1,239 research outputs found
Star Formation and the Interstellar Medium In Nearby Tidal Streams (SAINTS): Spitzer Mid-infrared Spectroscopy and Imaging of Intergalactic Star-forming Objects
A spectroscopic analysis of 10 intergalactic star forming objects (ISFOs) and
a photometric analysis of 67 ISFOs in a sample of 14 interacting systems is
presented. The majority of the ISFOs have relative polycyclic aromatic
hydrocarbon (PAH) band strengths similar to those of nearby spiral and
starburst galaxies. In contrast to what is observed in blue compact dwarfs
(BCDs) and local giant HII regions in the Milky Way (NGC 3603) and the
Magellanic Clouds (30 Doradus and N 66), the relative PAH band strengths in
ISFOs correspond to models with a significant PAH ion fraction (<50%) and
bright emission from large PAHs (~100 carbon atoms). The [NeIII]/[NeII] and
[SIV]/[SIII] line flux ratios indicate moderate levels of excitation with an
interstellar radiation field that is harder than the majority of the Spitzer
Infrared Nearby Galaxies Survey and starburst galaxies, but softer than BCDs
and local giant HII regions. The ISFO neon line flux ratios are consistent with
a burst of star formation < 6 million years ago. Most of the ISFOs have
~million solar masses of warm molecular hydrogen with a likely origin in
photo-dissociation regions (PDRs). Infrared Array Camera photometry shows the
ISFOs to be bright at 8 um, with one third having [4.5] - [8.0] > 3.7, i.e.,
enhanced non-stellar emission, most likely due to PAHs, relative to normal
spirals, dwarf irregulars and BCD galaxies. The relative strength of the 8 um
emission compared to that at 3.6 um or 24 um separates ISFOs from dwarf
galaxies in Spitzer two color diagrams. The infrared power in two thirds of the
ISFOs is dominated by emission from grains in a diffuse interstellar medium.
One in six ISFOs have significant emission from PDRs, contributing ~30 % - 60 %
of the total power. ISFOs are young knots of intense star formation.Comment: Accepted in ApJ. 49 pages 9 figure
Utility of Experimental Design in Automatic Target Recognition Performance Evaluation
This research investigates current practices in test and evaluation of classification algorithms, and recommends improvements. We scrutinize the evaluation of automatic target recognition algorithms and rationalize the potential for improvements in the accepted methodology. We propose improvements through the use of an experimental design approach to testing. We demonstrate the benefits of improvements by simulating algorithm performance data and using both methodologies to generate evaluation results. The simulated data is varied to test the sensitivity of the benefits to a broad set of outcomes. The opportunities for improvement are threefold. First, the current practice of \u27one-at-a-time factor variation (only one factor is varied in each test condition) fails to capture the effect of multiple factors. Next, the coarse characterization of data misses the opportunity to reduce the estimate of noise in test through the observation of uncontrolled factors. Finally, the lack of advanced data reduction and analysis tools renders analysis and reporting tedious and inefficient. This research addresses these shortcomings and recommends specific remedies through factorial testing, detailed data characterization, and logistic regression. We show how these innovations improve the accuracy and efficiency of automatic target recognition performance evaluation
Longitudinal variations, the opposition effect and monochromatic albedos for Mars
Magnitude at zero phase, phase coefficient, and monochromatic albedo computed for Mars as function of wavelengt
A Cosmic Ray Resolution to the Superbubble Energy-Crisis
Superbubbles (SBs) are amongst the greatest injectors of energy into the
Galaxy, and have been proposed to be the acceleration site of Galactic cosmic
rays. They are thought to be powered by the fast stellar winds and powerful
supernova explosions of massive stars in dense stellar clusters and
associations. Observations of the SB 'DEM L192' in the neighboring Large
Magellenic Cloud (LMC) galaxy show that it contains only about one-third the
energy injected by its constituent stars via fast stellar winds and supernovae.
It is not yet understood where the excess energy is going, thus, the so-called
'energy crisis'. We show here that it is very likely that a significant
fraction of the unaccounted for energy is being taken up in accelerating cosmic
rays, thus bolstering the argument for the SB origin of cosmic rays.Comment: Accepted for publication in ApJ
Calibration of Computational Models with Categorical Parameters and Correlated Outputs via Bayesian Smoothing Spline ANOVA
It has become commonplace to use complex computer models to predict outcomes
in regions where data does not exist. Typically these models need to be
calibrated and validated using some experimental data, which often consists of
multiple correlated outcomes. In addition, some of the model parameters may be
categorical in nature, such as a pointer variable to alternate models (or
submodels) for some of the physics of the system. Here we present a general
approach for calibration in such situations where an emulator of the
computationally demanding models and a discrepancy term from the model to
reality are represented within a Bayesian Smoothing Spline (BSS) ANOVA
framework. The BSS-ANOVA framework has several advantages over the traditional
Gaussian Process, including ease of handling categorical inputs and correlated
outputs, and improved computational efficiency. Finally this framework is then
applied to the problem that motivated its design; a calibration of a
computational fluid dynamics model of a bubbling fluidized which is used as an
absorber in a CO2 capture system
Resolving Star Formation on Sub-Kiloparsec Scales in the High-Redshift Galaxy SDP.11 Using Gravitational Lensing
We investigate the properties of the interstellar medium, star formation, and
the current-day stellar population in the strongly-lensed star-forming galaxy
H-ATLAS J091043.1-000321 (SDP.11), at z = 1.7830, using new Herschel and ALMA
observations of far-infrared fine-structure lines of carbon, oxygen and
nitrogen. We report detections of the [O III] 52 um, [N III] 57 um, and [O I]
63 um lines from Herschel/PACS, and present high-resolution imaging of the [C
II] 158 um line, and underlying continuum, using ALMA. We resolve the [C II]
line emission into two spatially-offset Einstein rings, tracing the red- and
blue-velocity components of the line, in the ALMA/Band-9 observations at 0.2"
resolution. The values seen in the [C II]/FIR ratio map, as low as ~ 0.02% at
the peak of the dust continuum, are similar to those of local ULIRGs,
suggesting an intense starburst in this source. This is consistent with the
high intrinsic FIR luminosity (~ 3 x 10^12 Lo), ~ 16 Myr gas depletion
timescale, and < 8 Myr timescale since the last starburst episode, estimated
from the hardness of the UV radiation field. By applying gravitational lensing
models to the visibilities in the uv-plane, we find that the lensing
magnification factor varies by a factor of two across SDP.11, affecting the
observed line profiles. After correcting for the effects of differential
lensing, a symmetric line profile is recovered, suggesting that the starburst
present here may not be the result of a major merger, as is the case for local
ULIRGs, but instead could be powered by star-formation activity spread across a
3-5 kpc rotating disk.Comment: 17 pages, 8 figures, 3 tables, accepted for publication in the
Astrophysical Journa
Soybean insects in Missouri
New 10/87/5M--Cover.Title from JPEG cover page (University of Missouri Digital Library, viewed Mar. 24, 2010)
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