Dust Patches Research Articles

Experimental and analytical methods for thermal infrared spectroscopy of complex dust coatings in a simulated asteroid environment

Abstract Airless bodies in the Solar system are commonly dominated by complex regolith mixtures consisting of coarse and fine particulates. These materials often manifest as coatings with the potential to modify or obscure the spectral signatures of underlying substrates. This can make accurate spectral analysis of surface materials challenging, especially for thermal infrared (TIR) techniques of which the spectral properties concurrently depend on grain size and albedo. Further complexity is presented when these coatings occur as discontinuous patterns in which some substrate is exposed and some is masked. Discontinuous patterns are distinguished by scale as having macroscopic or microscopic discontinuity, with the former being patches of homogeneous dust covering portions of the substrate and the latter being randomly distributed individual particles on the substrate. Investigations of asteroid (101955) Bennu’s surface by NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer have revealed contradictions between spectral and thermophysical results that are hypothesized to indicate the presence of thin and/or laterally discontinuous dust coatings. To address this, we constructed an environment chamber that enables the controlled deposition of size-regulated dust particles in coatings with varying continuity and thickness. TIR spectra of coated substrates acquired in a simulated asteroid environment are used to investigate the extent to which dust coatings of different thicknesses and arrangements contribute to orbital spectral signatures of airless body surfaces.

Preliminary findings in the rolling behavior of Mules (Equus caballus x Equus asinus)

In order to investigate and create an ethogram of the rolling behavior of mules (Equus caballus × Equus asinus) in comparison to that of horses (Equus caballus), we observed a domestic free-range, mixed group of 17 horses and 11 mules for two consecutive days (12 h/day), filming all the rolling events. From these footages, we were able to register the occurrence of specific behaviors that characterize the rolling: sniffing the ground prior to lie down; tail swishing; resting in recumbence; scratching and shaking. Moreover, we also observed two social dimensions that are possibly involved with the rolling behavior: 1) Social facilitation - once an animal started to roll, others in the group copied its behavior and 2) Demarcation - animals tended to return to roll in the same dust patches. In this equine group, mules rolled more frequently than horses and also exhibited more of the specific behaviors tail swishing, resting and scratching. Moreover, in the rolling events exhibited by the mules, the social facilitation and demarcation occurred more than in the horses. As a preliminary study, we pointed some important differences between the rolling behavior of horses and mules. Considering the lack of knowledge in this regards such findings could be useful to spread ideas for future studies concerning the mules behavior and to improve the welfare conditions of these animals.

Slices reconstructing algorithm for single image dedusting

For solving the image degradation in the non-uniform dusting environment with multiple scattering lights, the slices reconstructing algorithm for single image was proposed for dust elimination in the paper. Firstly, the slices along the depth orientation were produced based on McCartney model in dust environment. Secondly, the union algorithm of dust detection was used to detect dust patches in the slices where non-dust areas were reserved while the dust zones were marked as the candidate detecting areas of the next slice image. Then, the image was reconstructed by combining these non-dust areas of each slice and the dust zone of the last slice. Finally, the faster guided filter was applied to the reconstructed area. The experimental results had proved that the reconstruction algorithm could get rid of dust in object image not only effectively but also fast. The paper's work had laid the foundation for object detection and recognition work had based on computer vision in dust's environment.

Ram pressure stripping in the Virgo Cluster

Gas can be violently stripped from their galaxy disks in rich clusters, and be dispersed over 100kpc-scale tails or plumes. Young stars have been observed in these tails, suggesting they are formed in situ. This will contribute to the intracluster light, in addition to tidal stripping of old stars. We want to quantify the efficiency of intracluster star formation. We present CO(1--0) and CO(2--1) observations, made with the IRAM-30m telescope, towards the ram-pressure stripped tail northeast of NGC4388 in Virgo. HII regions found all along the tails, together with dust patches have been targeted. We detect molecular gas in 4 positions along the tail, with masses between 7x10$^5$ to 2x10$^6$ M$_\odot$. Given the large distance from the NGC 4388 galaxy, the molecular clouds must have formed in situ, from the HI gas plume. We compute the relation between surface densities of star formation and molecular gas in these regions, and find that the star formation has very low efficiency. The corresponding depletion time of the molecular gas can be up to 500 Gyr and more. Since this value exceeds a by far Hubble time, this gas will not be converted into stars, and will stay in a gaseous phase to join the intracluster medium.

