Radio observations of supernova remnant G1.9+0.3 Luken, Kieran J; Filipović, Miroslav D; Maxted, Nigel I ...
Monthly notices of the Royal Astronomical Society,
02/2020, Letnik:
492, Številka:
2
Journal Article
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ABSTRACT
We present 1–10 GHz radio continuum flux density, spectral index, polarization, and rotation measure (RM) images of the youngest known Galactic supernova remnant (SNR) G1.9+0.3, using ...observations from the Australia Telescope Compact Array. We have conducted an expansion study spanning eight epochs between 1984 and 2017, yielding results consistent with previous expansion studies of G1.9+0.3. We find a mean radio continuum expansion rate of (0.78 ± 0.09) per cent yr−1 (or ∼8900 km s−1 at an assumed distance of 8.5 kpc), although the expansion rate varies across the SNR perimetre. In the case of the most recent epoch between 2016 and 2017, we observe faster-than-expected expansion of the northern region. We find a global spectral index for G1.9+0.3 of −0.81 ± 0.02 (76 MHz–10 GHz). Towards the northern region, however, the radio spectrum is observed to steepen significantly (∼−1). Towards the two so-called (east and west) ‘ears’ of G1.9+0.3, we find very different RM values of 400–600 and 100–200 rad m2, respectively. The fractional polarization of the radio continuum emission reaches (19 ± 2) per cent, consistent with other, slightly older, SNRs such as Cas A.
Ecological assessments over large spatial scales require that anthropogenic impacts be distinguishable above natural variation, and that monitoring tools are implemented to maximise impact detection ...and minimise cost. For three heavily modified and four relatively ‘pristine’ estuaries (disturbance category), chemical indicators (metals and PAHs) of anthropogenic stress were measured in benthic sediments, suspended sediments and deployed oysters, together with other environmental variables. These were compared with infaunal and hard-substrate invertebrate communities. Univariate analyses were useful for comparing contaminant loads between different monitoring tools and identified the strongest relationships between benthic and suspended sediments. However, multivariate analyses were necessary to distinguish ecological response to anthropogenic stressors from environmental “noise” over a large spatial scale and to identify sites that were being impacted by contaminants. These analyses provide evidence that suspended sediments are a useful alternative monitoring tool to detect potential anthropogenic impacts on benthic (infaunal and hard-substrate) communities.
► Ecological assessments require that anthropogenic impacts be distinguishable. ► Contaminant and environmental variables were measured in multiple estuaries. ► Variables were compared with benthic infauna and hard-substrate invertebrates. ► Multivariate analyses of monitoring tools important to explain ecological impacts. ► Suspended sediment a useful alternate monitoring tool in impact assessment.
Anthropogenic impacts can be consistently distinguished from natural environmental variation over large spatial scales using the appropriate monitoring tool for the ecological community.
Abstract
A collision between two molecular clouds is one possible candidate for high-mass star formation. The H ii region RCW 36, located in the Vela molecular ridge, contains a young star cluster (∼ ...1 Myr old) and two O-type stars. We present new CO observations of RCW 36 made with NANTEN2, Mopra, and ASTE using 12CO(J = 1–0, 2–1, 3–2) and 13CO(J = 2–1) emission lines. We have discovered two molecular clouds lying at the velocities VLSR ∼ 5.5 and 9 km s−1. Both clouds are likely to be physically associated with the star cluster, as verified by the good spatial correspondence among the two clouds, infrared filaments, and the star cluster. We also found a high intensity ratio of ∼ 0.6–1.2 for CO J = 3–2/1–0 toward both clouds, indicating that the gas temperature has been increased due to heating by the O-type stars. We propose that the O-type stars in RCW 36 were formed by a collision between the two clouds, with a relative velocity separation of 5 km s−1. The complementary spatial distributions and the velocity separation of the two clouds are in good agreement with observational signatures expected for O-type star formation triggered by a cloud–cloud collision. We also found a displacement between the complementary spatial distributions of the two clouds, which we estimate to be 0.3 pc assuming the collision angle to be 45° relative to the line-of-sight. We estimate the collision timescale to be ∼ 105 yr. It is probable that the cluster age found by Ellerbroek et al. (2013b, A&A, 558, A102) is dominated by the low-mass members which were not formed under the triggering by cloud–cloud collision, and that the O-type stars in the center of the cluster are explained by the collisional triggering independently from the low-mass star formation.
A series of new radio-continuum (
λ
=20, 13, 6 and 3 cm) mosaic images focused on the NGC 55 galactic system were produced using archived observational data from the Australia Telescope Compact ...Array. These new images are both very sensitive (down to rms=33
μ
Jy) and feature high angular resolution (down to <4″). Using these newly created images, 66 previously unidentified discrete sources are identified. Of these sources, 46 were classified as background sources, 11 as H
ii
regions and 6 as supernova remnant candidates. This relatively low number of SNR candidates detected coupled with the low number of large H
ii
regions is consistent with the estimated low star formation rate of the galaxy at 0.06
M
⊙
year
−1
. Our spectral index map shows that the core of galaxy appears to have a shallow spectral index between
α
=−0.2 and −0.4. This indicates that the core of the galaxy is a region of high thermal radiation output.
