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MIRIS observation of near-infrared diffuse Galactic light
摘要： We report near-infrared (IR) observations of high Galactic latitude clouds to investigate diffuse Galactic light (DGL), which is starlight scattered by interstellar dust grains. The observations were performed at 1.1 and 1.6 μm with a wide-field camera instrument, the Multi-purpose Infra-Red Imaging System (MIRIS) onboard the Korean satellite STSAT-3. The DGL brightness is measured by correlating the near-IR images with a far-IR 100 μm map of interstellar dust thermal emission. The wide-field observation of DGL provides the most accurate DGL measurement achieved to-date. We also find a linear correlation between optical and near-IR DGL in the MBM32 field. To study interstellar dust properties in MBM32, we adopt recent dust models with and without μm-sized very large grains and predict the DGL spectra, taking into account the reddening effect of the interstellar radiation field. The result shows that the observed color of the near-IR DGL is closer to the model spectra without very large grains. This may imply that dust growth in the observed MBM32 field is not active owing to the low density of its interstellar medium.
关键词： scattering,dust, extinction,ISM: clouds,infrared: ISM
更新于2025-09-23 15:22:29
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Dust spectrum and polarisation at 850 <i>μ</i> m in the massive IRDC G035.39-00.33
摘要： Context. The sub-millimetre polarisation of dust emission from star-forming clouds carries information on grain properties and on the effects that magnetic fields have on cloud evolution. Aims. Using observations of a dense filamentary cloud G035.39-00.33, we aim to characterise the dust emission properties and the variations of the polarisation fraction. Methods. JCMT SCUBA-2/POL-2 observations at 850 μm were combined with Planck 850 μm (353 GHz) data to map polarisation fraction at small and large scales. With previous total intensity SCUBA-2 observations (450 and 850 μm) and Herschel data, the column densities were determined via modified black-body fits and via radiative transfer modelling. Models were constructed to examine how the observed polarisation angles and fractions depend on potential magnetic field geometries and grain alignment processes. Results. POL-2 data show clear changes in the magnetic field orientation. These are not in contradiction with the uniform orientation and almost constant polarisation fraction seen by Planck, because of the difference in the beam sizes and the POL-2 data being affected by spatial filtering. The filament has a peak column density of N(H2) ~ 4 × 10^22 cm^-2, a minimum dust temperature of T ~ 12 K, and a mass of ~4300 M☉ for the area N(H2) > 5 × 10^21 cm^-2. The ratio of sub-millimetre and J-band optical depths is τ(250 μm)/τ(J) ~ 2.5 × 10^-3, more than four times the typical values for diffuse medium. The polarisation fraction decreases as a function of column density to p ~ 1% in the central filament. Because of noise, the observed decrease of p(N) is significant only at N(H2) > 2 × 10^22 cm^-2. The observations suggest that the grain alignment is not constant. Although the data can be explained with a complete loss of alignment at densities above n(H2) ~ 10^4 cm^-3 or using the predictions of radiative torques alignment, the uncertainty of the field geometry and the spatial filtering of the SCUBA-2 data prevent strong conclusions. Conclusions. The G035.39-00.33 filament shows strong signs of dust evolution and the low polarisation fraction is suggestive of a loss of polarised emission from its densest parts. Key words. ISM: clouds – infrared: ISM – submillimeter: ISM – dust, extinction – stars: formation – stars: protostars
关键词： infrared: ISM,dust, extinction,submillimeter: ISM,stars: protostars,stars: formation,ISM: clouds
更新于2025-09-19 17:15:36
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Infrared Detection of Abundant CS in the Hot Core AFGL 2591 at High Spectral Resolution with SOFIA/EXES
摘要： We have performed a 5–8 μm spectral line survey of the hot molecular core associated with the massive protostar AFGL 2591, using the Echelon-Cross-Echelle Spectrograph (EXES) on board the Stratospheric Observatory for Infrared Astronomy (SOFIA). We have supplemented these data with a ground-based study in the atmospheric M band around 4.5 μm using the iSHELL instrument on the Infrared Telescope Facility (IRTF), and the full N-band window from 8 to 13 μm using the Texas Echelon Cross Echelle Spectrograph (TEXES) on the IRTF. Here we present the ?rst detection of rovibrational transitions of CS in this source. The absorption lines are centered on average around ?10 km s?1 and the line widths of CS compare well with the hot component of 13CO (around 10 km s?1). Temperatures for CS, hot 13CO, and 12CO v = 1–2 agree well and are around 700 K. We derive a CS abundance of 8 × 10?3 and 2 × 10?6 with respect to CO and H2, respectively. This enhanced CS abundance with respect to the surrounding cloud (1 × 10?8) may re?ect sublimation of H2S ice followed by gas-phase reactions to form CS. Transitions are in local thermodynamic equilibrium and we derive a density of >107 cm?3, which corresponds to an absorbing region of <0.04″. EXES observations of CS are likely to probe deeply into the hot core, to the base of the out?ow. Submillimeter and infrared observations trace different components of the hot core as revealed by the difference in systemic velocities, line widths, and temperatures, as well as the CS abundance.
