Browsing by Subject "dust"

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  • Zhou, Putian; Keskinen, Jukka-Pekka; Makkonen, Risto Juhani (2018)
  • Haikala, L. K.; Salinas, R.; Richtler, T.; Gomez, M.; Gahm, G. F.; Mattila, K. (2021)
    Context. An intriguing silhouette of a small dust patch can be seen against the disk of the S0 galaxy NGC 3269 in the Antlia cluster in optical images. The images do not provide any clue as to whether the patch is a local Jupiter mass-scale cloudlet or a large extragalactic dust complex.Aims. We aim to resolve the nature of this object: is it a small Galactic cloudlet or an extragalactic dust complex?Methods. ALMA and APEX spectroscopy and Gemini GMOS long-slit spectroscopy were used to measure the velocity of the patch and the NGC 3269 disk radial velocity curve.Results. A weak 16 2.5 km s(-1) wide (CO)-C-12(2-1) T-MB 19 +/- 2.5. mK line in a 2 .('') . '' 2 by 2 .('') .'' 12 beam associated with the object was detected with ALMA. The observed heliocentric velocity, V-r,V- hel=3878 +/- 5.0 km s(-1), immediately establishes the extragalactic nature of the object. The patch velocity is consistent with the velocity of the nucleus of NGC 3269, but not with the radial velocity of the NGC 3269 disk of the galaxy at its position. The similar to 4 '' angular size of the patch corresponds to a linear size of similar to 1 kpc at the galaxy's Hubble distance of 50.7 Mpc. The mass estimated from the (CO)-C-12(2-1) emission is similar to 1.4x10(6)(d/50.7 Mpc)M-2(circle dot), while the attenuation derived from the optical spectrum implies a dust mass of similar to 2.6x10(4)(d/50.7 Mpc)M-2(circle dot). The derived attenuation ratio A ' (B)/(A ' (B)-A ' (R)) of 1.6 +/- 0.11 is substantially lower than the corresponding value for the mean Milky Way extinction curve for point sources (2.3).Conclusions. We established the extragalactic nature of the patch, but its origin remains elusive. One possibility is that the dust patch is left over from the removal of interstellar matter in NGC 3269 through the interaction with its neighbour, NGC 3268.
  • Lucke, Bernhard; Sandler, Amir; Vanselow, Kim André; Bruins, Hendrik J.; Abu-Jaber, Nizar; Baeumler, Rupert; Porat, Naomi; Kouki, Paula (2019)
    Archaeological structures are often filled with sediments and may serve as effective dust traps. The physical parameters and chemical composition of archaeological soils in hilltop ruins, ancient runoff-collecting terraces, and cleanout spoils of cisterns were determined in the Petra region in southern Jordan and the Northern Negev in Israel. Different types of ruins are characterized by certain soil structures, but could not be distinguished with regard to substrate composition. This reflects a predominance of aeolian processes for primary sedimentation, while fluvial processes seem to only re-distribute aeolian material. In the Petra region, the physical and chemical properties of all archaeological soils show a significant local contribution from associated weathered rocks. Compared to modern settled dust, archaeological soils in Southern Jordan are enriched with various major and trace elements associated with clays and oxide coatings of fine silt particles. This seems connected with preferential fixation of silt and clay by surface crusts, and a role of moisture in sedimentation processes as calcareous silt was found to be deposited in greater amounts when associated with precipitation. In contrast, the contribution of rocks is negligible in the Negev due to greater rock hardness and abundant biological crusts that seal surfaces. Archaeological soils in the Negev are chemically similar to current settled dust, which consists of complex mixtures of local and remote sources, including significant portions of recycled material from paleosols. Archaeological soils are archives of Holocene dust sources and aeolian sedimentation processes, with accretion rates exceeding those of Pleistocene hilltop loess in the Negev. Comparison with Pleistocene paleosols suggests that dust sources did not change significantly, but disappearance of snow could have reduced dust accumulation during the Holocene.
