1,568 research outputs found
Catalog of Isolated Galaxies Selected from the 2MASS Survey
We search for isolated galaxies based on the automatic identification of
isolated sources from the Two Micron All-Sky Survey (2MASS) followed by a
visual inspection of their surroundings. We use the modified Karachentseva
criterion to compile a catalog of 3227 isolated galaxies (2MIG), which contains
6% of 2MASS Extended Sources Catalog (or 2MASX) sources brighter than Ks = 12
mag with angular diameters a_K > 30 arcsec. The catalog covers the entire sky
and has an effective depth of z = 0.02. The 2493 very isolated objects of the
catalog, which we include into the 2MVIG catalog, can be used as a reference
sample to investigate the effects of the environment on the structure and
evolution of galaxies located in regions with extremely low density of matter.Comment: 19 pages, 13 figure
How Barred is the NIR Nearby Universe? An analysis using 2MASS
We determine a firm lower limit to the bar fraction of 0.58 in the nearby
universe using J+H+Ks-band images for 134 spirals from 2MASS. With a mean
deprojected semi-major axis of 5.1 kpc, and a mean deprojected ellipticity of
0.45 this local bar sample lays the ground work for studies on bar formation
and evolution at high redshift.Comment: In the proceedings "Penetrating Bars through Masks of Cosmic Dust:
The Hubble Tuning Fork strikes a New Note
The Bulk Motion of Flat Edge-On Galaxies Based on 2MASS Photometry
We report the results of applying the 2MASS Tully-Fisher (TF) relations to
study the galaxy bulk flows. For 1141 all-sky distributed flat RFGC galaxies we
construct J, H, K_s TF relations and find that Kron magnitudes show
the smallest dispersion on the TF diagram. For the sample of 971 RFGC galaxies
with V_{3K} < 18000 km/s we find a dispersion and an
amplitude of bulk flow V= 199 +/-61 km/s, directed towards l=301 degr +/-18
degr, b=-2 degr +/-15 degr. Our determination of low-amplitude coherent flow is
in good agreement with a set of recent data derived from EFAR, PSCz, SCI/SCII
samples. The resultant two- dimensional smoothed peculiar velocity field traces
well the large-scale density variations in the galaxy distributions. The
regions of large positive peculiar velocities lie in the direction of the Great
Attractor and Shapley concentration. A significant negative peculiar velocity
is seen in the direction of Bootes and in the direction of the Local void. A
small positive peculiar velocity (100 -- 150 km/s) is seen towards the
Pisces-Perseus supercluster, as well as the Hercules - Coma - Corona Borealis
supercluster regions.Comment: 10 pages, 5 figures. A&A/2003/3582 accepted 15.05.200
Infrared luminosities of galaxies in the Local Volume
Near-infrared properties of 451 galaxies with distances D \leq 10 Mpc are
considered basing on the all-sky two micron survey (2MASS). A luminosity
function of the galaxies in the K-band is derived within [-25,-11] mag. The
local (D < 8 Mpc) luminosity density is estimated to be 6.8*10^8 L_sun/Mpc^3
that exceeds (1.5+-0.1) times the global cosmic density in the K-band. Virial
mass-to-K-luminosity ratios are determined for nearby groups and clusters. In
the luminosity range of (5*10^{10} - 2*10^{13})L_sun, the groups and clusters
follow the relation \lg(M/L_K) propto (0.27+-0.03) lg(L_K) with a scatter of
\~0.1 comparable to errors of the observables. The mean ratio ~=
(20-25) M_sun/L_sun for the galaxy systems turns out to be significantly lower
than the global ratio, (80-90)M_sun/L_sun, expected in the standard
cosmological model with the matter density of Omega_m =0.27. This discrepancy
can be resolved if most of dark matter in the universe is not associated with
galaxies and their systems.Comment: 15 pages, 7 figures. Astronomy Letters, submitte
Galaxies behind the Galactic plane: First results and perspectives from the VVV Survey
Vista Variables in The Via Lactea (VVV) is an ESO variability survey that is
performing observations in near infrared bands (ZYJHKs) towards the Galactic
bulge and part of the disk with the completeness limits at least 3 mag deeper
than 2MASS. In the present work, we searched in the VVV survey data for
background galaxies near the Galactic plane using ZYJHKs photometry that covers
1.636 square degrees. We identified 204 new galaxy candidates by analyzing
colors, sizes, and visual inspection of multi-band (ZYJHKs) images. The galaxy
candidates colors were also compared with the predicted ones by star counts
models considering a more realistic extinction model at the same completeness
limits observed by VVV. A comparison of the galaxy candidates with the expected
one by Milennium simulations is also presented. Our results increase the number
density of known galaxies behind the Milky Way by more than one order of
magnitude. A catalog with galaxy properties including ellipticity, Petrosian
radii and ZYJHKs magnitudes is provided, as well as comparisons of the results
with other surveys of galaxies towards Galactic plane.Comment: 27 pages, 10 figures, 2 tables; in press at The Astronomical Journa
Caltech Faint Field Galaxy Redshift Survey IX: Source detection and photometry in the Hubble Deep Field Region
Detection and photometry of sources in the U_n, G, R, and K_s bands in a 9x9
arcmin^2 region of the sky, centered on the Hubble Deep Field, are described.
The data permit construction of complete photometric catalogs to roughly
U_n=25, G=26, R=25.5 and K_s=20 mag, and significant photometric measurements
somewhat fainter. The galaxy number density is 1.3x10^5 deg^{-2} to R=25.0 mag.
