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Far-infrared and submillimeter continuum emission from the dark globule B335 was observed. The spectrum is that of optically thin thermal emission from dust with temperature 13-16 K. The estimated dust mass is 0.07-0.17 solar masses. The observed luminosity, 5 solar luminosities, can be supplied by the interstellar radiation field.
A theoretical parameter study of the temperature and chemical structure of photodissociation regions (PDRs) and their resultant spectrum is presented. The models, which solve for the chemical and thermal steady state of a one-dimensional slab exposed to an incident FUV flux, relate the observed line and continuum emission from these regions to physical parameters of interest. Intensities of numerous fine-structure lines, the molecular rotational transitions (C-12)O J = 1-0 and H2 0-0 S(0), and the dust continuum intensities at 60 and 100 microns are predicted, and the column density of FUV-pumped vibrationally excited H2 is estimated.
Theoretical predictions about dust and gas in star forming regions are tested by observing a 4 arcmin region surrounding the radio continuum source in 5201. The object was mapped in two far infrared wavelengths and found to show significant extended emission. Under the assumption that the molecular gas is heated solely via thermal coupling with the dust, the volume density was mapped in 5201. The ratios of infrared optical depth to CO column density were calculated for a number of positions in the source. Near the center of the cloud the values are found to be in good agreement with other determinations for regions with lower column density. In addition, the observations suggest significant molecular destruction in the outer parts of the object. Current models of gas heating were used to calculate a strong limit for the radius of the far infrared emitting grains, equal to or less than 0.15 micron. Grains of about this size are required by the observation of high temperature (T equal to or greater than 20 K) gas in many sources.
Far-infrared maps of W51/G49.5-0.4, W51/G49.4-0.3, and the DR 21 W75 S regions are presented. The simultaneous 50 and 100 micron maps enable a determination of the dust temperature and density structure in these areas. In G49.5-0.4 a luminosity and dust column-density peak at the position of the W51-Main maser is found, suggesting that this is the dominant luminosity source in W51. In G49.4-0.3 three components associated with the three known 2.7 GHz sources are resolved. A comparison of the total far-infrared luminosity with the radio continuum brightness in both G49.5-0.4 and G49.4-0.3 shows that the ratio of Lyman continuum to total luminosity of the exciting stars in not consistent with excitation by a single ZAMS star if most of the Lyman continuum photons are being absorbed bay gas rather than dust. In DR 21 micron far-infrared data and some new 2-20 micron results reveal a region of hot dust associated with the 2 micron H2 emission to the east and west of DR 21. Finally, a new 1.5-100 micron 'protostellar' source 2 deg north of W75 S at the position of a 1 mm continuum peak is reported.
The intensity of the diffuse 1 to 5 micron sky emission from which solar system and Galactic foregrounds have been subtracted is in excess of that expected from energy released by galaxies and stars that formed during the z < 5 redshift interval. The spectral signature of this excess near-infrared background light (NIRBL) component is almost identical to that of reflected sunlight from the interplanetary dust cloud, and could therefore be the result of the incomplete subtraction of this foreground emission component from the diffuse sky maps. Alternatively, this emission component could be extragalactic. Its spectral signature is consistent with that of redshifted continuum and recombination line emission from H-II regions formed by the first generation of very massive stars. In this talk I will present the implications of this excess emission for our understanding of the zodiacal dust cloud, the formation rate of Pop III stars, and the TeV gamma-ray opacity to nearby blazars.
Analyses of IR data of Comet West in the region 0.9-2.5 microns are presented. The spectra were observed with a resolution of 4.6/cm, and the solar-type star Eta Boo was also observed for comparison purposes. The cometary continuum was found to increase slightly from 10,000-5500/cm, and display thermal emission above 5500/cm due to dust particles in the coma. The cometary emissions were identified with CN and C2, with the C2 transitions displaying unblended singlet and triplet systems. It is noted that no emissions or absorptions due to ice of any form were detected.
