125 research outputs found
Measurement of the Cosmic Optical Background using the Long Range Reconnaissance Imager on New Horizons
The cosmic optical background is an important observable that constrains
energy production in stars and more exotic physical processes in the universe,
and provides a crucial cosmological benchmark against which to judge theories
of structure formation. Measurement of the absolute brightness of this
background is complicated by local foregrounds like the Earth's atmosphere and
sunlight reflected from local interplanetary dust, and large discrepancies in
the inferred brightness of the optical background have resulted. Observations
from probes far from the Earth are not affected by these bright foregrounds.
Here we analyze data from the Long Range Reconnaissance Imager (LORRI)
instrument on NASA's New Horizons mission acquired during cruise phase outside
the orbit of Jupiter, and find a statistical upper limit on the optical
background's brightness similar to the integrated light from galaxies. We
conclude that a carefully performed survey with LORRI could yield uncertainties
comparable to those from galaxy counting measurements.Comment: 35 pages, 11 figures, published in Nature Communication
Measurement of the temperature and polarization anisotropies in the cosmic microwave background with QUaD.
This thesis paper describes QUaD, a millimetric polarimeter designed to precisely measure the temperature and polarization anisotropics in the cosmic microwave background (CMB) radiation. QUaD was built and integrated between 2000 and 2004, and commissioned at the south pole in the austral summer of 2004/2005. First light was achieved in February 2005, and QUaD acquired a full austral winter of data during that year. Modifications to the instrument were performed in the austral summer of 2005/2006, and QUaD is currently taking a second season of data. A third season is planned. QUaD is composed of a cryogenically cooled receiver mounted on a Cassegrain telescope using a 2.6 m primary mirror. The detectors are polarization sensitive Neutron Transmutation Doped germanium bolometers which are coupled to the optics via single- moded corrugated feed horns. These detectors are split between two frequency bands, 100 and 150 GHz, and the optics allow angular resolutions of 6.0 and 4.0 arcminutes in these two bands. The performance of the instrument has been characterized using extensive laboratory data, a battery of tests performed during commissioning, and specially designed measurements during the observing season. QUaD uses constant elevation azimuth scans with 15 degree lengths, allowing reconstruction of all 6 CMB power spectra in the range 50 < £ < 2000. Customized software and analysis methods are required to transform data time series from the telescope to refined data products. QUaD data have provided the most accurate measurements of the £-mode CMB power spectrum to date, as well as measurements of T-mode power competitive with the best high angular resolution experiments. These measurements provide a wealth of information, and both confirm our model for the early Universe as well as constrain cosmological parameters. Furthermore, QUaD measures the formation of structure after recombination, and can constrain the physics of inflation
Spatial and Temporal Stability of Airglow Measured in the Meinel Band Window at 1191.3 nm
We report on the temporal and spatial fluctuations in the atmospheric
brightness in the narrow band between Meinel emission lines at 1191.3 nm using
an R=320 near-infrared instrument. We present the instrument design and
implementation, followed by a detailed analysis of data taken over the course
of a night from Table Mountain Observatory. The absolute sky brightness at this
wavelength is found to be 5330 +/- 30 nW m^-2 sr^-1, consistent with previous
measurements of the inter-band airglow at these wavelengths. This amplitude is
larger than simple models of the continuum component of the airglow emission at
these wavelengths, confirming that an extra emissive or scattering component is
required to explain the observations. We perform a detailed investigation of
the noise properties of the data and find no evidence for a noise component
associated with temporal instability in the inter-line continuum. This result
demonstrates that in several hours of ~100s integrations the noise performance
of the instrument does not appear to significantly degrade from expectations,
giving a proof of concept that near-IR line intensity mapping may be feasible
from ground-based sites.Comment: 15 figures, submitted to PAS
A Measurement of the Cosmic Optical Background and Diffuse Galactic Light Scaling from the R < 50 AU New Horizons-LORRI Data
Direct photometric measurements of the cosmic optical background (COB)
provide an important point of comparison to both other measurement
methodologies and models of cosmic structure formation, and permit a cosmic
consistency test with the potential to reveal additional diffuse sources of
emission. The COB has been challenging to measure from Earth due to the
difficulty of isolating it from the diffuse light scattered from interplanetary
dust in our solar system. We present a measurement of the COB using data taken
by the Long-Range Reconnaissance Imager (LORRI) on NASA's New Horizons mission,
considering all data acquired to 47 AU. We employ a blind methodology where our
analysis choices are developed against a subset of the full data set, which is
then unblinded. Dark current and other instrumental systematics are accounted
for, including a number of sources of scattered light. We fully characterize
and remove structured and diffuse astrophysical foregrounds including bright
stars, the integrated starlight from faint unresolved sources, and diffuse
galactic light. For the full data set, we find the surface brightness of the
COB to be 21.98 1.23 (stat.)