Galaxy number counts have slopes dlog N/dm=0.42, 0.33, 0.27 and 0.31 in the
U_n, G, R and K_s bands, consistent with previous studies and the trend that
fainter galaxies are, on average, bluer. Galaxy catalogs selected in the R and
K_s bands are presented, containing 3607 and 488 sources, in field areas of
74.8 and 59.4 arcmin^2, to R=25.5 and and K_s=20 mag.Comment: Accepted for publication in ApJS; some tables and slightly nicer
figures available at http://www.sns.ias.edu/~hogg/deep
Identification of novel subgroup a variants with enhanced receptor binding and replicative capacity in primary isolates of anaemogenic strains of feline leukaemia virus
<b>BACKGROUND:</b>
The development of anaemia in feline leukaemia virus (FeLV)-infected cats is associated with the emergence of a novel viral subgroup, FeLV-C. FeLV-C arises from the subgroup that is transmitted, FeLV-A, through alterations in the amino acid sequence of the receptor binding domain (RBD) of the envelope glycoprotein that result in a shift in the receptor usage and the cell tropism of the virus. The factors that influence the transition from subgroup A to subgroup C remain unclear, one possibility is that a selective pressure in the host drives the acquisition of mutations in the RBD, creating A/C intermediates with enhanced abilities to interact with the FeLV-C receptor, FLVCR. In order to understand further the emergence of FeLV-C in the infected cat, we examined primary isolates of FeLV-C for evidence of FeLV-A variants that bore mutations consistent with a gradual evolution from FeLV-A to FeLV-C.<p></p>
<b>RESULTS:</b>
Within each isolate of FeLV-C, we identified variants that were ostensibly subgroup A by nucleic acid sequence comparisons, but which bore mutations in the RBD. One such mutation, N91D, was present in multiple isolates and when engineered into a molecular clone of the prototypic FeLV-A (Glasgow-1), enhanced replication was noted in feline cells. Expression of the N91D Env on murine leukaemia virus (MLV) pseudotypes enhanced viral entry mediated by the FeLV-A receptor THTR1 while soluble FeLV-A Env bearing the N91D mutation bound more efficiently to mouse or guinea pig cells bearing the FeLV-A and -C receptors. Long-term in vitro culture of variants bearing the N91D substitution in the presence of anti-FeLV gp70 antibodies did not result in the emergence of FeLV-C variants, suggesting that additional selective pressures in the infected cat may drive the subsequent evolution from subgroup A to subgroup C.<p></p>
<b>CONCLUSIONS:</b>
Our data support a model in which variants of FeLV-A, bearing subtle differences in the RBD of Env, may be predisposed towards enhanced replication in vivo and subsequent conversion to FeLV-C. The selection pressures in vivo that drive the emergence of FeLV-C in a proportion of infected cats remain to be established
Global anisotropy of arrival directions of ultra-high-energy cosmic rays: capabilities of space-based detectors
Planned space-based ultra-high-energy cosmic-ray detectors (TUS, JEM-EUSO and
S-EUSO) are best suited for searches of global anisotropies in the distribution
of arrival directions of cosmic-ray particles because they will be able to
observe the full sky with a single instrument. We calculate quantitatively the
strength of anisotropies associated with two models of the origin of the
highest-energy particles: the extragalactic model (sources follow the
distribution of galaxies in the Universe) and the superheavy dark-matter model
(sources follow the distribution of dark matter in the Galactic halo). Based on
the expected exposure of the experiments, we estimate the optimal strategy for
efficient search of these effects.Comment: 19 pages, 7 figures, iopart style. v.2: discussion of the effect of
the cosmic magnetic fields added; other minor changes. Simulated UHECR
skymaps available at http://livni.inr.ac.ru/UHECRskymaps
Binary Galaxies in the Local Supercluster and Its Neighborhood
We report a catalog of 509 pairs identified among 10403 nearby galaxies with
line-of-sight velocities V_LG < 3500 km/s.We selected binary systems in
accordance with two criteria (bounding and temporal), which require the
physical pair of galaxies to have negative total energy and its components to
be located inside the zero-velocity surface. We assume that individual galaxy
masses are proportional to their total K-band luminosities, M = L_K x 6M/L. The
catalog gives the magnitudes and morphological types of galaxies and also the
projected (orbital) masses and pair isolation indices. The component
line-of-sight velocity differences and projected distances of the binary
systems considered have power-law distributions with the median values of 35
km/s and 123 kpc, respectively. The median mass-to-K-band luminosity ratio is
equal to 11 M/L, and its uncertainty is mostly due to the errors of measured
velocities. Our sample of binary systems has a typical density contrast of d
ro/ro_c ~ 500 and a median crossing time of about 3.5 Gyr. We point out the
substantial fraction of binary systems consisting of late-type dwarf galaxies,
where the luminosities of both components are lower than that of the Small
Magellanic Cloud. The median projected distance for 41 such pairs is only 30
kpc, and the median difference of their line-of-sight velocities is equal to 14
km/s which is smaller than the typical error for radial-velocity (30 km/s).
This specific population of gas-rich dwarf binary galaxies such as I Zw 18 may
be at the stage immediately before merging of its components. Such objects,
which are usually lost in flux-limited (and not distance-limited) samples
deserve a thorough study in the HI radio line with high spatial and velocity
resolution.Comment: published in Astrophysical Bulletin, 2008, Vol. 63, No. 4, pp.
299-34
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