We present H(exp 13)CO(exp +) (J= 1-0) and HNC (J= 1-0) maps of regions in Serpens South, Serpens Main, and NGC 1333 containing filaments. We also observe the Serpens regions using H(exp 13)CN (J= 1-0). These dense gas tracer molecular line observations carried out with CARMA have an angular resolution of approximately 7", a spectral resolution of approximately 0.16 km s (exp -1), and a sensitivity of 50-100 mJy beam (exp -1). Although the large-scale structure compares well with the Herschel dust continuum maps, we resolve finer structure within the filaments identified by Herschel. The H(exp 13)CO(exp +) emission distribution agrees with the existing CARMA diazenylium(exp +) (J= 1-0) maps, so they trace the same morphology and kinematics of the filaments. The H(exp 13)CO(exp +) maps additionally reveal that many regions have multiple structures partially overlapping in the line of sight. In two regions, the velocity differences are as high as 1.4 km s(exp -1). We identify eight filamentary structures having typical widths of 0.03 - 0.08 pc in these tracers. At least 50% of the filamentary structures have distinct velocity gradients perpendicular to their major axis, with average values in the range of 4-10 km s(exp -1) pc (exp -1). These findings are in support of the theoretical models of filament formation by 2D inflow in the shock layer created by colliding turbulent cells. We also find evidence of velocity gradients along the length of two filamentary structures; the gradients suggest that these filaments are inflowing toward the cloud core.
Continuum polarization over the UV-to-microwave range is due to dichroic extinction (or emission) by asymmetric, aligned dust grains. Scattering can also be an important source of polarization, especially at short wavelengths. Because of both grain alignment and scattering physics, the wavelength dependence of the polarization, generally, traces the size of the aligned grains. Similarly because of the differing wavelength dependencies of dichroic extinction and scattering polarization, the two can generally be reliably separated. Ultraviolet (UV) polarimetry therefore provides a unique probe of the smallest dust grains (diameter<0.09 μm ), their mineralogy and interaction with the environment. However, the current observational status of interstellar UV polarization is very poor with less than 30 lines of sight probed. With the modern, quantitative and well-tested, theory of interstellar grain alignment now available, we have the opportunity to advance the understanding of the interstellar medium (ISM) by executing a systematic study of the UV polarization in the ISM of the Milky Way and near-by galaxies. The Polstar mission will provide the sensitivity and observing time needed to carry out such a program (probing hundreds of stars in the Milky Way and dozens of stars in the LMC/SMC), addressing questions of dust composition as a function of size and location, radiation- and magnetic-field characteristics as well as unveiling the carrier of the 2175 Å extinction feature. In addition, using high-resolution UV line spectroscopy Polstar will search for and probe the alignment of, and polarization from, aligned atoms and ions - so called “Ground State Alignment”, a potentially powerful new probe of magnetic fields in the diffuse ISM.
The shape of the spectral energy distribution of active galaxies in the EUV soft X-ray band (13.6 eV to 1 keV) is uncertain because obscuration by dust and gas can hamper our view of the continuum. To investigate the shape of the spectral energy distribution in this energy band, we have generated a set of photoionization models which reproduce the small dispersion found in correlations between high-ionization mid-infrared emission lines in a sample of hard X-ray selected AGN. Our calculations show that a broken power-law continuum model is sufficient to reproduce the [Ne V]14.32 microns/[Ne III], [Ne V]24.32 microns/[O IV]25.89 micron and [O IV] 25.89 microns/[Ne III] ratios, and does not require the addition of a "big bump" EUV model component. We constrain the EUV-soft X-ray slope, alpha(sub i), to be between 1.5 - 2.0 and derive a best fit of alpha(sub i) approx. 1.9 for Seyfert 1 galaxies, consistent with previous studies of intermediate redshift quasars. If we assume a blue bump model, most sources in our sample have derived temperatures between T(sub BB) = 10(exp 5.18) K to 10(exp 5.7) K, suggesting that the peak of this component spans a large range of energies extending from approx. (Lambda)600 A to > (Lambda)1900 A. In this case, the best fitting peak energy that matches the mid-infrared line ratios of Seyfert 1 galaxies occurs between approx. (Lambda)700-(Lambda)1000 A. Despite the fact that our results do not rule out the presence of an EUV bump, we conclude that our power-law model produces enough photons with energies > 4 Ry to generate the observed amount of mid-infrared emission in our sample of BAT AGN.
