A bird’s eye view of the universe
Telescopes have come a long way since William Herschel invented the first reflecting telescope in 1789. The latest adaptation of his telescope for space astronomy, launched in 2009, has the largest mirror of its kind with a diameter of 3.5 metres and operates at infrared wavelengths of 60 to 600 microns.
“It takes pictures and measures spectra of planets in our solar system like Neptune and Jupiter as well as distant galaxies and everything in between,” said Christine Wilson, professor in the Department of Physics and Astronomy at McMaster University. “Herschel is good at seeing dust emission from galaxies and emission lines in spectra from gas in galaxies.”
Wilson has used the telescope to survey 13 nearby galaxies. “We use high resolution images to see what’s going on with those galaxies and interpret what’s happening in galaxies that are much farther away,” said Wilson. The Herschel mission ran for about four years. When the telescope ran out of liquid helium, a cooling agent, it stoppped working.
Wilson is part of a team that built SPIRE, one of Herschel’s three instruments. SPIRE collected data in the form of images and spectra. Atoms and molecules can be identified by the frequency they emit while the intensity of the lines they produce indicates their quantity. “Carbon monoxide emits very characteristic lines,” Wilson explained. “It’s a very regular pattern that’s easy to recognize.”
Initial spectral data from two galaxies showed strong lines, but the type of molecule producing some of the strongest lines was a mystery. “We didn’t know what it was,” said Wilson. “We didn’t know if it was this molecule or that molecule. If it was methanol, for example, we would have seen more lines.” After consulting with colleagues and the spectral line catalogue, the team concluded that they were looking at water.
“It was a bit of a eureka moment,” said Wilson. “The galaxy is the remnant of a merger between two galaxies. Two nuclei that came together can still be seen separately. It looked like water was coming from one nucleus and not the other. Why does one nucleus have water and the other doesn’t?” Although water is expected to be found in clouds, it’s usually absent when it freezes to dust particles and vapourizes when the dust is heated or shocked.
Wilson is currently focusing more of her research efforts on data from ALMA, the world’s most sophisticated ground-based radio telescope located in the Chilean Andes. “ALMA can see really fine detail of star formation and galaxies,” said Wilson. Astronomers from around the world, including Canada, the United States, Europe, Japan, Taiwan, Korea, and Chile, use ALMA for a wide variety of research.
My work involves all aspects of observational star formation and the molecular interstellar medium, both in our own Galaxy and in other galaxies. I am particularly interested in the properties of giant molecular clouds, the nature of the interstellar medium in dwarf galaxies, the mechanisms regulating star formation rates and efficiencies in galaxies, and the properties of low-mass protostars in nearby molecular clouds. A large part of my observational work is concentrated in the regime of millimeter-wave radio interferometry, where high-resolution images of the emission from molecules in the interstellar medium can be obtained. However, many of these problems require a multi-wavelenght approach and so I have used a variety of optical and radio telescopes, including the Submillimeter Array (SMA), the James Clerk Maxwell Telescope (JCMT), and the Herschel Space Observatory . In 2013-2014 I was on research leave at the Atacama Large Millimeter Array (ALMA) and the North American ALMA Science Center .
Here are some of the projects that my group is currently working on:
- JINGLE, a survey of ~200 nearby galaxies in CO and dust emission using the JCMT
- a large survey of HI-selected galaxies within 25 Mpc to study the dense molecular gas associated with star formation, the gas-to-dust mass ratio, and to look for variations and correlations with galaxy type, mass, star formation rate, metallicity, etc. (The JCMT Nearby Galaxy Legacy Survey, with former graduate student Angus Mok, and roughly 50 collaborators).
- a detailed study of the dense gas in the nearest interacting galaxy system known as "the Antennae" using ALMA and Herschel (involving graduate student Ashley Bemis and former graduate student Max Schirm)
- a major survey of 14 nearby luminous infrared galaxies to determine the distribution, kinematics, and physical conditions of the gas and dust, to compare with simulations of galaxy mergers to understand how the gas and star formation rates evolve during the merger process, and as a well-studied local sample to understand high-redshift submillimeter galaxies (with former graduate student Kaz Sliwa and various collaborators)
From 1999-2014 I was the Canadian Project Scientist for the Atacama Large Millimeter Array (ALMA), which was recommended as the highest priority for Canadian participation in a major, new, ground-based observatory in the report of the Long Range Planning Panel, "The Origins of Structure in the Universe" . ALMA began Early Science observations in September 2011. I am an Associate Scientist with the SPIRE instrument for the Herschel Space Observatory , which operated from 2009 to 2013. I am also a member of the Board of Trustess of Associate Universities, Inc.
Here is where you can find my 2013-2014 sabbatical blog which has both science and personal entries.
Star formation and the interstellar medium in galaxies; observational radio and far-infrared astronomy.
