Dust Distribution Research Articles

Numerical investigation and passive control of dust pollution on a minivan

A dynamic model using a discrete phase approach was developed to study dust pollution on a minivan's side and rear surfaces. Numerical simulations, validated by road tests, analyzed dust concentration and distribution. A significant factor in sidewall dust pollution is the pressure difference inside and outside the wheel cavity, particularly behind the wheel cavity, which affects about 40% of the sidewall. Large trailing vortices at the rear create a low-pressure zone, leading to rear dust pollution characterized by low concentration, large area, and dispersed regions. Aerodynamic devices were proposed to mitigate pollution. Simulations showed that side attachments, such as wheel deflectors, wheel cavity baffle, and mudguards, reduce aerodynamic drag and sidewall dust pollution, with wheel cavity baffles reducing the affected area by about 48.98%. Rear attachments, like diffusers and roof deflector, minimize rear dust pollution, with roof deflector reducing the area by approximately 87.24%. These findings highlight the effectiveness of aerodynamic modifications in controlling dust pollution on a minivan.

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.

Imprints of the Local Bubble and Dust Complexity on Polarized Dust Emission

Using 3D dust maps and Planck polarized dust emission data, we investigate the influence of the 3D geometry of the nearby interstellar medium (ISM) on the statistics of the dust polarization on large ( 80′ ) scales. We test recent models that assume that the magnetic field probed by the polarized dust emission is preferentially tangential to the Local Bubble wall, but we do not find an imprint of the Local Bubble geometry on the dust polarization fraction. We also test the hypothesis that the complexity of the 3D dust distribution drives some of the measured variation of the dust polarization fraction. We compare sight lines with similar total column densities and find that, on average, the dust polarization fraction decreases when the dust column is substantially distributed among multiple components at different distances. Conversely, the dust polarization fraction is higher for sight lines where the dust is more concentrated in 3D space. This finding is statistically significant for the dust within 1.25 kpc, but the effect disappears if we only consider dust within 270 pc. In conclusion, we find that the extended 3D dust distribution, rather than solely the dust associated with the Local Bubble, plays a role in determining the observed dust polarization fraction at 80′. This conclusion is consistent with a simple analytical prediction and remains robust under various modifications to the analysis. These results illuminate the relationship between the 3D geometry of the ISM and tracers of the interstellar magnetic field. We discuss implications for our understanding of the polarized dust foreground to the cosmic microwave background.

Novel Insights on the Dust Distribution in the Zodiacal Dust Cloud from PSP/WISPR Observations at Large Elongations

The Wide-Field Imager for Solar Probe (WISPR) on the Parker Solar Probe (PSP) mission maps the brightness produced by the zodiacal dust cloud (ZDC) from an historically unprecedented viewpoint. The brightness results from the scattering of photospheric light by dust particles in the ZDC, and is called zodiacal light (ZL). We exploit the PSP nominal science encounters in orbits 10 through 16 for an in-depth study of the location and brightness evolution of the symmetry axis of the ZL in images taken with the WISPR outer telescope (WISPR-O). During these 11 day encounters, PSP covered heliocentric distances between 0.25 and 0.0617 au (∼53.78−13.28 R ☉) and ∼255° in helioecliptic longitude from within the orbital plane of Venus. The unique WISPR-O viewpoint, which comprises line-of-sight elongations of 80° ± 27°, has led to further insights about the ZDC. Namely, we find that the gravitational pull of the planets warps the ZDC symmetry plane and shifts the ZDC towards the solar system barycenter, creating an east–west asymmetry in the ZL brightness. Additionally, our analysis provides the first consistent observational evidence of a circumsolar dust enhancement resulting from the sublimation of dust grains at ∼25 R ☉. Overall, the WISPR observations from the PSP platform are opening a new window in the remote sensing of the ZDC.

