560 research outputs found
AMI Large Array radio continuum observations of Spitzer c2d small clouds and cores
We perform deep 1.8 cm radio continuum imaging towards thirteen protostellar
regions selected from the Spitzer c2d small clouds and cores programme at high
resolution (25") in order to detect and quantify the cm-wave emission from
deeply embedded young protostars. Within these regions we detect fifteen
compact radio sources which we identify as radio protostars including two
probable new detections. The sample is in general of low bolometric luminosity
and contains several of the newly detected VeLLO sources. We determine the 1.8
cm radio luminosity to bolometric luminosity correlation, L_rad -L_bol, for the
sample and discuss the nature of the radio emission in terms of the available
sources of ionized gas. We also investigate the L_rad-L_IR correlation and
suggest that radio flux density may be used as a proxy for the internal
luminosity of low luminosity protostars.Comment: submitted MNRA
The LOFAR Magnetism Key Science Project
Measuring radio waves at low frequencies offers a new window to study cosmic
magnetism, and LOFAR is the ideal radio telescope to open this window widely.
The LOFAR Magnetism Key Science Project (MKSP) draws together expertise from
multiple fields of magnetism science and intends to use LOFAR to tackle
fundamental questions on cosmic magnetism by exploiting a variety of
observational techniques. Surveys will provide diffuse emission from the Milky
Way and from nearby galaxies, tracking the propagation of long-lived cosmic-ray
electrons through magnetic field structures, to search for radio halos around
spiral and dwarf galaxies and for magnetic fields in intergalactic space.
Targeted deep-field observations of selected nearby galaxies and suspected
intergalactic filaments allow sensitive mapping of weak magnetic fields through
Rotation Measure (RM) grids. High-resolution observations of protostellar jets
and giant radio galaxies reveal structures on small physical scales and at high
redshifts, whilst pulsar RMs map large-scale magnetic structures of the
Galactic disk and halo in revolutionary detail. The MKSP is responsible for the
development of polarization calibration and processing, thus widening the
scientific power of LOFAR.Comment: Proceedings of "Magnetic Fields in the Universe: From Laboratory and
Stars to Primordial Structures", 2011 Aug. 21-27 in Zakopane/Poland, eds. M.
Soida et a
Signatures from a merging galaxy cluster and its AGN population : LOFAR observations of Abell 1682
Reproduced with permission from Astronomy & Astrophysics. © 2019 ESOWe present LOFAR data from 110-180 MHz of the merging galaxy cluster Abell 1682, alongside archival optical, radio, and X-ray data. Our images of 6 arcsec in resolution at low frequencies reveal new structures associated with numerous radio galaxies in the cluster. At a resolution of 20 arcsec we see diffuse emission throughout the cluster over hundreds of kiloparsecs, indicating particle acceleration mechanisms are in play as a result of the cluster merger event and powerful active galactic nuclei. We show that a significant part of the cluster emission is from an old radio galaxy with very steep spectrum emission (having a spectral index of α < -2.5). Furthermore, we identify a new region of diffuse steep-spectrum emission (α < -1.1) as a candidate for a radio halo which is co-spatial with the centre of the cluster merger. We suggest its origin as a population of old and mildly relativistic electrons left over from radio galaxies throughout the cluster which have been re-accelerated to higher energies by shocks and turbulence induced by the cluster merger event. We also note the discovery of six new giant radio galaxies in the vicinity of Abell 1682.Peer reviewedFinal Accepted Versio
AMI-LA radio continuum observations of Spitzer c2d small clouds and cores: Perseus region
We present deep radio continuum observations of the cores identified as
deeply embedded young stellar objects in the Perseus molecular cloud by the
Spitzer c2d programme at a wavelength of 1.8 cm with the Arcminute Microkelvin
Imager Large Array (AMI-LA). We detect 72% of Class 0 objects from this sample
and 31% of Class I objects. No starless cores are detected. We use the flux
densities measured from these data to improve constraints on the correlations
between radio luminosity and bolometric luminosity, infrared luminosity and,
where measured, outflow force. We discuss the differing behaviour of these
objects as a function of protostellar class and investigate the differences in
radio emission as a function of core mass. Two of four possible very low
luminosity objects (VeLLOs) are detected at 1.8 cm.Comment: 18 pages, 9 figures, accepted MNRA
Magnetic Field Tomography in Nearby Galaxies with the Square Kilometre Array
Magnetic fields play an important role in shaping the structure and evolution
of the interstellar medium (ISM) of galaxies, but the details of this
relationship remain unclear. With SKA1, the 3D structure of galactic magnetic
fields and its connection to star formation will be revealed. A highly
sensitive probe of the internal structure of the magnetoionized ISM is the
partial depolarization of synchrotron radiation from inside the volume.
