159 research outputs found
A 3D view of molecular hydrogen in Supernova 1987A
Supernova (SN) 1987A is the only young SN in which H_2 has been detected in
the ejecta. The properties of the H_2 are important for understanding the
explosion and the ejecta chemistry. Here, we present new VLT/SINFONI
observations of H_2 in SN 1987A, focussing on the 2.12 \mu m (1,0)S(1) line. We
find that the 3D emissivity is dominated by a single clump in the southern
ejecta, with weaker emission being present in the north along the plane of the
circumstellar ring. The lowest observed velocities are in the range 400-800
km/s, in agreement with previous limits on inward mixing of H. The brightest
regions of H_2 coincide with faint regions of H\alpha, which can be explained
by H\alpha being powered by X-ray emission from the ring, while the H_2 is
powered by 44Ti. A comparison with ALMA observations of other molecules and
dust shows that the brightest regions of H_2, CO and SiO occupy different parts
of the inner ejecta and that the brightest H_2 clump coincides with a region of
very weak dust emission. The latter is consistent with theoretical predictions
that the H_2 should form in the gas phase rather than on dust grains.Comment: Accepted for publication in Ap
Insulin, Ascorbate, and Glucose Have a Much Greater Influence Than Transferrin and Selenous Acid on the In Vitro Growth of Engineered Cartilage in Chondrogenic Media
The primary goal of this study was to characterize the response of chondrocyte-seeded agarose constructs to varying concentrations of several key nutrients in a chondrogenic medium, within the overall context of optimizing the key nutrients and the placement of nutrient channels for successful growth of cartilage tissue constructs large enough to be clinically relevant in the treatment of osteoarthritis (OA). To this end, chondrocyte-agarose constructs (phi4x2.34 mm, 30x106 cells/mL) were subjected to varying supplementation levels of insulin (0× to 30× relative to standard supplementation), transferrin (0x to 30x), selenous acid (0x to 10x), ascorbate (0x to 30x), and glucose (0x to 3x). The quality of resulting engineered tissue constructs was evaluated by their compressive modulus (E-Y), tensile modulus (E+Y), hydraulic permeability (k), and content of sulfated glycosaminoglycans (sGAG) and collagen (COL); DNA content was also quantified. Three control groups from two separate castings of constructs (1x concentrations of all medium constituents) were used. After 42 days of culture, values in each of these controls were, respectively, E-Y=518 plus or minus 78, 401 plus or minus 113, 236 plus or minus 67 kPa; E+Y=1420 plus or minus 430, 1140 plus or minus 490, 1240 plus or minus 280 kPa; k=2.3 plus or minus 0.8x10-3, 5.4 plus or minus 7.0x10-3, 3.3 plus or minus 1.3x10-3 mm4/N times s; sGAG=7.8 plus or minus 0.3, 6.3 plus or minus 0.4, 4.1 plus or minus 0.5%/ww; COL=1.3 plus or minus 0.2, 1.1 plus or minus 0.3, 1.4 plus or minus 0.4%/ww; and DNA=11.5 plus or minus 2.2, 12.1 plus or minus 0.6, 5.2 plus or minus 2.8 μg/disk. The presence of insulin and ascorbate was essential, but their concentrations may drop as low as 0.3x without detrimental effects on any of the measured properties; excessive supplementation of ascorbate (up to 30x) was detrimental to E-Y, and 30x insulin was detrimental to both E+Y and E-Y. The presence of glucose was similarly essential, and matrix elaboration was significantly dependent on its concentration (p less than 10-6), with loss of functional properties, composition, and cellularity observed at less than or equal to 0.3x; excessive glucose supplementation (up to 3x) showed no detrimental effects. In contrast, transferrin and selenous acid had no influence on matrix elaboration. These findings suggest that adequate distributions of insulin, ascorbate, and glucose, but not necessarily of transferrin and selenous acid, must be ensured within large engineered cartilage constructs to produce a viable substitute for joint tissue lost due to OA
The unusual ISM in blue and dusty gas-rich galaxies (BADGRS)
The Herschel-ATLAS unbiased survey of cold dust in the local Universe is dominated by a surprising population of very blue (FUV-K 0.5 fHI=MHI/(M∗+M+HI)>0.5 ). Dubbed ‘Blue and Dusty Gas-Rich Sources’ (BADGRS) they have cold diffuse dust temperatures, and the highest dust-to-stellar mass ratios of any galaxies in the local Universe. Here, we explore the molecular interstellar medium in a representative sample of BADGRS, using very deep CO(J up =1,2,3) CO(Jup=1,2,3) observations across the central and outer disc regions. We find very low CO brightnesses (Tp = 5–30 mK), despite the bright far-infrared emission and metallicities in the range 0.5 < Z/Z⊙ < 1.0. The CO line ratios indicate a range of conditions with R 21 =T 21 b /T 10 b =0.6−2.1 R21=Tb21/Tb10=0.6−2.1 and R 31 =T 32 b /T 10 b =0.2−1.2 R31=Tb32/Tb10=0.2−1.2 . Using a metallicity-dependent conversion from CO luminosity to molecular gas mass, we find M H 2 /M d ∼7−27 MH2/Md∼7−27 and Σ H 2 =0.5−6M ⊙ pc −2 ΣH2=0.5−6M⊙pc−2 , around an order of magnitude lower than expected. The BADGRS have lower molecular gas depletion time-scales (τd ∼ 0.5 Gyr) than other local spirals, lying offset from the Kennicutt–Schmidt relation by a similar factor to Blue Compact Dwarf galaxies. The cold diffuse dust temperature in BADGRS (13–16 K) requires an interstellar radiation field 10–20 times lower than that inferred from their observed surface brightness. We speculate that the dust in these sources has either a very clumpy geometry or a very different opacity in order to explain the cold temperatures and lack of CO emission. BADGRS also have low UV attenuation for their UV colour suggestive of an SMC-type dust attenuation curve, different star formation histories or different dust/star geometry. They lie in a similar part of the IRX-β space as z z ∼ 5 galaxies and may be useful as local analogues for high gas fraction galaxies in the early Universe