Where Dust Comes From: Global Assessment of Dust Source Attributions With AeroCom Models

AbstractThe source of dust in the global atmosphere is an important factor to better understand the role of dust aerosols in the climate system. However, it is a difficult task to attribute the airborne dust over the remote land and ocean regions to their origins since dust from various sources are mixed during long‐range transport. Recently, a multi‐model experiment, namely the AeroCom‐III Dust Source Attribution (DUSA), has been conducted to estimate the relative contribution of dust in various locations from different sources with tagged simulations from seven participating global models. The BASE run and a series of runs with nine tagged regions were made to estimate the contribution of dust emitted in East‐ and West‐Africa, Middle East, Central‐ and East‐Asia, North America, the Southern Hemisphere, and the prominent dust hot spots of the Bodélé and Taklimakan Deserts. The models generally agree in large scale mean dust distributions, however models show large diversity in dust source attribution. The inter‐model differences are significant with the global model dust diversity in 30%–50%, but the differences in regional and seasonal scales are even larger. The multi‐model analysis estimates that North Africa contributes 60% of global atmospheric dust loading, followed by Middle East and Central Asia sources (24%). Southern hemispheric sources account for 10% of global dust loading, however it contributes more than 70% of dust over the Southern Hemisphere. The study provides quantitative estimates of the impact of dust emitted from different source regions on the globe and various receptor regions including remote land, ocean, and the polar regions synthesized from the seven models.

A Comparative Study of Ultraluminous Infrared Galaxies in the IRAS and SDSS Surveys

We present a comprehensive study of ultraluminous infrared galaxies (ULIRGs), leveraging data from the Infrared Astronomical Satellite Faint Source Catalogue and the spectroscopic catalog in the Sloan Digital Sky Survey Data Release 16. Our meticulous crossmatching technique significantly enhances the reliability of ULIRG identification, resulting in the identification of 283 reliable ULIRGs, including 102 new detections, while discarding 120 previously reported false sources. Covering a redshift range of z = 0.018–0.996, with a median redshift of z¯=0.259 , our uniform sample reveals apparent interaction features in approximately 40% of ULIRGs, increasing to 92% for those with z < 0.1. Through optical spectra analysis, it is indicated that over 58% of ULIRGs host an active galactic nucleus (AGN), which is twice as high as detections based solely on infrared colors. Moreover, a pronounced excess of radio emissions associated with AGN activity results in a steeper radio–far-infrared correlation. Notably, Type I ULIRGs exhibit properties similar to those of narrow-line Seyfert 1 galaxies, with an elevated incidence rate of Mg ii broad absorption lines (16.7%), surpassing that of typical optically selected quasars by over tenfold, consistent with current evolutionary models. We anticipate that forthcoming telescopes such as the China Space Station Telescope and Leighton Chajnantor Telescope will provide deeper insights into ULIRG morphology, dust distribution, molecular gas, and AGN activity.

Exocomet Models in Transit: Light Curve Morphology in the Optical—Near Infrared Wavelength Range

Following the widespread practice of exoplanetary transit simulations, various presumed components of an extrasolar system can be examined in numerically simulated transits, including exomoons, rings around planets, and the deformation of exoplanets. Template signals can then be used to efficiently search for light curve features that mark specific phenomena in the data, and they also provide a basis for feasibility studies of instruments and search programs. In this paper, we present a method for exocomet transit light curve calculations using arbitrary dust distributions in transit. The calculations, spanning four distinct materials (carbon, graphite, pyroxene, and olivine), and multiple dust grain sizes (100–300 nm, 300–1000 nm, and 1000–3000 nm) encompass light curves in VRJHKL bands. We also investigated the behavior of scattering colors. We show that multicolor photometric observations are highly effective tools in the detection and characterization of exocomet transits. They provide information on the dust distribution of the comet (encoded in the light curve shape), while the color information itself can reveal the particle size change and material composition of the transiting material, in relation to the surrounding environment. We also show that the typical cometary tail can result in the wavelength dependence of the transit timing. We demonstrate that multi-wavelength observations can yield compelling evidence for the presence of exocomets in real observations.