Dust trapping accelerates the coagulation of dust particles, and, thus, it represents an initial step toward the formation of planetesimals. We report H-band (1.6 microns) linear polarimetric observations and 0.87 mm interferometric continuum observations toward a transitional disk around LkH(alpha) 330. As a result, a pair of spiral arms were detected in the H-band emission, and an asymmetric (potentially arm-like) structure was detected in the 0.87 mm continuum emission. We discuss the origin of the spiral arm and the asymmetric structure and suggest that a massive unseen planet is the most plausible explanation. The possibility of dust trapping and grain growth causing the asymmetric structure was also investigated through the opacity index (beta) by plotting the observed spectral energy distribution slope between 0.87 mm from our Submillimeter Array observation and1.3 mm from literature. The results imply that grains are indistinguishable from interstellar medium-like dust in the east side (beta = 2.0 +/- 0.5) but are much smaller in the west side beta = 0.7+0.5 -0.4, indicating differential dust size distribution between the two sides of the disk. Combining the results of near-infrared and submillimeter observations, we conjecture that the spiral arms exist at the upper surface and an asymmetric structure resides in the disk interior. Future observations at centimeter wavelengths and differential polarization imaging in other bands (Y-K) with extreme AO imagers are required to understand how large dust grains form and to further explore the dust distribution in the disk.
Theoretical predictions about dust and gas in star-forming regions are tested by observing a 4-arcmin region surrounding the radio continuum source in S201. The object was mapped in two far-infrared wavelengths and found to show significant extended emission. Under the assumption that the molecular gas is heated solely via thermal coupling with the dust, the volume density was mapped in S201. The ratios of infrared optical depth to CO column density were calculated for a number of positions in the source. Near the center of the cloud the values are found to be in good agreement with other determinations for regions with lower column density. In addition, the observations suggest significant molecular destruction in the outer parts of the object. Current models of gas heating were used to calculate a strong limit for the radius of the far-infrared emitting grains, a equal to or less than 0.15 micron. Grains of about this size are required by the observation of high temperature (T equal to or greater than 20 K) gas in many sources.
Molecular line surveys and fully sampled spectral line maps at 1.3 and 0.87 mm are used to examine the physical and chemical characteristics of the extreme Class I sources IRAS 4A and 4B in the L1450/NGC 1333 molecular cloud complex. A very well collimated, jetlike molecular flow emanates from IRAS 4A, with a dynamical age of a few thousand years. Symmetric, clumpy structure along the outflow lobes suggests that there is considerable variability in the mass-loss rate or wind velocity even at this young age. Molecular emission lines toward IRAS 4A and 4B are observed to be weak in the velocity range corresponding to quiescent material surrounding the young stellar objects (YSOs). Depletion factors of 10-20 are observed for all molecules, including CO, even for very conservative mass estimates from the measured millimeter and submillimeter dust continuum. However, abundance scaled with respect to CO are similar to other dark molecular cloud cores. Such depletions could be mimicked by high dust and optical depths or increased grain emissivities at the observing frequencies of 230 and 435 GHz, but the millimeter and submillimeter spectral energy distributions suggest that this is unlikely over the single-dish size scales of 5000-10,000 AU. Dense, outflowing gas is found to be kinematically, but not spatially, distinct from the quiescent material on these size scales. If CO is used as a chemical standard for the high-velocity gas, we find substantial enhancements in abundances of several molecules in outflowing material, most notably CS, SIO, and CH3OH. The SiO emission is kinematically well displaced from the bulk cloud velocity and likely arises from directly shocked material. As is the case for CO, however, the outflow features from more volatile species are centered near the cloud velocity and are often characterized by quite low rotational temperatures. We suggest that grain-grain collisions induced by velocity shear zones surrounding the outflow axes transiently desorb the grain mantles, resulting in large abundance enhancements of selected species. Similar results have recently been obtained in several other low-mass YSOs, where outflowing gas is often both kinematically and spatailly distinct, and are illustrative of the ability of accretion and outflow processes to simultaneously modify the composition of the gas and dust surrounding young stars.
