Year: 2021
Type: article
Abstract: The PAH model predicts many weak emission features in the 1–5 μm 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 μm region. Apart from the 3.3 μm band and plateau, PAH spectroscopy across most of the 1–5 μm 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 ≡ N stretching bands of deuterated PAHs, cyano-PAHs (PAH-C≡N), and the overtones and combinations of the strong PAH bands that dominate the 5–20 μm 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 μm that arise from CD versus C ≡ N.
Authors: L. J. Allamandola, C. Boersma, T. J. Lee, J. D. Bregman, P. Temi
Institution: Ames Research Center
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Awards: G2418495314, G3137953545, THE PURPOSE OF OUR PROPOSED RESEARCH IS TO MODEL AND CALIBRATE THE PAH INDICATORS BETWEEN AND WITHIN A VARIETY OF OBJECTS PROBING DIFFERENT TYPES OF ASTROPHYSICAL ENVIRONMENTS. MUCH OF THE RESEARCH WILL RELY ON THE TOOLS AND INNOVATIVE PARADIGMS DEVELOPED AS PART OF THE NASA AMES PAH IR SPECTROSCOPIC DATABASE (PAHDB; HTTP://WWW.ASTROCHEM.ORG/PAHDB/). IN ANTICIPATION OF JWST CONSIDERABLE EFFORT WILL BE PUT INTO EXTENDING AND PREPARING PAHDB TO BE THE GO-TO TOOLKIT FOR ASTRONOMICAL DATA ANALYZES AND INTERPRETATION. THIS WILL BE ACHIEVED BY IMPROVING THE CONTENT TOOLS WEBSITE EMISSION MODELS FITTING ALGORITHMS ETC. THAT MAKE UP PAHDB., THE OBJECTIVES OF THIS PROPOSAL ARE TO PROVIDE DIAGNOSTIC TOOLS TO SEARCH FOR THE PRESENCE OF CARBON MATERIALS IN SPACE AND STUDY THEIR EVOLUTION. TO THIS END WE INTEND TO MEASURE IN THE LABORATORY THE SPECTRAL PROPERTIES AND CHARACTERISTICS OF POLYCYCLIC AROMATIC HYDROCARBONS (PAHS) AND CARBON-BEARING MOLECULES CLUSTERS AND NANOPARTICLES IN EMISSION USING TWO COMPLEMENTARY HIGHLY-SENSITIVE LASER BASED TECHNIQUES LASER INDUCED FLUORESCENCE (LIF) AND LASER INDUCED INCANDESCENCE (LII). THESE LABORATORY MEASUREMENTS PERFORMED UNDER ASTROPHYSICALLY RELEVANT CONDITIONS WILL HELP DETECT AND CHARACTERIZE THE GAS PHASE MOLECULES AND CLUSTERS AS WELL AS THE SOLID GRAINS (DUST PARTICLES). THE COSMIC SIMULATION FACILITY (COSMIC) DEVELOPED AT NASA AMES WILL BE USED TO STUDY NEUTRAL AND IONIZED MOLECULES AND CLUSTERS IN A PULSED SUPERSONIC JET-COOLED PLASMA EXPANSION I.E. ISOLATED IN A COLLISION-FREE ENVIRONMENT AND AT LOW TEMPERATURE (50-100K) REPRESENTATIVE OF THE INTERSTELLAR ENVIRONMENT. WE INTEND TO BUILD AN EXTENSIVE GAS-PHASE EMISSION DATABASE FOR INTERSTELLAR ANALOGS OF NEUTRAL AND IONIC PAHS PAHCLUSTERS AND LARGE CARBON MOLECULES THAT CAN BE DIRECTLY COMPARED TO SPACE DATA FOR THE UNAMBIGUOUS DETECTION OF SPECIFIC SPECIES IN SPACE. IN PARTICULAR PAH-RELATED PHOTOPRODUCTS SUCH AS HYDROGENATED PAHS (HN-PAHS) NITROGENATED PAHS (PANHS) AND POLYYNYL-SUBSTITUTED PAHS WILL BE CONSIDERED IN THIS PROJECT SINCE THEY ARE PROBABLY PRESENT IN THE ISM AND MAY CONTRIBUTE TO THE OBSERVED AROMATIC EMISSION BANDS.
OpenAlex ID: W3193718067