2,550 research outputs found
Searching for additional heating - [OII] emission in the diffuse ionized gas of NGC891, NGC4631 and NGC3079
We present spectroscopic data of ionized gas in the disk--halo regions of
three edge-on galaxies, NGC 891, NGC 4631 and NGC 3079, covering a wavelength
range from [\ion{O}{2}] 3727\AA to [\ion{S}{2}] 6716.4\AA.
The inclusion of the [\ion{O}{2}] emission provides new constraints on the
properties of the diffuse ionized gas (DIG), in particular, the origin of the
observed spatial variations in the line intensity ratios. We used three
different methods to derive electron temperatures, abundances and ionization
fractions along the slit. The increase in the [\ion{O}{2}]/H line ratio
towards the halo in all three galaxies requires an increase either in electron
temperature or in oxygen abundance. Keeping the oxygen abundance constant
yields the most reasonable results for temperature, abundances, and ionization
fractions. Since a constant oxygen abundance seems to require an increase in
temperature towards the halo, we conclude that gradients in the electron
temperature play a significant role in the observed variations in the optical
line ratios from extraplanar DIG in these three spiral galaxies.Comment: 43 pages, 29 figure
THE IMPACT OF RECLAMATION ON ACCEPTABLE STRIP MINING ROYALTY PAYMENTS
Resource /Energy Economics and Policy,
Exploring the phase diagram of the two-impurity Kondo problem
A system of two exchange-coupled Kondo impurities in a magnetic field gives
rise to a rich phase space hosting a multitude of correlated phenomena.
Magnetic atoms on surfaces probed through scanning tunnelling microscopy
provide an excellent platform to investigate coupled impurities, but typical
high Kondo temperatures prevent field-dependent studies from being performed,
rendering large parts of the phase space inaccessible. We present an integral
study of pairs of Co atoms on insulating Cu2N/Cu(100), which each have a Kondo
temperature of only 2.6 K. In order to cover the different regions of the phase
space, the pairs are designed to have interaction strengths similar to the
Kondo temperature. By applying a sufficiently strong magnetic field, we are
able to access a new phase in which the two coupled impurities are
simultaneously screened. Comparison of differential conductance spectra taken
on the atoms to simulated curves, calculated using a third order transport
model, allows us to independently determine the degree of Kondo screening in
each phase.Comment: paper: 14 pages, 4 figures; supplementary: 3 pages, 1 figure, 1 tabl
Boundedness properties of fermionic operators
The fermionic second quantization operator is shown to be
bounded by a power of the number operator given that the operator
belongs to the -th von Neumann-Schatten class, . Conversely,
number operator estimates for imply von Neumann-Schatten
conditions on . Quadratic creation and annihilation operators are treated as
well.Comment: 15 page
Emission Line Ratios and Variations in Temperature and Ionization State in the Diffuse Ionized Gas of Five Edge-on Galaxies
We present spectroscopic observations of ionized gas in the disk-halo regions
of five edge-on galaxies, covering a wavelength range from [OII] 3727A to [SII]
6716.4A. The inclusion of the [OII] emission provides additional constraints on
the properties of the diffuse ionized gas (DIG), in particular, the origin of
the observed spatial variations in the line intensity ratios. We have derived
electron temperatures, ionization fractions and abundances along the slit. Our
data include both slit positions parallel and perpendicular to the galactic
disks. This allowed us to examine variations in the line intensity ratios with
height above the midplane as well as distance from the galactic centers. The
observed increase in the [OII]/Halpha line ratio towards the halo seems to
require an increase in electron temperature caused by a non-ionizing heating
mechanism. We conclude that gradients in the electron temperature can play a
significant role in the observed variations in the optical emission line ratios
from extraplanar DIG.Comment: accepted for publication in ApJ, 43 pages including 26 figure
Controlled complete suppression of single-atom inelastic spin and orbital cotunnelling
The inelastic portion of the tunnel current through an individual magnetic
atom grants unique access to read out and change the atom's spin state, but it
also provides a path for spontaneous relaxation and decoherence. Controlled
closure of the inelastic channel would allow for the latter to be switched off
at will, paving the way to coherent spin manipulation in single atoms. Here we
demonstrate complete closure of the inelastic channels for both spin and
orbital transitions due to a controlled geometric modification of the atom's
environment, using scanning tunnelling microscopy (STM). The observed
suppression of the excitation signal, which occurs for Co atoms assembled into
chain on a CuN substrate, indicates a structural transition affecting the
d orbital, effectively cutting off the STM tip from the spin-flip
cotunnelling path.Comment: 4 figures plus 4 supplementary figure
Evidence for an Additional Heat Source in the Warm Ionized Medium of Galaxies
Spatial variations of the [S II]/H-Alpha and [N II]/H-Alpha line intensity
ratios observed in the gaseous halo of the Milky Way and other galaxies are
inconsistent with pure photoionization models. They appear to require a
supplemental heating mechanism that increases the electron temperature at low
densities n_e. This would imply that in addition to photoionization, which has
a heating rate per unit volume proportional to n_e^2, there is another source
of heat with a rate per unit volume proportional to a lower power of n_e. One
possible mechanism is the dissipation of interstellar plasma turbulence, which
according to Minter & Spangler (1997) heats the ionized interstellar medium in
the Milky Way at a rate ~ 1x10^-25 n_e ergs cm^-3 s^-1. If such a source were
present, it would dominate over photoionization heating in regions where n_e <
0.1 cm^-3, producing the observed increases in the [S II]/H-Alpha and [N
II]/H-Alpha intensity ratios at large distances from the galactic midplane, as
well as accounting for the constancy of [S II]/[N II], which is not explained
by pure photoionization. Other supplemental heating sources, such as magnetic
reconnection, cosmic rays, or photoelectric emission from small grains, could
also account for these observations, provided they supply to the warm ionized
medium ~ 10^-5 ergs s^-1 per cm^2 of Galactic disk.Comment: 10 pages, 1 figur
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