关键词： ISM: abundances,line: pro?les,infrared: ISM,ISM: individual objects (AFGL 2591),astrochemistry,line: identi?cation
更新于2025-09-10 09:29:36
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Far-infrared molecular lines from low- to high-mass star forming regions observed with <i>Herschel</i>
摘要： Aims. Our aim is to study the response of the gas-to-energetic processes associated with high-mass star formation and compare it with previously published studies on low- and intermediate-mass young stellar objects (YSOs) using the same methods. The quanti?ed far-IR line emission and absorption of CO, H2O, OH, and [O i] reveals the excitation and the relative contribution of di?erent atomic and molecular species to the gas cooling budget. Methods. Herschel/PACS spectra covering 55–190 μm are analyzed for ten high-mass star forming regions of luminosities Lbol ～ 104?106 L(cid:4) and various evolutionary stages on spatial scales of ～104 AU. Radiative transfer models are used to determine the contribution of the quiescent envelope to the far-IR CO emission. Results. The close environments of high-mass protostars show strong far-IR emission from molecules, atoms, and ions. Water is detected in all 10 objects even up to high excitation lines, often in absorption at the shorter wavelengths and in emission at the longer wavelengths. CO transitions from J = 14?13 up to typically 29?28 (Eu/kB ～ 580?2400 K) show a single temperature component with a rotational temperature of Trot ～ 300 K. Typical H2O excitation temperatures are Trot ～250 K, while OH has Trot ～ 80 K. Far-IR line cooling is dominated by CO (～75%) and, to a smaller extent, by [O i] (～20%), which becomes more important for the most evolved sources. H2O is less important as a coolant for high-mass sources because many lines are in absorption. Conclusions. Emission from the quiescent envelope is responsible for ～45–85% of the total CO luminosity in high-mass sources compared with only ～10% for low-mass YSOs. The highest?J lines (Jup ≥ 20) originate most likely in shocks, based on the strong correlation of CO and H2O with physical parameters (Lbol, Menv) of the sources from low- to high-mass YSOs. The excitation of warm CO described by Trot ～ 300 K is very similar for all mass regimes, whereas H2O temperatures are ～100 K high for high-mass sources compared with low-mass YSOs. The total far-IR cooling in lines correlates strongly with bolometric luminosity, consistent with previous studies restricted to low-mass YSOs. Molecular cooling (CO, H2O, and OH) is ～4 times greater than cooling by oxygen atoms for all mass regimes. The total far-IR line luminosity is about 10?3 and 10?5 times lower than the dust luminosity for the low- and high-mass star forming regions, respectively.
关键词： stars: protostars,infrared: ISM,molecular processes,astrochemistry,ISM: jets and outflows
更新于2025-09-10 09:29:36
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Ray-tracing 3D dust radiative transfer with DART-Ray: code upgrade and public release
摘要： We present an extensively updated version of the purely ray-tracing 3D dust radiation transfer code DART-Ray. The new version includes five major upgrades: 1) a series of optimizations for the ray-angular density and the scattered radiation source function; 2) the implementation of several data and task parallelizations using hybrid MPI+OpenMP schemes; 3) the inclusion of dust self-heating; 4) the ability to produce surface brightness maps for observers within the models in HEALPix format; 5) the possibility to set the expected numerical accuracy already at the start of the calculation. We tested the updated code with benchmark models where the dust self-heating is not negligible. Furthermore, we performed a study of the extent of the source influence volumes, using galaxy models, which are critical in determining the efficiency of the DART-Ray algorithm. The new code is publicly available, documented for both users and developers, and accompanied by several programmes to create input grids for different model geometries and to import the results of N-body and SPH simulations. These programmes can be easily adapted to different input geometries, and for different dust models or stellar emission libraries.