- "JINGLE, a JCMT legacy survey of dust and gas for galaxy evolution studies - I. Survey overview and first results", A. Saintonge, C. D. Wilson, T. Xiao, et al., MNRAS, 481, 3497 (2018)
- "Exploring the CO/CN line ratio in nearby galaxies with the ALMA archive", C. D. WIlson, MNRAS, 477, 2926 (2018)
- "The JCMT nearby galaxies legacy survey - X. Environmental effects on the molecular gas and star formation properties of spiral galaxies ", A. Mok, C. D. Wilson, et al., MNRAS, 456, 4384 (2016)
- "The Dense Gas in the Largest Molecular Complexes of the Antennae: HCN and HCO+ Observations of NGC 4038/39 Using ALMA ", M. R. P. Schirm, C. D. Wilson, S. C. Madden and D. L. Clements, ApJ, 823, 87 (2015)
- "Extreme Dust Disks in Arp 220 as Revealed by ALMA ", C. D. Wilson, N. Rangwala, J. Glenn, et al., ApJ, 789, L36 (2014)
- "Herschel-SPIRE Fourier Transform Spectrometer Observations of Excited CO and [C I] in the Antennae (NGC 4038/39): Warm and Cold Molecular Gas ", M. R. P. Schirm, C. D. Wilson, T. J. Parkin, et al., ApJ, 781, 101 (2014)
- "Regional Variations in the Dense Gas Heating and Cooling in M51 from Herschel Far-infrared Spectroscopy ", T. J. Parkin, C. D. Wilson, M. R. P. Schirm, et al. ApJ, 776, 65 (2013)
Department of Physics & Astronomy
Dear Prospective Graduate Student,
Star formation is one of the critical processes that drives galaxy evolution in the local universe. Yet the underlying physics of the dependence of the star formation process on the properties of the interstellar medium, which provides the fuel for star formation, remains poorly understood. The structure of the interstellar medium itself can in turn be affected by the presence of star formation, through heating, ionization, and shocks, leading to a complex interplay and exchange of energy and matter between gas and stars.
My work involves all aspects of observational star formation and the molecular interstellar medium, both in our own Galaxy and in other galaxies. My recent work with my students and postdoc includes: a survey of the effects of environment on the molecular gas in galaxies (with Angus Mok, currently a postdoc at the University of Toledo); a large survey of nearby luminous infrared galaxies to understand star formation in extreme environments (with Kaz Sliwa, currently employed by EA Kitchener); a survey of the warm dense molecular gas in two nearby interacting galaxy systems to determine the gas mass and and star formation properties (with Max Schirm, currently employed by EA Kitchener); studying the critical phase in the formation of a massive star when its ionizing radiation starts to present a barrier to continued accretion (with Pam Klaassen, currently on staff at the Astronomy Technology Centre in Edinburgh), and measuring the mass function of massive clumps of gas in several nearby molecular clouds to try to understand the earliest phases of massive star formation (with Mike Reid, currently an Assistant Professor at the University of Toronto).
I am the only radio astronomy faculty member at McMaster and I also have experience working with data at optical and infrared wavelengths. I have been involved with the Atacama Large Millimeter Array (ALMA) for over a decade. ALMA is a large international collaboration involving Europe, North America, and Japan and recently completed its construction in northern Chile. ALMA began "Early Science" observations in 2011 and my students and I have been successful in getting observing time with ALMA . In addition to observing with ground-based telescopes like the James Clerk Maxwell Telescope (JCMT) and the Submillimeter Array (SMA), I also use data from the Herschel Space Observatory, which operated from 2009-2013. I'm currently putting a major effort into two new large surveys of nearby galaxies with the JCMT, as well as continuing involvement in large surveys using data from Herschel. All these surveys have lots of scope for graduate students to get involved.
I currently have 2 Ph.D. students (Nathan Brunetti, Hao He) and 1 M.Sc. student (Blake Ledger) working with me, along with co-supervising Ph.D. student Ryan Chown with Prof. Laura Parker. I plan to take on one or two new students in fall 2021; co-supervision with another McMaster faculty member is a possibility. I like to start new M.Sc. students on a project for which I have the data already. I have lots of possibilities for M.Sc. projects at the moment, such as studying the dust content of nearby galaxies to measure how the gas content varies with galaxy type or using Herschel observations to study the earliest phases of low mass or massive star formation in a nearby molecular cloud. With Ph.D. students, I like to give them time to define their own project and I don't worry too much if it takes a year or so to settle on a project and start taking and analyzing data. My Ph.D. students often do a lot of observing and rapidly reach the point where they are doing all their own observations. There is a lot of scope for potential Ph.D. projects in the surveys I'm involved with, or you can define your own project from scratch.
Please feel free to contact me if you think this is a research area you might be interested in or if you have any other questions.