Different configurations of magnetic field and ionized gas within the
resolution element of the telescope lead to frequency-dependent changes in the
observed degree of polarization. The results of spectro-polarimetric
observations are tied to physical structure in the ISM through comparison with
detailed modeling, supplemented with the use of new analysis techniques that
are being actively developed and studied within the community such as Rotation
Measure Synthesis. The SKA will enable this field to come into its own and
begin the study of the detailed structure of the magnetized ISM in a sample of
nearby galaxies, thanks to its extraordinary wideband capabilities coupled with
the combination of excellent surface brightness sensitivity and angular
resolution.Comment: 11 pages, 1 figure; to appear as part of 'Cosmic Magnetism' in
Proceedings 'Advancing Astrophysics with the SKA (AASKA14)', PoS(AASKA14)10
Sunyaev-Zel'dovich observations of galaxy clusters out to the virial radius with the Arcminute Microkelvin Imager
We present observations using the Small Array of the Arcminute Microkelvin
Imager (AMI; 14-18 GHz) of four Abell and three MACS clusters spanning
0.171-0.686 in redshift. We detect Sunyaev-Zel'dovich (SZ) signals in five of
these without any attempt at source subtraction, although strong source
contamination is present. With radio-source measurements from high-resolution
observations, and under the assumptions of spherical -model,
isothermality and hydrostatic equilibrium, a Bayesian analysis of the data in
the visibility plane detects extended SZ decrements in all seven clusters over
and above receiver noise, radio sources and primary CMB imprints. Bayesian
evidence ratios range from 10^{11}:1 to 10^{43}:1 for six of the clusters and
3000:1 for one with substantially less data than the others. We present
posterior probability distributions for, e.g., total mass and gas fraction
averaged over radii internal to which the mean overdensity is 1000, 500 and
200, r_200 being the virial radius. Reaching r_200 involves some extrapolation
for the nearer clusters but not for the more-distant ones. We find that our
estimates of gas fraction are low (compared with most in the literature) and
decrease with increasing radius. These results appear to be consistent with the
notion that gas temperature in fact falls with distance (away from near the
cluster centre) out to the virial radius.Comment: 18 pages, 10 figures, submitted to MNRAS (updated authors and fixed
Figure 1
Spitzer characterisation of dust in an anomalous emission region: the Perseus cloud
Anomalous microwave emission is known to exist in the Perseus cloud. One of
the most promising candidates to explain this excess of emission is electric
dipole radiation from rapidly rotating very small dust grains, commonly
referred to as spinning dust. Photometric data obtained with the Spitzer Space
Telescope have been reprocessed and used in conjunction with the dust emission
model DUSTEM to characterise the properties of the dust within the cloud. This
analysis has allowed us to constrain spatial variations in the strength of the
interstellar radiation field (), the mass abundances of the
PAHs and VSGs relative to the BGs (Y and Y), the
column density of hydrogen (N) and the equilibrium dust
temperature (T). The parameter maps of Y,
Y and are the first of their kind to be
produced for the Perseus cloud, and we used these maps to investigate the
physical conditions in which anomalous emission is observed. We find that in
regions of anomalous emission the strength of the ISRF, and consequently the
equilibrium temperature of the dust, is enhanced while there is no significant
variation in the abundances of the PAHs and the VSGs or the column density of
hydrogen. We interpret these results as an indication that the enhancement in
might be affecting the properties of the small
stochastically heated dust grains resulting in an increase in the spinning dust
emission observed at 33 GHz. This is the first time that such an investigation
has been performed, and we believe that this type of analysis creates a new
perspective in the field of anomalous emission studies, and represents a
powerful new tool for constraining spinning dust models.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Recommended from our members
Was UV spectral solar irradiance lower during the recent low sunspot minimum?