1.36 (cal.) nW m sr. This result supports recent
determinations that find a factor of 2 3 more light than
expected from the integrated light from galaxies and motivate new diffuse
intensity measurements with more capable instruments that can support spectral
measurements over the optical and near-IR.Comment: 36 pages, 22 figures, 8 tables; accepted for publication in Ap
Environmental Testing of Tritium-Phosphor Glass Vials for Use in Long-Life Radioisotope Power Conversion Units
Power generation in extreme environments, such as the outer solar system, the night side of planets, or other low-illumination environments, currently presents a technology gap that challenges NASA's ambitious scientific goals. We are developing a radioisotope power cell (RPC) that utilizes commercially available tritium light sources and standard 1.85 eV InGaP2 photovoltaic cells to convert beta particle energy to electric energy. In the test program described here, we perform environmental tests on commercially available borosilicate glass vials internally coated with a ZnS luminescent phosphor that are designed to contain gaseous tritium in our proposed power source. Such testing is necessary to ensure that the glass containing the radioactive tritium is capable of withstanding the extreme environments of launch and space for extended periods of time
Imaging the Thermal and Kinematic Sunyaev-Zel'dovich Effect Signals in a Sample of Ten Massive Galaxy Clusters: Constraints on Internal Velocity Structures and Bulk Velocities
We have imaged the Sunyaev-Zel'dovich (SZ) effect signals at 140 and 270 GHz
towards ten galaxy clusters with Bolocam and AzTEC/ASTE. We also used Planck
data to constrain the signal at large angular scales, Herschel-SPIRE images to
subtract the brightest galaxies that comprise the cosmic infrared background
(CIB), Chandra imaging to map the electron temperature of the
intra-cluster medium (ICM), and HST imaging to derive models of each galaxy
cluster's mass density. The galaxy clusters gravitationally lens the background
CIB, which produced an on-average reduction in brightness towards the galaxy
clusters' centers after the brightest galaxies were subtracted. We corrected
for this deficit, which was between 5-25% of the 270 GHz SZ effect signal
within . Using the SZ effect measurements, along with the X-ray
constraint on , we measured each galaxy cluster's average line of sight
(LOS) velocity within , with a median per-cluster uncertainty
of +-700 km/s. We found an ensemble-mean of 430+-210 km/s, and an
intrinsic cluster-to-cluster scatter of 470+-340 km/s. We also
obtained maps of over each galaxy cluster's face with an angular
resolution of 70". All four galaxy clusters previously identified as having a
merger oriented along the LOS showed an excess variance in these maps at a
significance of 2-4, indicating an internal rms of 1000
km/s. None of the six galaxy clusters previously identified as relaxed or plane
of sky mergers showed any such excess variance.Comment: Accepted for publication in Ap
Multi-component Decomposition of Cosmic Infrared Background Fluctuations
The near-infrared background between 0.5 and 2 μm contains a wealth of information related to radiative processes in the universe. Infrared background anisotropies encode the redshift-weighted total emission over cosmic history, including any spatially diffuse and extended contributions. The anisotropy power spectrum is dominated by undetected galaxies at small angular scales and a diffuse background of Galactic emission at large angular scales. In addition to these known sources, the infrared background also arises from intrahalo light (IHL) at z < 3 associated with tidally stripped stars during galaxy mergers. Moreover, it contains information on the very first galaxies from the epoch of reionization (EoR). The EoR signal has a spectral energy distribution (SED) that goes to zero near optical wavelengths due to Lyman absorption, while other signals have spectra that vary smoothly with frequency. Due to differences in SEDs and spatial clustering, these components may be separated in a multi-wavelength-fluctuation experiment. To study the extent to which EoR fluctuations can be separated in the presence of IHL, and extragalactic and Galactic foregrounds, we develop a maximum likelihood technique that incorporates a full covariance matrix among all the frequencies at different angular scales. We apply this technique to simulated deep imaging data over a 2 × 45 deg^2 sky area from 0.75 to 5 μm in 9 bands and find that such a "frequency tomography" can successfully reconstruct both the amplitude and spectral shape for representative EoR, IHL, and the foreground signals
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