1,084 research outputs found
Herschel observations of gamma-ray burst host galaxies: implications for the topology of the dusty interstellar medium
Long-duration gamma-ray bursts (GRBs) are indisputably related to star
formation, and their vast luminosity in gamma rays pin-points regions of star
formation independent of galaxy mass. As such, GRBs provide a unique tool for
studying star forming galaxies out to high-z independent of luminosity. Most of
our understanding of the properties of GRB hosts (GRBHs) comes from optical and
near-infrared (NIR) follow-up observations, and we therefore have relatively
little knowledge of the fraction of dust-enshrouded star formation that resides
within GRBHs. Currently ~20% of GRBs show evidence of significant amounts of
dust along the line of sight to the afterglow through the host galaxy, and
these GRBs tend to reside within redder and more massive galaxies than GRBs
with optically bright afterglows. In this paper we present Herschel
observations of five GRBHs with evidence of being dust-rich, targeted to
understand the dust attenuation properties within GRBs better. Despite the
sensitivity of our Herschel observations, only one galaxy in our sample was
detected (GRBH 070306), for which we measure a total star formation rate (SFR)
of ~100Mstar/yr, and which had a relatively high stellar mass
(log[Mstar]=10.34+0.09/-0.04). Nevertheless, when considering a larger sample
of GRBHs observed with Herschel, it is clear that stellar mass is not the only
factor contributing to a Herschel detection, and significant dust extinction
along the GRB sightline (A_{V,GRB}>1.5~mag) appears to be a considerably better
tracer of GRBHs with high dust mass. This suggests that the extinguishing dust
along the GRB line of sight lies predominantly within the host galaxy ISM, and
thus those GRBs with A_{V,GRB}>1~mag but with no host galaxy Herschel
detections are likely to have been predominantly extinguished by dust within an
intervening dense cloud.Comment: 14 pages, 7 figures. Accepted for publication in A&
CLOVER - A new instrument for measuring the B-mode polarization of the CMB
We describe the design and expected performance of Clover, a new instrument
designed to measure the B-mode polarization of the cosmic microwave background.
The proposed instrument will comprise three independent telescopes operating at
90, 150 and 220 GHz and is planned to be sited at Dome C, Antarctica. Each
telescope will feed a focal plane array of 128 background-limited detectors and
will measure polarized signals over angular multipoles 20 < l < 1000. The
unique design of the telescope and careful control of systematics should enable
the B-mode signature of gravitational waves to be measured to a
lensing-confusion-limited tensor-to-scalar ratio r~0.005.Comment: 4 pages, 5 figures. To appear in the proceedings of the XXXVIXth
Rencontres de Moriond "Exploring the Universe
Multiwaveband Observations of Quasars with Flat Radio Spectra and Strong Millimeter Emission
We present multiwaveband observations of a well selected sample of 28 quasars
and two radio galaxies with flat radio spectra and strong millimeter wave
emission (referred to here as FSRQ's). The observations include multifrequency
VLBI measurements, X-ray observations with ROSAT and submillimeter observations
with the JCMT. Particularly interesting among many findings is a correlation
between the X-ray to millimeter spectral index and fraction of flux density
contained in the VLBI core. This tendency toward higher X-ray fluxes from
sources with stronger jet emission implies that the knots in the jet are the
prominent source of X-rays.Comment: 38 pages, 17 figures, 12 tables, accepted for publication in Ap J
Suppl, May 199
On the form of growing strings
Patterns and forms adopted by Nature, such as the shape of living cells, the
geometry of shells and the branched structure of plants, are often the result
of simple dynamical paradigms. Here we show that a growing self-interacting
string attached to a tracking origin, modeled to resemble nascent polypeptides
in vivo, develops helical structures which are more pronounced at the growing
end. We also show that the dynamic growth ensemble shares several features of
an equilibrium ensemble in which the growing end of the polymer is under an
effective stretching force. A statistical analysis of native states of proteins
shows that the signature of this non-equilibrium phenomenon has been fixed by
evolution at the C-terminus, the growing end of a nascent protein. These
findings suggest that a generic non-equilibrium growth process might have
provided an additional evolutionary advantage for nascent proteins by favoring
the preferential selection of helical structures.Comment: 4 pages, 3 figures. Accepted for publication in Phys. Rev. Let
Line Polarization of Molecular Lines at Radio Frequencies: The case of DR21(OH)
We present polarization observations in DR21(OH) from thermal dust emission
at 3 mm and from CO J=1-0 line emission. The observations were obtained using
the Berkeley-Illinois-Maryland Association array. Previous observations of this
region at 1.3 mm for the polarized continuum emission, and also the CO J=2-1