Introduction to a Special Issue of Aeolian Research Airborne mineral dust contaminants: Impacts on human health and the environment.

Introduction to a Special Issue of Aeolian Research Airborne mineral dust contaminants: Impacts on human health and the environment.

Spectrophotometric Investigations of Blue Compact Dwarf Galaxies: Markarian 35

We present results from a detailed spectrophotometric analysis of the blue compact dwarf galaxy Mrk 35 (Haro 3), based on deep optical (BVRI) and near-IR (JHK) imaging, Hα narrowband observations, and long-slit spectroscopy. The optical emission of the galaxy is dominated by a central young starburst, with a barlike shape, while an underlying component of stars, with elliptical isophotes and red colors, extends more than 4 kpc from the galaxy center. High-resolution Hα and color maps allow us to identify the star-forming regions, to spatially discriminate them from the older stars, and to recognize several dust patches. We derive colors and Hα parameters for all the identified star-forming knots. Observables derived for each knot are corrected for the contribution of the underlying older stellar population, the contribution by emission lines, and from interstellar extinction, and compared with evolutionary synthesis models. We find that the contributions of these three factors are by no means negligible and that they significantly vary across the galaxy. Therefore, careful quantification and subtraction of emission lines, galaxy host contribution, and interstellar reddening at every galaxy position are essential to derive the properties of the young stars in blue compact dwarfs. We find that we can reproduce the colors of all the knots with an instantaneous burst of star formation and the Salpeter initial mass function with an upper mass limit of 100 M☉. In all cases the knots are just a few Myr old. The underlying population of stars has colors consistent with being several Gyr old.

Mid-Infrared Emission from Elliptical Galaxies: Sensitivity to Stellar Age

Mid-infrared observations (3.6-24 μm) of normal giant elliptical galaxies with the Spitzer Space Telescope are consistent with pure populations of very old stars with no evidence of younger stars. Most of the stars in giant elliptical galaxies are old, but the mean stellar age determined from Balmer absorption in optical spectra can appear much younger due to a small admixture of younger stars. The mean stellar age can also be determined from the spectral energy distribution in the mid-infrared, which decreases with time relative to the optical emission and shifts to shorter wavelengths. The observed flux ratios F8 μm/F3.6 μm and F24 μm/F3.6 μm for elliptical galaxies with the oldest Balmer line ages are lower than predicted by recent models of single stellar populations. For elliptical galaxies with the youngest Balmer line ages in our sample, 3-5 Gyr, the flux ratios F24 μm/F3.6 μm are identical to those of the oldest stars. When theoretical mid-IR spectra of old (12 Gyr) and young stellar populations are combined, errors in the F24 μm/F3.6 μm observations are formally inconsistent with a mass fraction of young stars that exceeds ~1%. This is less than the fraction of young stars expected in discussions of recent surveys of elliptical galaxies at higher redshifts. However, this inconsistency between Balmer line ages and those inferred from mid-IR observations must be regarded as provisional until more accurate observations and theoretical spectra become available. Finally, there is no evidence to date that central disks or patches of dust commonly visible in optical images of elliptical galaxies contribute sensibly to the mid-IR spectrum.

The 2dF QSO Redshift Survey -- X. Lensing of background QSOs by galaxy groups

We cross-correlate QSOs from the 2dF Survey with galaxy groups. The galaxy samples are limited to B < 20.5. We use an objective algorithm to detect galaxy groups. A 3sigma anti-correlation is observed between QSOs and galaxy groups. This paucity of faint QSOs around groups is neither a selection effect nor due to restrictions on the placement of 2dF fibres. By observing the colours of QSOs on the scales of the anti-correlation, we limit dust in galaxy groups, finding a maximum reddening of E(b_j-r) < 0.012 at the 95% level. The small amount of dust thus inferred is insufficient to cause the anti-correlation, supporting the suggestion by Croom & Shanks that the signal is due to gravitational lensing. The possibility remains that tailored dust models, such as grey dust, heavy patches of dust or a combination of dust and lensing, could explain the anti-correlation. Assuming the signal is caused by lensing rather than dust, we measure the average velocity dispersion of a Singular Isothermal Sphere that would cause the anti-correlation as around 1150 km/s. Simulations reject 600 km/s at the 5% significance level. We also model foreground lenses as NFW haloes and measure the typical mass within 1.5 Mpc/h of the halo centre as M_{1.5} = (1.2 +/- 0.9) x 10^{15} solarmasses/h. Regardless of whether we utilise a SIS or NFW dark matter profile, our model favours more mass in groups than accounted for in a universe with density parameter Omega_m = 0.3. Detailed simulations and galaxy group redshifts will significantly reduce the current systematic uncertainties in these $\Omega_m$ estimates. Reducing the remaining uncertainty will require larger QSO and galaxy group surveys (abridged).

