Revisiting the dust destruction efficiency of supernovae

Dust destruction by supernovae is one of the main processes removing dust from the interstellar medium (ISM). Estimates of the efficiency of this process, both theoretical and observational, typically assume a shock propagating into a homogeneous medium, whereas the ISM possesses significant substructure in reality. We self-consistently model the dust and gas properties of the shocked ISM in three supernova remnants (SNRs), using X-ray and infrared (IR) data combined with corresponding emission models. Collisional heating by gas with properties derived from X-ray observations produces dust temperatures too high to fit the far-IR fluxes from each SNR. An additional colder dust component is required, which has a minimum mass several orders of magnitude larger than that of the warm dust heated by the X-ray emitting gas. Dust-to-gas mass ratios indicate that the majority of the dust in the X-ray emitting material has been destroyed, while the fraction of surviving dust in the cold component is plausibly close to unity. As the cold component makes up virtually all the total dust mass, destruction timescales based on homogeneous models, which cannot account for multiple phases of shocked gas and dust, may be significantly overestimating actual dust destruction efficiencies, and subsequently underestimating grain lifetimes

Properties of shocked dust grains in supernova remnants

Shockwaves driven by supernovae both destroy dust and reprocess the surviving grains, greatly affecting the resulting dust properties of the interstellar medium (ISM). While these processes have been extensively studied theoretically, observational constraints are limited. We use physically-motivated models of dust emission to fit the infrared (IR) spectral energy distributions of seven Galactic supernova remnants, allowing us to determine the distribution of dust mass between diffuse and dense gas phases, and between large and small grain sizes. We find that the dense ($\sim 10^3 \,{\rm cm}^{-3}$), relatively cool ($\sim 10^3 \, {\rm K}$) gas phase contains $>90\%$ of the dust mass, making the warm dust located in the X-ray emitting plasma ($\sim 1 \,{\rm cm}^{-3}$/$10^6 \, {\rm K}$) a negligible fraction of the total, despite dominating the mid-IR emission. The ratio of small ($\lesssim 10 \, {\rm nm}$) to large ($\gtrsim 0.1 \, {\rm \mu m}$) grains in the cold component is consistent with that in the ISM, and possibly even higher, whereas the hot phase is almost entirely devoid of small grains. This suggests that grain shattering, which processes large grains into smaller ones, is ineffective in the low-density gas, contrary to model predictions. Single-phase models of dust destruction in the ISM, which do not account for the existence of the cold swept-up material containing most of the dust mass, are likely to greatly overestimate the rate of dust destruction by supernovae.Comment: 13 pages, 12 figures. MNRAS accepte

Revisiting the dust destruction efficiency of supernovae

Dust destruction by supernovae is one of the main processes removing dust from the interstellar medium (ISM). Estimates of the efficiency of this process, both theoretical and observational, typically assume a shock propagating into a homogeneous medium, whereas the ISM possesses significant substructure in reality. We self-consistently model the dust and gas properties of the shocked ISM in three supernova remnants (SNRs), using X-ray and infrared (IR) data combined with corresponding emission models. Collisional heating by gas with properties derived from X-ray observations produces dust temperatures too high to fit the far-IR fluxes from each SNR. An additional colder dust component is required, which has a minimum mass several orders of magnitude larger than that of the warm dust heated by the X-ray emitting gas. Dust-to-gas mass ratios indicate that the majority of the dust in the X-ray emitting material has been destroyed, while the fraction of surviving dust in the cold component is plausibly close to unity. As the cold component makes up virtually all the total dust mass, destruction timescales based on homogeneous models, which cannot account for multiple phases of shocked gas and dust, may be significantly overestimating actual dust destruction efficiencies, and subsequently underestimating grain lifetimes

The dust content of the Crab Nebula

We have modelled the near-infrared to radio images of the Crab Nebula with a Bayesian SED model to simultaneously fit its synchrotron, interstellar (IS), and supernova dust emission. We infer an IS dust extinction map with an average AV = 1.08 ± 0.38 mag, consistent with a small contribution (22 per cent) to the Crab’s overall infrared emission. The Crab’s supernova dust mass is estimated to be between 0.032 and 0.049 M (for amorphous carbon grains) with an average dust temperature Tdust = 41 ± 3 K, corresponding to a dust condensation efficiency of 8–12 per cent. This revised dust mass is up to an order of magnitude lower than some previous estimates, which can be attributed to our different IS dust corrections, lower SPIRE flux densities, and higher dust temperatures than were used in previous studies. The dust within the Crab is predominantly found in dense filaments south of the pulsar, with an average V-band dust extinction of AV = 0.20–0.39 mag, consistent with recent optical dust extinction studies. The modelled synchrotron power-law spectrum is consistent with a radio spectral index αradio = 0.297 ± 0.009 and an infrared spectral index αIR = 0.429 ± 0.021. We have identified a millimetre excess emission in the Crab’s central regions, and argue that it most likely results from two distinct populations of synchrotron emitting particles. We conclude that the Crab’s efficient dust condensation (8–12 per cent) provides further evidence for a scenario where supernovae can provide substantial contributions to the IS dust budgets in galaxies

