A NEW GALACTIC EXTINCTION MAP OF THE CYGNUS REGION

New observations withHerschel allow accurate measurement of the equilibrium temperature of large dust grains heated by the interstellar radiation field (ISRF), which is critical in deriving dust column density and masses. We present temperature maps derived from the Herschel SPIRE and PACS data in two fields along the Galactic plane, obtained as part of the Hi-GAL survey during the Herschel science demonstration phase (SDP). We analyze the distribution of the dust temperature spatially, as well as along the two lines-of-sight (LOS) through the Galaxy. The zero-level offsets in the Herschel maps were established by comparison with the IRAS and Planck data at comparable wavelengths. We derive maps of the dust temperature and optical depth by adjusting a detailed model for dust emission at each pixel. The dust temperature maps show variations in the ISRF intensity and reveal the intricate mixture of the warm dust heated by massive stars and the cold filamentary structures of embedded molecular clouds. The dust optical depth at 250 μm is well correlated with the gas column density, but with a significantly higher dust emissivity than in the solar neighborhood. We correlate the optical depth with 3-D cubes of the dust extinction to investigate variations in the ISRF strength and dust abundance along the line of sight through the spiral structure of the Galaxy. We show that the warmest dust along the LOS is located in the spiral arms of the Galaxy, and we quantify their respective IR contribution.

In this study, we derived a galactic extinction map in high ecliptic latitudes for $ \mid{\beta}\mid$$ >$ 30$ ^\circ$ . The dust temperature distribution was derived from the intensities at 100 and 140 $ \mu$ m with a spatial resolution of 5$ '$ . The intensity at 140 $ \mu$ m was derived from the intensities at 60 and 100 $ \mu$ m of the IRAS data, assuming two tight correlations between the intensities at 60, 100, and 140 $ \mu$ m of the COBE/DIRBE data. We found that these correlations can be separated into two correlations by the antenna temperature of the radio continuum at 41 GHz. Because the present study can trace the 5$ '$-scale spatial variation in the dust temperature distribution, it has an advantage over the extinction map derived by Schlegel, Finkbeiner, and Davis (1998, ApJ, 500, 525), who used the DIRBE maps to derive the dust temperature distribution with a spatial resolution of 1$ ^\circ$ . We estimated the accuracy of our method by comparing it with that of Schlegel, Finkbeiner, and Davis (1998, ApJ, 500, 525). The spatial-resolution difference was found to be significant. The area in which the significant difference is confirmed occupies 28% of the region for $ \mid{\beta}\mid$$ >$ 30$ ^\circ$ . With respect to the estimated extragalactic reddening, the present study has an advantage over the extinction map derived by Dobashi (2011, PASJ, 63, 1), which was based on the 2MASS Point Source Catalog, because our extinction map was derived based on far-infrared emission. Dobashi's extinction map exhibits a maximum value that is lower than that of our map in the galactic plane, and a signal-to-noise ratio that is lower than that of our map in high galactic latitudes. This significant difference is confirmed in 81% of the region for $ \mid{\beta}\mid$$ >$ 30$ ^\circ$ . In the areas where the significant differences are confirmed, the extinction should be estimated using our method, rather than the previous methods.

A comparison is made of the far-IR emission detected by IRAS at 60 and 100 microns and the emission from C(-13)O in B18 and Heiles' Cloud 2. The results show that both these clouds have extended emission at the studied wavelengths and that this emission is correlated with the integrated intensity of (C-13)O emission. The dust temperature and optical depth, the gas column density, the mass of gas and dust, and the far-IR luminosity are derived and presented. The analysis shows that the dust optical depth is much better correlated with the gas column density than with the far-IR intensity. The dust temperature is found to be anticorrelated with the gas column density, suggesting that these clouds are externally heated by the interstellar radiation field. The far-IR luminosity-to-mass ratios for the clouds are substantially less than the average for the inner Galaxy.