Star Formation Associated with the X‐Ray Jet in Centaurus A

Blue stars are identified in the region of the inner gaseous filaments in the radio lobe northeast of the main body of the radio galaxy Centaurus A (NGC 5128). Comparison between the X-ray images recently acquired with the Chandra Observatory and optical images shows that the X-ray jet passes just north of the diffuse region DF 6 identified by Dufour & van den Bergh (1978). In an 88 × 88 field centered on the inner filaments, UBV photometry has been obtained for stars brighter than V = 24.5 mag. The photometry has been used to identify 31 blue stars with V brighter than 23.0 mag. Positions, photometry, and finding charts are given. We believe that most of these stars formed from the interaction of the jet with local concentrations of dust and gas. DF 6 itself is resolved into a tight association of blue stars that are evidently young. Other loose groups are observed and compared with the loose aggregates seen farther out. The brightest blue stars are presumably the youngest stars and tend to lie close to the X-ray jet. We suggest that the raw material for star formation is found in dust patches of small angular size in the area and that star formation is triggered by shocks initiated by the jet. The brightest blue object, with V = 18.85 mag, is most likely a peculiar foreground star and a point X-ray source. The second brightest blue object, with V = 20.11 mag, is slightly diffuse and thus probably an unresolved cluster at the distance of NGC 5128.

Atomic and molecular gas in the merger galaxy NGC 1316 (Fornax A) and its environment

We present and interpret observations of atomic and molecular gas toward the southern elliptical galaxy NGC 1316 (Fornax A), a strong double-lobe radio source with a disturbed optical morphology that includes numerous shells and loops. The 12 CO(1{0), 12 CO(2{1), and Hi observations were made with SEST and the VLA. CO emission corresponding to a total molecular hydrogen mass of5 10 8 M was detected towards the central position as well as northwest and southeast of the nucleus in the regions of the dust patches. The origin of that gas is likely external and due to accretion of one or several small gas-rich galaxies. Hi was not detected in the central region of NGC 1316, but2 10 7 M of atomic gas was found towards the giant Hii region discovered by Schweizer (1980) located 6: 0 7 (or 36.2 kpc) from the nucleus. Hi was also found at three other locations in the outer part of NGC 1316. The Hi distributions and kinematics of the two nearby spiral companions of NGC 1316, NGC 1317 (a barred galaxy to the north) and NGC 1310 (to the west) could be studied. Both galaxies have unusually small Hi disks that may have been aected by ram-pressure stripping.

ROSATX−Ray Observations of the Radio Galaxy NGC 1316 (Fornax A)

We have observed NGC 1316 (Fornax A) with the ROSAT HRI. In this paper, we present the results of these observations and complement them with the spectral analysis of the archival PSPC data. The spectral properties suggest the presence of a significant component of thermal X-ray emission (greater than 60%), amounting to ~109 M☉ of hot interstellar matter (ISM). Within 3' from the nucleus of NGC 1316, the HRI X-ray surface brightness falls as r-2. In the inner ~40'', the X-ray surface brightness is significantly elongated ( ~ 0.3). This flattened X-ray feature is confirmed by a straightforward statistics test as well as moment analysis. By comparing the morphology of the X-ray emission with the distribution of optical dust patches, we find that the X-ray emission is significantly reduced at the locations where the dust patches are more pronounced, indicating that at least some of the X-ray photons are absorbed by the cold ISM. We also compare the distribution of the hot and cold ISM with that of the ionized gas, using recently obtained Hα CCD data. We find that the ionized gas is distributed roughly along the dust patches and follows the large-scale X-ray distribution at r > 1' from the nucleus. However, there is no one-to-one correspondence between ionized gas and hot gas. Both morphological relations and kinematics suggest different origins for hot and cold ISM. The radio jets in projection appear to pass perpendicularly through the central X-ray ellipsoid. Comparison of thermal and radio pressures suggests that the radio jets are confined by the surrounding hot gaseous medium.

