2,216 research outputs found
Information Management System for the California State Water Resources Control Board (SWRCB)
A study was made to establish the requirements for an integrated state-wide information management system for water quality control and water quality rights for the State of California. The data sources and end requirements were analyzed for the data collected and used by the numerous agencies, both State and Federal, as well as the nine Regional Boards under the jurisdiction of the State Board. The report details the data interfaces and outlines the system design. A program plan and statement of work for implementation of the project is included
Seeking large-scale magnetic fields in a pure-disk dwarf galaxy NGC 2976
It is still unknown how magnetic field-generation mechanisms could operate in
low-mass dwarf galaxies. Here, we present a detailed study of a nearby
pure-disk dwarf galaxy NGC 2976. Unlike previously observed dwarf objects, this
galaxy possesses a clearly defined disk. For the purpose of our studies, we
performed deep multi-frequency polarimetric observations of NGC 2976 with the
VLA and Effelsberg radio telescopes. Additionally, we supplement them with
re-imaged data from the WSRT-SINGS survey. The magnetic field morphology
discovered in NGC 2976 consists of a southern polarized ridge. This structure
does not seem to be due to just a pure large-scale dynamo process (possibly
cosmic-ray driven) at work in this object, as indicated by the RM data and
dynamo number calculations. Instead, the field of NGC 2976 is modified by past
gravitational interactions and possibly also by ram pressure inside the M 81
galaxy group environment. The estimates of total (7 muG) and ordered (3 muG)
magnetic field strengths, as well as degree of field order (0.46), which is
similar to those observed in spirals, suggest that tidally generated magnetized
gas flows can further enhance dynamo action in the object. NGC 2976 is
apparently a good candidate for the efficient magnetization of its
neighbourhood. It is able to provide an ordered (perhaps also regular) magnetic
field into the intergalactic space up to a distance of about 5 kpc. Tidal
interactions (and possibly also ram pressure) can lead to the formation of
unusual magnetic field morphologies (like polarized ridges) in galaxies out of
the star-forming disks, which do not follow any observed component of the
interstellar medium (ISM), as observed in NGC 2976. These galaxies are able to
provide ordered magnetic fields far out of their main disks.Comment: 16 page
HI observations of the nearest starburst galaxy NGC 253 with the SKA precursor KAT-7
We present HI observations of the Sculptor Group starburst spiral galaxy NGC
253, obtained with the Karoo Array Telescope (KAT-7). KAT-7 is a pathfinder for
the SKA precursor MeerKAT, under construction. The short baselines and low
system temperature of the telescope make it very sensitive to large scale, low
surface brightness emission. The KAT-7 observations detected 33% more flux than
previous VLA observations, mainly in the outer parts and in the halo for a
total HI mass of M. HI can be found at
large distances perpendicular to the plane out to projected distances of ~9-10
kpc away from the nucleus and ~13-14 kpc at the edge of the disk. A novel
technique, based on interactive profile fitting, was used to separate the main
disk gas from the anomalous (halo) gas. The rotation curve (RC) derived for the
HI disk confirms that it is declining in the outer parts, as seen in previous
optical Fabry-Perot measurements. As for the anomalous component, its RC has a
very shallow gradient in the inner parts and turns over at the same radius as
the disk, kinematically lagging by ~100 km/sec. The kinematics of the observed
extra planar gas is compatible with an outflow due to the central starburst and
galactic fountains in the outer parts. However, the gas kinematics shows no
evidence for inflow. Analysis of the near-IR WISE data, shows clearly that the
star formation rate (SFR) is compatible with the starburst nature of NGC 253.Comment: 18 pages, 20 figures, 8 Tables. Accepted for publication to MNRA
The radial variation of HI velocity dispersions in dwarfs and spirals
Gas velocity dispersions provide important diagnostics of the forces
counteracting gravity to prevent collapse of the gas. We use the 21 cm line of
neutral atomic hydrogen (HI) to study HI velocity dispersion and HI phases as a
function of galaxy morphology in 22 galaxies from The HI Nearby Galaxy Survey
(THINGS). We stack individual HI velocity profiles and decompose them into
broad and narrow Gaussian components. We study the HI velocity dispersion and
the HI surface density, as a function of radius. For spirals, the velocity
dispersions of the narrow and broad components decline with radius and their
radial profiles are well described by an exponential function. For dwarfs,
however, the profiles are much flatter. The single Gaussian dispersion profiles
are, in general, flatter than those of the narrow and broad components. In most
cases, the dispersion profiles in the outer disks do not drop as fast as the
star formation profiles, derived in the literature. This indicates the
importance of other energy sources in driving HI velocity dispersion in the
outer disks. The radial surface density profiles of spirals and dwarfs are
similar. The surface density profiles of the narrow component decline more
steeply than those of the broad component, but not as steep as what was found
previously for the molecular component. As a consequence, the surface density
ratio between the narrow and broad components, an estimate of the mass ratio
between cold HI and warm HI, tends to decrease with radius. On average, this
ratio is lower in dwarfs than in spirals. This lack of a narrow, cold HI
component in dwarfs may explain their low star formation activity.Comment: Accepted for publication in The Astronomical Journal, 13 pages, 10
figures, 4 table
Resolved magnetic structures in the disk-halo interface of NGC 628
Magnetic fields are essential to fully understand the interstellar medium
(ISM) and its role in the disk-halo interface of galaxies is still poorly
understood. Star formation is known to expel hot gas vertically into the halo
and these outflows have important consequences for mean-field dynamo theory in
that they can be efficient in removing magnetic helicity. We perform new
observations of the nearby face-on spiral galaxy NGC 628 with the Karl G.