High angular resolution far-infrared observations at 143 & 185 \micron, using the TIFR 1-m balloon borne telescope, are presented for two Galactic star forming complexes associated with IRAS 00494+5617 and 05327-0457. The latter map also reveals the cold dust in OMC-3. The HIRES processed IRAS maps at 12, 25, 60 & 100 micron have also been presented for comparison. Both these regions are illuminated at the edges by high mass stars with substantial UV flux.The present study is aimed at quantifying the role of the nearby stars vis-a-vis embedded young stellar objects in the overall heating of these sources. Based on the FIR observations at 143 & 185 micron carried out simultaneously with almost identical angular resolution, reliable dust temperature and optical depth maps have been generated for the brighter regions of these sources. Radiative transfer modeling in spherical geometry has been carried out to extract physical parameters of these sources by considering the observational constraints like : spectral energy distribution, angular size at different wavelengths, dust temperature distribution etc. It has been concluded that for both IRAS 00494+5617 and IRAS 05327-0457, the embedded energy sources play the major role in heating them with finite contribution from the nearby stars. The best fit model for IRAS 00494+5617 is consistent with a simple two phase clump-interclump picture with $\sim$ 5% volume filling factor (of clumps) and a density contrast of $\approx$ 80.

We present arcsecond resolution, 10.8, 11.7, and 18.2 μm images of the central few parsecs of the Galaxy. These images show for the first time the clumpiness of the dust in the western arc. The 11.7 and 18.2 μm images of part of the western arc were used to evaluate the dust temperature and optical depth distribution of this region. We see several mid-infrared emission peaks that coincide with dust temperature peaks and regions of low optical depth, and we infer the presence of embedded sources in the western arc. Minimum luminosity estimates for two of these sources (5 × 104 L⊙ and 2 × 104 L⊙) suggest that the circumnuclear ring is being locally heated by relatively young stars.

In order to determine the distribution of dust in the cloud associated with the star-forming region Cepheus A, we have obtained new, high angular resolution far-infrared (FIR) maps (at 50 and 100 μm) of this extended infrared source and polarimetric images (1.65 and 2.2 μm) of the reflection nebulosity, IRS 6, associated with this young stellar object. From our FIR maps we calculate the dust temperature and optical depth at 100 μm. Cepheus A has moderate optical depths (τ<SUB>100</SUB> μm ≤ 0.6), and its dust temperature ranges from 30 to 55 K. The two-dimensional map of the 100 microns optical depth indicates that there is a region of lower dust column density near the peak of the FIR emission. A radiative transfer code was used to model the available photometry and the FIR data of Cepheus A. A spherical dust cloud with a central young star was assumed, and the input parameters in this model were varied in order to reproduce the spectral energy distribution and the high angular resolution profiles at FIR wavelengths. The model that gives the best fit to the observations requires a dust cloud of the following characteristics: R<SUB>outer</SUB> = 0.5 pc, R<SUB>inner</SUB> = 0.07 pc, τ<SUB>100</SUB> = 0.15, α = 1.5, where R<SUB>outer</SUB>, R<SUB>inner</SUB>, τ<SUB>100</SUB> and α are the outer radius, inner radius, optical depth at 100 μm, and the exponent of the power law in the emitting-dust density gradient: n<SUB>d</SUB>(r) = n<SUB>0</SUB>(r/r<SUB>0</SUB>)<SUP>-α</SUP>. The inner radius used in this model (R<SUB>inner</SUB> = 0.07 pc) is similar in size to the "cavity" derived from the two-dimensional map of the dust optical depth at 100 μm. For small distances (r &lt; 0.15 pc) from the infrared peak, a second density gradient is derived from the distribution of the near-infrared (NIR) polarization. In this inner region of the dust cloud the NIR polarization distribution indicates that the density of the scattering dust should remain constant or increase slightly with distance. Our results are consistent with current star formation theories: a young stellar object surrounded by an infalling envelope with a characteristic density distribution of: n<SUB>d</SUB>(r) ∝r<SUP>-1.5</SUP>, a circumstellar disk, and a cavity (R<SUB>inner</SUB> ∼ 0.07 pc) in which n<SUB>d</SUB> is constant, created by the dispersal of the initial dust cloud by a strong stellar wind.