The accretion burst of the massive young stellar object G323.46−0.08

Context. Accretion bursts from low-mass young stellar objects (YSOs) have been known for many decades. In recent years, the first accretion bursts of massive YSOs (MYSOs) have been observed. These phases of intense protostellar growth are of particular importance for studying massive star formation. Bursts of MYSOs are accompanied by flares of Class II methanol masers (hereafter masers), which are caused by an increase in exciting mid-infrared (MIR) emission. They can lead to long-lasting thermal afterglows of the dust continuum radiation visible at infrared (IR) and (sub)millimeter (hereafter (sub)mm) wavelengths. Furthermore, they might cause a scattered light echo. The G323.46−0.08 (hereafter G323) event, which shows all these features, extends the small sample of known MYSO bursts. Aims. Maser observations of the MYSO G323 show evidence of a flare, which was presumed to be caused by an accretion burst. This should be verified with IR data. We used time-dependent radiative transfer (TDRT) to characterize the heating and cooling timescales for eruptive MYSOs and to infer the main burst parameters. Methods. Burst light curves, as well as the pre-burst spectral energy distribution (SED) were established from archival IR data. The properties of the MYSO, including its circumstellar disk and envelope, were derived by using static radiative transfer modeling of pre-burst data. For the first time, TDRT was used to predict the temporal evolution of the SED. Observations with SOFIA/HAWC+ were performed to constrain the burst energy from the strength of the thermal afterglow. Image subtraction and ratioing were applied to reveal the light echo. Results. The G323 accretion burst is confirmed. It reached its peak in late 2013/early 2014 with a Ks-band increase of ∼2.5 mag. Both Ks-band and integrated maser flux densities follow an exponential decay. TDRT indicates that the duration of the thermal afterglow in the far-infrared (FIR) can exceed the burst duration by years. The latter was proved by SOFIA observations, which indicate a flux increase of (14.2 ± 4.6)% at 70 μm and (8.5 ± 6.1)% at 160 μm in 2022 (2 yr after the burst ended). A one-sided light echo emerged that was propagating into the interstellar medium. Conclusions. The burst origin of the G323 maser flare has been verified. TDRT simulations revealed the strong influence of the burst energetics and the local dust distribution on the strength and duration of the afterglow. The G323 burst is probably the most energetic MYSO burst that has been observed so far. Within 8.4 yr, an energy of (0.9−0.8+2.5) × 1047 erg was released. The short timescale points to the accretion of a compact body, while the burst energy corresponds to an accumulated mass of at least (7−6+20) MJup and possibly even more if the protostar is bloated. In this case, the accretion event might have triggered protostellar pulsations, which give rise to the observed maser periodicity. The associated IR light echo is the second observed from a MYSO burst.

Ray tracing through absorbing dielectric media in the Schwarzschild spacetime

Abstract General Relativity describes the trajectories of light-rays through curved spacetime near a massive object. In addition to gravitational lensing, we include an absorbing dielectric medium given by a complex refractive index known as the Drude model. When absorption is included the eikonal becomes complex, with the imaginary part related to the absorption along a ray between emission and observation points. We extend results from the literature to include dispersion in the index of refraction. The complex Hamiltonian splits into a real part that describes the equations of motion and a constraint equation that governs the momentum loss in the system. We work in coordinates which are fully real, with a real metric in physical spacetime. We assume the dust and plasma distributions of the Drude matter to coincide and vary as a power-law $1/r^h$. We find that transmission requires $h&gt;1$, otherwise exponential absorption occurs along ray paths. We use ray-tracing through strongly absorbing matter near the surface of the compact star, as well as specializing to a point-lens in the weak-field limit with weakly absorbing matter to generate potentially observable light curves for distant observers. In the appropriate limits, our theory reproduces results from the literature.&amp;#xD;

Research on particle size distribution and composition of road deposit dust in Xi'an: From the perspective of non-exhaust emissions