We present observations of the Trumpler 14/Carina I region carried out using the Stratospheric Terahertz Observatory 2. The Trumpler 14/Carina I region is in the western part of the Carina Nebula ...Complex (CNC), which is one of the most extreme star-forming regions in the Milky Way. We observed Trumpler 14/Carina I in the 158 m transition of C ii with a spatial resolution of 48″ and a velocity resolution of 0.17 km s−1. The observations cover a 0 25 by 0 28 area with central position l = 297 34, b = −0 60. The kinematics show that bright C ii structures are spatially and spectrally correlated with the surfaces of CO clouds, tracing the photodissociation region (PDR) and ionization front of each molecular cloud. Along seven lines of sight (LOSs) that traverse Tr 14 into the dark ridge to the southwest, we find that the C ii luminosity from the H ii region is 3.7 times that from the PDR. In the same LOS, we find in the PDRs an average ratio of 1 : 4.1 : 5.6 for the mass in atomic gas : dark CO gas : molecular gas traced by CO. Comparing multiple gas tracers, including H i 21 cm, C ii, CO, and radio recombination lines, we find that the H ii regions of the CNC are well described as H ii regions with one side freely expanding toward us, consistent with the Champagne model of ionized gas evolution. The dispersal of the GMC in this region is dominated by EUV photoevaporation; the dispersal timescale is 20-30 Myr.
A series of new radio-continuum (lambda=20, 13, 6 and 3 cm) mosaic images focused on the NGC 55 galactic system were produced using archived observational data from the Australia Telescope Compact ...Array. These new images are both very sensitive (down to rms=33 muJy) and feature high angular resolution (down to <4''). Using these newly created images, 66 previously unidentified discrete sources are identified. Of these sources, 46 were classified as background sources, 11 as Hii regions and 6 as supernova remnant candidates. This relatively low number of SNR candidates detected coupled with the low number of large Hii regions is consistent with the estimated low star formation rate of the galaxy at 0.06 M ^sub ^year^sup -1^. Our spectral index map shows that the core of galaxy appears to have a shallow spectral index between alpha=-0.2 and -0.4. This indicates that the core of the galaxy is a region of high thermal radiation output.PUBLICATION ABSTRACT
Using high-resolution data of the \(^{12}\)CO and \(^{13}\)CO (\(J\)=1-0}) line emission from The Mopra Southern Galactic Plane CO Survey in conjunction with neutral hydrogen observations from the ...Southern Galactic Plane Survey (SGPS) and mid-infrared Spitzer data, we have explored the large-scale environment of the supernova remnant Kes 41. On the basis of these data, we identified for the first time the parent cloud of Kes 41 in its whole extension and surveyed the HII regions, masers, and the population of massive young stellar objects in the cloud. The whole unveiled giant cloud, located at the kinematic distance of 12.0 \(\pm\) 3.6 kpc, whose average total mass and size are \(\sim\)10-30 \(\times10^5\) M\(_\odot\) and $\sim$$26^{\prime}\(, also shines in \)\gamma\(-rays, as revealed by the Large Area Telescope on board the Fermi satellite. We determined a high average proton density \)\sim\(500-1000~cm\)^{-3}\( in the large molecular complex, of which protons from the neutral atomic and ionised gases comprise only \)\sim$15%.
We present 1 to 10GHz radio continuum flux density, spectral index, polarisation and Rotation Measure (RM) images of the youngest known Galactic Supernova Remnant (SNR) G1.9+0.3, using observations ...from the Australia Telescope Compact Array (ATCA). We have conducted an expansion study spanning 8 epochs between 1984 and 2017, yielding results consistent with previous expansion studies of G1.9+0.3. We find a mean radio continuum expansion rate of (\(0.78 \pm 0.09\)) per cent year\(^{-1}\) (or \(\sim8900\) km s\(^{-1}\) at an assumed distance of 8.5 kpc), although the expansion rate varies across the SNR perimeter. In the case of the most recent epoch between 2016 and 2017, we observe faster-than-expected expansion of the northern region. We find a global spectral index for G1.9+0.3 of \(-0.81\pm0.02\) (76 MHz\(-\)10 GHz). Towards the northern region, however, the radio spectrum is observed to steepen significantly (\(\sim -\)1). Towards the two so called (east & west) "ears" of G1.9+0.3, we find very different RM values of 400-600 rad m\(^{2}\) and 100-200 rad m\(^{2}\) respectively. The fractional polarisation of the radio continuum emission reaches (19 \(\pm\) 2)~per~cent, consistent with other, slightly older, SNRs such as Cas~A.
We present observations of the Trumpler 14/Carina I region carried out using the Stratospheric Terahertz Observatory 2 (STO2). The Trumpler 14/Carina I region is in the west part of the Carina Nebula ...Complex, which is one of the most extreme star-forming regions in the Milky Way. We observed Trumpler 14/Carina I in the 158 \(\mu\)m transition of C\,{\sc ii} with a spatial resolution of 48\(''\) and a velocity resolution of 0.17 km s\(^{-1}\). The observations cover a 0.25\(^\circ\) by 0.28\(^\circ\) area with central position {\it l} = 297.34\(^\circ\), {\it b} = -0.60\(^\circ\). The kinematics show that bright C\,{\sc ii} structures are spatially and spectrally correlated with the surfaces of CO clouds, tracing the photodissociation region and ionization front of each molecular cloud. Along 7 lines of sight that traverse Tr 14 into the dark ridge to the southwest, we find that the C\,{\sc ii} luminosity from the HII region is 3.7 times that from the PDR. In same los we find in the PDRs an average ratio of 1:4.1:5.6 for the mass in atomic gas:dark-CO gas: molecular gas traced by CO. Comparing multiple gas tracers including HI 21cm, C\,{\sc ii}, CO, and radio recombination lines, we find that the HII regions of the Carina Nebula Complex are well-described as HII regions with one-side freely expanding towards us, consistent with the champagne model of ionized gas evolution. The dispersal of the GMC in this region is dominated by EUV photoevaporation; the dispersal timescale is 20-30 Myr.
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