\n Aims. Dust properties appear to vary according to the environment in\nwhich the dust evolves. Previous observational indications of these\nvariations in the far-infrared (FIR) and submillimeter (submm)\nspectral range are scarce and limited to specific regions of the\nsky. To determine whether these results can be generalised to\nlarger scales, we study the evolution in dust emissivities from the\nFIR to millimeter (mm) wavelengths, in the atomic and molecular\ninterstellar medium (ISM), along the Galactic plane towards the outer\nGalaxy.\n Methods. We correlate the dust FIR to mm emission\nwith the HI and CO emission, which are taken to trace the atomic and molecular phases,\nrespectively. The study is carried out using the DIRBE data from 100 to\n240 μm, the Archeops data from 550 μm to 2.1 mm, and the WMAP\ndata at 3.2 mm (W band), in regions with Galactic latitude \n|b| ≤ 30°, over the Galactic longitude range (75° &lt; l &lt;\n198°) observed with Archeops. We estimate the average dust\ntemperature in each phase and divide the emission spectral energy\ndistribution (SED) by a black body at this temperature to\nderive the emissivity profile. A detailed verification of the impact\nof the implied simplification, such as temperature mixing along the\nline of sight, is provided.\n Results. In all regions studied, the emissivity spectra in both the atomic\nand molecular phases are steeper in the FIR (β = 2.4) than in the submm and mm (β = 1.5). We find significant variations in the spectral shape of the dust emissivity as a function\nof the dust temperature in the molecular phase. Regions of similar\ndust temperature in the molecular and atomic gas exhibit similar\nemissivity spectra. Regions where the dust is significantly colder in\nthe molecular phase show a significant increase in emissivity for\nthe range 100–550 μm. We exclude the possibility of this effect being an\nartifact of our temperature determination or the assumptions\nmade. This result supports the hypothesis of grain coagulation in\nthese regions, confirming results obtained over small fractions of the\nsky in previous studies and allowing us to expand these results to the\ncold molecular environments in general of the outer MW. Possible\nreasons for the observed emissivity increase in the molecular phase that\nvanishes in the mm range are discussed by comparison with dust models, involving dust aggregation and solid state physics\nprocesses specific to amorphous material. We note that it is the first\ntime that these effects have been demonstrated by direct measurement of the\nemissivity, while previous studies were based only on thermal\narguments.\n

We studied the dust properties of two cavity structures (namely FIC21+54 and FIC16-56) nearby Asymptotic Giant Branch stars using Infrared Astronomical Satellite (IRAS) maps. Dust color temperature, Planck function, dust mass, and visual extinction with their distribution within the region of interest were examined. The temperature of dust was found to lie in the range of 22.24 ± 0.81 K to 23.27 ± 0.21 K, and 25.12 ± 0.43 K to 26.17 ± 0.62 K, and the mass of dust was obtained within the range of 4.21 × 1026 kg to 3.6 × 1027 kg, and 2.1 × 1027 kg to 3.31 × 1028 kg, for FIC21+54 and FIC16-56, respectively. Some unusual behaviors on the distribution of dust temperature indicated the effect of nearby sources within the studied structures. Moreover, we observed the trend of dust particles along the major and minor diameters, and plots represented that the particles were oscillating with a sinusoidal pattern in both cavities. The negative slope between 25 µm and 60 µm in far-infrared spectral distribution was encountered for both structures, which portrayed less number density of particles in 60 µm band; interaction between AGB wind and the ambient interstellar medium could be the possible reason behind this. These findings support the prior results for two new cavity structures nearby AGB stars within the galactic plane -10° &lt; b &lt; +10°.