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

A Galactic dust devil: far-infrared observations of the Tornado supernova remnant candidate

We present complicated dust structures within multiple regions of the candidate supernova remnant (SNR) the ‘Tornado’ (G357.7–0.1) using observations with Spitzer and Herschel. We use point process mapping, PPMAP, to investigate the distribution of dust in the Tornado at a resolution of 8 arcsec, compared to the native telescope beams of 5–36 arcsec. We find complex dust structures at multiple temperatures within both the head and the tail of the Tornado, ranging from 15 to 60 K. Cool dust in the head forms a shell, with some overlap with the radio emission, which envelopes warm dust at the X-ray peak. Akin to the terrestrial sandy whirlwinds known as ‘dust devils’, we find a large mass of dust contained within the Tornado. We derive a total dust mass for the Tornado head of 16.7 M_⊙⁠, assuming a dust absorption coefficient of κ₃₀₀ = 0.56 m² kg⁻¹⁠, which can be explained by interstellar material swept up by a SNR expanding in a dense region. The X-ray, infrared, and radio emission from the Tornado head indicate that this is a SNR. The origin of the tail is more unclear, although we propose that there is an X-ray binary embedded in the SNR, the outflow from which drives into the SNR shell. This interaction forms the helical tail structure in a similar manner to that of the SNR W50 and microquasar SS 433

A galactic dust devil: far-infrared observations of the tornado supernova remnant candidate

We present complicated dust structures within multiple regions of the candidate supernova remnant (SNR) the ‘Tornado’ (G357.7−0.1) using observations with Spitzer and Herschel. We use Point Process Mapping, PPMAP, to investigate the distribution of dust in the Tornado at a resolution of 8″, compared to the native telescope beams of 5 − 36″. We find complex dust structures at multiple temperatures within both the head and the tail of the Tornado, ranging from 15 to 60 K. Cool dust in the head forms a shell, with some overlap with the radio emission, which envelopes warm dust at the X-ray peak. Akin to the terrestrial sandy whirlwinds known as ‘Dust Devils’, we find a large mass of dust contained within the Tornado. We derive a total dust mass for the Tornado head of 16.7 M⊙⁠, assuming a dust absorption coefficient of κ300 =0.56m2kg−1⁠, which can be explained by interstellar material swept up by a SNR expanding in a dense region. The X-ray, infra-red, and radio emission from the Tornado head indicate that this is a SNR. The origin of the tail is more unclear, although we propose that there is an X-ray binary embedded in the SNR, the outflow from which drives into the SNR shell. This interaction forms the helical tail structure in a similar manner to that of the SNR W50 and microquasar SS433

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

Co-producing principles to guide health research: an illustrative case study from an eating disorder research clinic

There is significant value in co-produced health research, however power-imbalances within research teams can pose a barrier to people with lived experience of an illness determining the direction of research in that area. This is especially true in eating disorder research, where the inclusion of co-production approaches lags other research areas. Appealing to principles or values can serve to ground collaborative working. Despite this, there has not been any prior attempt to co-produce principles to guide the work of a research group and serve as a basis for developing future projects. The aim of this piece of work was to co-produce a set of principles to guide the conduct of research within our lived experience led research clinic, and to offer an illustrative case for the value of this as a novel co-production methodology. A lived experience panel were recruited to our eating disorder research group. Through an iterative series of workshops with the members of our research clinic (composed of a lived experience panel, clinicians, and researchers) we developed a set of principles which we agreed were important in ensuring both the direction of our research, and the way in which we wanted to work together. Six key principles were developed using this process. They were that research should aim to be: 1) real world—offering a clear and concrete benefit to people with eating disorders, 2) tailored—suitable for marginalised groups and people with atypical diagnoses, 3) hopeful—ensuring that hope for recovery was centred in treatment, 4) experiential—privileging the ‘voice’ of people with eating disorders, 5) broad—encompassing non-standard therapeutic treatments and 6) democratic—co-produced by people with lived experience of eating disorders. We reflect on some of the positives as well as limitations of the process, highlighting the importance of adequate funding for longer-term co-production approaches to be taken, and issues around ensuring representation of minority groups. We hope that other health research groups will see the value in co-producing principles to guide research in their own fields, and will adapt, develop, and refine this novel methodology