Road dust, containing tire-road wear particles, atmospheric dust, or construction-related particles, contaminates road environments and poses a health hazard when inhaled by humans. To further explore the particle size and composition of road deposit dust, this study collects these particles in Xi'an, considering various road grades, materials, service conditions, sections, and locations. The collected particles undergo electron microscopy, laser particle size, thermal, mass spectrometry, infrared spectroscopy, and inductively coupled plasma analyses. Qualitative and quantitative analysis of the particles has been conducted, leading to the following conclusions: Asphalt & tire contribute 8.5% of the road deposit dust, while wear from calcium carbonate accounts for approximately 30%. The average particle size on urban roads (392 μm) is 1.25 times that of rural roads (312 μm). The smaller particles on rural roads are more easily resuspended and inhaled, posing health risks and requiring more attention. Brake zones, which often have 1.4 times the metal content compared to mid-sections, including potentially carcinogenic chromium (Cr), should receive focused watering and adsorption due to brake zone where is also at intersections and pedestrian crossing. New roads, which generate 3-6 times more organic matter than old roads, requires continuous cleaning after opening to traffic. Surface-blocked asphalt concrete (AC) pavements, as their lack of pores can lead to easy re-suspension of deposited particles due to tire-road interaction should also be attention. This study aims to contribute to the field of traffic-related dust pollution cleaning strategies and non-exhaust emissions mitigation measures in the future.

Aircraft engine dust ingestion at global airports

Abstract. Atmospheric mineral dust aerosol constitutes a threat to aircraft engines from deterioration of internal components. Here we fulfil an overdue need to quantify engine dust ingestion at airports worldwide. The vertical distribution of dust is of key importance since ascent/descent rates and engine power both vary with altitude and affect dust ingestion. We use representative jet engine power profile information combined with vertically and seasonally varying dust concentrations to calculate the “dust dose” ingested by an engine over a single ascent or descent. Using the Copernicus Atmosphere Monitoring Service (CAMS) model reanalysis, we calculate climatological and seasonal dust dose at 10 airports for 2003–2019. Dust doses are mostly largest in Northern Hemisphere summer for descent, with the largest at Delhi in June–August (JJA; 6.6 g) followed by Niamey in March–May (MAM; 4.7 g) and Dubai in JJA (4.3 g). Holding patterns at altitudes coincident with peak dust concentrations can lead to substantial quantities of dust ingestion, resulting in a larger dose than the take-off, climb, and taxi phases. We compare dust dose calculated from CAMS to spaceborne lidar observations from two dust datasets derived from the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP). In general, seasonal and spatial patterns are similar between CAMS and CALIOP, though large variations in dose magnitude are found, with CAMS producing lower doses by a factor of 1.9 to 2.8, particularly when peak dust concentration is very close to the surface. We show that mitigating action to reduce engine dust damage could be achieved, firstly by moving arrivals and departures to after sunset and secondly by altering the altitude of the holding pattern away from that of the local dust peak altitude, reducing dust dose by up to 44 % and 41 % respectively. We suggest that a likely low bias of dust concentration in the CAMS reanalysis should be considered by aviation stakeholders when estimating dust-induced engine wear.

Numerical study on the gas-solid diffusion characteristics of airflow and dust particles in metal mine blasting excavation under three hybrid ventilation modes