We apply the Finkbeiner et al. (1999) two-component thermal dust emission model to the Planck HFI maps. This parametrization of the far-infrared dust spectrum as the sum of two modified blackbodies serves as an important alternative to the commonly adopted single modified blackbody (MBB) dust emission model. Analyzing the joint Planck/DIRBE dust spectrum, we show that two-component models provide a better fit to the 100-3000 GHz emission than do single-MBB models, though by a lesser margin than found by Finkbeiner et al. (1999) based on FIRAS and DIRBE. We also derive full-sky 6.1' resolution maps of dust optical depth and temperature by fitting the two-component model to Planck 217-857 GHz along with DIRBE/IRAS 100 micron data. Because our two-component model matches the dust spectrum near its peak, accounts for the spectrum's flattening at millimeter wavelengths, and specifies dust temperature at 6.1' FWHM, our model provides reliable, high-resolution thermal dust emission foreground predictions from 100 to 3000 GHz. We find that, in diffuse sky regions, our two-component 100-217 GHz predictions are on average accurate to within 2.2%, while extrapolating the Planck Collaboration (2013a) single-MBB model systematically underpredicts emission by 18.8% at 100 GHz, 12.6% at 143 GHz and 7.9% at 217 GHz. We calibrate our two-component optical depth to reddening, and compare with reddening estimates based on stellar spectra. We find the dominant systematic problems in our temperature/reddening maps to be zodiacal light on large angular scales and the cosmic infrared background anisotropy on small angular scales.

Context. Symbiotic Miras represent a class of peculiar binaries whose nature is still not well understood. Physical properties of the circumstellar dust and associated physical mechanisms play an important role in understanding the evolution of symbiotic binaries and the interaction between their components. We present a model of inner dust regions around the cool Mira component of the symbiotic nova RR Tel based on the near-IR terrestrial photometry and infrared ISO spectra. Aims. Our goal is to find a comprehensive and consistent model of the circumstellar inner dust regions around the Mira component that can explain the observed photometric and spectroscopic features in the near- and mid-infrared. Methods. Available JHKL photometric observations from South African Astronomical Observatory were collected and corrected for Mira pulsations as well as for interstellar reddening to follow temporal changes of the near-infrared colours. Spectral energy distributions (SEDs) from 1 to 13 μm during obscuration epoch were reconstructed with the simultaneously available ISO/SWS spectra and JHKL magnitudes. The dust properties were determined by modelling both the reconstructed SEDs and the near-IR colours using the DUSTY numerical code. This 1D code solves radiative transfer through the circumstellar dust by calculating the dust temperature profile assuming spherical symmetry. Results. The Mira pulsation period of 387 days was found and confirmed with two independent fitting methods. A long-term variation of ∼7000 days, which cannot be attributed to orbital motion, was obtained from the analysis of the near-IR magnitudes. Reconstructed infrared SEDs were modelled successfully by a single dust shell with dust distribution enhanced by radiatively driven stellar winds. Mira temperature, dust sublimation temperature, grain diameter, density distribution, and optical depth have been obtained. Our model shows a maximum dust grain diameter of 4 μm, which is larger than expected and can be explained by grain growth in conditions of increased mass loss during obscuration epochs. Obscurations in the near-IR can be understood as a result of change of the dust optical depth and of the mass loss rate of Mira component. Change of the dust temperature on the inner boundary of the dust shell with pulsation phase have been identified by SED modelling. Assuming a gas-to-dust ratio of 200, we found a variable mass loss rate between 2.3 and 9.0 ×10 −6 M� /yr and estimated the distance to RR Tel to be 2.7 kpc. Our results suggest a relatively low influence of

view Abstract Citations (1) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Identification of active star formation regions in the galactic plane Ananth, A. G. ; Nagaraja, B. V. Abstract The galactic distribution of 2.2 micron infrared brightness derived from discrete sources exhibits higher fluxes at galactic longitudes, l = 8 deg, l = 18 deg, l = 30 deg, and l = 42 deg and shows that at these galactic longitudes, the 2.6 mm emission line of CO is strongly correlated with the 115-196 micron far-infrared brightness distribution. The dust temperatures computed for these regions show a larger value compared to the equilibrium dust temperature, indicating the presence of a local source of heating and suggests that star formation is still active at these locations in the galactic plane. Publication: The Astrophysical Journal Pub Date: August 1982 DOI: 10.1086/160202 Bibcode: 1982ApJ...259..664A Keywords: Brightness Distribution; Cosmic Dust; Infrared Astronomy; Interstellar Matter; Molecular Clouds; Star Formation; Brightness Temperature; Carbon Monoxide; Emission Spectra; Energy Spectra; Astrophysics full text sources ADS |