  • Popp, Thomas; De Leeuw, Gerrit; Bingen, Christine; Bruehl, Christoph; Capelle, Virginie; Chedin, Alain; Clarisse, Lieven; Dubovik, Oleg; Grainger, Roy; Griesfeller, Jan; Heckel, Andreas; Kinne, Stefan; Klueser, Lars; Kosmale, Miriam; Kolmonen, Pekka; Lelli, Luca; Litvinov, Pavel; Mei, Linlu; North, Peter; Pinnock, Simon; Povey, Adam; Robert, Charles; Schulz, Michael; Sogacheva, Larisa; Stebel, Kerstin; Zweers, Deborah Stein; Thomas, Gareth; Tilstra, Lieuwe Gijsbert; Vandenbussche, Sophie; Veefkind, Pepijn; Vountas, Marco; Xue, Yong (2016)
    Producing a global and comprehensive description of atmospheric aerosols requires integration of ground-based, airborne, satellite and model datasets. Due to its complexity, aerosol monitoring requires the use of several data records with complementary information content. This paper describes the lessons learned while developing and qualifying algorithms to generate aerosol Climate Data Records (CDR) within the European Space Agency (ESA) Aerosol_cci project. An iterative algorithm development and evaluation cycle involving core users is applied. It begins with the application-specific refinement of user requirements, leading to algorithm development, dataset processing and independent validation followed by user evaluation. This cycle is demonstrated for a CDR of total Aerosol Optical Depth (AOD) from two subsequent dual-view radiometers. Specific aspects of its applicability to other aerosol algorithms are illustrated with four complementary aerosol datasets. An important element in the development of aerosol CDRs is the inclusion of several algorithms evaluating the same data to benefit from various solutions to the ill-determined retrieval problem. The iterative approach has produced a 17-year AOD CDR, a 10-year stratospheric extinction profile CDR and a 35-year Absorbing Aerosol Index record. Further evolution cycles have been initiated for complementary datasets to provide insight into aerosol properties (i.e., dust aerosol, aerosol absorption).
  • Juvela, Mika; Neha, Sharma; Mannfors, Emma; Saajasto, Mika; Ysard, Nathalie; Pelkonen, Veli-Matti (2020)
    Context. LDN 1642 is a rare example of a star-forming, high-latitude molecular cloud. The dust emission of LDN 1642 has already been studied extensively in the past, but its location also makes it a good target for studies of light scattering.Aims. We wish to study the near-infrared (NIR) light scattering in LDN 1642, its correlation with the cloud structure, and the ability of dust models to simultaneously explain observations of sub-millimetre dust emission, NIR extinction, and NIR scattering.Methods. We used observations made with the HAWK-I instrument to measure the NIR surface brightness and extinction in LDN 1642. These data were compared with Herschel observations of dust emission and, with the help of radiative transfer modelling, with the predictions calculated for different dust models.Results. We find, for LDN 1642, an optical depth ratio tau (250 mu m)/tau (J) approximate to 10(-3), confirming earlier findings of enhanced sub-millimetre emissivity. The relationships between the column density derived from dust emission and the NIR colour excesses are linear and consistent with the shape of the standard NIR extinction curve. The extinction peaks at A(J) = 2.6 mag, and the NIR surface brightness remains correlated with N(H-2) without saturation. Radiative transfer models are able to fit the sub-millimetre data with any of the tested dust models. However, these predict an NIR extinction that is higher and an NIR surface brightness that is lower than based on NIR observations. If the dust sub-millimetre emissivity is rescaled to the observed value of tau (250 mu m)/tau (J), dust models with high NIR albedo can reach the observed level of NIR surface brightness. The NIR extinction of the models tends to be higher than in the direct extinction measurements, which is also reflected in the shape of the NIR surface brightness spectra.Conclusions. The combination of emission, extinction, and scattering measurements provides strong constraints on dust models. The observations of LDN 1642 indicate clear dust evolution, including a strong increase in the sub-millimetre emissivity, which has not been fully explained by the current dust models yet.
