554 research outputs found
Supernova Remnants in the Magellanic Clouds. V. The Complex Interior Structure of the N206 SNR
The N206 supernova remnant (SNR) in the Large Magellanic Cloud (LMC) has long
been considered a prototypical "mixed morphology" SNR. Recent observations,
however, have added a new twist to this familiar plot: an elongated,
radially-oriented radio feature seen in projection against the SNR face.
Utilizing the high resolution and sensitivity available with the Hubble Space
Telescope, Chandra, and XMM-Newton, we have obtained optical emission-line
images and spatially resolved X-ray spectral maps for this intriguing SNR. Our
findings present the SNR itself as a remnant in the mid to late stages of its
evolution. X-ray emission associated with the radio "linear feature" strongly
suggests it to be a pulsar-wind nebula (PWN). A small X-ray knot is discovered
at the outer tip of this feature. The feature's elongated morphology and the
surrounding wedge-shaped X-ray enhancement strongly suggest a bow-shock PWN
structure.Comment: 41 pages including 7 figures, accepted for publication by the
Astrophysical Journa
Outflows and Massive Stars in the protocluster IRAS 05358+3543
We present new near-IR H2, CO J=2-1, and CO J = 3-2 observations to study
outflows in the massive star forming region IRAS 05358+3543. The
Canada-France-Hawaii Telescope H2 images and James Clerk Maxwell Telescope CO
data cubes of the IRAS 05358 region reveal several new outflows, most of which
emerge from the dense cluster of sub-mm cores associated with the Sh 2-233IR NE
cluster to the northeast of IRAS 05358. We used Apache Point Observatory (APO)
JHK spectra to determine line of sight velocities of the outflowing material.
Analysis of archival VLA cm continuum data and previously published VLBI
observations reveal a massive star binary as a probable source of one or two of
the outflows. We have identified probable sources for 6 outflows and candidate
counterflows for 7 out of a total of 11 seen to be originating from the IRAS
05358 clusters. We classify the clumps within Sh 2-233IR NE as an early
protocluster and Sh 2-233IR SW as a young cluster, and conclude that the
outflow energy injection rate approximately matches the turbulent decay rate in
Sh 2-233IR NE.Comment: 15 figures, 42 pages, accepted for publication in the Astrophysical
Journal. Full size figures are included at
http://casa.colorado.edu/~ginsbura/iras05358.htm. Data can be accessed from
figshare: http://figshare.com/articles/IRAS_05358_3543_Data_Cubes/80631
An Expanding HI Photodissociated Region Associated with the Compact HII Region G213.880-11.837 in the GGD 14 Complex
We present high angular and spectral resolution HI 21~cm line observations
toward the cometary-shaped compact HII region G213.880-11.837 in the GGD~14
complex.The kinematics and morphology of the photodissociated region, traced by
the HI line emission, reveal that the neutral gas is part of an expanding flow.
The kinematics of the HI gas along the major axis of G213.880-11.837 shows that
the emission is very extended toward the SE direction, reaching LSR radial
velocities in the tail of about 14 km/s. The ambient LSR radial velocity of the
molecular gas is 11.5 km/s, which suggests a champagne flow of the HI gas. This
is the second (after G111.61+0.37) cometary HII/HI region known.Comment: Accepted for publication in the Astronomical Journal (10 pages, 4
figures, 1 table
Direct Access to Unnatural Cyclobutane ?-Amino Acids through Visible Light Catalyzed [2+2]-Cycloaddition
In this work, we report the first selective, photocatalyzed [2+2]-cycloaddition of dehydroamino acids with styrene-type olefins. This simple, mild, and scalable approach relies on the use of the triplet energy transfer catalyst [Ir(dFCF(3)ppy(2))dtbpy]PF6 under visible light irradiation and provides fast access to value-added substituted strained cyclobutane alpha-amino acid derivatives. © 2022 The Authors. Published by American Chemical Society
Is a Classical Language Adequate in Assessing the Detectability of the Redshifted 21cm Signal from the Early Universe?
