- Professor of Astronomy
The interstellar medium of the Galaxy is the great reservoir from which stars are born and to which they return much of their mass. Composed primarily of H and He, the interstellar medium can take many forms depending on the temperature, density, and radiation field. Under certain conditions, the majority of the H will be in molecular form. The resulting aggregations of molecular gas can come in 2 basic types: large entities which can encompass up to a million solar masses and extend up to 50 parsecs, or distinctly smaller objects with masses less than a thousand solar masses and sizes on the order of a few parsecs. The smaller clouds can be subdivided into 3 basic kinds of objects: diffuse, translucent, and dark clouds, depending on their opacity to ultraviolet radiation and to certain considerations involving their astrochemistry.
My past work has primarily focused on translucent molecular clouds. These objects can be studied both by optical and radio techniques. Their chemistry is simpler than that of the dark molecular clouds but, unlike the diffuse clouds, chemical species more complex than diatomics can be found (such as H2CO, C3H2, etc.). Although translucent clouds are distributed throughout the Galactic plane, they are most easily seen at high Galactic latitudes, away from the background confusion caused by dark clouds and giant molecular clouds along the Galactic plane. The overwhelming majority of the so-called high-latitude molecular clouds turn out to be translucent clouds. In the last decade, my research has focussed on three principal areas: 1) The large-scale distribution of molecular gas at high Galactic latitudes. 2) Quantifying the turbulence characteristics of small molecular clouds. 3) Developing a new technique to obtain the mass of small molecular clouds.
I am currently studying the diffuse molecular component of the ISM (i.e., the atomic/molecular interface in small interstellar clouds) using the CH 3335 MHz emission line and the OH 1665 and 1667 MHz lines. I have also begun studying intermediate velocity molecular clouds with my graduate student, Allison Smith.
List of Past Graduate Students Receiving Degrees:
John Geremia, MS, 1994. Master’s Thesis title: “The Excitation Temperature of CH in Diffuse Molecular Clouds.”
Sharon Holcomb, MS, 1997, Master’s Thesis title: “A Survey of High-Latitude Molecular Clouds in the Southern Galactic Hemisphere.”
Thomas Hearty, Ph.D., 1997, Dissertation title: “Star Formation at High Galactic Latitude.”
Raymond Chastain, Ph.D., 2005, Dissertation title: “A Study of Three Molecular Structures at High Galactic Latitude.”
Elizabeth Wennerstrom, MS, 2007, Master’s Thesis title: “A Survey of Hydroxyl in Three Translucent Molecular Clouds.”
Adam Schneider, MS, 2008, Master’s Thesis title: “A Search for Young Stellar Objects in MBM 12.”
Marcus Alexander, MS, 2008, Master’s Thesis title: “Gaussian Deconvolution of 21 cm HI Spectra.”
Samantha Blair, Ph.D., 2008, Dissertation title: “A Search for Prebiotic Organic Molecules in the Outer Galaxy.”
David Cotten, Ph.D., 2011, Dissertation title: “Diffuse Molecular Gas in Cloud Envelopes and the Galaxy.”
Allison J. Smith, MS, 2013, Master’s Thesis title: “Intermediate Velocity Molecular Clouds at High Galactic Latitude.”
“AzTEC 1.1 mm Observations of the MBM 12 Molecular Cloud,” M.J. Kim, S. Kim, M.S. Yun, G.W. Wilson, I. Aretxaga, J.P. Williams, D.H. Hughes, A. Humphrey, J.E. Austermann, T.A. Perera, P.D. Mauskopf, L. Magnani, and Y.-W. Kang, Astrophys. J., 746, 11 (2012).
“Molecular gas and stars in the translucent cloud MBM 18 (LDN 1569),” J. Brand, J.G.A. Wouterloot, & L. Magnani ,Astron. & Astrophys., 547, 85 (2012).
“Hydroxyl as a Tracer of H2 in the Envelope of MBM40,” D.L. Cotten, L. Magnani, E.A. Wennerstrom, J.S. Onello, K.A. Douglas, Astron. J., 144, 163 (2012).