  • Schirmer, T.; Abergel, A.; Verstraete, L.; Ysard, N.; Juvela, M.; Jones, A. P.; Habart, E. (2020)
    Context. Micro-physical processes on interstellar dust surfaces are tightly connected to dust properties (i.e. dust composition, size, and shape) and play a key role in numerous phenomena in the interstellar medium (ISM). The large disparity in physical conditions (i.e. density and gas temperature) in the ISM triggers an evolution of dust properties. The analysis of how dust evolves with the physical conditions is a stepping stone towards a more thorough understanding of interstellar dust.Aims. We highlight dust evolution in the Horsehead nebula photon-dominated region.Methods. We used Spitzer/IRAC (3.6, 4.5, 5.8 and 8 mu m) and Spitzer/MIPS (24 mu m) together with Herschel/PACS (70 and 160 mu m) and Herschel/SPIRE (250, 350 and 500 mu m) to map the spatial distribution of dust in the Horsehead nebula over the entire emission spectral range. We modelled dust emission and scattering using the THEMIS interstellar dust model together with the 3D radiative transfer code SOC.Results. We find that the nano-grain dust-to-gas ratio in the irradiated outer part of the Horsehead is 6-10 times lower than in the diffuse ISM. The minimum size of these grains is 2-2.25 times larger than in the diffuse ISM, and the power-law exponent of their size distribution is 1.1-1.4 times lower than in the diffuse ISM. In the denser part of the Horsehead nebula, it is necessary to use evolved grains (i.e. aggregates, with or without an ice mantle).Conclusions. It is not possible to explain the observations using grains from the diffuse medium. We therefore propose the following scenario to explain our results. In the outer part of the Horsehead nebula, all the nano-grain have not yet had time to re-form completely through photo-fragmentation of aggregates and the smallest of the nano-grain that are sensitive to the radiation field are photo-destroyed. In the inner part of the Horsehead nebula, grains most likely consist of multi-compositional mantled aggregates.
  • Micelotta, Elisabetta R.; Juvela, Mika; Padoan, Paolo; Ristorcelli, Isabelle; Alina, Dana; Malinen, Johanna (2021)
    Context. The all-sky survey from the Planck space telescope has revealed that thermal emission from Galactic dust is polarized on scales ranging from the whole sky down to the inner regions of molecular clouds. Polarized dust emission can therefore be used as a probe for magnetic fields on different scales. In particular, the analysis of the relative orientation between the density structures and the magnetic field projected on the plane of the sky can provide information on the role of magnetic fields in shaping the structure of molecular clouds where star formation takes place.Aims. The orientation of the magnetic field with respect to the density structures has been investigated using different methods. The goal of this paper is to explicitly compare two of these: the Rolling Hough Transform (RHT) and the gradient technique (GRAD).Methods. We generated synthetic surface brightness maps at 353 GHz (850 mu m) via magnetohydrodynamic simulations. We applied RHT and GRAD to two morphologically different regions identified in our maps. Region 1 is dominated by a dense and thick filamentary structure with some branches, while Region 2 includes a thinner filament with denser knots immersed in a more tenuous medium. Both methods derive the relative orientation between the magnetic field and the density structures, to which we applied two statistics, the histogram of relative orientation and the projected Rayleigh statistic, to quantify the variations of the relative orientation as a function of column density.Results. Both methods find areas with significant signal, and these areas are substantially different. In terms of relative orientations, in all our considered cases the predominant orientation of the density structures is perpendicular to the direction of the magnetic field. When the methods are applied to the same selected areas the results are consistent with each other in Region 2 but show some noticeable differences in Region 1. In Region 1, RHT globally finds the relative orientation becoming more perpendicular for increasing column density, while GRAD, applied at the same resolution as RHT, gives the opposite trend. These disparities are caused by the intrinsic differences in the methods and in the structures that they select.Conclusions. Our results indicate that the interpretation of the relative orientation between the magnetic field and density structures should take into account the specificity of the methods used to determine such orientation. The combined use of complementary techniques such as RHT and GRAD provides more complete information, which can be advantageously used to better understand the physical mechanisms operating in magnetized molecular clouds.