The Infrared Spectrograph on the Spitzer Space Telescope was used for observations of the Kepler supernova remnant, with all four instrument modules targeted on the bright infrared knot located at 17h30m35.80s,-21d28m54.0s (J2000). The low spectral resolution modules data show a dust continuum spectrum consistent with dust grains heated by high-energy electrons, while the high resolution modules data show atomic emission line ratios consistent with excitation by a high velocity shock of greater than 100 kilometers per second and electron densities of approximately 1,000 per centimeter. The abundance ratios for the six detected elements show signs of heavy-element enhancement. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology. Support for this work was provided by NASA's Office of Space Science.
Context: The mini-spiral is a feature of the interstellar medium in the central approx.2 pc of the Galactic center. It is composed of several streamers of dust and ionised and atomic gas with temperatures between a few 100 K to 10(exp 4) K. There is evidence that these streamers are related to the so-called circumnuclear disk of molecular gas and are ionized by photons from massive, hot stars in the central parsec. Aims: We attempt to constrain the emission mechanisms and physical properties of the ionized gas and dust of the mini-spiral region with the help of our multiwavelength data sets. Methods: Our observations were carried out at 1.3 mm and 3 mm with the mm interferometric array CARMA in California in March and April 2009, with the MIR instrument VISIR at ESO's VLT in June 2006, and the NIR Bry with VLT NACO in August 2009. Results: We present high resolution maps of the mini-spiral, and obtain a spectral index of 0.5 +/- 0.25 for Sgr A *, indicating an inverted synchrotron spectrum. We find electron densities within the range 0.8-1.5 x 10(exp 4)/cu cm for the mini-spiral from the radio continuum maps, along with a dust mass contribution of approx. 0.25 Mo from the MIR dust continuum. and extinctions ranging from 1.8-3 at 2.16 microns in the Bry line. Conclusions: We observe a mixture of negative and positive spectral indices in our 1.3 mm and 3 mm observations of the extended emission of the mini-spiral, which we interpret as evidence that there are a range of contributions to the thermal free-free emission by the ionized gas emission and by dust at 1.3 mm.
This paper presents the low-resolution spectra of 170 planetary nebulae observed by IRAS, most of which were not included in the Atlas of Low-Resolution Spectra. These have been classified into eight groups based upon the spectral morphology, with emphasis on the dust continuum rather than the spectral lines. The Low-Resolution Spectrometer (LRS) spectra are nearly evenly divided between spectra which show only a dust continuum with no lines, and spectra where there are strong lines with a dust continuum appearing longwards of about 15 microns. A study has been made of the strength of the 11.3-micron PAH emission feature as a function of the nebular C/O ratio, combining ground-based and LRS data. The C/O ratio for IC 2621 is derived from IUE spectra and used in this study. The 11.3-micron feature is present with essentially constant strength in all nebulae with C/O above about 1. Only marginal evidence exists for its presence below C/O about 1 and then at a level about 5 times lower than in carbon-rich nebulae.
Resonant fluorescence of molecular hydrogen has been observed in the reflection nebula IC 63 with the IUE satellite. Both the noncoherent resonant scattering and the dissociative continuum are shown to agree well with molecular theory. Extended red emission is also found in this nebula and may be physically related to the dissociation of H2.
We have detected the T Tauri star, DO Tauri, in a 0.6'-resolution VLA map of 43.3 GHz (l = 7 mm) continuum emission. Upper limits to the flux densities at 8.4 and 22.5 GHz limit the contribution of free-free emission due to a compact ionized wind to less than 49%.
Measurements of far-infrared continuum emission from the central regions of 30 late-type galaxies, 24 of which were previously unreported, are given. Photometry covering wavelengths from 40 to 160 microns has been obtained, yielding information on luminosities, temperatures, and dust masses for most. Good correlations of the far-infrared luminosity with blue colors, reddening, and molecular line radiation are found, supporting the identification of the sources with the molecular cloud component in these galaxies, and strengthening the identification of the energy sources as the young massive stars formed from those clouds. Comparisons with 10-micron data indicate that such data are useful for statistical studies, but have too much scatter to use directly in the analysis of individual sources. Strong correlation with nonthermal radio continuum emission and radio-to-optical flux ratios suggest that massive star formation underlies a wide range of galactic activity.