339 research outputs found
CBI limits on 31 GHz excess emission in southern HII regions
We have mapped four regions of the southern Galactic plane at 31 GHz with the
Cosmic Background Imager. From the maps, we have extracted the flux densities
for six of the brightest \hii regions in the southern sky and compared them
with multi-frequency data from the literature. The fitted spectral index for
each source was found to be close to the theoretical value expected for
optically thin free-free emission, thus confirming that the majority of flux at
31 GHz is due to free-free emission from ionised gas with an electron
temperature of K.
We also found that, for all six sources, the 31 GHz flux density was slightly
higher than the predicted value from data in the literature. This excess
emission could be due to spinning dust or another emission mechanism.
Comparisons with m data indicate an average dust emissivity of
K (MJy/sr), or a 95 per cent confidence limit of K (MJy/sr). This is lower than that found in diffuse clouds at high
Galactic latitudes by a factor of . The most significant detection
() was found in (RCW49) and may account for up to
per cent of the total flux density observed at 31 GHz. Here, the
dust emissivity of the excess emission is K (MJy/sr) and
is within the range observed at high Galactic latitudes.
Low level polarised emission was observed in all six sources with
polarisation fractions in the range per cent. This is likely to be
mainly due to instrumental leakage and is therefore upper an upper limit to the
free-free polarisation. It corresponds to an upper limit of per cent
for the polarisation of anomalous emission.Comment: Accepted in MNRAS. 12 pages, 10 figures, 5 table
Digital compensation of the side-band-rejection ratio in a fully analog 2SB sub-millimeter receiver
In observational radio astronomy, sideband-separating receivers are
preferred, particularly under high atmospheric noise, which is usually the case
in the sub-millimeter range. However, obtaining a good rejection ratio between
the two sidebands is difficult since, unavoidably, imbalances in the different
analog components appear. We describe a method to correct these imbalances
without making any change in the analog part of the sideband-separating
receiver, specifically, keeping the intermediate-frequency hybrid in place.
This opens the possibility of implementing the method in any existing receiver.
We have built hardware to demonstrate the validity of the method and tested it
on a fully analog receiver operating between 600 and 720GHz. We have tested the
stability of calibration and performance vs time and after full resets of the
receiver. We have performed an error analysis to compare the digital
compensation in two configurations of analog receivers, with and without
intermediate frequency (IF) hybrid. An average compensated sideband rejection
ratio of 46dB is obtained. Degradation of the compensated sideband rejection
ratio on time and after several resets of the receiver is minimal. A receiver
with an IF hybrid is more robust to systematic errors. Moreover, we have shown
that the intrinsic random errors in calibration have the same impact for
configuration without IF hybrid and for a configuration with IF hybrid with
analog rejection ratio better than 10dB. Compensated rejection ratios above
40dB are obtained even in the presence of high analog rejection. The method is
robust allowing its use under normal operational conditions at any telescope.
We also demonstrate that a full analog receiver is more robust against
systematic errors. Finally, the error bars associated to the compensated
rejection ratio are almost independent of whether IF hybrid is present or not
SiO Outflows in the Most Luminous and Massive Protostellar Sources of the Southern Sky
(Abridged) High-mass star formation is far less understood than low-mass star
formation. It entails molecular outflows, which disturb the protostellar clump.
Studying these outflows and the shocked gas they cause is key for a better
understanding of this process. This study aims to characterise the behaviour of
molecular outflows in the most massive protostellar sources in the Southern
Galaxy by looking for evolutionary trends and associating shocked gas with
outflow activity. We present APEX SEPIA180 observations (beamwidth 36")
of SiO outflow candidates of a sample of 32 luminous and dense clumps,
candidates to harbouring Hot Molecular Cores. We study the SiO(4-3) line
emission, an unambiguous tracer of shocked gas and recent outflow activity, the
HCO(2-1) and HCO(2-1) lines. 78% of our sample present SiO
emission. Nine of these also have wings in the HCO line, indicating outflow
activity. The SiO emission of these 9 sources is more intense and wider than
the rest, suggesting that the outflows in this group are faster and more
energetic. Three positive correlations between the outflow properties were
found, which suggest that more energetic outflows bear to mobilise more
material. No correlation was found between the evolutionary stage indicator
and SiO outflow properties, supporting that outflows happen throughout
the whole high-mass star formation process. We conclude that sources with both
SiO emission and HCO wings and sources with only SiO emission are in
virtually the same advanced stage of evolution in the high-mass star formation
process. The former present more massive and more powerful SiO outflows than
the latter. Thus, looking for more outflow signatures such as HCO wings
could help identify more massive and active massive star-forming regions in
