322 research outputs found
The Wyoming Survey for H-alpha. I. Initial Results at z ~ 0.16 and 0.24
The Wyoming Survey for H-alpha, or WySH, is a large-area, ground-based,
narrowband imaging survey for H-alpha-emitting galaxies over the latter half of
the age of the Universe. The survey spans several square degrees in a set of
fields of low Galactic cirrus emission. The observing program focuses on
multiple dz~0.02 epochs from z~0.16 to z~0.81 down to a uniform
(continuum+line) luminosity at each epoch of ~10^33 W uncorrected for
extinction (3sigma for a 3" diameter aperture). First results are presented
here for 98+208 galaxies observed over approximately 2 square degrees at
redshifts z~0.16 and 0.24, including preliminary luminosity functions at these
two epochs. These data clearly show an evolution with lookback time in the
volume-averaged cosmic star formation rate. Integrals of Schechter fits to the
extinction-corrected H-alpha luminosity functions indicate star formation rates
per co-moving volume of 0.009 and 0.014 h_70 M_sun/yr/Mpc^3 at z~0.16 and 0.24,
respectively. The formal uncertainties in the Schechter fits, based on this
initial subset of the survey, correspond to uncertainties in the cosmic star
formation rate density at the >~40% level; the tentative uncertainty due to
cosmic variance is 25%, estimated from separately carrying out the analysis on
data from the first two fields with substantial datasets.Comment: To appear in the Astronomical Journa
The ACS Nearby Galaxy Survey Treasury. X. Quantifying the Star Cluster Formation Efficiency of Nearby Dwarf Galaxies
We study the relationship between the field star formation and cluster
formation properties in a large sample of nearby dwarf galaxies. We use optical
data from the Hubble Space Telescope and from ground-based telescopes to derive
the ages and masses of the young (t_age < 100Myr) cluster sample. Our data
provides the first constraints on two proposed relationships between the star
formation rate of galaxies and the properties of their cluster systems in the
low star formation rate regime. The data show broad agreement with these
relationships, but significant galaxy-to-galaxy scatter exists. In part, this
scatter can be accounted for by simulating the small number of clusters
detected from stochastically sampling the cluster mass function. However, this
stochasticity does not fully account for the observed scatter in our data
suggesting there may be true variations in the fraction of stars formed in
clusters in dwarf galaxies. Comparison of the cluster formation and the
brightest cluster in our sample galaxies also provide constraints on cluster
destruction models.Comment: 16 pages, 9 figures, Accepted to Ap
Implementation of environmentally compliant cleaning and insulation bonding for MNASA
Historically, many subscale and full-scale rocket motors have employed environmentally and physiologically harmful chemicals during the manufacturing process. This program examines the synergy and interdependency between environmentally acceptable materials for solid rocket motor insulation applications, bonding, corrosion inhibiting, painting, priming, and cleaning, and then implements new materials and processes in subscale motors. Tests have been conducted to eliminate or minimize hazardous chemicals used in the manufacture of modified-NASA materials test motor (MNASA) components and identify alternate materials and/or processes following NASA Operational Environmental Team (NOET) priorities. This presentation describes implementation of high pressure water refurbishment cleaning, aqueous precision cleaning using both Brulin 815 GD and Jettacin, and insulation case bonding using ozone depleting chemical (ODC) compliant primers and adhesives
Fluorescence resonance energy transfer between organic dyes adsorbed onto nano-clay and Langmuir-Blodgett (LB) films
In this communication we investigate two dyes N,N' -dioctadecyl thiacyanine
perchlorate (NK) and octadecyl rhodamine B chloride (RhB) in Langmuir and
Langmuir-Blodgett (LB) films with or with out a synthetic clay laponite.
