▪ Abstract Our understanding of the evolution of organic molecules, and their voyage from molecular clouds to the early solar system and Earth, has changed dramatically. Incorporating recent observ...

/pdf/organic-molecules-in-the-interstellar-medium-comets-and-14nzw41xt5.pdf

Organic Molecules in the Interstellar Medium, Comets, and Meteorites: A Voyage from Dark Clouds to the Early Earth

The energy sources of nine infrared luminous galaxies (IRLGs) are diagnosed based on their ground-based 3-4 μm spectra. Both the equivalent width of the 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission feature and the 3.3 μm PAH to far-infrared luminosity ratio (L3.3/LFIR) are analyzed. Assuming that nuclear compact starburst activity in these sources produces the 3.3 μm PAH emission as strongly as that in starburst galaxies with lower far-infrared luminosities, the following results are found. For six IRLGs, both the observed equivalent widths and the L3.3/LFIR ratios are too small to explain the bulk of their far-infrared luminosities by compact starburst activity, indicating that active galactic nucleus (AGN) activity is a dominant energy source. For the other three IRLGs, while the 3.3 μm PAH equivalent widths are within the range of starburst galaxies, the L3.3/LFIR ratios after correction for screen dust extinction are a factor of ~3 smaller. The uncertainty in the dust extinction correction factor and in the scatter of the intrinsic L3.3/LFIR ratios for starburst galaxies does not allow a determination of the ultimate energy sources for these three IRLGs.

Energy Diagnoses of Nine Infrared Luminous Galaxies Based on 3-4 Micron Spectra

https://sservi.nasa.gov/wp-content/uploads/2014/03/2014-DPC-Iapetus-Organics-Icarus.pdf

Aromatic and aliphatic organic materials on Iapetus: Analysis of Cassini VIMS data

We confirm the first detection of the molecular ion H in an extragalactic object, the highly obscured ultraluminous galaxy IRAS 08572+3915 NW. We also have detected absorption lines of the fundamental band of CO in this galaxy. The CO absorption consists of a cold component close to the systemic velocity and warm, highly blueshifted and redshifted components. The warm blueshifted component is remarkably strong and broad and extends at least to -350 km s-1. Some analogies can be drawn between the H and cold CO in IRAS 08572+3915 NW and the same species seen toward the Galactic center. The profiles of the warm CO components are not those expected from a dusty torus of the type thought to obscure active galactic nuclei. They are probably formed close to the dust continuum surface near the buried and active nucleus and are probably associated with an unusual and energetic event there.

/pdf/the-interstellar-medium-of-iras-08572-3915-nw-h3-and-warm-3gma3fvoka.pdf

The Interstellar Medium of IRAS 08572+3915 NW: H3+ and Warm High-Velocity CO

We report the detection of a 9.7 ?m silicate dust absorption feature toward the Cygnus A nucleus. Its optical depth is, however, significantly smaller than that expected from the dust extinction toward the background L-band emission region (AV ~ 150 mag). We argue that the most likely explanation for the small optical depth is that the obscuring dust exists so close to the central engine that a temperature gradient occurs. Our calculation confirms that the small optical depth and the spectral energy distribution at 3-30 ?m can be quantitatively reproduced by this explanation. Combining this picture with the huge active galactic nucleus (AGN) luminosity, the emission properties of Cygnus A are consistent with those of a type 2 quasar, that is, a highly luminous AGN that is highly obscured (AV > 50 mag) by a dusty torus with an inner radius of less than 10 pc and not by greater than a few hundred parsec scale dust in the host galaxy.

The 9.7 Micron Silicate Dust Absorption toward the Cygnus A Nucleus and the Inferred Location of the Obscuring Dust

We present the first survey of the 3.4μm hydrocarbon absorption feature in active and IRAS galaxies. Comparison of our data with galactic studies of this feature provides insight into the nature of dust grains around active nuclei, and holds the potential to improve our understanding of interstellar dust.

Studies of NIR Dust Absorption Features in the Nuclei of Active and IRAS Galaxies

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Studies of NIR Dust Absorption Features in the Nuclei of Active and IRAS Galaxies