1,696 research outputs found
Transient behavior of surface plasmon polaritons scattered at a subwavelength groove
We present a numerical study and analytical model of the optical near-field
diffracted in the vicinity of subwavelength grooves milled in silver surfaces.
The Green's tensor approach permits computation of the phase and amplitude
dependence of the diffracted wave as a function of the groove geometry. It is
shown that the field diffracted along the interface by the groove is equivalent
to replacing the groove by an oscillating dipolar line source. An analytic
expression is derived from the Green's function formalism, that reproduces well
the asymptotic surface plasmon polariton (SPP) wave as well as the transient
surface wave in the near-zone close to the groove. The agreement between this
model and the full simulation is very good, showing that the transient
"near-zone" regime does not depend on the precise shape of the groove. Finally,
it is shown that a composite diffractive evanescent wave model that includes
the asymptotic SPP can describe the wavelength evolution in this transient
near-zone. Such a semi-analytical model may be useful for the design and
optimization of more elaborate photonic circuits whose behavior in large part
will be controlled by surface waves.Comment: 12 pages, 10 figure
Fine-Structure FeII* Emission and Resonant MgII Emission in z = 1 Star-Forming Galaxies
We present a study of the prevalence, strength, and kinematics of ultraviolet
FeII and MgII emission lines in 212 star-forming galaxies at z = 1 selected
from the DEEP2 survey. We find FeII* emission in composite spectra assembled on
the basis of different galaxy properties, indicating that FeII* emission is
prevalent at z = 1. In these composites, FeII* emission is observed at roughly
the systemic velocity. At z = 1, we find that the strength of FeII* emission is
most strongly modulated by dust attenuation, and is additionally correlated
with redshift, star-formation rate, and [OII] equivalent width, such that
systems at higher redshifts with lower dust levels, lower star-formation rates,
and larger [OII] equivalent widths show stronger FeII* emission. We detect MgII
emission in at least 15% of the individual spectra and we find that objects
showing stronger MgII emission have higher specific star-formation rates,
smaller [OII] linewidths, larger [OII] equivalent widths, lower dust
attenuations, and lower stellar masses than the sample as a whole. MgII
emission strength exhibits the strongest correlation with specific
star-formation rate, although we find evidence that dust attenuation and
stellar mass also play roles in the regulation of MgII emission. Future
integral field unit observations of the spatial extent of FeII* and MgII
emission in galaxies with high specific star-formation rates, low dust
attenuations, and low stellar masses will be important for probing the
morphology of circumgalactic gas.Comment: 29 pages, 22 figures, 2 tables; accepted to Ap
The Persistence of Cool Galactic Winds in High Stellar Mass Galaxies Between z~1.4 and ~1
We present an analysis of the MgII 2796, 2803 and FeII 2586, 2600 absorption
line profiles in coadded spectra of 468 galaxies at 0.7 < z < 1.5. The galaxy
sample, drawn from the Team Keck Treasury Redshift Survey of the GOODS-N field,
has a range in stellar mass (M_*) comparable to that of the sample at z~1.4
analyzed in a similar manner by Weiner et al. (2009; W09), but extends to lower
redshifts and has specific star formation rates which are lower by ~0.6 dex. We
identify outflows of cool gas from the Doppler shift of the MgII absorption
lines and find that the equivalent width (EW) of absorption due to outflowing
gas increases on average with M_* and star formation rate (SFR). We attribute
the large EWs measured in spectra of the more massive, higher-SFR galaxies to
optically thick absorbing clouds having large velocity widths. The outflows
have hydrogen column densities N(H) > 10^19.3 cm^-2, and extend to velocities
of ~500 km/s. While galaxies with SFR > 10 Msun/yr host strong outflows in both
this and the W09 sample, we do not detect outflows in lower-SFR (i.e., log
M_*/Msun < 10.5) galaxies at lower redshifts. Using a simple galaxy evolution
model which assumes exponentially declining SFRs, we infer that strong outflows
persist in galaxies with log M_*/Msun > 10.5 as they age between z=1.4 and z~1,
presumably because of their high absolute SFRs. Finally, using high resolution
HST/ACS imaging in tandem with our spectral analysis, we find evidence for a
weak trend (at 1 sigma significance) of increasing outflow absorption strength
with increasing galaxy SFR surface density.Comment: Submitted to ApJ. 25 pages, 19 figures, Figure 2 reduced in
resolution. Uses emulateapj forma
Low-ionization Line Emission from Starburst Galaxies: A New Probe of Galactic-Scale Outflows
We study the kinematically narrow, low-ionization line emission from a
bright, starburst galaxy at z = 0.69 using slit spectroscopy obtained with
Keck/LRIS. The spectrum reveals strong absorption in MgII and FeII resonance
transitions with Doppler shifts of -200 to -300 km/s, indicating a cool gas
outflow. Emission in MgII near and redward of systemic velocity, in concert
with the observed absorption, yields a P Cygni-like line profile similar to
those observed in the Ly alpha transition in Lyman Break Galaxies. Further, the
MgII emission is spatially resolved, and extends significantly beyond the
emission from stars and HII regions within the galaxy. Assuming the emission
has a simple, symmetric surface brightness profile, we find that the gas
extends to distances > ~7 kpc. We also detect several narrow FeII*
fine-structure lines in emission near the systemic velocity, arising from
energy levels which are radiatively excited directly from the ground state. We
suggest that the MgII and FeII* emission is generated by photon scattering in
the observed outflow, and emphasize that this emission is a generic prediction
of outflows. These observations provide the first direct constraints on the
minimum spatial extent and morphology of the wind from a distant galaxy.