samples of similarly evolved sources, as well as sources with older outflow
activity.Comment: 24 pages, 37 figures, 11 table
A molecular shell with star formation toward the supernova remnant G349.7+0.2
A field of ~38'x38' around the supernova remnant (SNR) G349.7+0.2 has been
surveyed in the CO J=1-0 transition with the 12 Meter Telescope of the NRAO,
using the On-The-Fly technique. The resolution of the observations is 54". We
have found that this remnant is interacting with a small CO cloud which, in
turn, is part of a much larger molecular complex, which we call the ``Large CO
Shell''. The Large CO Shell has a diameter of about 100 pc, an H_2 mass of
930,000 solar masses, and a density of 35 cm-3. We investigate the origin of
this structure and suggest that an old supernova explosion ocurred about 4
million years ago, as a suitable hypothesis. Analyzing the interaction between
G349.7+0.2 and the Large CO Shell, it is possible to determine that the shock
front currently driven into the molecular gas is a non-dissociative shock
(C-type), in agreement with the presence of OH 1720 MHz masers. The positional
and kinematical coincidence among one of the CO clouds that constitute the
Large CO Shell, an IRAS point-like source and an ultracompact H II region,
indicate the presence of a recently formed star. We suggest that the formation
of this star was triggered during the expansion of the Large CO Shell, and
suggest the possibility that the same expansion also created the progenitor
star of G349.7+0.2. The Large CO Shell would then be one of the few
observational examples of supernova-induced star formation.Comment: accepted in Astronomical Journal, corrected typo in the abstract (in
first line, 38' instead of 38"
Triggered massive star formation associated with the bubble HII region Sh2-39 (N5)
Aims. Aiming at studying the physical properties of Galactic IR bubbles and to explore their impact in triggering massive star formation, we perform a multiwavelength analysis of the bubble Hii region Sh2-39 (N5) and its environs. Methods. To analyze the molecular gas we use CO(3-2) and HCO+ (4-3) line data obtained with the on-the-fly technique from the ASTE telescope. To study the distribution and physical characteristics of the dust, we make use of archival data from ATLASGAL, Herschel, and MSX, while the ionized gas was studied making use of an NVSS image. We use public WISE, Spitzer, and MSX point source catalogs to search for infrared candidate YSOs in the region. To investigate the stellar cluster [BDS2003]6 we use IR spectroscopic data obtained with the ARCoIRIS spectrograph, mounted on Blanco 4-m Telescope at CTIO, and new available IR Ks band observations from the VVVeXtended ESO Public Survey (VVVX). Results. The new ASTE observations allowed the molecular gas component in the velocity range from 30 km s−1 to 46 km s−1 , associated with Sh2-39, to be studied in detail. The morphology of the molecular gas suggests that the ionized gas is expanding against its parental cloud. We have identified four molecular clumps, that were likely formed by the expansion of the ionization front, and determined some of their physical and dynamical properties. Clumps having HCO+ and 870 µm counterparts show evidence of gravitational collapse. We identified several candidate YSOs across the molecular component. Their spatial distribution, as well as the fragmentation time derived for the collected layers of the molecular gas, suggest that massive star formation might have been triggered by the expansion of the nebula via the collect and collapse mechanism. The spectroscopical distance obtained for the stellar cluster [BDS2003]6, placed over one of the collapsing clumps in the border of the Hii region, reveals that this cluster is physically associated with the neabula and gives more support to the triggered massive star formation scenario. A radio continuum data analysis indicates that the nebula is older and expands at lower velocity than typical IR Galactic bubblesFil: Duronea, Nicolas Urbano. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones CientÃficas. Instituto Argentino de RadioastronomÃa. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto Argentino de RadioastronomÃa; ArgentinaFil: Cappa, Cristina Elisabeth. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones CientÃficas. Instituto Argentino de RadioastronomÃa. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Instituto Argentino de RadioastronomÃa; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y GeofÃsicas; ArgentinaFil: Bronfman, L.. Universidad de Chile. Facultad de Ciencias Fisicas y Matematicas; ChileFil: Borissova, J.. Universidad de Valparaiso; ChileFil: Gromadzki, M.. Universidad de Valparaiso; Chil
Dust-Gas Scaling Relations and OH Abundance in the Galactic ISM
Observations of interstellar dust are often used as a proxy for total gas
column density . By comparing thermal dust data
(Release 1.2) and new dust reddening maps from Pan-STARRS 1 and 2MASS (Green et
al. 2018), with accurate (opacity-corrected) HI column densities and
newly-published OH data from the Arecibo Millennium survey and 21-SPONGE, we
confirm linear correlations between dust optical depth , reddening
and the total proton column density in the range
(130)10cm, along sightlines with no molecular gas
detections in emission. We derive an / ratio of
(9.41.6)10cmmag for purely atomic sightlines
at 5, which is 60 higher than the canonical value of
Bohlin et al. (1978). We report a 40 increase in opacity