We investigate the FIR properties of a sample of BCDs observed by AKARI. By utilizing the data at wavelengths of $\lambda =65 \mu$m, 90 $\mu$m, and 140 $\mu$m, we find that the FIR colours of the BCDs are located at the natural high-temperature extension of those of the Milky Way and the Magellanic Clouds. This implies that the optical properties of dust in BCDs are similar to those in the Milky Way. Indeed, we explain the FIR colours by assuming the same grain optical properties, which may be appropriate for amorphous dust grains, and the same size distribution as those adopted for the Milky Way dust. Since both interstellar radiation field and dust optical depth affect the dust temperature, it is difficult to distinguish which of these two physical properties is responsible for the change of FIR colours. Then, in order to examine if the dust optical depth plays an important role in determining the dust temperature, we investigate the correlation between FIR colour (dust temperature) and dust-to-gas ratio. We find that the dust temperature tends to be high as the dust-to-gas ratio decreases but that this trend cannot be explained by the effect of dust optical depth. Rather, it indicates a correlation between dust-to-gas ratio and interstellar radiation field. Although the metallicity may also play a role in this correlation, we suggest that the dust optical depth could regulate the star formation activities, which govern the interstellar radiation field. We also mention the importance of submillimetre data in tracing the emission from highly shielded low-temperature dust.

We present a survey of ∼ 800 square degrees of the galactic plane observed with the QUaD telescope. The primary product of the survey are maps of Stokes I, Q and U parameters at 100 and 150 GHz, with spatial resolution 5 and 3.5 arcminutes respectively. Two regions are covered, spanning approximately 245 − 295◦and 315 − 5 ◦in galactic longitude l, and −4 &lt; b &lt; +4 ◦in galactic latitude b. At 0.02◦ square pixel size, the median sensitivity is 74 and 107 kJy/sr at 100 GHz and 150 GHz respectively in I, and 98 and 120 kJy/sr for Q and U. In total intensity, we find an average spectral index of α = 2.35±0.01(stat)±0.02(sys) for |b| ≤ 1◦, indicative of emission components other than thermal dust. A comparison to published dust, synchrotron and free-free models implies an excess of emission in the 100 GHz QUaD band, while better agreement is found at 150 GHz. A smaller excess is observed when comparing QUaD 100 GHz data to WMAP 5-year W band; in this case the excess is likely due to the wider bandwidth of QUaD. Combining the QUaD and WMAP data, a two-component spectral fit to the inner galactic plane (|b| ≤ 1◦) yields mean spectral indices of αs = −0.32 ± 0.03 and αd = 2.84 ± 0.03; the former is interpreted as a combination of the spectral indices of synchrotron, free-free and dust, while the second is attributed largely to the thermal dust continuum. In the same galactic latitude range, the polarization data show a high degree of alignment perpendicular to the expected galactic magnetic field direction, and exhibit mean polarization fraction 1.38±0.08(stat)±0.1(sys)% at 100 GHz and 1.70±0.06(stat)±0.1(sys)% at 150 GHz. We find agreement in polarization fraction between QUaD 100 GHz and WMAP W band, the latter giving 1.1±0.4%.

Searches for gravitational microlensing events are traditionally concentrated on the central regions of the Galactic bulge but many microlensing events are expected to occur in the Galactic plane, far from the Galactic Center. Owing to the difficulty in conducting high-cadence observations of the Galactic plane over its vast area, which are necessary for the detection of microlensing events, their global properties were hitherto unknown. Here, we present results of the first comprehensive search for microlensing events in the Galactic plane. We searched an area of almost 3000 square degrees along the Galactic plane ( , 0° &lt; l &lt; 50°, 190° &lt; l &lt; 360°) observed by the Optical Gravitational Lensing Experiment (OGLE) during 2013–2019 and detected 630 events. We demonstrate that the mean Einstein timescales of Galactic plane microlensing events are on average three times longer than those of Galactic bulge events, with little dependence on the Galactic longitude. We also measure the microlensing optical depth and event rate as a function of Galactic longitude and demonstrate that they exponentially decrease with the angular distance from the Galactic Center (with the characteristic angular scale length of 32°). The average optical depth decreases from 0.5 × 10−6 at l = 10° to 1.5 × 10−8 in the Galactic anticenter. We also find that the optical depth in the longitude range 240° &lt; l &lt; 330° is asymmetric about the Galactic equator, which we interpret as a signature of the Galactic warp.

