4,874 research outputs found
MRC B0319-454: Probing the large-scale structure with a giant radio galaxy
We present an investigation of the relationships between the radio properties
of a giant radio galaxy MRC B0319-454 and the surrounding galaxy distribution
with the aim of examining the influence of intergalactic gas and gravity
associated with the large-scale structure on the evolution in the radio
morphology. Our new radio continuum observations of the radio source, with high
surface brightness sensitivity, images the asymmetries in the megaparsec-scale
radio structure in total intensity and polarization. We compare these with the
3-D galaxy distribution derived from galaxy redshift surveys. Galaxy density
gradients are observed along and perpendicular to the radio axis: the
large-scale structure is consistent with a model wherein the galaxies trace the
ambient intergalactic gas and the evolution of the radio structures are
ram-pressure limited by this associated gas. Additionally, we have modeled the
off-axis evolution of the south-west radio lobe as deflection of a buoyant jet
backflow by a transverse gravitational field: the model is plausible if
entrainment is small. The case study presented here is a demonstration that
giant radio galaxies may be useful probes of the warm-hot intergalactic medium
believed to be associated with moderately over dense galaxy distributions.Comment: 27 pages, 15 figures, accepted for publication in MNRA
The radio-ultraviolet spectral energy distribution of the jet in 3C273
We present deep VLA and HST observations of the large-scale jet in 3C 273
matched to 0.3" resolution. The observed spectra show a significant flattening
in the infrared-ultraviolet wavelength range. The jet's emission cannot
therefore be assumed to arise from a single electron population and requires
the presence of an additional emission component. The observed smooth
variations of the spectral indices along the jet imply that the physical
conditions vary correspondingly smoothly. We determine the maximum particle
energy for the optical jet using synchrotron spectral fits. The slow decline of
the maximum energy along the jet implies particle reacceleration acting along
the entire jet. In addition to the already established global anti-correlation
between maximum particle energy and surface brightness, we find a weak positive
correlation between small-scale variations in maximum particle energy and
surface brightness. The origin of these conflicting global and local
correlations is unclear, but they provide tight constraints for reacceleration
models.Comment: 28 pages, lots of figures, accepted for publication in A&
Investigations of electron emission characteristics of low work function surfaces Final report, 27 Sep. 1964 - 28 Sep. 1966
Electron emission characteristics of low work function surface
Neutrino Signatures and the Neutrino-Driven Wind in Binary Neutron Star Mergers
We present VULCAN/2D multigroup flux-limited-diffusion radiation-hydrodynamics simulations of binary neutron star mergers, using the Shen equation of state, covering ≳ 100 ms, and starting from azimuthal-averaged two-dimensional slices obtained from three-dimensional smooth-particle-hydrodynamics simulations of Rosswog & Price for 1.4M☉ (baryonic) neutron stars with no initial spins, co-rotating spins, or counter-rotating spins. Snapshots are post-processed at 10 ms intervals with a multiangle neutrino-transport solver. We find polar-enhanced neutrino luminosities, dominated by ¯νe and “νμ” neutrinos at the peak, although νe emission may be stronger at late times. We obtain typical peak neutrino energies for νe, ¯νe, and “νμ” of ∼12, ∼16, and ∼22 MeV, respectively. The supermassive neutron star (SMNS) formed from the merger has a cooling timescale of ≾ 1 s. Charge-current neutrino reactions lead to the formation of a thermally driven bipolar wind with (M·) ∼ 10^−3 M☉ s^−1 and baryon-loading in the polar regions, preventing any production of a γ-ray burst prior to black hole formation. The large budget of rotational free energy suggests that magneto-rotational effects could produce a much-greater polar mass loss. We estimate that ≾ 10^−4 M☉ of material with an electron fraction in the range 0.1–0.2 becomes unbound during this SMNS phase as a result of neutrino heating. We present a new formalism to compute the νi ¯νi annihilation rate based on moments of the neutrino-specific intensity computed with our multiangle solver. Cumulative annihilation rates, which decay as ∼t^−1.8, decrease over our 100 ms window from a few ×1050 to ∼ 1049 erg s−1, equivalent to a few ×10^54 to ∼10^53 e−e+ pairs per second
Detection of Extended Hot Water in the Outflow from NGC 2071
We report the results of spectroscopic mapping observations carried out
toward a ~1 min x 1 min region within the northern lobe of the outflow from NGC
2071 using the Infrared Spectrograph (IRS) of the Spitzer Space Telescope.
These observations covered the 5.2-37 um spectral region and have led to the
detection of a number of ionic, atomic, and molecular lines, including
fine-structure emission of Si+, Fe+, S++, S, the S(0)-S(7) pure rotational
lines of H2, the R(3) and R(4) transitions of HD, and at least 11 transitions
of H2O. In addition, the 6.2, 7.4, 7.6, 7.9, 8.6 and 11.3 um PAH emission bands
were also observed and several transitions of OH were tentatively detected.
Most of the detected line transitions were strong enough to map including, for
the first time, three transitions of hot H2O. We find that: (1) the water
emission is extended; (2) the extended emission is aligned with the outflow;
and, (3) the spatial distribution of the water emission generally follows that
observed for H2. Based on the measured line intensities, we derive an HD
abundance relative to H2 of 1.1-1.8 10^-5 and an H2O number density of 12-2
cm^3. The H2 density in the water-emitting region is not well constrained by
our observations, but is likely between 3 10^4 and 10^6 cm^3, yielding an H2O
abundance relative to H2 of between 2 10^-5 and 6 10^-4. Future observations
planned for the Herschel Space Observatory should greatly improve the density
estimate, and thus our knowledge of the H2O abundance, for the water-emitting
regions reported here. Finally, we note a possible departure from the H2O
ortho-to-para ratio of 3:1 expected for water formed in hot post-shocked gas,
suggesting that a significant fraction of the water vapor we detect may arise
from H2O sputtered from cold dust grains.Comment: 35 pages, 15 figures, 4 tables, accepted for publication in Ap
Internal report cluster 1: Urban freight innovations and solutions for sustainable deliveries (3/4)
Technical report about sustainable urban freight solutions, part 3 of
- …