Observed changes in isotherms of RhB in absence and presence of nano-clay
platelets indicate the incorporation of clay platelets onto RhB-clay hybrid
films. AFM image confirms the incorporation of clay in hybrid films. FRET was
observed in clay dispersion and LB films with and without clay. Efficiency of
energy transfer was maximum in LB films with clay.Comment: 15 pages 5 figures, 1 tabl
The Wyoming Survey for H-alpha. III. A Multi-wavelength Look at Attenuation by Dust in Galaxies out to z~0.4
We report results from the Wyoming Survey for H-alpha (WySH), a comprehensive
four-square degree survey to probe the evolution of star-forming galaxies over
the latter half of the age of the Universe. We have supplemented the H-alpha
data from WySH with infrared data from the Spitzer Wide-area Infrared
Extragalactic (SWIRE) Survey and ultraviolet data from the Galaxy Evolution
Explorer (GALEX) Deep Imaging Survey. This dataset provides a multi-wavelength
look at the evolution of the attenuation by dust, and here we compare a
traditional measure of dust attenuation (L(TIR)/L(FUV)) to a diagnostic based
on a recently-developed robust star formation rate (SFR) indicator,
[H-alpha_obs+24-micron]/H-alpha_obs. With such data over multiple epochs, the
evolution in the attenuation by dust with redshift can be assessed. We present
results from the ELAIS-N1 and Lockman Hole regions at z~0.16, 0.24, 0.32 and
0.40. While the ensemble averages of both diagnostics are relatively constant
from epoch to epoch, each epoch individually exhibits a larger attenuation by
dust for higher star formation rates. Hence, an epoch to epoch comparison at a
fixed star formation rate suggests a mild decrease in dust attenuation with
redshift.Comment: 30 pages, 9 figure
Resolved Near-infrared Stellar Populations in Nearby Galaxies
We present near-infrared (NIR) color-magnitude diagrams (CMDs) for the resolved stellar populations within 26 fields of 23 nearby galaxies (≲ 4 Mpc), based on images in the F110W and F160W filters taken with the Wide-Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). The CMDs are measured in regions spanning a wide range of star formation histories, including both old dormant and young star-forming populations. We match key NIR CMD features with their counterparts in more familiar optical CMDs, and identify the red core helium-burning (RHeB) sequence as a significant contributor to the NIR flux in stellar populations younger than a few 100 Myr old. The strength of this feature suggests that the NIR mass-to-light ratio can vary significantly on short timescales in star-forming systems. The NIR luminosity of star-forming galaxies is therefore not necessarily proportional to the stellar mass. We note that these individual RHeB stars may also be misidentified as old stellar clusters in images of nearby galaxies. For older stellar populations, we discuss the CMD location of asymptotic giant branch (AGB) stars in the HST filter set and explore the separation of AGB subpopulations using a combination of optical and NIR colors. We empirically calibrate the magnitude of the NIR tip of the red giant branch in F160W as a function of color, allowing future observations in this widely adopted filter set to be used for distance measurements. We also analyze the properties of the NIR red giant branch (RGB) as a function of metallicity, showing a clear trend between NIR RGB color and metallicity. However, based on the current study, it appears unlikely that the slope of the NIR RGB can be used as an effective metallicity indicator in extragalactic systems with comparable data. Finally, we highlight issues with scattered light in the WFC3, which becomes significant for exposures taken close to a bright Earth limb
Use of Anticoagulant Rodenticides in Single-Family Neighborhoods Along an Urban-Wildland Interface in California
Urbanization poses many threats for many wildlife species. In addition to habitat loss and fragmentation, non-target wildlife species are vulnerable to poisoning by rodenticides, especially acutely toxic second generation anticoagulant rodenticides (SGARs). Although such poisonings are well documented for birds and mammals worldwide, the pathways by which these widely available compounds reach non-target wildlife have not been adequately studied, particularly in urban landscapes. Long-term studies of wild carnivores in and around Santa Monica Mountains National Recreation Area, a national park north of Los Angeles, have documented \u3e85% exposure to anticoagulant rodenticides among bobcats, coyotes, and mountain lions. To investigate potential mechanisms of transfer of chemicals from residential users of rodenticides to non-target wildlife in the Santa Monica Mountains in Los Angeles County, California, we distributed surveys to residents in two study areas on the north (San Fernando Valley) and south (Bel Air-Hollywood Hills) slopes of these mountains. We assessed knowledge of residents about the environmental effects of rodenticides, and for information about individual application of chemicals. We asked for the same information from pest control operators (PCOs) in both study areas. Forty residents completed the survey in the San Fernando Valley area, and 20 residents completed the survey in Bel Air-Hollywood Hills. Despite the small number of total responses, we documented a number of important findings. Homeowners (as opposed to gardeners or PCOs) were the primary applicators of rodenticides, predominantly SGARs, and awareness of the hazards of secondary poisoning to wildlife was not consistent. Some residents reported improperly applying rodenticides (e.g., exceeding prescribed distances from structures), and in one instance a respondent reported observing dead animals outside after placing poison inside a structure. Improper application of SGARs that ignores label guidelines occurs in neighborhoods along the urban–wildland interface, thereby providing a transmission pathway for chemical rodenticides to reach native wildlife. Moreover, the responses suggest that even on-label use (e.g. placing poisons inside) can create risk for non-target wildlife