A detailed analysis is presented of solar UV spectral irradiance for the period between May 2003 and August 2005, when data are available from both the Solar Ultraviolet pectral Irradiance Monitor (SUSIM) instrument (on board the pper Atmosphere Research Satellite (UARS) spacecraft) and the Solar Stellar Irradiance Comparison Experiment (SOLSTICE) instrument (on board the Solar Radiation and Climate Experiment (SORCE) satellite). The ultimate aim is to develop a data composite that can be used to accurately determine any differences between the “exceptional” solar minimum at the end of solar cycle 23 and the previous minimum at the end of solar cycle 22 without having to rely on proxy data to set the long‐term change. SUSIM data are studied because they are the only data available in the “SOLSTICE gap” between the end of available UARS SOLSTICE data and the start of the SORCE data. At any one wavelength the two data sets are considered too dissimilar to be combined into a meaningful composite if any one of three correlations does not exceed a threshold of 0.8. This criterion removes all wavelengths except those in a small range between 156 nm and 208 nm, the longer wavelengths of which influence ozone production and heating in the lower stratosphere. Eight different methods are employed to intercalibrate the two data sequences. All methods give smaller changes between the minima than are seen when the data are not adjusted; however, correcting the SUSIM data to allow for an exponentially decaying offset drift gives a composite that is largely consistent with the unadjusted data from the SOLSTICE instruments on both UARS and SORCE and in which the recent minimum is consistently lower in the wave band studied
Spinning dust emission: the effect of rotation around a non-principal axis
We investigate the rotational emission from dust grains that rotate around
non- principal axes. We argue that in many phases of the interstellar medium,
the smallest grains, which dominate spinning dust emission, are likely to have
their nutation state (orientation of principal axes relative to the angular
momentum vector) randomized during each thermal spike. We recompute the
excitation and damping rates associated with rotational emission from the grain
permanent dipole, grain-plasma interactions, infrared photon emission, and
collisions. The resulting spinning dust spectra gener- ally show a shift toward
higher emissivities and peak frequencies relative to previous calculations.Comment: Version accepted for publication in MNRAS. The derivation of the
emission spectrum was clarified. The companion code, SPDUST.2, can be
downloaded from http://www.tapir.caltech.edu/~yacine/spdust/spdust.htm
The Climate-system Historical Forecast Project: providing open access to seasonal forecast ensembles from centers around the globe
Fil: Tompkins, Adrian M.. The Abdus Salam; ItaliaFil: Ortiz de Zarate, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Centre National de la Recherche Scientifique; FranciaFil: Saurral, Ramiro Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Centre National de la Recherche Scientifique; FranciaFil: Vera, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Centre National de la Recherche Scientifique; FranciaFil: Saulo, Andrea Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Defensa. Secretaria de Planeamiento. Servicio Meteorológico Nacional; ArgentinaFil: Merryfield, William J.. Canadian Centre for Climate Modelling and Analysis; CanadáFil: Sigmond, Michael. Canadian Centre for Climate Modelling and Analysis; CanadáFil: Lee, Woo Sung. Canadian Centre for Climate Modelling and Analysis; CanadáFil: Baehr, Johanna. Universitat Hamburg; AlemaniaFil: Braun, Alain. Météo-France; FranciaFil: Amy Butler. National Ocean And Atmospheric Administration; Estados UnidosFil: Déqué, Michel. Météo-France; FranciaFil: Doblas Reyes, Francisco J.. Institució Catalana de Recerca i Estudis Avancats; España. Barcelona Supercomputing Center - Centro Nacional de Supercomputacion; EspañaFil: Gordon, Margaret. Met Office; Reino UnidoFil: Scaife, Adam A.. University of Exeter; Reino UnidoFil: Yukiko Imada. Japan Meteorological Agency. Meteorological Research Institute. Climate Research Department; JapónFil: Masayoshi Ishii. Japan Meteorological Agency. Meteorological Research Institute. Climate Research Department; JapónFil: Tomoaki Ose. Japan Meteorological Agency. Meteorological Research Institute. Climate Research Department; JapónFil: Kirtman, Ben. University of Miami; Estados UnidosFil: Kumar, Arun. National Ocean And Atmospheric Administration; Estados UnidosFil: Müller, Wolfgang A.. Max-Planck-Institut für Meteorologie; AlemaniaFil: Pirani, Anna. Université Paris-Saclay; FranciaFil: Stockdale, Tim. European Centre for Medium-Range Weather; Reino UnidoFil: Rixen, Michel. World Meteorological Organization. World Climate Research Programme; SuizaFil: Yasuda, Tamaki. Japan Meteorological Agency. Climate Prediction Division; Japó
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