Dust Sputtering Research Articles

Inhibited destruction of dust by supernova in a clumpy medium

The decrease rate of dust mass due to strong shock waves (vs≥150 km s−1) from supernovae (SNe) estimated for the Milky Way interstellar medium significantly exceeds the overall production rate by both asymptotic giant branch stars and core collapse SNe. The interplay between the production and destruction rates is critically important for evaluation of the net dust outcome from SNe at different conditions. In light of this, we study the dynamics of initially polydisperse dust grains pre-existing in an ambient medium swept up the SN shock front depending on magnitude of inhomogeneity (clumpiness) in the medium. We find that dust destruction inside the bubble is inhibited in more inhomogeneous medium: the larger amount of dust survives for the higher dispersion of density. This trend is set by the interrelation between radiative gas cooling and dust sputtering in different environment. After several radiative times the mass fraction of the survived dust saturates at the level almost independent on the gas mean density. We note that for more clumpy medium the distributions of dust over thermal phases of a gas inside the bubble and over sizes are smoother and flatter in comparison with those in a nearly homogeneous medium.

The survival and entrainment of molecules and dust in galactic winds

ABSTRACT Recent years have seen excellent progress in modelling the entrainment of T ∼ 104 K atomic gas in galactic winds. However, the entrainment of cool, dusty T ∼ 10–100 K molecular gas, which is also observed outflowing at high velocity, is much less understood. Such gas, which can be 105 times denser than the hot wind, appears extremely difficult to entrain. We run 3D wind-tunnel simulations with photoionization self-shielding and evolve thermal dust sputtering and growth. Unlike almost all such simulations to date, we do not enforce any artificial temperature floor. We find efficient molecular gas formation and entrainment, as well as dust survival and growth through accretion. Key to this success is the formation of large amounts of 104 K atomic gas via mixing, which acts as a protective ‘bubble wrap’ and reduces the cloud overdensity to χ ∼ 100. This can be understood from the ratio of the mixing to cooling time. Before entrainment, when shear is large, tmix/tcool ≲ 1, and gas cannot cool below the ‘cooling bottleneck’ at 5000 K. Thus, the cloud survival criterion is identical to the well-studied purely atomic case. After entrainment, when shear falls, tmix/tcool > 1, and the cloud becomes multiphase, with comparable molecular and atomic masses. The broad temperature PDF, with abundant gas in the formally unstable $50 \, {\rm K} \lt T \lt 5000 \, {\rm K}$ range, agrees with previous ISM simulations with driven turbulence and radiative cooling. Our findings have implications for dusty molecular gas in stellar and active galactic nuclei outflows, cluster filaments, ‘jellyfish’ galaxies, and asymptomatic giant branch winds.

Dust sputtering within the inner heliosphere: a modelling study

Abstract. The aim of this study is to investigate through modelling how sputtering by impacting solar wind ions influences the lifetime of dust particles in the inner heliosphere near the Sun. We consider three typical dust materials, silicate, Fe0.4Mg0.6O, and carbon, and describe their sputtering yields based on atomic yields given by the Stopping and Range of Ions in Matter (SRIM) package. The influence of the solar wind is characterized by plasma density, solar wind speed, and solar wind composition, and we assume for these parameter values that are typical for fast solar wind, slow solar wind, and coronal mass ejection (CME) conditions to calculate the sputtering lifetimes of dust. To compare the sputtering lifetimes to typical sublimation lifetimes, we use temperature estimates based on Mie calculations and material vapour pressure derived with the MAGMA chemical equilibrium code. We also compare the sputtering lifetimes to the Poynting–Robertson lifetime and to the collision lifetime. We present a set of sputtering rates and lifetimes that can be used for estimating dust destruction in the fast and slow solar wind and during CME conditions. Our results can be applied to solid particles of a few nanometres and larger. The sputtering lifetimes increase linearly with the size of particles. We show that sputtering rates increase during CME conditions, primarily because of the high number densities of heavy ions in the CME plasma. The shortest sputtering lifetimes we find are for silicate, followed by Fe0.4Mg0.6O and carbon. In a comparison between sputtering and sublimation lifetimes we concentrate on the nanodust population. The comparison shows that sublimation is the faster destruction process within 0.1 AU for Fe0.4Mg0.6O, within 0.05 AU for carbon dust, and within 0.07 AU for silicate dust. The destruction by sputtering can play a role in the vicinity of the Sun. We discuss our findings in the context of recent F-corona intensity measurements onboard Parker Solar Probe.