Estimates of these parameters are crucial for understanding the impact of
outflows in driving galaxy evolution.Comment: Submitted to ApJL. 6 pages, 4 figures. Uses emulateapj forma
The DEEP2 Redshift Survey: Lyman Alpha Emitters in the Spectroscopic Database
We present the first results of a search for Lyman-alpha emitters (LAEs) in
the DEEP2 spectroscopic database that uses a search technique that is different
from but complementary to traditional narrowband imaging surveys. We have
visually inspected ~20% of the available DEEP2 spectroscopic data and have
found nine high-quality LAEs with clearly asymmetric line profiles and an
additional ten objects of lower quality, some of which may also be LAEs. Our
survey is most sensitive to LAEs at z=4.4-4.9 and that is indeed where all but
one of our high-quality objects are found. We find the number density of our
spectroscopically-discovered LAEs to be consistent with those found in
narrowband imaging searches. The combined, averaged spectrum of our nine
high-quality objects is well fit by a two-component model, with a second,
lower-amplitude component redshifted by ~420 km/s with respect to the primary
Lyman-alpha line, consistent with large-scale outflows from these objects. We
conclude by discussing the advantages and future prospects of blank-sky
spectroscopic surveys for high-z LAEs.Comment: Accepted for publication in Ap
Cryogenic On-Orbit Liquid Depot Storage, Acquisition, and Transfer satellite (COLD-SAT) feasibility study
The Cryogenic On-Orbit Liquid Depot Storage, Acquisition, and Transfer Satellite (COLD-SAT) is an experimental spacecraft launched from an expendable launch vehicle which is designed to investigate the systems and technologies required for efficient, effective, and reliable management of cryogenic fluid in the reduced gravity space environment. The COLD-SAT program will provide the necessary data base and provide low-g proving of fluid and thermal models of cryogenic storage, transfer, and resupply concepts and processes. A conceptual approach was developed and an overview of the results of the 24 month COLD-SAT Phase A feasibility is described which includes: (1) a definition of the technology needs and the accompanying experimental 3 month baseline mission; (2) a description of the experiment subsystem, major features and rationale for satisfaction of primary and secondary experiment requirements using liquid hydrogen as the test fluid; and (3) a presentation of the conceptual design of the COLD-SAT spacecraft subsystems which support the on-orbit experiment with emphasis on areas of greatest challenge
Electromagnetic Polarisability of the Nucleon in Chiral Perturbation Theory
We compute the polarisability of the nucleon to leading order in chiral
perturbation theory. The contributions from kaons and baryon resonances as
intermediate states are included in addition to the contribution from pions and
nucleons that had been previously computed. The isoscalar operators are
dominated by the infrared behaviour of pion loops giving rise to a
coefficient. In contrast, the isovector operators are dominated by loops
involving kaons, giving a coefficient, and further demonstrates that
the strange quark is an important component of the nucleon. In addition, the
inclusion of the decuplet of baryon resonances as intermediate states
substantially modifies the result found from the octet baryons alone for the
isoscalar polarisability.Comment: 11 pages (uses harvmac, figures available upon request) , UCSD/PTH
92-30, QUSTH-92-0
Collective modes and correlations in one-component plasmas
The static and time-dependent potential and surface charge correlations in a
plasma with a boundary are computed for different shapes of the boundary. The
case of a spheroidal or spherical one-component plasma is studied in detail
because experimental results are available for such systems. Also, since there
is some knowlegde both experimental and theoretical about the electrostatic
collective modes of these plasmas, the time-dependent correlations are computed
using a method involving these modes.Comment: 20 pages, plain TeX, submitted to Phys. Rev.
- …