171 research outputs found
Centimeter-wave continuum radiation from the rho Ophiuchi molecular cloud
The rho Oph molecular cloud is undergoing intermediate-mass star formation.
UV radiation from its hottest young stars heats and dissociates exposed layers,
but does not ionize hydrogen. Only faint radiation from the Rayleigh-Jeans tail
of ~10-100K dust is expected at wavelengths longwards of 3mm. Yet Cosmic
Background Imager (CBI) observations reveal that the rho Oph W
photo-dissociation region (PDR) is surprisingly bright at centimetre
wavelengths. We searched for interpretations consistent with the WMAP radio
spectrum, new ISO-LWS parallel mode images and archival Spitzer data.
Dust-related emission mechanisms at 1 cm, as proposed by Draine & Lazarian, are
a possibility. But a magnetic enhancement of the grain opacity at 1cm is
inconsistent with the morphology of the dust column maps Nd and the lack of
detected polarization. Spinning dust, or electric-dipole radiation from
spinning very small grains (VSGs), comfortably explains the radio spectrum,
although not the conspicuous absence from the CBI data of the infrared
circumstellar nebulae around the B-type stars S1 and SR~3. Allowing for VSG
depletion can marginally reconcile spinning dust with the data. As an
alternative interpretation we consider the continuum from residual charges in
rho Oph W, where most of carbon should be photoionised by the close binary
HD147889 (B2IV, B3IV). Electron densities of ~100 cm^{-3}, or H-nucleus
densities n_H > 1E6 cm^{-3}, are required to interpret rho Oph W as the CII
Stromgren sphere of HD147889. However the observed steep and positive
low-frequency spectral index would then require optically thick emission from
an hitherto unobserved ensemble of dense clumps or sheets with a filling factor
~1E-4 and n_H ~ 1E7 cm^{-3}.Comment: accepted for publication in MNRA
Cross-correlating Carbon Monoxide Line-intensity Maps with Spectroscopic and Photometric Galaxy Surveys
Line-intensity mapping (LIM or IM) is an emerging field of observational
work, with strong potential to fit into a larger effort to probe large-scale
structure and small-scale astrophysical phenomena using multiple complementary
tracers. Taking full advantage of such complementarity means, in part,
undertaking line-intensity surveys with galaxy surveys in mind. We consider the
potential for detection of a cross-correlation signal between COMAP and blind
surveys based on photometric redshifts (as in COSMOS) or based on spectroscopic
data (as with the HETDEX survey of Lyman- emitters). We find that
obtaining accuracy in redshifts and
sources per Mpc with spectroscopic redshift determination
should enable a CO-galaxy cross spectrum detection significance at least twice
that of the CO auto spectrum. Either a future targeted spectroscopic survey or
a blind survey like HETDEX may be able to meet both of these requirements.Comment: 19 pages + appendix (31 pages total), 16 figures, 6 tables; accepted
for publication in Ap
Joint power spectrum and voxel intensity distribution forecast on the CO luminosity function with COMAP
We develop a framework for joint constraints on the CO luminosity function
based on power spectra (PS) and voxel intensity distributions (VID), and apply
this to simulations of COMAP, a CO intensity mapping experiment. This Bayesian
framework is based on a Markov chain Monte Carlo (MCMC) sampler coupled to a
Gaussian likelihood with a joint PS + VID covariance matrix computed from a
large number of fiducial simulations, and re-calibrated with a small number of
simulations per MCMC step. The simulations are based on dark matter halos from
fast peak patch simulations combined with the
model of Li et al. (2016). We find that the relative power to constrain the CO
luminosity function depends on the luminosity range of interest. In particular,
the VID is more sensitive at both small and large luminosities, while the PS is
more sensitive at intermediate luminosities. The joint analysis is superior to
using either observable separately. When averaging over CO luminosities ranging
between , and over 10 cosmological realizations
of COMAP Phase 2, the uncertainties (in dex) are larger by 58 % and 30 % for
the PS and VID, respectively, when compared to the joint analysis (PS + VID).