Thermal and non-thermal dust sputtering in hydrodynamical simulations of the multiphase interstellar medium

We study the destruction of interstellar dust via sputtering in supernova (SN) shocks using three-dimensional hydrodynamical simulations. With a novel numerical framework, we follow both sputtering and dust dynamics governed by direct collisions, plasma drag and betatron acceleration. Grain-grain collisions are not included and the grain-size distribution is assumed to be fixed. The amount of dust destroyed per SN is quantified for a broad range of ambient densities and fitting formulae are provided. Integrated over the grain-size distribution, nonthermal (inertial) sputtering dominates over thermal sputtering for typical ambient densities. We present the first simulations that explicitly follow dust sputtering within a turbulent multiphase interstellar medium. We find that the dust destruction timescales $\tau$ are 0.35 Gyr for silicate dust and 0.44 Gyr for carbon dust in solar neighborhood conditions. The SN environment has an important impact on $\tau$. SNe that occur in preexisting bubbles destroy less dust as the destruction is limited by the amount of dust in the shocked gas. This makes $\tau$ about 2.5 times longer than the estimate based on results from a single SN explosion. We investigate the evolution of the dust-to-gas mass ratio (DGR), and find that a spatial inhomogeneity of $\sim$ 14\% develops for scales below 10 pc. It locally correlates positively with gas density but negatively with gas temperature even in the exterior of the bubbles due to incomplete gas mixing. This leads to a $\sim$ 30\% lower DGR in the volume filling warm gas compared to that in the dense clouds.

ON THE FORMATION OF MOLECULAR CLUMPS IN QSO OUTFLOWS

ABSTRACT We study the origin of the cold molecular clumps in quasar outflows, recently detected in CO and HCN emission. We first describe the physical properties of such radiation-driven outflows and show that a transition from a momentum- to an energy-driven flow must occur at a radial distance of . During this transition, the shell of swept-up material fragments due to Rayleigh–Taylor instabilities, but these clumps contain little mass and are likely to be rapidly ablated by the hot gas in which they are immersed. We then explore an alternative scenario in which clumps form from thermal instabilities at , possibly containing enough dust to catalyze molecule formation. We investigate this process with 3D two-fluid (gas+dust) numerical simulations of a kpc3 patch of the outflow, including atomic and dust cooling, thermal conduction, dust sputtering, and photoionization from the QSO radiation field. In all cases, dust grains are rapidly destroyed in years; and while some cold clumps form at later times, they are present only as transient features, which disappear as cooling becomes more widespread. In fact, we only find a stable two-phase medium with dense clumps if we artificially enhance the QSO radiation field by a factor of 100. This result, together with the complete destruction of dust grains, renders the interpretation of molecular outflows a very challenging problem.

The gas-to-dust mass ratio of Centaurus A as seen by Herschel★

We present photometry of the nearby galaxy NGC 5128 (Centaurus A) observed with the PACS and SPIRE instruments on board the Herschel Space Observatory, at 70, 160, 250, 350 and 500 {\mu}m, as well as new CO J = 3-2 observations taken with the HARP-B instrument on the JCMT. Using a single component modified blackbody, we model the dust spectral energy distribution within the disk of the galaxy using all five Herschel wavebands, and find dust temperatures of ~30 K towards the centre of the disk and a smoothly decreasing trend to ~20 K with increasing radius. We find a total dust mass of (1.59 \pm 0.05) \times 10^7 M\odot, and a total gas mass of (2.7 \pm 0.2) \times 10^9 M\odot. The average gas-to-dust mass ratio is 103 \pm 8 but we find an interesting increase in this ratio to approximately 275 toward the centre of Cen A. We discuss several possible physical processes that may be causing this effect, including dust sputtering, jet entrainment and systematic variables such as the XCO factor. Dust sputtering by X-rays originating in the AGN or the removal of dust by the jets are our most favoured explanations.

Dust as a Gas Carrier

Dust in space can collect particles from surrounding plasma and transport them over long distances. Release of the implanted particles can then change the mass composition in a particular place of the space. The depth of ion penetration into the dust body strongly depends on an initial mutual energy and differs with ion species as well as with the grain composition. The same holds for diffusion constant of implanted ions (already neutralized) exiting back to the free space. We have used our measurements of the release of Ar ions implanted into glassy carbon dust grains for determination of the diffusion coefficient. Our calculations provide the limits for the amount of gas that can be dissolved in the grain as well as its release rate. We discuss the influence of the dust sputtering and dust temperature on the aforementioned quantities.