polarized emission have been made before. Our continuum polarization results
are consistent with those results. However, the direction of the linear
polarization for the J=1-0 is perpendicular to that of the CO J=2-1
polarization. This unexpected result was explored by obtaining numerical
solutions to the multilevel, radiative transfer equations for a gas with
anisotropic optical depths. We find that in addition to the anisotropic optical
depths, anisotropic excitation due to a source of radiation that is external to
the CO is needed to understand the orthogonality in the directions of
polarization. The continuum emission by dust grains at the core of DR21(OH) is
sufficient to provide this external radiation. The CO polarization must arise
in relatively low density (nH2 ~ 100 [cm^-3]) envelope gas. We infer B ~ 10
[micro Gauss] in this gas, which implies that the envelope is subcritical.Comment: Accepted for publication in Ap
Cm-Wavelength Total Flux and Linear Polarization Properties of Radio-Loud BL Lacertae Objects
Results from a long-term program to quantify the range of behavior of the
cm-wavelength total flux and linear polarization variability properties of a
sample of 41 radio-loud BL Lac objects using weekly to tri-monthly observations
with the University of Michigan 26-m telescope operating at 14.5, 8.0, and 4.8
GHz are presented; these observations are used to identify class-dependent
differences between these BL Lacs and QSOs in the Pearson-Readhead sample. The
BL Lacs are found to be more highly variable in total flux density than the
QSOs, exhibiting changes that are often nearly-simultaneous and of comparable
amplitude at 14.5 and 4.8 GHz in contrast to the behavior in the QSOs and
supporting the existence of class-dependent differences in opacity within the
parsec-scale jet flows. Structure function analyses of the flux observations
quantify that a characteristic timescale is identifiable in only 1/3 of the BL
Lacs. The time-averaged fractional linear polarizations are only on the order
of a few percent and are consistent with the presence of tangled magnetic
fields within the emitting regions. In many sources a preferred long-term
orientation of the EVPA is present; when compared with the VLBI structural
axis, no preferred position angle difference is identified. The polarized flux
typically exhibits variability with timescales of months to a few years and
shows the signature of a propagating shock during several resolved outbursts.
The observations indicate that the source emission is predominately due to
evolving source components and support the occurrence of more frequent shock
formation in BL Lac parsec-scale flows than in QSO jets. The differences in
variability behavior and polarization between BL Lacs and QSOs can be explained
by differences in jet stability.Comment: 1 LaTex (aastex) file, 21 postscript figure files, 2 external LaTex
table files. To appear in the Astrophysical Journa
SMA Imaging of CO(3-2) Line and 860 micron Continuum of Arp 220 : Tracing the Spatial Distribution of Luminosity
We used the Submillimeter Array (SMA) to image 860 micron continuum and
CO(3-2) line emission in the ultraluminous merging galaxy Arp 220, achieving a
resolution of 0.23" (80 pc) for the continuum and 0.33" (120 pc) for the line.
The CO emission peaks around the two merger nuclei with a velocity signature of
gas rotation around each nucleus, and is also detected in a kpc-size disk
encompassing the binary nucleus. The dust continuum, in contrast, is mostly
from the two nuclei. The beam-averaged brightness temperature of both line and
continuum emission exceeds 50 K at and around the nuclei, revealing the
presence of warm molecular gas and dust. The dust emission morphologically
agrees with the distribution of radio supernova features in the east nucleus,
as expected when a starburst heats the nucleus. In the brighter west nucleus,
however, the submillimeter dust emission is more compact than the supernova
distribution. The 860 micron core, after deconvolution, has a size of 50-80 pc,
consistent with recent 1.3 mm observations, and a peak brightness temperature
of (0.9-1.6)x10^2 K. Its bolometric luminosity is at least 2x10^{11} Lsun and
could be ~10^{12} Lsun depending on source structure and 860 micron opacity,
which we estimate to be of the order of tau_{860} ~ 1 (i.e., N_{H_2} ~ 10^{25}
cm^{-2}). The starbursting west nuclear disk must have in its center a dust
enshrouded AGN or a very young starburst equivalent to hundreds of super star
clusters. Further spatial mapping of bolometric luminosity through
submillimeter imaging is a promising way to identify the heavily obscured
heating sources in Arp 220 and other luminous infrared galaxies.Comment: ApJ. in press. 26 pages, 10 figure
Functional and Biogenetical Heterogeneity of the Inner Membrane of Rat-Liver Mitochondria
Rat liver mitochondria were fragmented by a combined technique of swelling, shrinking, and sonication. Fragments of inner membrane were separated by density gradient centrifugation. They differed in several respects: electronmicroscopic appearance, phospholipid and cytochrome contents, electrophoretic behaviour of proteins and enzymatic activities.