Dust pollution has long been a challenge in the blasting excavation of underground metal mines, and uncontrolled diffusion of dust particles seriously endangers the health and safety of workers as well as the environment in underground space. Most existing research on dust diffusion focuses on fully mechanized coal mining face or borehole drilling, where the dust source emission characteristics differ significantly from metal mine blasting excavation. Furthermore, it is still unclear how the ventilation modes of Far-Pressing-Far-Absorption (FPFA), Near-Pressing-Far-Absorption (NPFA), and Far-Pressing-Near-Absorption (FPNA) affect the mechanism of dust diffusion in the breathing zone. In this work, gas-solid flow characteristics in a typical metal mine blasting tunnel are numerically studied based on Euler-Lagrange method. The interphase forces between airflow and dust particles are comprehensively modeled, and the particle diffusion effect caused by fluid turbulence is described by the discrete random walk model. Five typical regions for airflow disorder phenomena in the working tunnel are predicted, including the jet development region, the return airflow core region, the airflow reversal region, the airflow recirculation region, and the secondary flow region. The spatial distribution of dust exhibits nonuniform characteristics under turbulent airflow transport. The time results of the monitored dust concentration reveal that the junction of the working tunnel and the return airway is a key area of focus for the prevention and control of dust pollution. Among the three ventilation modes, the Far-Pressing-Near-Absorption (FPNA) ventilation mode has the best dust removal efficiency. The supply vent further from the blasting face allows the jet to fully develop, while the exhaust vent closer to the blasting face allows dust particles to be drawn in and discharged earlier. Under the condition of fixed total power consumption for the supply and exhaust fans, a larger exhaust airflow velocity helps remove dust from the breathing zone.

Simulations on Levitation and Spatial Distribution of Charged Dust on the Moon Surface

The levitation of charged dust, which may cause serious hazards to astronauts and lunar rovers, has been one of the most significant challenges in lunar exploration. Here we simulate lunar sheath potentials in different solar wind conditions and solar zenith angles (SZAs) on the lunar surface by the particle-in-cell method. The simulated potentials exhibit two types of distributions as a function of height, depending on the SZAs. For SZA ∼ 0°–70°, the nonmonotonic distribution with positive surface potential dominates in the photoelectron sheath. For SZA >∼81°, the monotonic distribution with negative surface potential is observed in the plasma sheath. With the calculated potentials and the assumption that the dust radius distribution exponentially decreases, we further investigate spatial distributions of the dust levitated above the surface. It is found that number density of the levitating lunar dust is enhanced at the terminator (SZA ∼ 81°) in the plasma sheath. In the photoelectron sheath it gradually decreases as the SZA increases from 0° to 70°. Further calculations of the potential and the derived electrostatic field suggest that the dust spatial distributions can be influenced by the bulk velocity, number density, and temperature of the solar wind. Those findings deepen our understanding of lunar surface charging and the mechanism of lunar dust levitation, which can provide technical support for lunar explorations.

Supernova Ejecta with Crystalline Silicate Dust in the Supernova Remnant MSH 15–52

IRAS 15099-5856 in the young supernova remnant (SNR) MSH 15−52 is the first and only SNR-associated object with crystalline silicate dust detected so far, although its nature and the origin of the crystalline silicate are still unclear. In this paper, we present high-resolution mid-infrared (MIR) imaging observations of the bright central compact source IRS1 of IRAS 15099-5856 to study the spatial distributions of gas and dust and the analysis of its Spitzer MIR spectrum to explore the origin of IRS1. The MIR images obtained with the T-ReCS attached on the Gemini South telescope show a complicated, inhomogeneous morphology of IRS1 with bright clumps and diffuse emission in [Ne ii] 12.81 μm and Qa 18.30 μm, which confirms that IRS1 is an extended source externally heated by the nearby O star Muzzio 10, a candidate for the binary companion of the progenitor star. The Spitzer MIR spectrum reveals several ionic emission lines including a strong [Ne ii] 12.81 μm line, but no hydrogen line is detected. We model the spectrum using the photoionization code Cloudy with varying elemental composition. The elemental abundance of IRS1 derived from the model is close to that of supernova (SN) ejecta with depleted hydrogen and enhanced metals, particularly neon, argon, and iron. Our results imply that IRS1 originates from the SN ejecta and suggest the possibility of the formation of crystalline silicate in newly formed SN dust.