Jansky Very Large Array (JVLA) at S-band and the Effelsberg 100-m telescope at
frequencies of 2.6 GHz and 8.35 GHz. We obtain some of the most sensitive radio
continuum images in both total and linearly polarised intensity of any external
galaxy observed so far in addition to high-quality images of Faraday depth and
polarisation angle from which we obtained evidence for drivers of magnetic
turbulence in the disk-halo connection. Such drivers include a superbubble
detected via a significant Faraday depth gradient coinciding with a HI hole. We
observe an azimuthal periodic pattern in Faraday depth with a pattern
wavelength of 3.7 0.1 kpc, indicating Parker instabilities. The lack of a
significant anti-correlation between Faraday depth and magnetic pitch angle
indicates that these loops are vertical in nature with little helical twisting,
unlike in IC 342. We find that the magnetic pitch angle is systematically
larger than the morphological pitch angle of the polarisation arms which gives
evidence for the action of a large-scale dynamo where the regular magnetic
field is not coupled to the gas flow and obtains a significant radial
component. We additionally discover a lone region of ordered magnetic field to
the north of the galaxy with a high degree of polarisation and a small pitch
angle, a feature that has not been observed in any other galaxy so far and is
possibly caused by an asymmetric HI hole.Comment: 25 pages, Accepted for publication in Astronomy and Astrophysic
Accurate Recovery of H i Velocity Dispersion from Radio Interferometers
Gas velocity dispersion measures the amount of disordered motion of a rotating disk. Accurate estimates of this parameter are of the utmost importance because the parameter is directly linked to disk stability and star formation. A global measure of the gas velocity dispersion can be inferred from the width of the atomic hydrogen (H I) 21 cm line. We explore how several systematic effects involved in the production of H I cubes affect the estimate of H I velocity dispersion. We do so by comparing the H I velocity dispersion derived from different types of data cubes provided by The H I Nearby Galaxy Survey. We find that residual-scaled cubes best recover the H I velocity dispersion, independent of the weighting scheme used and for a large range of signal-to-noise ratio. For H I observations, where the dirty beam is substantially different from a Gaussian, the velocity dispersion values are overestimated unless the cubes are cleaned close to (e.g., ˜1.5 times) the noise level
Gravitation as a Casimir interaction
Gravitation is considered to be one of the four fundamental interactions in
nature. However, one has so far failed to observe the graviton, the quantum
particle that is believed to transmit the gravitational force at a distance -
the analogue to the photon in electromagnetism. Maybe it is now time to
re-evaluate the status of the gravitation as a fundamental interaction. Here,
we propose a completely new interpretation of gravitation. In this description
the gravitational force is no longer a fundamental force. It is an induced
force, a dispersion force, and the analogue to the Casimir force in
electromagnetism. The fundamental force is in our description a force between
particles with a parabolic interaction potential. In our model the nucleons are
made up from these particles. We find the retarded dispersion force between
these composite particles has the correct distance dependence, 1/r. If this
interpretation is correct it has a broad range of implications. Our view on the
fundamental concept mass is altered; our view on the expansion of the Universe
may change
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