DUSTY WIND-BLOWN BUBBLES

Spurred by recent observations of 24 micron emission within wind-blown bubbles, we study the role that dust can play in such environments, and build an approximate model of a particular wind-blown bubble, `N49.' First, we model the observations with a dusty wind-blown bubble, and then ask whether dust could survive within N49 to its present age (estimated to be 5x10^5 to 10^6 years). We find that dust sputtering and especially dust-gas friction would imply relatively short timescales (t ~ 10^4 years) for dust survival in the wind-shocked region of the bubble. To explain the 24 micron emission, we postulate that the grains are replenished within the wind-blown bubble by destruction of embedded, dense cloudlets of ISM gas that have been over-run by the expanding wind-blown bubble. We calculate the ablation timescales for cloudlets within N49 and find approximate parameters for the embedded cloudlets that can replenish the dust; the parameters for the cloudlets are roughly similar to those observed in other nebula. Such dust will have an important effect on the bubble: including simple dust cooling in a wind-blown bubble model for N49, we find that the luminosity is higher by approximately a factor of six at a bubble age of about 10^4 years. At ages of 10^7 years, the energy contained in the bubble is lower by about a factor of eight if dust is included; if dust must be replenished within the bubble, the associated accompanying gas mass will also be very important to wind-blown bubble cooling and evolution. While more detailed models are certainly called for, this work illustrates the possible strong importance of dust in wind-blown bubbles, and is a first step toward models of dusty, wind-blown bubbles.

Dust Sputtering by Reverse Shocks in Supernova Remnants

We consider sputtering of dust grains, believed to be formed in cooling supernovae ejecta, under the influence of reverse shocks. In the regime of self-similar evolution of reverse shocks, we can follow the evolution of ejecta density and temperature analytically as a function of time in different parts of the ejecta, and calculate the sputtering rate of graphite and silicate grains embedded in the ejecta as they encounter the reverse shock. Through analytic (1D) calculations, we find that a fraction of dust mass ($ 1\hbox{--}20$% for silicates and %$\le 5$% for graphites) can be sputtered by reverse shocks, the fraction varying with the grain size distribution and the steepness of the density profile of the ejecta mass. It is expected that many more grains will get sputtered in the region between the forward and reverse shocks, so that our analytical results provide a lower limit to the destroyed fraction of dust mass.

Interaction between single dust grains and ions or electrons: laboratory measurements and their consequences for the dust dynamics

The present paper reviews our latest, and brings several new, results on charging of dust grains of various materials and sizes. Charging processes of dust in space and their influence on the dust dynamics are analyzed in laboratory simulations of secondary emission, field ion and electron emissions, and dust sputtering. Single micrometre-sized grains and grain clusters are stored in a hyperbolic quadrupole field under ultra-high vacuum conditions for long time periods. The charge state of the grain and its evolution are recorded while the grain is exposed to ion or electron beams of various energies and fluxes. The influence of the secondary electron emission on the charge state is measured and compared with a computer model. Limitations on the grain charge by the field electron and ion emission are considered next. The measurements allow analyzing field emission from conductive and dielectric grains. The existence of long-lived surface states on insulating materials, which are probably responsible for the anomalous behavior of field electron emission and the low threshold of the field ion emission, is indicated. The observation of sputtering by energetic ions showing a surprising anisotropic erosion of a conductive grain is analyzed. The sputtering and the field ion emission are discussed as possible sources of the so-called pick-up ions.

SpitzerObservations of Transient, Extended Dust in Two Elliptical Galaxies: New Evidence of Recent Feedback Energy Release in Galactic Cores

Spitzer observations of extended dust in two optically normal elliptical galaxies provide a new confirmation of buoyant feedback outflow in the hot gas atmospheres around these galaxies. AGN feedback energy is required to prevent wholesale cooling and star formation in these group-centered galaxies. In NGC 5044 we observe interstellar (presumably PAH) emission at 8 μm out to about 5 kpc. Both NGC 5044 and NGC 4636 have extended 70 μm emission from cold dust exceeding that expected from stellar mass loss. The sputtering lifetime of this extended dust in the ~1 keV interstellar gas, ~107 yr, establishes the time when the dust first entered the hot gas. Evidently the extended dust originated in dusty disks or clouds, commonly observed in elliptical galaxy cores, that were disrupted, heated, and buoyantly transported outward. The surviving central dust in NGC 5044 and NGC 4636 has been disrupted into many small filaments. It is remarkable that the asymmetrically extended 8 μm emission in NGC 5044 is spatially coincident with Hα+[N II] emission from warm gas. A calculation shows that dust-assisted cooling in buoyant hot gas moving out from the galactic core can cool within a few kiloparsecs in ~107 yr, explaining the optical line emission observed. The X-ray images of both galaxies are disturbed. All timescales for transient activity—restoration of equilibrium and buoyant transport in the hot gas, dynamics of surviving dust fragments, and dust sputtering—are consistent with a central release of feedback energy in both galaxies about 107 years ago.