DUST AND IONIZED GAS IN ELLIPTICAL GALAXIES

DUST AND IONIZED GAS IN ELLIPTICAL GALAXIES

The opacity of spiral disks

The opacity of the disks of spiral galaxies can be evaluated by studying the gaseous component in edge-on galaxies in several wavelength regions. By combining data of the galaxy NGC 891 at 21 cm (H I), 2.6 mm (CO), and Hα, we show that the outer regions are transparent, while the inner regions, out to the radius to which CO is detected, could be optically thick. For the small galaxy NGC 100, such data indicate that this galaxy is by and large transparent, despite the presence of dust patches in the optical image

Interstellar matter in early-type galaxies - Optical observations

Results of optical observations of 26 bright elliptical galaxies selected on the basis of IRAS data are discussed. Optical broadband imaging (using B and R filters) and narrow-band imaging (using H-alpha interference filters) have been performed to study dust patches and ionized gas. Long-split spectroscopy has also been made to determine gas kinematics and relative line ratios. The spectroscopic data confirm the presence and distribution of interstellar matter (dust lanes and ionized gas) seen in the direct imaging. Decoupled kinematics of interstellar gas and stars favors an external origin of the interstellar matter. However, for one isolated galaxy, an internal origin is not excluded. The rotation curves determined by optical emission lines are symmetric around the center in most galaxies observed. Galaxy masses and mass-to-light ratios are estimated using the rotation curves of the ionized gas.

Neutral Hydrogen Observations of the Dwarf Elliptical Galaxies NGC 185 and NGC 205

In this note we report the detection and mapping of neutral hydrogen in two dwarf elliptical galaxies NGC 185 and NGC 205. Both are companions to M 31 and both are classified as peculiar owing to the presence of obscurring dust patches near their nuclei. Both galaxies also contain a small population of blue, presumably young stars (Hodge 1963, 1973).

The inner structure of the optical jet in NGC 5128

view Abstract Citations (45) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The inner structure of the optical jet in NGC 5128. Dufour, R. J. ; van den Bergh, S. Abstract Image processing of multicolor plates of NGC 5128 obtained with the CTIO 4-m telescope has revealed a chain of faint elongated diffuse emission regions that are located between the nucleus of NGC 5128 and the 'outer jet' discovered by Blanco et al. (1975). Apparently associated with this new 'inner jet' are two possibly nonstellar blue knots, a number of small dust patches, and perhaps an elongated filament of Hα emission. Since the surface brightness of the darkest dust clouds apparently associated with the jet is at least 1 mag lower than that of the surrounding regions, these clouds must be located on the near side of the galaxy. Combined with available radial-velocity data, this result indicates that the jet is moving radially outward from the nucleus of NGC 5128. Publication: The Astrophysical Journal Pub Date: December 1978 DOI: 10.1086/182834 Bibcode: 1978ApJ...226L..73D Keywords: Galactic Structure; Radio Sources (Astronomy); Ubv Spectra; Cosmic Dust; H Alpha Line; Image Processing; Photographic Plates; Astrophysics; Galaxies:Jets; Galaxies:Radio Sources full text sources ADS | data products SIMBAD (1) NED (1)

Dust patches in globular clusters

view Abstract Citations (18) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dust patches in globular clusters. Kanagy, S. P. ; Wyatt, S. P. Abstract Previous observations of dark regions in globular star clusters are briefly reviewed, and three high-galactic-latitude globular clusters containing previously reported dark regions (M3, M13, and M15) are examined quantitatively by means of calibrated UBVR photography. A total of five dark regions are studied; extinctions are estimated and evaluated as a function of position in the most prominent dark patches or lanes. Values of R not far from 3 are obtained, indicating that the behavior of the obscuring material is apparently consistent with that of normal interstellar dust grains. Three possible explanations of the dark regions are considered, and an interpretation based on the obscuring effects of intracluster dust clouds is assumed. It is suggested that typical cloud masses are of the order of 0.003 solar mass and that the dust grains originate from the heavy elements involved in the gaseous mass loss from the few hundred cluster stars that at any moment are passing through late phases in their evolution. It is noted that the total grain mass in a globular cluster is reasonably consistent with the production rate in the outer atmospheres of globular-cluster red giants. Publication: The Astronomical Journal Pub Date: July 1978 DOI: 10.1086/112260 Bibcode: 1978AJ.....83..779K Keywords: Astronomical Photometry; Cosmic Dust; Galactic Evolution; Globular Clusters; Star Clusters; Granular Materials; Interstellar Extinction; Star Distribution; Astrophysics; Dust:Globular Clusters; Globular Clusters:Multicolor Photometry full text sources ADS |