This method is generally applicable to any other random field, with a
complicated likelihood, as long a fast simulation procedure is available.Comment: 13 pages, 5 figures. As accepted to Ap
A novel methodology for macroscale, thermal characterization of carbon fiber-reinforced polymer for integrated aircraft electrical power systems
Carbon fiber-reinforced polymer (CFRP) is increasingly used for aero-structure applications due to their high strength-to-weight ratio. The integration of the on-board electrical power system (EPS) with CFRP is challenging due to the requirement to thermally and electrically isolate these systems to meet existing safety standards. By capturing the thermal characteristics of CFRP at a macro (component) scale for CFRP components, it is possible to understand, and design for, the increased integration of the EPS into CFRP aero-components. A significant challenge is to develop a macroscale characterization of CFRP, which is not only of an appropriate fidelity for compatibility with systems-level models of an EPS but also can be used to represent different geometries of CFRP components. This paper presents a novel methodology for capturing a transient, macroscale thermal characterization of CFRP with regard to component layup and geometry (thickness). The methodology uses experimentally derived thermal responses of specific resin and ply orientation CFRP samples to create a generalized relationship for the prediction of thermal transfer in other sample thicknesses of the same material type. This methodology can be used to characterize thermal gradients across CFRP components in aircraft EPS integration applications, ultimately informing the optimized integration of the EPS with CFRP
Mapping Cosmic Dawn and Reionization: Challenges and Synergies
Cosmic dawn and the Epoch of Reionization (EoR) are among the least explored
observational eras in cosmology: a time at which the first galaxies and
supermassive black holes formed and reionized the cold, neutral Universe of the
post-recombination era. With current instruments, only a handful of the
brightest galaxies and quasars from that time are detectable as individual
objects, due to their extreme distances. Fortunately, a multitude of
multi-wavelength intensity mapping measurements, ranging from the redshifted 21
cm background in the radio to the unresolved X-ray background, contain a
plethora of synergistic information about this elusive era. The coming decade
will likely see direct detections of inhomogenous reionization with CMB and 21
cm observations, and a slew of other probes covering overlapping areas and
complementary physical processes will provide crucial additional information
and cross-validation. To maximize scientific discovery and return on
investment, coordinated survey planning and joint data analysis should be a
high priority, closely coupled to computational models and theoretical
predictions.Comment: 5 pages, 1 figure, submitted to the Astro2020 Decadal Survey Science
White Paper cal
Pneumococcal conjugate vaccine implementation in middle-income countries
Since 2000, the widespread adoption of pneumococcal conjugate vaccines (PCVs) has had a major impact in the prevention of pneumonia. Limited access to international financial support means some middle-income countries (MICs) are trailing in the widespread use of PCVs. We review the status of PCV implementation, and discuss any needs and gaps related to low levels of PCV implementation in MICs, with analysis of possible solutions to strengthen the PCV implementation process in MICs
Inference of Antibiotic Resistance and Virulence among Diverse Group A Streptococcus Strains Using emm Sequencing and Multilocus Genotyping Methods
typing (direct sequencing of the genomic segment coding for the antigenic portion of the M protein) or by multilocus genotyping methods. Phenotype analysis, including critical AbR typing, is generally achieved by much slower and more laborious direct culture-based methods. type and the associated AbR and virulence phenotypes. types
COMAP Early Science: VII. Prospects for CO Intensity Mapping at Reionization
We introduce COMAP-EoR, the next generation of the Carbon Monoxide Mapping
Array Project aimed at extending CO intensity mapping to the Epoch of
Reionization. COMAP-EoR supplements the existing 30 GHz COMAP Pathfinder with
two additional 30 GHz instruments and a new 16 GHz receiver. This combination
of frequencies will be able to simultaneously map CO(1--0) and CO(2--1) at
reionization redshifts () in addition to providing a significant
boost to the sensitivity of the Pathfinder. We examine a set of
existing models of the EoR CO signal, and find power spectra spanning several
orders of magnitude, highlighting our extreme ignorance about this period of
cosmic history and the value of the COMAP-EoR measurement. We carry out the
most detailed forecast to date of an intensity mapping cross-correlation, and
find that five out of the six models we consider yield signal to noise ratios
(S/N) for COMAP-EoR, with the brightest reaching a S/N above 400.
We show that, for these models, COMAP-EoR can make a detailed measurement of
the cosmic molecular gas history from , as well as probe the
population of faint, star-forming galaxies predicted by these models to be
undetectable by traditional surveys. We show that, for the single model that
does not predict numerous faint emitters, a COMAP-EoR-type measurement is
required to rule out their existence. We briefly explore prospects for a
third-generation Expanded Reionization Array (COMAP-ERA) capable of detecting
the faintest models and characterizing the brightest signals in extreme detail.Comment: Paper 7 of 7 in series. 19 pages, 10 figures, to be submitted to Ap
COMAP Early Science: III. CO Data Processing
We describe the first season COMAP analysis pipeline that converts raw
detector readouts to calibrated sky maps. This pipeline implements four main
steps: gain calibration, filtering, data selection, and map-making. Absolute
gain calibration relies on a combination of instrumental and astrophysical
sources, while relative gain calibration exploits real-time total-power
variations. High efficiency filtering is achieved through spectroscopic
common-mode rejection within and across receivers, resulting in nearly
uncorrelated white noise within single-frequency channels. Consequently,
near-optimal but biased maps are produced by binning the filtered time stream
into pixelized maps; the corresponding signal bias transfer function is
estimated through simulations. Data selection is performed automatically
through a series of goodness-of-fit statistics, including and
multi-scale correlation tests. Applying this pipeline to the first-season COMAP
data, we produce a dataset with very low levels of correlated noise. We find
that one of our two scanning strategies (the Lissajous type) is sensitive to
residual instrumental systematics. As a result, we no longer use this type of
scan and exclude data taken this way from our Season 1 power spectrum
estimates. We perform a careful analysis of our data processing and observing
efficiencies and take account of planned improvements to estimate our future
performance. Power spectrum results derived from the first-season COMAP maps
are presented and discussed in companion papers.Comment: Paper 3 of 7 in series. 26 pages, 23 figures, submitted to Ap
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