
because the caustic mass is estimated directly from the mass profile, so it is
less affected by substructure.Comment: 21 pages, 17 figures, 5 tables, Accepted to MNRA
Phenoloxidase activity acts as a mosquito innate immune response against infection with semliki forest virus
Several components of the mosquito immune system including the RNA interference (RNAi), JAK/STAT, Toll and IMD pathways have previously been implicated in controlling arbovirus infections. In contrast, the role of the phenoloxidase (PO) cascade in mosquito antiviral immunity is unknown. Here we show that conditioned medium from the Aedes albopictus-derived U4.4 cell line contains a functional PO cascade, which is activated by the bacterium Escherichia coli and the arbovirus Semliki Forest virus (SFV) (Togaviridae; Alphavirus). Production of recombinant SFV expressing the PO cascade inhibitor Egf1.0 blocked PO activity in U4.4 cell- conditioned medium, which resulted in enhanced spread of SFV. Infection of adult female Aedes aegypti by feeding mosquitoes a bloodmeal containing Egf1.0-expressing SFV increased virus replication and mosquito mortality. Collectively, these results suggest the PO cascade of mosquitoes plays an important role in immune defence against arboviruses
The Northern Sky Optical Cluster Survey III: A Cluster Catalog Covering Pi Steradians
We present the complete galaxy cluster catalog from the Northern Sky Optical
Cluster Survey, a new, objectively defined catalog of candidate galaxy clusters
at z<0.25 drawn from the Digitized Second Palomar Observatory Sky Survey
(DPOSS). The data presented here cover the Southern Galactic Cap, as well as
the less-well calibrated regions of the Northern Galactic Cap. In addition, due
to improvements in our cluster finder and measurement methods, we provide an
updated catalog for the well-calibrated Northern Galactic Cap region previously
published in Paper II. The complete survey covers 11,411 square degrees, with
over 15,000 candidate clusters. We discuss improved photometric redshifts,
richnesses and optical luminosities which are provided for each cluster. A
variety of substructure measures are computed for a subset of over 11,000
clusters. We also discuss the derivation of dynamical radii r_200 and its
relation to cluster richness. A number of consistency checks between the three
areas of the survey are also presented, demonstrating the homogeneity of the
catalog over disjoint sky areas. We perform extensive comparisons to existing
optically and X-ray selected cluster catalogs, and derive new X-ray
luminosities and temperatures for a subset of our clusters. We find that the
optical and X-ray luminosities are well correlated, even using relatively
shallow ROSAT All Sky Survey and DPOSS data. This survey provides a good
comparison sample to the MaxBCG catalog based on Sloan Digital Sky Survey Data,
and complements that survey at low redshifts 0.07<z<0.1.Comment: To appear in A
The complete genome sequence of Corynebacterium pseudotuberculosis FRC41 isolated from a 12-year-old girl with necrotizing lymphadenitis reveals insights into gene-regulatory networks contributing to virulence
Trost E, Ott L, Schneider J, et al. The complete genome sequence of Corynebacterium pseudotuberculosis FRC41 isolated from a 12-year-old girl with necrotizing lymphadenitis reveals insights into gene-regulatory networks contributing to virulence. BMC Genomics. 2010;11(1): 728