A complete catalogue of dusty supernova remnants in the Galactic plane
We search for far-infrared (FIR) counterparts of known supernova remnants (SNRs) in the Galactic plane (360° in longitude and b=±1∘) at 70–500 μm with Herschel. We detect dust signatures in 39 SNRs out of 190, made up of 13 core-collapse supernovae (CCSNe), including 4 Pulsar Wind Nebulae (PWNe), and 2 Type Ia SNe. A further 24 FIR detected SNRs have unknown types. We confirm the FIR detection of ejecta dust within G350.1−0.3, adding to the known sample of ∼ 10 SNRs containing ejecta dust. We discover dust features at the location of a radio core at the centre of G351.2+0.1, indicating FIR emission coincident with a possible Crab-like compact object, with dust temperature and mass of T_d = 45.8 K and M_d = 0.18 M⊙, similar to the PWN G54.1+0.3. We show that the detection rate is higher among young SNRs. We produce dust temperature maps of 11 SNRs and mass maps of those with distance estimates, finding dust at temperatures 15 ≲ T_d ≲ 40 K. If the dust is heated by shock interactions the shocked gas must be relatively cool and/or have a low density to explain the observed low grain temperatures
Using dust, gas and stellar mass selected samples to probe dust sources and sinks in low metallicity galaxies
We combine samples of nearby galaxies with Herschel photometry selected on their dust, metal, H I and stellar mass content, and compare these to chemical evolution models in order to discriminate between different dust sources. In a companion paper, we used an H I-selected sample of nearby galaxies to reveal a subsample of very gas-rich (gas fraction >80 per cent) sources with dust masses significantly below predictions from simple chemical evolution models, and well below Md/M* and Md/Mgas scaling relations seen in dust and stellar-selected samples of local galaxies. We use a chemical evolution model to explain these dust-poor, but gas-rich, sources as well as the observed star formation rates (SFRs) and dust-to-gas ratios. We find that (i) a delayed star formation history is required to model the observed SFRs; (ii) inflows and outflows are required to model the observed metallicities at low gas fractions; (iii) a reduced contribution of dust from supernovae (SNe) is needed to explain the dust-poor sources with high gas fractions. These dust-poor, low stellar mass galaxies require a typical core-collapse SN to produce 0.01-0.16 M⊙ of dust. To match the observed dust masses at lower gas fractions, significant grain growth is required to counteract the reduced contribution from dust in SNe and dust destruction from SN shocks. These findings are statistically robust, though due to intrinsic scatter it is not always possible to find one single model that successfully describes all the data. We also show that the dust-to-metal ratio decreases towards lower metallicity
The Herschel-ATLAS data release 1: I. Maps, catalogues and number counts
We present the first major data release of the largest single key-project in area carried out in open time with the Herschel Space Observatory. The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) is a survey of 600 deg2 in five photometric bands – 100, 160, 250, 350 and 500 μm – with the Photoconductor Array Camera and Spectrometer and Spectral and Photometric Imaging Receiver (SPIRE) cameras. In this paper and the companion Paper II, we present the survey of three fields on the celestial equator, covering a total area of 161.6 deg2 and previously observed in the Galaxy and Mass Assembly (GAMA) spectroscopic survey. This paper describes the Herschel images and catalogues of the sources detected on the SPIRE 250 μm images. The 1σ noise for source detection, including both confusion and instrumental noise, is 7.4, 9.4 and 10.2 mJy at 250, 350 and 500 μm. Our catalogue includes 120 230 sources in total, with 113 995, 46 209 and 11 011 sources detected at >4σ at 250, 350 and 500 μm. The catalogue contains detections at >3σ at 100 and 160 μm for 4650 and 5685 sources, and the typical noise at these wavelengths is 44 and 49 mJy. We include estimates of the completeness of the survey and of the effects of flux bias and also describe a novel method for determining the true source counts. The H-ATLAS source counts are very similar to the source counts from the deeper HerMES survey at 250 and 350 μm, with a small difference at 500 μm. Appendix A provides a quick start in using the released data sets, including instructions and cautions on how to use them
ALMA observations of molecules in Supernova 1987A
Supernova (SN) 1987A has provided a unique opportunity to study how SN ejecta evolve in 30 years time scale. We report our ALMA spectral observations of SN 1987A, taken in 2014, 2015 and 2016, with detections of CO, 28SiO, HCO+ and SO, with weaker lines of 29SiO.