Three types of inner membrane fractions were isolated. The first type is characterized by a high activity of metal chelatase, low activities of succinate-cytochrome c reductase and of glycerolphosphate dehydrogenase, as well as by a high phospholipid content and low contents of cytochromes aa3 and b.
The second type displays maximal activities of glycerolphosphate dehydrogenase and metal chelatase, but contains relatively little cytochromes and has low succinate-cytochrome c reductase activity.
The third type exhibits highest succinate-cytochrome c reductase activity, a high metal chelatase activity and highest cytochrome contents. However, this fraction was low in both glycerolphosphate dehydrogenase activity and phospholipid content. This fraction was also richest in the following enzyme activities: cytochrome oxidase, oligomycin-sensitive ATPase, proline oxidase, 3-hydroxybutyrate dehydrogenase and rotenone-sensitive NADH-cytochrome c reductase.
Amino acid incorporation in vitro and in vivo in the presence of cycloheximide occurs predominantly into inner membrane fractions from the second type.
These data suggest that the inner membrane is composed of differently organized parts, and that polypeptides synthesized by mitochondrial ribosomes are integrated into specific parts of the inner membrane
37 GHz observations of a large sample of BL Lacertae objects
We present 37 GHz data obtained at Metsahovi Radio Observatory in 2001
December - 2005 April for a large sample of BL Lacertae objects. We also report
the mean variability indices and radio spectral indices in frequency intervals
5 - 37 GHz and 37 - 90 GHz. Approximately 34 % of the sample was detected at 37
GHz, 136 BL Lacertae objects in all. A large majority of the detected sources
were low-energy BL Lacs (LBLs). The variability index values of the sample were
diverse, the mean fractional variability of the sample being \Delta S_2 = 0.31.
The spectral indices also varied widely, but the average radio spectrum of the
sample sources is flat. Our observations show that many of the high-energy BL
Lacs (HBL), which are usually considered radio-quiet, can at times be detected
at 37 GHz.Comment: 12 pages, 5 figures + 5 tables. Published in Astronomical Journa
A Viewing Angle - Kinetic Luminosity Unification Scheme For BL Lacertae Objects
We propose a unified classification for BL Lac objects (BLs), focusing on the
synchrotron peak frequency of the spectral energy distribution. The unification
scheme is based on the angle Theta that describes the orientation of the
relativistic jet and on the electron kinetic luminosity Lambda of the jet. We
assume that Lambda scales with the size of the jet r in a self-similar fashion
(Lambda propto r^2), as supported by observational data. The jets are
self-similar in geometry and have the same pressure and median magnetic field
at the inlet, independent of size. The self-similarity is broken for the
highest energy electrons, which radiate mainly at high frequencies, since for
large sources they suffer more severe radiative energy losses over a given
fraction of the jet length. We calculate the optically thin synchrotron
spectrum using an accelerating inner jet model based on simple relativistic gas
dynamics and show that it can fit the observed infrared to X-ray spectrum of
PKS 2155--304. We couple the accelerating jet model to the unification scheme
and compare the results to complete samples of
BLs. The negative apparent evolution of X-ray selected BLs is explained as a
result of positive evolution of the jet electron kinetic luminosity
. We review observational arguments in favor of the existence of
scaled-down accretion disks and broad emission-line regions in BLs. The
proposed unification scheme can explain the lack of observed broad emission
lines in X-ray selected BLs, as well as the existence of those lines
preferentially in luminous radio-selected BLs. Finally, we review observational
arguments that suggest the extension of this unification scheme to all blazars.Comment: 32 pages, 8 figures, to be published in the ApJ (Oct 20, 1998
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