Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Dielectric Function of Astrodust and Predictions for Polarization in the 3.4$mu$m and 10$mu$m Features
128
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The dielectric function of interstellar dust material is modeled using observations of extinction and polarization in the infrared, together with estimates for the mass of interstellar dust. The astrodust material is assumed to be a mix of amorphous silicates and other materials, including hydrocarbons producing an absorption feature at 3.4$mu$m. The detailed shape of the 10$mu$m polarization profile depends on the assumed porosity and grain shape, but the 10$mu$m spectropolarimetric data are not yet good enough to clearly favor one shape over another, nor to constrain the porosity. The expected 3.4$mu$m feature polarization is consistent with existing upper limits, provided the 3.4$mu$m absorption is preferentially located in grain surface layers; a separate population of non-aligned carbonaceous grains is not required. We predict the 3.4$mu$m polarization feature to be $(Delta p)_{3.4mu{rm m}}/p(10mu{rm m})approx 0.016$, just below current upper limits. Polarization by the same grains at submm wavelengths is also calculated.
rate research
Read More
We present a detailed analysis of the Galaxy structure using an unWISE wide-field image at $3.4mu$m. We perform a 3D photometric decomposition of the Milky Way taking into account i) the projection of the Galaxy on the celestial sphere and ii) that the observer is located within the Galaxy at the solar radius. We consider a large set of photometric models starting with a pure disc model and ending with a complex model which consists of thin and thick discs plus a boxy-peanut-shaped bulge. In our final model, we incorporate many observed features of the Milky Way, such as the disc flaring and warping, several over-densities in the plane, and the dust extinction. The model of the bulge with the corresponding X-shape structure is obtained from N-body simulations of a Milky Way-like galaxy. This allows us to retrieve the parameters of the aforementioned stellar components, estimate their contribution to the total Galaxy luminosity, and constrain the position angle of the bar. The mass of the thick disc in our models is estimated to be 0.4-1.3 of that for the thin disc. The results of our decomposition can be directly compared to those obtained for external galaxies via multicomponent photometric decomposition.
We have determined the relation between the AGN luminosities at rest-frame 6 {mu}m associated to the dusty torus emission and at 2-10 keV energies using a complete, X-ray flux limited sample of 232 AGN drawn from the Bright Ultra-hard XMM-Newton Survey. The objects have intrinsic X-ray luminosities between 10^42 and 10^46 erg/s and redshifts from 0.05 to 2.8. The rest-frame 6 {mu}m luminosities were computed using data from the Wide-Field Infrared Survey Explorer and are based on a spectral energy distribution decomposition into AGN and galaxy emission. The best-fit relationship for the full sample is consistent with being linear, L_6 {mu}m $propto$ L_2-10 keV^0.99$pm$0.032, with intrinsic scatter, ~0.35 dex in log L_6 {mu}m. The L_6 {mu}m/L_2-10 keV luminosity ratio is largely independent on the line-of-sight X-ray absorption. Assuming a constant X-ray bolometric correction, the fraction of AGN bolometric luminosity reprocessed in the mid-IR decreases weakly, if at all, with the AGN luminosity, a finding at odds with simple receding torus models. Type 2 AGN have redder mid-IR continua at rest-frame wavelengths <12 {mu}m and are overall ~1.3-2 times fainter at 6 {mu}m than type 1 AGN at a given X-ray luminosity. Regardless of whether type 1 and type 2 AGN have the same or different nuclear dusty toroidal structures, our results imply that the AGN emission at rest-frame 6 {mu}m is not isotropic due to self-absorption in the dusty torus, as predicted by AGN torus models. Thus, AGN surveys at rest-frame 6 {mu}m are subject to modest dust obscuration biases.
We report measurements of the Diffuse Galactic Light (DGL) spectrum in the near-infrared, spanning the wavelength range 0.95-1.65 {mu}m by the Cosmic Infrared Background ExpeRiment (CIBER). Using the low-resolution spectrometer (LRS) calibrated for absolute spectro-photometry, we acquired long-slit spectral images of the total diffuse sky brightness towards four high-latitude fields spread over four sounding rocket flights. To separate the DGL spectrum from the total sky brightness, we correlated the spectral images with a 100 {mu}m intensity map, which traces the dust column density in optically thin regions. The measured DGL spectrum shows no resolved features and is consistent with other DGL measurements in the optical and at near-infrared wavelengths longer than 1.8 {mu}m. Our result implies that the continuum is consistently reproduced by models of scattered starlight in the Rayleigh scattering regime with a few large grains.
Local infrared (IR) luminosity functions (LFs) are necessary benchmarks for high-redshift IR galaxy evolution studies. Any accurate IR LF evolution studies require accordingly accurate local IR LFs. We present infrared galaxy LFs at redshifts redshifts of $z leq 0.3$ from AKARI space telescope, which performed an all-sky survey in six IR bands (9, 18, 65, 90, 140 and 160 micron) with 10 times better sensitivity than its precursor IRAS. Availability of 160 micron filter is critically important in accurately measuring total IR luminosity of galaxies, covering across the peak of the dust emission. By combining data from Wide-field Infrared Survey Explorer (WISE), Sloan Digital Sky Survey (SDSS) Data Release 13 (DR13), 6-degree Field Galaxy Survey (6dFGS) and the 2MASS Redshift Survey (2MRS), we created a sample of 15,638 local IR galaxies with spectroscopic redshifts, factor of 7 larger compared to previously studied AKARI -SDSS sample. After carefully correcting for volume effects in both IR and optical, the obtained IR LFs agree well with previous studies, but comes with much smaller errors. Measured local IR luminosity density is $Omega_{IR}=$ 1.19$pm$0.05 $times 10^{8}$ L$_{odot}$ Mpc$^{-3}$. The contributions from luminous infrared galaxies and ultra luminous infrared galaxies to IR are very small, 9.3 per cent and 0.9 per cent, respectively. There exists no future all sky survey in far-infrared wavelengths in the foreseeable future. The IR LFs obtained in this work will therefore remain an important benchmark for high-redshift studies for decades.
We present spectra of the 3.3 $mu$m and 11.2 $mu$m PAH features of a large number of (extra-) galactic sources, obtained with ISO-SWS. Clear variations are present in the profiles of these features. The sources are classified independently based on the 3.3 and 11.2 $mu$m feature profiles and peak positions. Correlations between these classes and those based on the 6--9 $mu$m features (Peeters et al. 2002) are found. Also, these classifications depend on the type of object. The observed pronounced contrast in the spectral variations for the CH modes (3.3 and 11.2 $mu$m bands) versus the CC modes (6.2, 7.7 and 8.6 $mu$m bands) is striking : the peak wavelengths of the features attributed to CC modes vary by $sim$15--80 cm$^{-1}$, while for the CH modes the variations are $sim$4--6.5 cm$^{-1}$. We summarize existing laboratory data and theoretical calculations of PAH molecules and complexes. In contrast to the 6.2 and 7.7 $mu$m components which are attributed to PAH cations, the 3.3 $mu$m feature appears to originate in neutral and/or negatively charged PAHs. We attribute the variations in peak position and profile of these features to the composition of the PAH family. The variations in FWHM of the 3.3 $mu$m feature remains an enigma while those of the 11.2 $mu$m can be explained by anharmonicity and molecular structure. The possible origin of the observed contrast in profile variations between the CH modes and the CC modes is highlighted.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