关键词： scattering,dust, extinction,radiative transfer,infrared: ISM,methods: numerical
更新于2025-09-09 09:28:46
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Uncertainties and biases of source masses derived from fits of integrated fluxes or image intensities
摘要： Fitting spectral distributions of total ?uxes or image intensities are two standard methods for estimating the masses of starless cores and protostellar envelopes. These mass estimates, which are the main source and basis of our knowledge of the origin and evolution of self-gravitating cores and protostars, are uncertain. It is important to clearly understand sources of statistical and systematic errors stemming from the methods and minimize the errors. In this model-based study, a grid of radiative transfer models of starless cores and protostellar envelopes was computed and their total ?uxes and image intensities were ?tted to derive the model masses. To investigate intrinsic e?ects related to the physical objects, all observational complications were explicitly ignored. Known true values of the numerical models allow assessment of the qualities of the methods and ?tting models, as well as the e?ects of nonuniform temperatures, far-infrared opacity slope, selected subsets of wavelengths, background subtraction, and angular resolutions. The method of ?tting intensities gives more accurate masses for more resolved objects than the method of ?tting ?uxes. With the latter, a ?tting model that assumes optically thin emission gives much better results than the one allowing substantial optical depths. Temperature excesses within the objects above the mass-averaged values skew their spectral shapes towards shorter wavelengths, leading to masses underestimated typically by factors 2?5. With a ?xed opacity slope deviating from the true value by a factor of 1.2, masses are inaccurate within a factor of 2. The most accurate masses are estimated by ?tting just two or three of the longest wavelength measurements. Conventional algorithm of background subtraction is a likely source of large systematic errors. The absolute values of masses of the unresolved or poorly resolved objects in star-forming regions are uncertain to within at least a factor of 2?3.
关键词： submillimeter: ISM,techniques: photometric,stars: formation,methods: data analysis,infrared: ISM,techniques: image processing
更新于2025-09-04 15:30:14
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Benchmarking the calculation of stochastic heating and emissivity of dust grains in the context of radiative transfer simulations
摘要： Context. Thermal emission by stochastically heated dust grains (SHGs) plays an important role in the radiative transfer (RT) problem for a dusty medium. It is therefore essential to verify that RT codes properly calculate the dust emission before studying the effects of spatial distribution and other model parameters on the simulated observables. Aims. We define an appropriate problem for benchmarking dust emissivity calculations in the context of RT simulations, specifically including the emission from SHGs. Our aim is to provide a self-contained guide for implementors of such functionality and to offer insight into the effects of the various approximations and heuristics implemented by the participating codes to accelerate the calculations. Methods. The benchmark problem definition includes the optical and calorimetric material properties and the grain size distributions for a typical astronomical dust mixture with silicate, graphite, and PAH components. It also includes a series of analytically defined radiation fields to which the dust population is to be exposed and instructions for the desired output. We processed this problem using six RT codes participating in this benchmark effort and compared the results to a reference solution computed with the publicly available dust emission code DustEM. Results. The participating codes implement different heuristics to keep the calculation time at an acceptable level. We study the effects of these mechanisms on the calculated solutions and report on the level of (dis)agreement between the participating codes. For all but the most extreme input fields, we find agreement within 10% across the important wavelength range 3 μm ≤ λ ≤ 1000 μm. Conclusions. We conclude that the relevant modules in RT codes can and do produce fairly consistent results for the emissivity spectra of SHGs. This work can serve as a reference for implementors of dust RT codes, and it will pave the way for a more extensive benchmark effort focusing on the RT aspects of the various codes.
关键词： dust, extinction,radiative transfer,infrared: ISM,methods: numerical,radiation mechanisms: thermal
更新于2025-09-04 15:30:14