  • Mönki, Jenni; Saastamoinen, Markku; Karikoski, Ninja; Rajamäki, Minna; Raekallio, Marja; Junnila, Jouni; Särkijärvi, Susanna; Norring, Marianna; Valros, Anna; Oranen Ben Fatma, Silja; Mykkänen, Anna (2021)
    Bedding materials affect stable air hygiene, and thus the development and exacerbation of equine asthma. There is limited knowledge concerning the effects of different types of bedding material on equine lower airway inflammation. The objective of our study was to investigate the effects of bedding materials on respiratory signs, tracheal mucus score, and lower airway cytology in healthy adult horses. The study design was a prospective controlled study, and the subjects were healthy adult riding school horses (n = 32) from a single stable. Wood shavings were compared to peat, which was used as a reference bedding material. Lower airway endoscopy and sampling (tracheal wash and bronchoalveolar lavage fluid) for cytological examination were performed after each 35-day bedding period. No difference between bedding periods was observed in the respiratory rate or tracheal mucus score. Tracheal wash neutrophil percentage with the wood shavings was higher compared to the previous (P = 0.040) or following (P = 0.0045) peat period. Bronchoalveolar lavage fluid neutrophil percentage with the wood shavings was higher compared to the following peat period (P <0.001). We conclude that, between the two bedding materials used in this study, peat caused less neutrophilic lower airway inflammation in horses. The information gained from this study may assist veterinarians and horse owners in selecting bedding materials, especially for horses suffering from equine asthma.
  • Meinander, Outi (Finnish Meteorological Institute, 2016)
    Finnish Meteorological Institute Contributions 125
    Light-absorbing impurities in the cryosphere are of hydrological, environmental and climatic importance. The wet and dry deposition of black carbon (BC), organic carbon (OC), and dust particles affect the optical properties and melt of snow and ice. In the Arctic region, the climatic effects are amplified, and surface albedo feedback is often cited as the main contributor. The aim of this thesis is to fill in some of the gaps in our knowledge of the effects of BC, OC, and Icelandic dust on snow in the European Arctic through a series of field and laboratory experiments and an analysis of the resulting data, including modeling. The thesis presents a new hypothesis on the snow density effects of light-absorbing impurities, an important quantity for climate modeling and remote sensing. Three processes are suggested to explain the proposed ”BC density effect”. Experimental results show that dirty snow releases melt water quicker than cleaner snow. The albedo of natural seasonally melting snow in Sodankylä, north of the Arctic Circle, is found to be asymmetric with respect to solar midday, thus indicating a change in the properties of the snow. The radiative transfer modeling results show that the observed solar zenith angle asymmetry results in a 2–4 % daily error for satellite snow albedo estimates. Surface albedo model results indicate that the biggest snow albedo changes due to BC are expected in the ultraviolet (UV) part of the electromagnetic spectrum. The albedo of natural seasonal snow measured in Sodankylä, is found to be lower than expected. Solar UV and visible (VIS) albedo values of 0.6–0.8 in the accumulation period and 0.5–0.7 during melting are observed. The low albedo values are explained to be due to large snow grain sizes up to ∼3 mm in diameter, meltwater surrounding the grains and increasing the effective grain size, and absorption caused by impurities in the natural snow (87 ppb BC and 2894 ppb OC). The BC contents of the surface snow layer at the Sodankylä Arctic Research Center, Finland, is higher than expected. Increased BC in spring time suggests surface accumulation of hydrophobic BC during snow melt. Some of the high BC concentrations are related to anthropogenic soot transported from the Kola Peninsula, Russia. The origin of OC can be anthropogenic or natural, and may include pollen, seeds, lichens, natural litter or microorganisms that reside in snow and ice. Iceland is the most important Arctic dust source, but a scientific assessment of its impacts on the cryosphere is currently unavailable and scientific results are urgently needed to investigate the role of Icelandic dust in Iceland and elsewhere, in the past, present and future. Experimental results on Icelandic volcanic ash show that a thin layer increases the snow and ice melt but that an ash layer exceeding a certain critical thickness causes insulation. The Arctic results of this thesis have relevance to the assessment of Arctic climate change, including modeling and satellite applications.
