Shai Hills Ghana, March 2010

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Astronomy 106

email
jfc9va at virginia.edu

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+1 434 924 3104

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P.O. Box 400325
Charlottesville, VA 22904


Research

The PRIMOS Project

Along with a small team of students and a post-doc, I've inherited the PRebiotic Interstellar MOlecular Survey (PRIMOS) from my advisor, Anthony Remijan. PRIMOS is a highly sensitive GBT spectrum of the Galactic center source Sagittarius B2(N) (Sgr B2(N)) from 1 to 50 GHz. Sgr B2(N) is likely the most complex high-mass star forming region in the Galaxy. It is host to hot X-ray emitting gas, on the order of a hundred known compact HII regions in which hydrogen around young stars is ionized, compact line emission and absorption by a spectacular diversity of molecules in hot cores, and extended emission by rotationally cold organic material. While this diversity in physical and chemical conditions can be overwhelming, it makes Sgr B2(N) a playground for exploring the limits of interstellar organic chemistry. For an overview of PRIMOS science or to access the data for use in your own science, visit the PRIMOS website.

Follow up observations with radio interferometry: the nitriles project
Analysis of PRIMOS data has inspired follow-up observations that map multiple transitions of chemically related molecules with the Compact Array in Australia and the VLA. One of the mapping projects explores the chemistry of nitriles, which are molecules with a CN triple bond, in order to test a proposed chemical formation pathway. A laboratory experiment conducted by the Pate Group microwave spectroscopy group (check them out -- well designed website, awesome instruments!) has shown that radical-radical and radical-neutral reactions and subsequent processing can account for the formation of the wide diversity of nitrile molecules observed in some regions of the ISM. A comparison of laboratory data with the PRIMOS spectrum produces evidence that this chemistry may be occuring in Sgr B2(N), but spatial distribution information (only obtainable with an interferometer) is needed to further test the hypothesis. To complete the observation, I was awarded Resident Shared Risk Observing (RSRO) time on the VLA. I spent the 2012 summer in Socorro, NM to complete my RSRO service. This was an incredible growth experience, in which I learned much about interferometric data reduction, the WIDAR correlator, and the development and decision making process for science and software at the VLA.

Automated spectral line reduction & analysis
As we enter the new age of broadband radio telescopes, an incredible wealth of spectral line data will stream in. With the upgraded VLA for example, all data is spectral in nature due to the design of the correlator, and the correlator's flexibility makes previously impossible spectral line projects easy. If we can handle this data effectively, we will very quickly build a picture of our chemical environment that is immensely more complete. To do so, the astrochemistry community must develop sophisticated methods of data reduction and analysis. PRIMOS is an optimal test case for developing automated spectral line reduction and analysis techniques, as it is an exhaustive survey of the richest known source in the Galaxy. I am working on this project currently, and may be interested in developing automated reduction and analysis techniques as a major component of my thesis work.

"Spiral arm cloud" chemistry
The first detections of molecules in the ISM were via line-of-sight absorption at optical wavelengths by CH and CN in the diffuse ISM. Radio telescopes have since been instrumental in revealing the composition of the diffuse ISM, showing the presence of primarily di- and tri-atomic molecules including NH3 , c-C3H2, H2CO CO, CS, H2S, SiO, HCO+, CH3OH, HCS+, HCN and HNC. The subject of diffuse cloud chemistry via line-of-sight absorption recently gained traction with Herschel key science projects including the PRISMAS and HEXOS projects, which have uncovered the chemistry of other small molecules including oxygenated species. PRIMOS data demonstrates the presence of a handful of larger organic molecules with no known formation paths in the diffuse ISM. "Spiral arm clouds" are diffuse clouds (n~102 - 103 cm -3 located in the Galactic plane, as opposed to high latitude clouds at high Galactic latitude.

SNR-MC interactions

I have become interested in molecular chemistry in astronomical sources whose molecular contents are poorly constrained, including supernova remnants (SNRs) interacting with an ambient interstellar medium. Massive stars explode as supernovae on timescales of 106 to 107 years, which can be less than the amount of time required for a star cluster to blow away the molecular cloud material in which it was born. This produces a situation in which a supernova remnant rams into an ambient molecular cloud, driving shocks into the molecular cloud. The number of known supernova remnant-molecular cloud (SNR-MC) systems has grown rapidly, from only a handful a dozen years ago to ~70 today. SNR-MCs may provide a statistically significant sample of shocked clumps of molecular gas, making a thorough study of shock chemistry possible. Observers have looked towards only a few SNR-MCs for molecular emission from molecules besides CO and CS, and this is becoming a hot subject in astrochemistry. In April, I conducted observations with the Onsala Space Observatory 20-meter telescpe in Onsala sweden in order to investigate these systems.