Andrew M. Burkhardt

HERSCHEL OBSERVATIONS OF EXTRAORDINARY SOURCES: ANALYSIS OF THE FULL HERSCHEL/HIFI MOLECULAR LINE SURVEY OF SAGITTARIUS B2(N) ∗

A sensitive broadband molecular line survey of the Sagittarius B2(N) star-forming region has been obtained with the Heterodyne Instrument for the Far-Infrared (HIFI) instrument on the Herschel Space Observatory, offering the first high spectral resolution look at this well-studied source in a wavelength region largely inaccessible from the ground (625–157 μm). From the roughly 8000 spectral features in the survey, a total of 72 isotopologues arising from 44 different molecules have been identified, ranging from light hydrides to complex organics, and arising from a variety of environments from cold and diffuse to hot and dense gas. We present a local thermodynamic equilibrium (LTE) model to the spectral signatures of each molecule, constraining the source sizes for hot core species with complementary Submillimeter Array interferometric observations and assuming that molecules with related functional group composition are cospatial. For each molecule, a single model is given to fit all of the emission and absorption features of that species across the entire 480–1910 GHz spectral range, accounting for multiple temperature and velocity components when needed to describe the spectrum. As with other HIFI surveys toward massive star-forming regions, methanol is found to contribute more integrated line intensity to the spectrum than any other species. We discuss the molecular abundances derived for the hot core where the LTE approximation is generally found to describe the spectrum well, in comparison to abundances derived for the same molecules in the Orion KL region from a similar HIFI survey. Notably, we find significantly higher abundances of amine- and amide-bearing molecules (CH_3NH_2, CH_2NH, and NH_2CHO) toward Sgr B2(N) than Orion KL and lower abundances of some complex oxygen-bearing molecules (CH_3OCHO in particular). In addition to information on the chemical composition of the hot core, the strong far-infrared dust continuum allows a number of molecules to be detected in absorption in the Sgr B2(N) envelope for the first time at high spectral resolution, and we discuss the possible physical origin of the kinematic components observed in absorption. Additionally, from the detection of new HOCO^+ transitions in absorption compared to published HCO^+ isotopic observations, we discuss constraints on the gas-phase CO_2 abundance and compare this to observations of the ice composition in the Galactic center region, and to CO_2 abundance estimates toward other high-mass star-forming regions. The reduced HIFI spectral scan and LTE model are made available to the public as a resource for future investigations of star-forming regions in the submillimeter and far-infrared.

Detection of the aromatic molecule benzonitrile (c-C6H5CN) in the interstellar medium

A specific interstellar aromatic molecule Aromatic molecules such as polycyclic aromatic hydrocarbons (PAHs) are known to exist in the interstellar medium owing to their characteristic infrared emission features. However, the infrared emission only indicates the general class of molecule, and identifying which specific molecular species are present is difficult. McGuire et al. used radio astronomy to detect rotational transitions of benzonitrile emitted from a well-known nearby cloud of interstellar gas (see the Perspective by Joblin and Cernicharo). This molecule may be a precursor to more complex PAHs. The identification of benzonitrile sheds light on the composition of aromatic material within the interstellar medium—material that will eventually be incorporated into new stars and planets. Science, this issue p. 202; see also p. 156 Radio astronomy is used to identify the aromatic molecule benzonitrile in the interstellar medium. Polycyclic aromatic hydrocarbons and polycyclic aromatic nitrogen heterocycles are thought to be widespread throughout the universe, because these classes of molecules are probably responsible for the unidentified infrared bands, a set of emission features seen in numerous Galactic and extragalactic sources. Despite their expected ubiquity, astronomical identification of specific aromatic molecules has proven elusive. We present the discovery of benzonitrile (c-C6H5CN), one of the simplest nitrogen-bearing aromatic molecules, in the interstellar medium. We observed hyperfine-resolved transitions of benzonitrile in emission from the molecular cloud TMC-1. Simple aromatic molecules such as benzonitrile may be precursors for polycyclic aromatic hydrocarbon formation, providing a chemical link to the carriers of the unidentified infrared bands.

CSO and Carma Observations of L1157. I. A Deep Search for Hydroxylamine (NH_2OH)

A deep search for the potential glycine precursor hydroxylamine (NH_2OH) using the Caltech Submillimeter Observatory (CSO) at λ = 1.3 mm and the Combined Array for Research in Millimeter-wave Astronomy at λ = 3 mm is presented toward the molecular outflow L1157, targeting the B1 and B2 shocked regions. We report non-detections of NH_2OH in both sources. We perform a non-LTE analysis of CH_3OH observed in our CSO spectra to derive the kinetic temperatures and densities in the shocked regions. Using these parameters, we derive upper limit column densities of NH_2OH of ≤1.4 × 10^(13) cm^(−2) and ≤1.5 × 10^(13) cm^(−2) toward the B1 and B2 shocks, respectively, and upper limit relative abundances of N_(NH_2OH)/N_H_2 ≤ 1.4 x 10^(-8) and ≤1.5 × 10^(−8), respectively.

Detection of Interstellar HC5O in TMC-1 with the Green Bank Telescope

We report the detection of the carbon-chain radical HC5O for the first time in the interstellar medium toward the cold core TMC-1 using the 100 m Green Bank Telescope. We observe four hyperfine components of this radical in the rotational transition that originates from the fine structure level of its ground state and calculate an abundance of , assuming an excitation temperature of K. No indication of HC3O, HC4O, or HC6O, is found in these or archival observations of the source, while we report tentative evidence for HC7O. We compare calculated upper limits and the abundance of HC5O to predictions based on (1) the abundance trend of the analogous HC n N family in TMC-1 and (2) a gas-grain chemical model. We find that the gas-grain chemical model well reproduces the observed abundance of HC5O, as well as the upper limits of HC3O, HC6O, and HC7O, but HC4O is overproduced. The prospects for astronomical detection of both shorter and longer HC n O chains are discussed.

Detection of HC5N and HC7N Isotopologues in TMC-1 with the Green Bank Telescope

We report the first interstellar detection of DC

First Results of an ALMA Band 10 Spectral Line Survey of NGC 6334I: Detections of Glycolaldehyde (HC(O)CH2OH) and a New Compact Bipolar Outflow in HDO and CS

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Spectroscopic fits to the alma science verification band 6 survey of the orion hot core and compact ridge

N and six

Carma observations of L1157: chemical complexity in the shocked outflow

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Non-detection of HC11N towards TMC-1: constraining the chemistry of large carbon-chain molecules

C-bearing isotopologues of HC

CSO and CARMA Observations of L1157. II. Chemical Complexity in the Shocked Outflow

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