A Critical Assessment of Stellar Mass Measurement Methods
In this paper we perform a comprehensive study of the main sources of random
and systematic errors in stellar mass measurement for galaxies using their
Spectral Energy Distributions (SEDs). We use mock galaxy catalogs with
simulated multi-waveband photometry (from U-band to mid-infrared) and known
redshift, stellar mass, age and extinction for individual galaxies. Given
different parameters affecting stellar mass measurement (photometric S/N
ratios, SED fitting errors, systematic effects, the inherent degeneracies and
correlated errors), we formulated different simulated galaxy catalogs to
quantify these effects individually. We studied the sensitivity of stellar mass
estimates to the codes/methods used, population synthesis models, star
formation histories, nebular emission line contributions, photometric
uncertainties, extinction and age. For each simulated galaxy, the difference
between the input stellar masses and those estimated using different simulation
catalogs, , was calculated and used to identify the most
fundamental parameters affecting stellar masses. We measured different
components of the error budget, with the results listed as follows: (1). no
significant bias was found among different codes/methods, with all having
comparable scatter; (2). A source of error is found to be due to photometric
uncertainties and low resolution in age and extinction grids; (3). The median
of stellar masses among different methods provides a stable measure of the mass
associated with any given galaxy; (4). The deviations in stellar mass strongly
correlate with those in age, with a weaker correlation with extinction; (5).
the scatter in the stellar masses due to free parameters are quantified, with
the sensitivity of the stellar mass to both the population synthesis codes and
inclusion of nebular emission lines studied.Comment: 33 pages, 20 Figures, Accepted for publication in Astrophysical
Journa
Automating Spacecraft Analysis: The Era of Ontological Modeling & Simulation
Verification by analysis is a predicted compliance of a design to imposed requirements. The levels of performance specified by performance requirements can be related to Technical Performance Measures (TPM) in a Model-Based Systems Engineering (MBSE) environment, but engineers performing verification by analysis are not commonly versed in professional Systems Engineering (SE) techniques or modeling languages such as SysML. As the formal application of Systems Engineering (SE) results in a diminution of time, effort, and money for large-scale projects, enabling technical engineers performing verification by analysis to contribute to MBSE improvements in the course of their daily work is financially incentivized. Ontologies applied to technical analysis methodologies are shown to improve the quality of verification by analysis activities while adhering to professional organization standards such as the International Council on Systems Engineering (INCOSE) SE Handbook and the National Aeronautics and Space Administration (NASA) standard 7009A: Standard for Models and Simulations
Instrumental performance and results from testing of the BLAST-TNG receiver, submillimeter optics, and MKID arrays
Polarized thermal emission from interstellar dust grains can be used to map
magnetic fields in star forming molecular clouds and the diffuse interstellar
medium (ISM). The Balloon-borne Large Aperture Submillimeter Telescope for
Polarimetry (BLASTPol) flew from Antarctica in 2010 and 2012 and produced
degree-scale polarization maps of several nearby molecular clouds with
arcminute resolution. The success of BLASTPol has motivated a next-generation
instrument, BLAST-TNG, which will use more than 3000 linear polarization
sensitive microwave kinetic inductance detectors (MKIDs) combined with a 2.5m
diameter carbon fiber primary mirror to make diffraction-limited observations
at 250, 350, and 500 m. With 16 times the mapping speed of BLASTPol,
sub-arcminute resolution, and a longer flight time, BLAST-TNG will be able to
examine nearby molecular clouds and the diffuse galactic dust polarization
spectrum in unprecedented detail. The 250 m detector array has been
integrated into the new cryogenic receiver, and is undergoing testing to
establish the optical and polarization characteristics of the instrument.
BLAST-TNG will demonstrate the effectiveness of kilo-pixel MKID arrays for
applications in submillimeter astronomy. BLAST-TNG is scheduled to fly from
Antarctica in December 2017 for 28 days and will be the first balloon-borne
telescope to offer a quarter of the flight for "shared risk" observing by the
community.Comment: Presented at SPIE Millimeter, Submillimeter, and Far-Infrared
Detectors and Instrumentation for Astronomy VIII, June 29th, 201
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