Numerical simulation of plume–surface interaction and lunar dust dispersion during lunar landing using four engines

As the lander approaches the lunar surface, the engine plumes impinge on the lunar regolith and entrain lunar dust from the surface. This plume–surface interaction and the resulting dispersion of lunar dust form a multi-physics, multi-scale problem, which becomes even more complex under multi-engine conditions. This study employed the direct simulation Monte Carlo method to simulate the plume–surface interaction flow field of a four-engine lunar lander at various landing altitudes and lunar surface angles. Flow characteristics were analyzed, and the impact of the plume and backflow on the lander was assessed. Subsequently, lunar dust simulation was conducted using the plume field as a basis. The study determined the spatial distribution of particles with different diameters at various landing altitudes and surface angles, as well as their impact velocities on the lander. Furthermore, taking into account the variations in the lander's altitude and attitude, a dynamic simulation of lunar dust during the landing process was conducted. This process resulted in the dynamic distribution of lunar dust during landing, laying the groundwork for real-time simulation of lunar dust distribution and reliable visualization during landing simulations. These findings are valuable for assessing and mitigating the hazards posed by lunar dust.

Bayesian analysis of the molecular emission and dust continuum of protoplanetary disks

Context. The MIRI instrument on board the James Webb Space Telescope probes the chemistry and dust mineralogy of the inner regions of protoplanetary disks. The observed spectra are unprecedented in their detail and reveal a rich chemistry with strong diversity between objects. This complicates interpretations that are mainly based on manual continuum subtraction and 0D slab models. Aims. We investigate the physical conditions under which the gas emits in protoplanetary disks. Based on MIRI spectra, we apply a full Bayesian analysis that provides the posterior distributions of dust and molecular properties, such as column densities and emission temperatures. Methods. To do so, we introduced the Dust Continuum Kit with Line emission from Gas (DuCKLinG), a Python-based model simultaneously describing the molecular line emission and the dust continuum of protoplanetary disks without large computational cost. The model describes the dust continuum emission by dust models with precomputed dust opacities. The molecular emission is based on LTE slab models but from extended radial ranges with gradients in column densities and emission temperatures. We compare the model to observations using Bayesian analysis with linear regression techniques to reduce the dimension of the parameter space. We benchmarked this model to a complex thermo-chemical ProDiMo model of AATau and fit the MIRI spectrum of GW Lup. The latter allowed for a comparison to the previous results obtained with single slab models and hand-fitted continuum. Results. We successfully decrease the computational time of the fitting method by a factor of 80 by eliminating linear parameters, such as the emission areas, from the Bayesian run. This approach does not significantly change the retrieved molecular parameters, and only the calculated errors on the optically thin dust masses slightly decrease. For an AA Tau ProDiMo mock observation, we find that the retrieved molecular conditions from DuCKLinG (column densities from 3 × 1018 cm−2 to 4 × 1020 cm−2, radial range from 0.2 au to 1.2 au, and temperature range from about 200 K to 400 K) fall within the true values from ProDiMo (column densities between 4 × 1017 cm-2 to 5 × 1020 cm−2, radial extent 0.1 au to 6.6 au, and temperature range from about 120 to 1000 K). The smaller DuCKLinG ranges can be explained by the relative flux contributions of the different parts of ProDiMo. The parameter posterior of GW Lup reinforces previously found results. The previously determined column densities fall within the retrieved ranges in this study for all examined molecules (CO2, H2O, HCN, and C2H2). Similar overlap is found for the temperatures with only the temperature range of HCN (from 570−60+60 to 750−70+90 K) not including the previously found value (875 K). This discrepancy may be due to the simultaneous fitting of all molecules compared to the step-by-step fitting of the previous study. There is statistically significant evidence for radial temperature and column density gradients for H2O and CO2 compared to the constant temperature and column density assumed in the 0D slab models. Additionally, HCN and C2H2 emit from a small region with near constant conditions. Due to the small selected wavelength range 13.6–16.3 µm, the dust properties are not well constrained for GW Lup. DuCKL inG can become an important tool to analyse the molecular emission and dust mineralogy of large samples based on JWST /MIRI spectra in an automated way.