Intergalactic medium metal enrichment through dust sputtering

We study the motion of dust grains into the intergalactic medium (IGM) around redshift z = 3, to test the hypothesis that grains can efficiently pollute the gas with metals through sputtering. We use the results available in the literature for radiation-driven dust ejection from galaxies as initial conditions and follow the motion onwards. Via this mechanism, grains are ejected into the IGM with velocities >100 km s −1 ;a sthey move supersonically, grains can be efficiently eroded by non-thermal sputtering. However, Coulomb and collisional drag forces effectively reduce the charged grain velocity. Up-to-date sputtering yields for graphite and silicate (olivine) grains have been derived using the code TRANSPORT OF IONS IN MATTER (TRIM), for which we provide analytic fits. After training our method on a homogeneous density case, we analyse the grain motion and sputtering in the IGM density field as derived from a � cold dark matter (CDM) cosmological simulation at z = 3.27. We found that only large (a 0.1µm) grains can travel up to considerable distances (few ×100 kpc physical) before being stopped. Resulting metallicities show a well-defined trend with overdensity δ. The maximum metallicities are reached for 10 <δ< 100 [corresponding to systems, in quasi-stellar object (QSO) absorption spectra, with 14.5 < log N (H I) < 16]. However the distribution of sputtered metals is very inhomogeneous, with only a small fraction of the IGM volume polluted by dust sputtering (filling factors of 18 per cent for Si and 6 per cent for C). For the adopted size distribution, grains are never completely destroyed; nevertheless, the extinction and gas photoelectric heating effects resulting from this population of intergalactic grains are well below current detection limits. Ke yw ords: dust, extinction ‐ intergalactic medium ‐ cosmology: miscellaneous.

The Effect of Dust Sputtering in Supernova Remnant

IRAS observations of supernova remnants (SNRs) reported that infrared luminosity from SNRs are very different, though some of them have same temperature. This is because infrared emittion depends on density of the dust grains.

Time‐dependent Cooling and Grain Destruction in Hot Dusty Plasmas: A Simplified Model and Principal Results

We present a simple method of including the principal effects of interstellar dust in hot gas evolution codes, including a consistent set of elemental abundances, their distribution among gas and grains in diffuse regions, the distribution of grain sizes, the sputtering of grains by impact with nuclei, and the cooling rate from gas-grain collisions. When combined with a gas evolution code, the time-dependent evolution of gas phase abundances, ion concentrations, and gas and grain cooling can be followed.Sample calculations are presented to explore the relative timescales for grain destruction and radiative cooling, the relative importance of grain and gas cooling coefficients in evolving gas, the overall significance of grain inclusion to the thermal history of the gas, and the possibility of comparative dating of hot gas regions via their X-ray spectral characteristics.We find that the straightforward comparison between the cooling coefficient of newly heated dust with that of gas in collisional equilibrium is particularly misleading. The cooling coefficient of newly heated material is overwhelmingly dominated by the nonequilibrium gas cooling, during which the ionization is rapidly rising and dust is being sputtered. The gas cooling coefficient drops rapidly during this brief period. Dust cooling also drops, because of the reduction in grain surface area. At high temperature, gas cooling soon falls below that of the grains, but grain cooling continues to fall rapidly, raising the gas cooling via the return of elements to the gas. For material whose temperature exceeds roughly 4 × 106 K, the total radiated energy during these "ion flash" and dust destruction epochs is small compared to the total energy in the system. Conversely, for temperatures below about 4 × 105 K, both grain destruction by ion sputtering and grain cooling are small. It is a somewhat remarkable coincidence: The range of temperature for which the dust destruction and radiative cooling timescales are comparable is also the temperature range for which grain and gas cooling rates are similar.We conclude that the inclusion of dust in codes will usually have little overall effect on the thermal and dynamical history of the gas. But there can be a quite significant alteration of the X-ray spectra of recently heated gas, behind "nonradiative" shocks, for example. Dust inclusion at least at our level of complexity is required in any models purporting to examine spectral details. As an example, the inability of shockwave models to produce the surprising intensity of the [Fe X] line in the nonradiative shocks of the Cygnus Loop was once used to argue that the shock was proceeding through a medium infested with microscopic interstellar clouds, evaporating them as it went. It was suggested that evaporative injection of low ion stages into the hot gas could potentially produce the [Fe X], as iron is being ionized. Dust sputtering should produce a similar effect. There is probably an important spectral line whose intensity and surface brightness distribution map the pattern and rate of dust destruction in the Cygnus Loop and hot gas elsewhere, but it will not be found in gas-phase-only models. Fortunately, at the level of complexity of our modeling, dust inclusion is straightforward.