  • Mattila, Kalevi; Haas, Martin; Haikala, Lauri; Jo, Y.-S.; Lehtinen, Kimmo; Leinert, Christoph; Väisänen, Petri (EDP Sciences, 2018)
    Astronomy & Astrophysics
    Context. Dark nebulae display a surface brightness because dust grains scatter light of the general interstellar radiation field (ISRF). High-galactic-latitudes dark nebulae are seen as bright nebulae when surrounded by transparent areas which have less scattered light from the general galactic dust layer. Aims. Photometry of the bright dark nebulae LDN 1780, LDN 1642, and LBN 406 shall be used to derive scattering properties of dust and to investigate the presence of UV fluorescence emission by molecular hydrogen and the extended red emission (ERE). Methods. We used multi-wavelength optical photometry and imaging at ground-based telescopes and archival imaging and spectroscopic UV data from the spaceborn GALEX and SPEAR/FIMS instruments. In the analysis we used Monte Carlo RT and both observational data and synthetic models for the ISRF in the solar neighbourhood. The line-of-sight extinctions through the clouds have been determined using near infrared excesses of background stars and the 200/250 μm far infrared emission by dust as measured using the ISO and Herschel space observatories. Results. The optical surface brightness of the three target clouds can be explained in terms of scattered light. The dust albedo ranges from ~0.58 at 3500 Å to ~0.72 at 7500 Å. The spectral energy distribution of LDN 1780 is explained in terms of optical depth and background scattered light effects instead of the original published suggestion in terms of ERE. The far-ultraviolet surface brightness of LDN 1780 cannot be explained by scattered light only. In LDN 1780, H2 fluorescent emission in the wavelength range 1400–1700 Å has been detected and analysed. Conclusions. Our albedo values are in good agreement with the predictions of the dust model of Weingartner and Draine and with the THEMIS CMM model for evolved core-mantle grains. The distribution of H2 fluorescent emission in LDN 1780 shows a pronounced dichotomy with a strong preference for its southern side where enhanced illumination is impinging from the Sco OB2 association and the O star ζ Oph. A good correlation is found between the H2 fluorescence and a previously mapped 21-cm excess emission. The H2 fluorescence emission in LDN 1780 has been modelled using a PDR code; the resulting values for H2 column density and the total gas density are consistent with the estimates derived from CO observations and optical extinction along the line of sight.
  • Planck Collaboration; Akrami, Y.; Keihanen, E.; Kiiveri, K.; Kurki-Suonio, H.; Lindholm, V.; Savelainen, M.; Valiviita, J. (2020)
    The study of polarized dust emission has become entwined with the analysis of the cosmic microwave background (CMB) polarization in the quest for the curl-like B-mode polarization from primordial gravitational waves and the low-multipole E-mode polarization associated with the reionization of the Universe. We used the new Planck PR3 maps to characterize Galactic dust emission at high latitudes as a foreground to the CMB polarization and use end-to-end simulations to compute uncertainties and assess the statistical significance of our measurements. We present PlanckEE, BB, and TE power spectra of dust polarization at 353 GHz for a set of six nested high-Galactic-latitude sky regions covering from 24 to 71% of the sky. We present power-law fits to the angular power spectra, yielding evidence for statistically significant variations of the exponents over sky regions and a difference between the values for the EE and BB spectra, which for the largest sky region are alpha (EE)=-2.42 +/- 0.02 and alpha (BB)=-2.54 +/- 0.02, respectively. The spectra show that the TE correlation and E/B power asymmetry discovered by Planck extend to low multipoles that were not included in earlier Planck polarization papers due to residual data systematics. We also report evidence for a positive TB dust signal. Combining data from Planck and WMAP, we have determined the amplitudes and spectral energy distributions (SEDs) of polarized foregrounds, including the correlation between dust and synchrotron polarized emission, for the six sky regions as a function of multipole. This quantifies the challenge of the component-separation procedure that is required for measuring the low-l reionization CMB E-mode signal and detecting the reionization and recombination peaks of primordial CMB B modes. The SED of polarized dust emission is fit well by a single-temperature modified black-body emission law from 353 GHz to below 70 GHz. For a dust temperature of 19.6 K, the mean dust spectral index for dust polarization is beta (P)(d) = 1.53 +/- 0.02 beta d P = 1.53 +/- 0.02 . The difference between indices for polarization and total intensity is beta (P)(d)-beta (I)(d) = 0.05 +/- 0.03 beta d P - beta d I =0.05 +/- 0.03 . By fitting multi-frequency cross-spectra between Planck data at 100, 143, 217, and 353 GHz, we examine the correlation of the dust polarization maps across frequency. We find no evidence for a loss of correlation and provide lower limits to the correlation ratio that are tighter than values we derive from the correlation of the 217- and 353 GHz maps alone. If the Planck limit on decorrelation for the largest sky region applies to the smaller sky regions observed by sub-orbital experiments, then frequency decorrelation of dust polarization might not be a problem for CMB experiments aiming at a primordial B-mode detection limit on the tensor-to-scalar ratio r similar or equal to 0.01 at the recombination peak. However, the Planck sensitivity precludes identifying how difficult the component-separation problem will be for more ambitious experiments targeting lower limits on r.