We find a dip in the SiO line profiles, suggesting that the ejecta morphology is likely elongated. The difference of the CO and SiO line profiles is consistent with hydrodynamic simulations, which show that Rayleigh-Taylor instabilities causes mixing of gas, with heavier elements much more disturbed, making more elongated structure.
Using 28SiO and its isotopologues, Si isotope ratios were estimated for the first time in SN 1987A. The estimated ratios appear to be consistent with theoretical predictions of inefficient formation of neutron rich atoms at lower metallicity, such as observed in the Large Magellanic Cloud (about half a solar metallicity).
The deduced large HCO+ mass and small SiS mass, which are inconsistent to the predictions of chemical model, might be explained by some mixing of elements immediately after the explosion. The mixing might have made some hydrogen from the envelope to sink into carbon and oxygen-rich zone during early days after the explosion, enabling the formation of a substantial mass of HCO+. Oxygen atoms may penetrate into silicon and sulphur zone, suppressing formation of SiS.
Our ALMA observations open up a new window to investigate chemistry, dynamics and explosive-nucleosynthesis in supernovae
ALMA spectral survey of Supernova 1987A-molecular inventory, chemistry, dynamics and explosive nucleosynthesis
We report the first molecular line survey of Supernova 1987A in the millimetre wavelength range. In the Atacama Large Millimeter/submillimeter Array (ALMA) 210–300 and 340–360 GHz spectra, we detected cold (20–170 K) CO, 28SiO, HCO+ and SO, with weaker lines of 29SiO from ejecta. This is the first identification of HCO+ and SO in a young supernova remnant. We find a dip in the J = 6–5 and 5–4 SiO line profiles, suggesting that the ejecta morphology is likely elongated. The difference of the CO and SiO line profiles is consistent with hydrodynamic simulations, which show that Rayleigh–Taylor instabilities cause mixing of gas, with heavier elements much more disturbed, making more elongated structure. We obtained isotopologue ratios of 28SiO/29SiO > 13, 28SiO/30SiO > 14 and 12CO/13CO > 21, with the most likely limits of 28SiO/29SiO >128, 28SiO/30SiO >189. Low 29Si and 30Si abundances in SN 1987A are consistent with nucleosynthesis models that show inefficient formation of neutron-rich isotopes in a low-metallicity environment, such as the Large Magellanic Cloud. The deduced large mass of HCO+ (∼5 × 10−6 M⊙) and small SiS mass (<6 × 10−5 M⊙) might be explained by some mixing of elements immediately after the explosion. The mixing might have caused some hydrogen from the envelope to sink into carbon- and oxygen-rich zones after the explosion, enabling the formation of a substantial mass of HCO+. Oxygen atoms may have penetrated into silicon and sulphur zones, suppressing formation of SiS. Our ALMA observations open up a new window to investigate chemistry, dynamics and explosive nucleosynthesis in supernovae
A catalogue of Galactic supernova remnants in the far-infrared: revealing ejecta dust in pulsar wind nebulae
We search for far-infrared counterparts of known supernova remnants (SNRs) in the Galactic plane (10° < |l| < 60°) at 70–500 μm using the Herschel Infrared Galactic Plane Survey (Hi-GAL). Of 71 sources studied, we find that 29 (41 per cent) SNRs have a clear FIR detection of dust emission associated with the SNR. Dust from 8 of these is in the central region, and 4 indicate pulsar wind nebulae (PWNe) heated ejecta dust. A further 23 have dust emission in the outer shell structures which is potentially related to swept-up material. Many Galactic SNe have dust signatures but we are biased towards detecting ejecta dust in young remnants and those with a heating source (shock or PWN). We estimate the dust temperature and mass contained within three PWNe, G11.2–0.3, G21.5–0.9, and G29.7–0.3, using modified blackbody fits. To more rigorously analyse the dust properties at various temperatures and dust emissivity index β, we use point process mapping (PPMAP). We find significant quantities of cool dust (at 20–40 K) with dust masses of Md = 0.34 ± 0.14 M⊙, Md = 0.29 ± 0.08 M⊙, and Md = 0.51 ± 0.13 M⊙ for G11.2–0.3, G21.5–0.9, and G29.7–0.3, respectively. We derive the dust emissivity index for the PWN ejecta dust in G21.5–0.3 to be β=1.4±0.5 compared to dust in the surrounding medium where β=1.8±0.1
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