Volume density maps of the 862 nm DIB carrier and interstellar dust. Hints on the role of carbon-rich ejecta from AGB stars

The carbonaceous macromolecules imprinting the numerous absorptions called diffuse interstellar bands (DIBs) in astronomical spectra are omnipresent in the Galaxy and beyond. They represent a considerable reservoir of organic matter. However, their chemical formulae, formation, and destruction sites remain unknown. Their spatial distribution and the local relation to other interstellar species is key to tracing their role in the lifecycle of organic matter. Volume density maps bring local instead of line-of-sight distributed information and allow for new diagnostics to be captured. We present the first large-scale volume (3D) density map of a DIB carrier and compare it with an equivalent map of interstellar dust. The DIB carrier map was obtained through hierarchical inversion of sim 202,000 measurements of the 8621 nm DIB obtained with the Gaia -RVS instrument. It covers about 4000 pc around the Sun in the Galactic plane. We built a dedicated interstellar dust map based on the extinction towards the same target stars. At the simeq 50 pc resolution of the maps, the shape of the 3D DIB distribution is found to be remarkably similar to the 3D distribution of dust. On the other hand, the DIB-to-dust local density ratio increases in low-dust areas. It is also increasing away from the disk, however, the minimum ratio is found to be shifted above the Galactic plane to Z=simeq +50pc. Finally, the average ratio is also surprisingly found to increase away from the Galactic Center. We suggest that the three latter trends may be indications of a dominant contribution of material from the carbon-rich category of dying giant stars to the formation of the carriers. Our suggestion is based on recent catalogs of asymptotic giant branch (AGB) stars and estimates of the mass fluxes of their C-rich and O-rich ejecta.

The COSMOS-Web ring: In-depth characterization of an Einstein ring lensing system at z ∼ 2

Aims. We provide an in-depth analysis of the COSMOS-Web ring, an Einstein ring at z ≈ 2 that we serendipitously discovered during the data reduction of the COSMOS-Web survey and that could be the most distant lens discovered to date. Methods. We extracted the visible and near-infrared photometry of the source and the lens from more than 25 bands. We combined these observations with far-infrared detections to study the dusty nature of the source and we derived the photometric redshifts and physical properties of both the lens and the source with three different spectral energy distribution (SED) fitting codes. Using JWST/NIRCam images, we also produced two lens models to (i) recover the total mass of the lens, (ii) derive the magnification of the system, (iii) reconstruct the morphology of the lensed source, and (iv) measure the slope of the total mass density profile of the lens. Results. We find the lens to be a very massive elliptical galaxy at z = 2.02 ± 0.02 with a total mass within the Einstein radius of Mtot(&lt;θEin = (3.66 ± 0.36) × 1011 M⊙ and a total stellar mass of M⋆ = 1.37−0.11+0.14 × 1011 M⊙. We also estimate it to be compact and quiescent with a specific star formation rate below 10−13 yr. Compared to stellar-to-halo mass relations from the literature, we find that the total mass of the lens within the Einstein radius is consistent with the presence of a dark matter (DM) halo of total mass Mh = 1.09−0.57+1.46 × 1013 M⊙. In addition, the background source is a M⋆ = (1.26 ± 0.17) × 1010 M⊙ star-forming galaxy (SFR ≈ (78 ± 15) M⊙ yr) at z = 5.48 ± 0.06. The morphology reconstructed in the source plane shows two clear components with different colors. Dust attenuation values from SED fitting and nearby detections in the far infrared also suggest that the background source could be at least partially dust-obscured. Conclusions. We find the lens at z ≈ 2. Its total, stellar, and DM halo masses are consistent within the Einstein ring, so we do not need any unexpected changes in our description of the lens such as changing its initial mass function or including a non-negligible gas contribution. The most likely solution for the lensed source is at z ≈ 5.5. Its reconstructed morphology is complex and highly wavelength dependent, possibly because it is a merger or a main sequence galaxy with a heterogeneous dust distribution.