  • Planck Collaboration; Aghanim, N.; Keihanen, E.; Kiiveri, K.; Kurki-Suonio, H.; Lindholm, V.; Savelainen, M.; Suur-Uski, A. -S.; Valiviita, J. (2020)
    Observations of the submillimetre emission from Galactic dust, in both total intensity I and polarization, have received tremendous interest thanks to the Planck full-sky maps. In this paper we make use of such full-sky maps of dust polarized emission produced from the third public release of Planck data. As the basis for expanding on astrophysical studies of the polarized thermal emission from Galactic dust, we present full-sky maps of the dust polarization fraction p, polarization angle psi, and dispersion function of polarization angles ?. The joint distribution (one-point statistics) of p and N-H confirms that the mean and maximum polarization fractions decrease with increasing N-H. The uncertainty on the maximum observed polarization fraction, (max) = 22.0(-1.4)(+3.5) p max = 22 . 0 - 1.4 + 3.5 % at 353 GHz and 80 ' resolution, is dominated by the uncertainty on the Galactic emission zero level in total intensity, in particular towards diffuse lines of sight at high Galactic latitudes. Furthermore, the inverse behaviour between p and ? found earlier is seen to be present at high latitudes. This follows the ?proportional to p(-1) relationship expected from models of the polarized sky (including numerical simulations of magnetohydrodynamical turbulence) that include effects from only the topology of the turbulent magnetic field, but otherwise have uniform alignment and dust properties. Thus, the statistical properties of p, psi, and ? for the most part reflect the structure of the Galactic magnetic field. Nevertheless, we search for potential signatures of varying grain alignment and dust properties. First, we analyse the product map ?xp, looking for residual trends. While the polarization fraction p decreases by a factor of 3-4 between N-H=10(20) cm(-2) and N-H=2x10(22) cm(-2), out of the Galactic plane, this product ?xp only decreases by about 25%. Because ? is independent of the grain alignment efficiency, this demonstrates that the systematic decrease in p with N-H is determined mostly by the magnetic-field structure and not by a drop in grain alignment. This systematic trend is observed both in the diffuse interstellar medium (ISM) and in molecular clouds of the Gould Belt. Second, we look for a dependence of polarization properties on the dust temperature, as we would expect from the radiative alignment torque (RAT) theory. We find no systematic trend of ?xp with the dust temperature T-d, whether in the diffuse ISM or in the molecular clouds of the Gould Belt. In the diffuse ISM, lines of sight with high polarization fraction p and low polarization angle dispersion ? tend, on the contrary, to have colder dust than lines of sight with low p and high ?. We also compare the Planck thermal dust polarization with starlight polarization data in the visible at high Galactic latitudes. The agreement in polarization angles is remarkable, and is consistent with what we expect from the noise and the observed dispersion of polarization angles in the visible on the scale of the Planck beam. The two polarization emission-to-extinction ratios, R-P/p and R-S/V, which primarily characterize dust optical properties, have only a weak dependence on the column density, and converge towards the values previously determined for translucent lines of sight. We also determine an upper limit for the polarization fraction in extinction, p(V)/E(B-V), of 13% at high Galactic latitude, compatible with the polarization fraction p approximate to 20% observed at 353 GHz. Taken together, these results provide strong constraints for models of Galactic dust in diffuse gas.