Martian dust, composed of micrometer-sized mineral particles, is a key parameter of the Martian atmosphere because of its high mobility and capacity to form dust storms and alter the heat balance of the atmosphere. These dust storms are part of the Martian dust cycle and can occur over a wide range of spatial and time scales (from sub-km to planetary scale, and from the minute to months). The dust studies are mostly concentrated on regional storms (&gt; 2000 km), which are detected using UV-VIS global imagers [1, 2] or thermal-IR spectrometers [3]. These observations provide information about the frequency and size of the storms. However, some characteristics of the dust cycle remain uncertain, such as the exact mechanisms of storm formation and growth processes, with implications for the predictability of dust storms and Global Dust Storms (GDS, storm at a planetary scale). Thus, it is important to study dust activity at a local scale, such as the local dust storms (&lt; 2000 km) which have not been massively detected (some detections by [2] and a few individual storm characterisations as [4]). We focus our work on detecting dust storms in the OMEGA/Mars Express (near-IR imaging spectrometer) dataset, which has a high enough spatial resolution (0.36-4.8 km/px) to detect local dust storms. More precisely, we develop a method to detect automatically dust storms using dust optical depth computation (at 0.9 µm) made by [5] from late Martian Year 26 to early MY 30 (including the MY 28 GDS). The 1st-level detection is to exclude OMEGA observations that are least likely to contain dust storms (dust optical depth &lt; 1.25). Then the 2nd-level detection principle is to identify pixel clusters of high optical depth within individual observations to identify storms, to confirm the detection using different criteria (e.g., decrease of surface reflectance) and to extract key characteristics of the storm (e.g., size, centroid, local time).Figure 1: Spatial distribution of the dust storms (local and regional) detected with OMEGA/MEx from late MY 26 to early MY 30 (without MY 28 GDS period). The background corresponds to a topography map (MOLA/MGS). With this 2-level method, we detected 287 dust storms (excluding the MY 28 GDS period during which 114 detections have been made) composed of 283 local and 4 regional. Here we summarised our results that will be presented in detail during the conference (notably by separating the local and regional dust storms). From the spatial distribution of the detections (Figure 1), we notice some known preferential areas such as the flushing dust storm channels (e.g., Acidalia-Chryse, Utopia-Isidis, see [1]) or Hellas Planitia, as well as next to the southern polar cap. The seasonal distribution of the detected storms (Figure 2) shows many detections in the Ls=240-270° period, particularly in MY 27, and also during the Ls=330-360° period, notably in MY 29. Interestingly, only a few storms were reported during these periods using UV-VIS imagery [1], suggesting that our method may be capturing local-scale events that were previously undetected. Another strength of OMEGA data is the local time coverage during the Mars Express mission, allowing the study of the time dependence. We noticed many detections from 10:00 to 18:00 with an increase (compared to the OMEGA local time coverage) at the end of the afternoon (16:00-18:00), and also some detections early in the morning (04:00-06:00).Figure 2: Seasonal distribution of the dust storms (local and regional) detected with OMEGA/MEx from late MY 26 to early MY 30 (without MY 28 GDS period). We also worked on the MY 28 GDS onset, for which one doubt remains about the formation area, specifically, whether it originated in Noachis (southern hemisphere) or Chryse (northern hemisphere). More precisely, the question is whether the precursory storm observed in Noachis initiated the GDS independently, or whether it was dependent on the one in Chryse. The consecutive OMEGA observations of these two areas (during the storms) show high dust optical depth values for Noachis and Chryse, but separated from each other by low optical depths, which could be interpreted as two separate clouds, and therefore a GDS onset in Noachis. We are currently working to evaluate the dust altitude by comparing dust optical depth retrievals at different wavelengths [6].