1,273 research outputs found
Submillimetre observations of the two-component magnetic field in M82
We observed the starburst galaxy M82 in 850 µm polarized light with the POL-2 polarimeter on the James Clerk Maxwell Telescope (JCMT). We interpret our observed polarization geometry as tracing a two-component magnetic field: a poloidal component aligned with the galactic ‘superwind’, extending to a height ∼350 pc above and below the central bar; and a spiral-arm-aligned, or possibly toroidal, component in the plane of the galaxy, which dominates the 850 µm polarized light distribution at galactocentric radii ≳2 kpc. Comparison of our results with recent High-resolution Airborne Wideband Camera Plus (HAWC+) measurements of the field in the dust entrained by the M82 superwind suggests that the superwind breaks out from the central starburst at ∼350 pc above the plane of the galaxy
The star-formation law at GMC scales in M33, the Triangulum Galaxy
We present a high spatial resolution study, on scales of 100pc, of the
relationship between star-formation rate (SFR) and gas content within Local
Group galaxy M33. Combining deep SCUBA-2 observations with archival GALEX,
SDSS, WISE, Spitzer and submillimetre Herschel data, we are able to model the
entire SED from UV to sub-mm wavelengths. We calculate the SFR on a
pixel-by-pixel basis using the total infrared luminosity, and find a total SFR
of /yr, somewhat lower than our other two measures
of SFR -- combined FUV and 24m SFR
(/yr) and SED-fitting tool MAGPHYS
(/yr). We trace the total gas using a
combination of the 21cm HI line for atomic hydrogen, and CO(=2-1)
data for molecular hydrogen. We have also traced the total gas using dust
masses. We study the star-formation law in terms of molecular gas, total gas,
and gas from dust. We perform an analysis of the star-formation law on a
variety of pixel scales, from 25 to 500
(100pc to 2kpc). At kpc scales, we find that a linear Schmidt-type power law
index is suitable for molecular gas, but the index appears to be much higher
with total gas, and gas from dust. Whilst we find a strong scale dependence on
the Schmidt index, the gas depletion timescale is invariant with pixel scale.Comment: 19 pages, 15 figures, accepted for publication in MNRA
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&
XMM—Newton surveys of the Canada—France Redshift Survey Fields — III. The environments of X-ray selected active galactic nuclei at 0.4 < z < 0.6
The environmental properties of a sample of 31 hard X-ray selected active galactic nuclei (AGN) are investigated, from scales of 500 kpc down to 30 kpc, and are compared to a control sample of inactive galaxies. All the AGN lie in the redshift range 0.4 < z < 0.6. The accretion luminosity density of the Universe peaks close to this redshift range, and the AGN in the sample have X-ray luminosities close to the knee in the hard X-ray luminosity function, making them representative of the population that dominated this important phase of energy conversion. Using both the spatial clustering amplitude and near-neighbour counts, it is found that the AGN have environments that are indistinguishable from normal, inactive galaxies over the same redshift range and with similar optical properties. Typically, the environments are of subcluster richness, in contrast to similar studies of high-z quasars, which are often found in clusters with comparable richness to the Abell R≥ 0 clusters. It is suggested that minor mergers with low-mass companions are a likely candidate for the mechanism by which these modest luminosity AGN are fuelle
An Investigation of Gravitational Lensing in the Southern BL Lac PKS 0537-441
The BL-Lac family of active galaxies possess almost featureless spectra and
exhibit rapid variability over their entire spectral range. A number of models
have been developed to explain these extreme properties, several of which have
invoked the action of microlensing by sub-stellar mass objects in a foreground
galaxy; this not only introduces variability, but also amplifies an otherwise
normal quasar source. Here we present recent spectroscopy and photometry of the
southern BL Lac PKS 0537-441; with an inferred redshift of z~0.9 it represents
one of the most distant and most luminous members of the BL Lac family. The
goal of the observations was not only to confirm the redshift of PKS~0537-441,
but also to determine the redshift of a putative galaxy along the line of sight
to the BL-Lac; it has been proposed that this galaxy is the host of
microlensing stars that account for PKS 0537-441's extreme properties. While
several observations have failed to detect any extended emission in PKS
0537-441, the HST imaging data presented here indicate the presence of a
galactic component, although we fail to identify any absorption features that
reveal the redshift of the emission. It is also noted that PKS 0537-441 is
accompanied by several small, but extended companions, located a few arcseconds
from the point-like BL-Lac source. Two possibilities present themselves; either
they represent true companions of PKS 0537-441, or are themselves
gravitationally lensed images of more distant sources.Comment: 13 Pages with 4 Figures; Accepted for Publication by the
Astrophysical Journa
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
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
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
Submillimeter detection of the Sunyaev -- Zel'dovich effect toward the most luminous X-ray cluster at z=0.45
We report on the detection of the Sunyaev -- Zel'dovich (SZ) signals toward
the most luminous X-ray cluster RXJ1347-1145 at Nobeyama Radio Observatory (21
and 43 GHz) and at James Clerk Maxwell Telescope (350 GHz). In particular the
latter is the first successful detection of the SZ temperature increment in the
submillimeter band which resolved the profile of a cluster of galaxies. Both
the observed spectral dependence and the radial profile of the SZ signals are
fully consistent with those expected from the X-ray observation of the cluster.
The combined analysis of 21GHz and 350GHz data reproduces the temperature and
core-radius of the cluster determined with the ROSAT and ASCA satellites when
we adopt the slope of the density profile from the X-ray observations.
Therefore our present data provide the strongest and most convincing case for
the detection of the submillimeter SZ signal from the cluster, as well as in
the Rayleigh -- Jeans regime. We also discuss briefly the cosmological
implications of the present results.Comment: 11 pages, The Astrophysical Journal (Letters), in pres
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
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