=/, when moving from the low column
density (510cm) to moderate column
density (510cm) regime, and suggest that
this rise is due to the evolution of dust grains in the atomic ISM. Failure to
account for HI opacity can cause an additional apparent rise in ,
of the order of a further 20. We estimate molecular hydrogen column
densities from our derived linear relations, and hence
derive the OH/H abundance ratio of 110
for all molecular sightlines. Our results show no evidence of systematic trends
in OH abundance with in the range
(0.110)10cm. This suggests
that OH may be used as a reliable proxy for H in this range, which includes
sightlines with both CO-dark and CO-bright gas.Comment: The revised manuscript is accepted for publication in The
Astrophysical Journa
Axonal degeneration induced by glutamate-excitotoxicity is mediated by necroptosis
Neuronal excitotoxicity induced by glutamate leads to cell death and functional impairment in a variety of central nervous system pathologies. Glutamate-mediated excitotoxicity triggers neuronal apoptosis in the cell soma as well as degeneration of axons and dendrites by a process associated to calcium increase and mitochondrial dysfunction. Importantly, degeneration of axons initiated by diverse stimuli, including excitotoxicity, has been proposed as an important pathological event leading to functional impairment in neurodegenerative conditions. Here we demonstrate that excitotoxicity-induced axonal degeneration proceeds by a mechanism dependent on the necroptotic kinases RIPK1, RIPK3 and the necroptotic mediator MLKL. Inhibition of RIPK1, RIPK3 or MLKL prevent key steps in the axonal degeneration cascade including mitochondrial depolarization, the opening of the permeability transition pore and calcium dysregulation in the axon. Interestingly, the same excitotoxic stimuli lead to apoptosis in the cell soma, demonstrating the co-activation of two independent degenerative mechanisms in different compartments of the same cell. The identification of necroptosis as a key mechanism of axonal degeneration after excitotoxicity is an important initial step to develop novel therapeutic strategies for nervous system disorders
Physical characterization of S169: A prototypical IR bubble associated with the massive star-forming region IRAS12326-6245
With the aim of studying the properties of Galactic IR bubbles and their
impact in massive star formation, we present a study of the IR bubble S169,
associated with the massive star forming region IRAS12326-6245. We used
CO(2-1),CO(2-1), CO(2-1), HCN(3-2), and HCO+(3-2) line data
obtained with the APEX telescope to study the properties of the molecular gas
in the nebula and the IRAS source . To analyze the properties and distribution
of the dust, we used IRAC-GLIMPSE, Herschel, and ATLASGAL data. The properties
of the ionized gas were studied using images obtained from the SUMSS survey and
SuperCOSMOS database. In our search for stellar and protostellar objects in the
region, we used IR and optical point source calalogs. The new APEX observations
allowed us to identify three molecular components associated with the nebula,
namely: at 39 km/s (component A), 25 km/s (component B), and 17 km/s
(component C). Six molecular condensations (MC1 to MC6) were identified in
component A, with MC3 (the densest and more massive one) being the molecular
counterpart of IRAS12326-6245. For this source, we estimated an H column
density up to 810 cm. To explain the morphology and
velocity of components A, B, and C, we propose a simple model consisting of a
partially complete semisphere-like structure expanding at ~ 12 km/s. The
introduction of this model has led to a discussion about the distance to both
S169 and IRAS12326-6245, which was estimated to be ~ 2 kpc. Several candidate
YSOs were identified, projected mostly onto the molecular condensations MC3,
MC4, and MC5, which indicates that the star-formation process is very active at
the borders of the nebula. A comparison between observable and modeled
parameters was not enough to discern whether the collect-and-collapse mechanism
is acting at the edge of S169.Comment: 17 pages, 12 figures. Accepted for publication in A&
Tracing H2 column density with atomic carbon (CI) and CO isotopologues
We present first results of neutral carbon ([CI], 3P1 - 3P0 at 492 GHz) and
carbon monoxide (13CO, J = 1 - 0) mapping in the Vela Molecular Ridge cloud C
(VMR-C) and G333 giant molecular cloud complexes with the NANTEN2 and Mopra
telescopes. For the four regions mapped in this work, we find that [CI] has
very similar spectral emission profiles to 13CO, with comparable line widths.
We find that [CI] has opacity of 0.1 - 1.3 across the mapped region while the
[CI]/13CO peak brightness temperature ratio is between 0.2 to 0.8. The [CI]
column density is an order of magnitude lower than that of 13CO. The H2 column
density derived from [CI] is comparable to values obtained from 12CO. Our maps
show CI is preferentially detected in gas with low temperatures (below 20 K),
which possibly explains the comparable H2 column density calculated from both
tracers (both CI and 12CO underestimate column density), as a significant
amount of the CI in the warmer gas is likely in the higher energy state
transition ([CI], 3P2 - 3P1 at 810 GHz), and thus it is likely that
observations of both the above [CI] transitions are needed in order to recover
the total H2 column density.Comment: accepted for publication in ApJ Letter
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