Vertical shear instability with dust evolution and consistent cooling times

Context. Gas in protoplanetary disks mostly cools via thermal accommodation with dust particles. Thermal relaxation is thus highly sensitive to the local dust size distributions and the spatial distribution of the grains. So far, the interplay between thermal relaxation and gas turbulence has not been dynamically modeled in hydrodynamic simulations of protoplanetary disks with dust. Aims. We aim to study the effects of the vertical shear instability (VSI) on the thermal relaxation times, and vice versa. We are particularly interested in the influence of the initial dust grain size on the VSI and whether the emerging turbulence is sustained over long timescales. Methods. We ran three axisymmetric hydrodynamic simulations of a protoplanetary disk including four dust fluids that initially resemble MRN size distributions of different initial grain sizes. From the local dust densities, we calculated the thermal accommodation timescale of dust and gas and used the result as the thermal relaxation time of the gas in our simulation. We included the effect of dust growth by applying the monodisperse dust growth rate and the typical growth limits. Results. We find that the emergence of the VSI is strongly dependent on the initial dust grain size. Coagulation also counteracts the emergence of hydrodynamic turbulence in our simulations, as shown by others before. Starting a simulation with larger grains (100 μm) generally leads to a less turbulent outcome. While the inner disk regions (within ∼70 au) develop turbulence in all three simulations, we find that the simulations with larger particles do not develop VSI in the outer disk. Conclusions. Our simulations with dynamically calculated thermal accommodation times based on the drifting and settling dust distribution show that the VSI, once developed in a disk, can be sustained over long timescales, even if grain growth is occurring. The VSI corrugates the dust layer and even diffuses the smaller grains into the upper atmosphere, where they can cool the gas. Whether the instability can emerge for a specific stratification depends on the initial dust grain sizes and the initial dust scale height. If the grains are initially ≳100 μm and if the level of turbulence is initially assumed to be low, we find no VSI turbulence in the outer disk regions.

High-resolution sampling in the eastern tropical North Atlantic reveals episodic Saharan dust deposition: implications for the marine carbon sink

In this study we present data collected between August 2017 and December 2018 from submarine sediment trap M1 located in the eastern tropical North Atlantic and determine lithogenic and biogenic fluxes, and grain-size distributions of aerosol dust. An unprecedented high sampling resolution of four days in combination with satellite imagery allowed the identification of thirteen major dust events of two types within the 468-day series. Seven dust events were classified as high-flux events identified by a deposition of &amp;gt;=25 mg m-2 d-1. The average dust deposition rate increased by 461.3% during these types of events. The remaining six events were characterized by a high composition of giant particles (&amp;gt;7.3 vol%). Seasonal variations of dust flux were recorded, with highest fluxes observed in spring at an average deposition rate of 14.8 mg m-2 d-1, and lowest fluxes in fall with an average rate of 8.6 mg m-2 d-1. The estimated total dust flux in the tropical North Atlantic was 4040.02 mg m-2 y-1. We suggest that most of the summer dust was likely transported over the sampling site at high altitudes while winter transport occurred closer to the sea surface, resulting in generally higher background fluxes. Grain-size distributions exhibited seasonal variations with increased occurrences of giant particles (&amp;gt;62.5 μm) in fall 2017 and spring, and less occurrences in winter and fall 2018. Grain-size sorting was high in spring and most variable in summer. Precipitation did not affect depositional fluxes or grain-size distributions of the aeolian dust significantly. Organic matter was deposited continuously at the sampling site with a deposition rate ranging from 14.4–862.25 mg m-2 d-1. Organic matter fluxes increased by 199.5% during high-flux dust events but decreased by 13.6% during anomalous grain-size events. Spring experienced the highest number of dust events (n=5). This unprecedented high-resolution dataset of dust deposition in marine sediment-traps enabled the distinction of dust events and their relation to organic matter flux. This suggests the possibility of a dust fertilization or mineral ballasting effect.