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Register a new userMeasurements of the mean diffuse galactic light spectrum in the 0.95 {mu}m to 1.65 {mu}m band from CIBER
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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.
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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.
The PAH model predicts many weak emission features in the 1-5 $mu$m region that can resolve significant questions that it has faced since its inception in the mid-80s. These features contain fundamental information about the PAH population that is inaccessible via the much stronger PAH bands in the 5-20 $mu$m region. Apart from the 3.3 $mu$m band and plateau, PAH spectroscopy across most of the 1-5 $mu$m region has been unexplored due to its low intrinsic intensity. ISO and Akari covered some of this wavelength range, but lacked the combined sensitivity and resolution to measure the predicted bands with sufficient fidelity. The spectroscopic capabilities of the NIRSpec instrument on board JWST will make it possible to measure and fully characterize many of the PAH features expected in this region. These include the fundamental, overtone and combination C-D and C$equiv$N stretching bands of deuterated PAHs, cyano-PAHs (PAH-C$equiv$ N), and the overtones and combinations of the strong PAH bands that dominate the 5-20 $mu$m region. These bands will reveal the amount of D tied up in PAHs, the PAH D/H ratio, the D distribution between PAH aliphatic and aromatic subcomponents, and delineate key stages in PAH formation and evolution on an object-by-object basis and within extended objects. If cyano-PAHs are present, these bands will also reveal the amount of cyano groups tied up in PAHs, determine the N/C ratio within that PAH subset, and distinguish between the bands near 4.5 $mu$m that arise from CD versus C$equiv$N.
We present Gran Telescopio CANARIAS CanariCam 8.7$mu$m imaging and 7.5-13$mu$m spectroscopy of six local systems known to host an active galactic nucleus (AGN) and have nuclear star formation. Our main goal is to investigate whether the molecules responsible for the 11.3$mu$m polyclyclic aromatic hydrocarbon (PAH) feature are destroyed in the close vicinity of an AGN. We detect 11.3$mu$m PAH feature emission in the nuclear regions of the galaxies as well as extended PAH emission over a few hundred parsecs. The equivalent width (EW) of the feature shows a minimum at the nucleus but increases with increasing radial distances, reaching typical star-forming values a few hundred parsecs away from the nucleus. The reduced nuclear EW are interpreted as due to increased dilution from the AGN continuum rather than destruction of the PAH molecules. We conclude that at least those molecules responsible for the 11.3$mu$m PAH feature survive in the nuclear environments as close as 10pc from the AGN and for Seyfert-like AGN luminosities. We propose that material in the dusty tori, nuclear gas disks, and/or host galaxies of AGN is likely to provide the column densities necessary to protect the PAH molecules from the AGN radiation field.
Frequency-modulated diode laser transient absorption spectra of the ethynyl radical have been recorded at wavelengths close to 1.66 $mu$m. The observed spectrum includes strong, regular, line patterns. The two main bands observed originate in the ground $tilde{X},^2Sigma^+$ state and its first excited bending vibrational level of $^2Pi$ symmetry. The upper states, of $^2Sigma^+$ symmetry at 6055.6 cm$^{-1}$ and $^2Pi$ symmetry at 6413.5 cm$^{-1}$, respectively, had not previously been observed and the data were analyzed in terms of an effective Hamiltonian representing their rotational and fine structure levels to derive parameters which can be used to calculate rotational levels up to J = 37/2 for the $^2Pi$ level and J = 29/2 for the $^2Sigma$ one. Additionally, a weaker series of lines have been assigned to absorption from the second excited bending, (020), level of $^2Sigma$ symmetry, to a previously observed state of $^2Pi$ symmetry near 6819 cm$^{-1}$. These strong absorption bands at convenient near-IR laser wavelengths will be useful for monitoring CCH radicals in chemical systems.
In this article we present the detection of the 69 {mu}m band of the crystalline olivine forsterite within the MESS key program of Herschel. We determine the temperature of the forsterite grains by fitting the 69 {mu}m band.
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