1,443 research outputs found
An Interacting Galaxy System Along a Filament in a Void
Cosmological voids provide a unique environment for the study of galaxy
formation and evolution. The galaxy population in their interior have
significantly different properties than average field galaxies. As part of our
Void Galaxy Survey (VGS), we have found a system of three interacting galaxies
(VGS_31) inside a large void. VGS_31 is a small elongated group whose members
are embedded in a common HI envelope. The HI picture suggests a filamentary
structure with accretion of intergalactic cold gas from the filament onto the
galaxies. We present deep optical and narrow band H_alpha data, optical
spectroscopy, near-UV and far-UV GALEX and CO(1-0) data. We find that one of
the galaxies, a Markarian object, has a ring-like structure and a tail evident
both in optical and HI. While all three galaxies form stars in their central
parts, the tail and the ring of the Markarian object are devoid of star
formation. We discuss these findings in terms of a gravitational interaction
and ongoing growth of galaxies out of a filament. VGS_31 is one of the first
observed examples of a filamentary structure in a void. It is an important
prototype for understanding the formation of substructure in a void. This
system also shows that the galaxy evolution in voids can be as dynamic as in
high density environments.Comment: 17 pages, 8 figures, accepted for publication in A
KK246, a dwarf galaxy with extended H I disk in the Local Void
We have found that KK 246, the only confirmed galaxy located within the
nearby Tully Void, is a dwarf galaxy with an extremely extended H I disk and
signs of an H I cloud with anomalous velocity. It also exhibits clear
misalignment between the kinematical major and minor axes, indicative of an
oval distortion, and a general misalignment between the H I and optical major
axes. We measure a H I mass of 1.05 +- 0.08 x 10^8 M_sun, and a H I extent 5
times that of the stellar disk, one of the most extended H I disks known. We
estimate a dynamical mass of 4.1 x 10^9 M_sun, making this also one of the
darkest galaxies known, with a mass-to-light ratio of 89. The relative
isolation and extreme underdense environment make this an interesting case for
examining the role of gas accretion in galaxy evolution.Comment: 15 pages, 8 figures, 2 tables, accepted for publication in A
From gas to galaxies
The unsurpassed sensitivity and resolution of the Square Kilometer Array
(SKA) will make it possible for the first time to probe the continuum emission
of normal star forming galaxies out to the edges of the universe. This opens
the possibility for routinely using the radio continuum emission from galaxies
for cosmological research as it offers an independent probe of the evolution of
the star formation density in the universe. In addition it offers the
possibility to detect the first star forming objects and massive black holes.
In deep surveys SKA will be able to detect HI in emission out to redshifts of
and hence be able to trace the conversion of gas into stars
over an era where considerable evolution is taking place. Such surveys will be
able to uniquely determine the respective importance of merging and accreting
gas flows for galaxy formation over this redshift range (i.e. out to when the
universe was only one third its present age). It is obvious that only SKA will
able to see literally where and how gas is turned into stars.
These and other aspects of SKA imaging of galaxies will be discussed.Comment: To be published in New Astronomy Reviews, Elsevier, Amsterdam as part
of "Science with the Square Kilometre Array", eds. C. Carilli and S.
Rawlings. 18 pages + 13 figures; high resolution version and other chapters
of "Science with the Square Kilometre Array" available at
http://www.skatelescope.org/pages/science_gen.ht
A blind H i survey in the Canes Venatici region
We have carried out a blind H i survey using the Westerbork Synthesis Radio Telescope to make an inventory of objects with small H i masses (between 106 and 108 Mâ) and to constrain the low-mass end of the H i mass function. The survey has been conducted in a part of the volume containing the nearby Canes Venatici groups of galaxies. The surveyed region covers an area on the sky of about 86 deg2 and a range in velocity from about â450 to about 1330 km sâ1. We find 70 sources in the survey by applying an automated searching algorithm. Two of the detections have not been catalogued previously, but they can be assigned an optical counterpart, based on visual inspection of the second-generation Digital Sky Survey images. Only one of the H i detections is without an optical counterpart. This object is detected in the vicinity of NGC 4822, and it has been already detected in previous H i studies. 19 of the objects have been detected for the first time in the 21-cm emission line in this survey. The distribution of the H i properties of our detections confirms our ability to find low-mass objects. 86 per cent of the detections have profile widths less than 130 km sâ1, and they can be considered dwarf galaxy candidates. The H i fluxes measured imply that this survey goes about 10 times deeper than any previous blind H i survey. The H i mass function and the optical properties of the detected sources will be discussed in future paper
Vacuum friction in rotating particles
We study the frictional torque acting on particles rotating in empty space.
At zero temperature, vacuum friction transforms mechanical energy into light
emission and produces particle heating. However, particle cooling relative to
the environment occurs at finite temperatures and low rotation velocities.
Radiation emission is boosted and its spectrum significantly departed from a
hot-body emission profile as the velocity increases. Stopping times ranging
from hours to billions of years are predicted for materials, particle sizes,
and temperatures accessible to experiment. Implications for the behavior of
cosmic dust are discussed.Comment: 4 figures, 10 pages, includes paper and supplementary information in
the appendi
Modelling of laboratory data of bi-directional reflectance of regolith surface containing Alumina
Bidirectional reflectance of a surface is defined as the ratio of the
scattered radiation at the detector to the incident irradiance as a function of
geometry. The accurate knowledge of the bidirectional reflection function (BRF)
of layers composed of discrete, randomly positioned scattering particles is
very essential for many remote sensing, engineering, biophysical applications
and in different areas of Astrophysics. The computations of BRF's for plane
parallel particulate layers are usually reduced to solve the radiative transfer
equation (RTE) by the existing techniques. In this work we present our
laboratory data on bidirectional reflectance versus phase angle for two sample
sizes of 0.3 and 1 of Alumina for the He-Ne laser at 632.8 nm (red) and
543.5nm(green) wavelength. The nature of the phase curves of the asteroids
depends on the parameters like- particle size, composition, porosity, roughness
etc. In our present work we analyse the data which are being generated using
single scattering phase function i.e. Mie theory considering particles to be
compact sphere. The well known Hapke formula will be considered along with
different particle phase function such as Mie and Henyey Greenstein etc to
model the laboratory data obtained at the asteroid laboratory of Assam
University.Comment: 5 pages, 5 figures [accepted for publication in Publications of the
Astronomical Society of Australia (PASA) on 8 June, 2011
REL: An Entity Linker Standing on the Shoulders of Giants
Entity linking is a standard component in modern retrieval system that is
often performed by third-party toolkits. Despite the plethora of open source
options, it is difficult to find a single system that has a modular
architecture where certain components may be replaced, does not depend on
external sources, can easily be updated to newer Wikipedia versions, and, most
important of all, has state-of-the-art performance. The REL system presented in
this paper aims to fill that gap. Building on state-of-the-art neural
components from natural language processing research, it is provided as a
Python package as well as a web API. We also report on an experimental
comparison against both well-established systems and the current
state-of-the-art on standard entity linking benchmarks
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