The classical radiometer equation is commonly used to calculate the
detectability of the 21cm emission by diffuse cosmic hydrogen at high
redshifts. However, the classical description is only valid in the regime where
the occupation number of the photons in phase space is much larger than unity
and they collectively behave as a classical electromagnetic field. At redshifts
z<20, the spin temperature of the intergalactic gas is dictated by the
radiation from galaxies and the brightness temperature of the emitting gas is
in the range of mK, independently from the existence of the cosmic microwave
background. In regions where the observed brightness temperature of the 21cm
signal is smaller than the observed photon energy, of 68/(1+z) mK, the
occupation number of the signal photons is smaller than unity. Neverethless,
the radiometer equation can still be used in this regime because the weak
signal is accompanied by a flood of foreground photons with a high occupation
number (involving the synchrotron Galactic emission and the cosmic microwave
background). As the signal photons are not individually distinguishable, the
combined signal+foreground population of photons has a high occupation number,
thus justifying the use of the radiometer equation.Comment: 4 pages, Accepted for publication in JCA
CMB polarization map derived from the WMAP 5 year data through Harmonic Internal Linear Combination
We have derived whole-sky CMB polarization maps from the WMAP 5 year
polarization data, using the Harmonic Internal Linear Combination (HILC)
method. Our HILC method incorporates spatial variability of linear weights in a
natural way and yields continuous linear weights over the entire sky. To
estimate the power spectrum of HILC maps, we have derived a unbiased quadratic
estimator, which is similar to the WMAP team's cross power estimator, but in a
more convenient form for HILC maps. From our CMB polarization map, we have
obtained TE correlation and E mode power spectra without applying any mask.
They are similar to the WMAP team's estimation and consistent with the WMAP
best-fit CDM model. Foreground reduction by HILC method is more
effective for high resolution and low noise data. Hence, our HILC method will
enable effective foreground reduction in polarization data from the Planck
surveyor.Comment: The whole sky CMB polarization map derived from the WMAP 5 year data
is available in the HEALPix FITS format at http://www.nbi.dk/~jkim/hilc v3:
matched with the accepted version, to appear in PRD. v4: fixed some pdf file
proble
A genome-wide study of Hardy–Weinberg equilibrium with next generation sequence data
Statistical tests for Hardy–Weinberg equilibrium have been an important tool for detecting genotyping errors in the past, and remain important in the quality control of next generation sequence data. In this paper, we analyze complete chromosomes of the 1000 genomes project by using exact test procedures for autosomal and X-chromosomal variants. We find that the rate of disequilibrium largely exceeds what might be expected by chance alone for all chromosomes. Observed disequilibrium is, in about 60% of the cases, due to heterozygote excess. We suggest that most excess disequilibrium can be explained by sequencing problems, and hypothesize mechanisms that can explain exceptional heterozygosities. We report higher rates of disequilibrium for the MHC region on chromosome 6, regions flanking centromeres and p-arms of acrocentric chromosomes. We also detected long-range haplotypes and areas with incidental high disequilibrium. We report disequilibrium to be related to read depth, with variants having extreme read depths being more likely to be out of equilibrium. Disequilibrium rates were found to be 11 times higher in segmental duplications and simple tandem repeat regions. The variants with significant disequilibrium are seen to be concentrated in these areas. For next generation sequence data, Hardy–Weinberg disequilibrium seems to be a major indicator for copy number variation.Peer ReviewedPostprint (published version
Formation of Disk Galaxies: Warm Dark Matter and the Angular Momentum problem
We have performed TreeSPH simulations of disk galaxy formation in various
warm dark matter (WDM) cosmologies. Our results indicate that for a range of
WDM free-streaming masses, the disk galaxy formation angular momentum problem
can be completely resolved by going to the WDM structure formation scenario,
without having to invoke stellar feedback processes at all. We also confirm our
previous suspicion, that part of the angular momentum problem is due to
numerical effects, most likely related to the shock capturing, artificial
viscosity used in SPH. Furthermore we find that we can match the observed
I-band Tully-Fisher (TF) relation, provided that the I-band mass-to-light ratio
of disk galaxies is about 0.8. We argue that this is quite a reasonable value
in comparison with various dynamical and spectrophotometric estimates,
including one given in this paper. We speculate that our success in matching
the TF relation may be due to WDM halos being less centrally concentrated than
CDM halos and suggest to check this exciting possibility with high resolution
simulations, in particular in low Omega_M, WDM cosmologies. Finally, we discuss
possible physical candidates for WDM particles extensively. We find that the
most promising are neutrinos with weaker or stronger interactions than normal,
majorons (light pseudogoldstone bosons) or mirror or shadow world neutrinos.Comment: 50 pages incl. 17 figures. Accepted for publication in Ap
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