The magnetic field threading the Galaxy's interstellar medium (ISM) is poorly revealed and its roles in cloud and star formation are unclear. Dr. Dan Clemens (Boston University) and his team are addressing these problems using a powerful instrument (Mimir, a near-infrared wide-field imaging polarimeter) coupled with substantial observing time (about 50 nights per year, with key project status) on the 1.8-meter Perkins telescope outside Flagstaff, Arizona. Presently, the team is about midway through the telescopic observations comprising the Galactic Plane Infrared Polarization Survey (GPIPS) and, through this award, will complete all GPIPS observations over the next four years. GPIPS expands existing optical/infrared (OIR) probes of the ISM magnetic field by four to five orders of magnitude, to about 500,000 stellar polarizations, and reveals the field five times more distant than seen before using OIR methods, to and beyond the nearest spiral arm and through dark clouds to a visual extinction of 25 magnitudes. GPIPS represents a huge increase in the data available for probing the Milky Way's magnetic field. The inner midplane region offers a wealth of correlative data concerning the stellar targets, as well as revealing a wide variety of distinctly different environments in the diffuse and dense ISM. The new magnetic field insight GPIPS will uncover will help test models across many size scales to gauge the role of the magnetic field in a wide range of ISM environments in the Galaxy.
The public release of high-quality, well-calibrated data products will allow other astronomers to mine the transformative GPIPS data for new discoveries, and to bring vital insight to other studies. The methods and approaches pioneered by GPIPS will guide future large-scale and follow-up studies. During the first three years of the survey, GPIPS and Mimir have had major impacts on the career development of research students, comprising the capstone astronomical experience for about 30 Boston University students to date, and enabling visitors and collaborators to obtain new data for a wide variety of projects. The team's suite of publically-available software tools and web sites make access to, and science with, Mimir data easy and efficient. Over the next four years, the team will leverage this base to higher levels of impact by developing and serving out a series of webcasts and podcasts, both for the general public on topics such as infrared astronomy, polarimetry, and magnetic fields, and for the research community (the GPIPS data products, the Mimir instrument and software). Finally, members of the team will work with the Boston University Scientific Visualization Center to develop exportable tools and/or shows to view and interact with the three-dimensional decomposition of the GPIPS data set and its relationships to other tracers of the ISM.
, which is a detailed examination of the the nature of the magnetic fields present in the interstellar space comprising the thin disk of our Milky Way galaxy. Our method of detection is to use near-infrared polarimetry of the light coming from unpolarized background stars. The intervening gas and dust clouds impress a weak linear polarization on the light that encodes the orientation of the magnetic field on the plane of the sky. In going to infrared wavelengths, GPIPS probed to farther distances and with better immunity to opaque dust effects than any previous survey. For this project period, finishing GPIPS took the form of completing all of the remaining telescopic observations, using the near-infrared imaging polarimeter instrument, Mimir, on the 1.8m Perkins telescope, located outside Flagstaff, Arizona. We did so, obtaining the final observation in October of 2013. In total, GPIPS utilized over 360 Perkins nights, spanning 8 years of observations. In addition, we fully processed the roughly 2 million images we obtained, generated high-level data products (deep, coadded images and catalogs of steller brightness and polarization) containing magnetic field probing information toward over 1 million stars. This represents a factor of 10,000 to 100,000 improvement over all previous polarization surveys covering the disk of the Milky Way. These data were checked for quality and robustness and have been electronically served out to the astronomical community and to the public via our website since March 2014. New astronomical science, using early GPIPS data and/or deeper Mimir observations, was also accomplished during this project period, resulting in some 22 refereed journal articles and nearly 50 presentations and exhibits. These studies included the first fully resolved map of magnetic field strength for a galactic molecular cloud, a measurement of mean magnetic field strengths associated with stellar wind driven bubbles in the galactic interstellar medium, full-galaxy polarization maps of three Milky Way analog external galaxies, and collaborative studies utilizing Mimir data that probe the nature of interstellar turbulence and magnetic fields in star-forming settings. The project was also very effective in helping to grow the scientific and technical work force. Five graduate students, seven undergraduate students, and three high school students all received training in astronomical observations, instruments, data collection and processing, computer programming, and scientific analyses and authorship. One PhD was earned by a project student and two undergraduates successfully defended Senior theses, based on research associated with GPIPS and/or Mimir. Twelve non-major undergraduates and one college dean took a field trip to Arizona (with the PI) to operate Mimir on the Perkins telescope, as a value-added classroom experience. A public 'roll-out' of GPIPS took place at the January 2013 American Astronomical Society meeting in Long Beach, CA, where our team exhibited a 40 by 3 foot banner that displayed (only!) 10% of the GPIPS data (since displaying all would have left the banner fully black). That banner was again displayed as part of a Q&A session after the PI's public presentation at the Boston Museum of Science in August 2013. The GPIPS data are served out via a dedicated website. That website also described the progress of the survey, in near real-time, and contains information on the goals, design, and implementation of the survey. A second dedicated website maintains current information about the Mimir instrument, so that potential users may plan how best to use it to collect their data. This site also serves out the 8 high-level computer software systems that reduce and analyze Mimir data, including all the GPIPS data. These systems include some 0.5 million lines of IDL code written within our research group as part of this project and its predecessor. All of this software, as well as example data, are available for download and use by the astronomical community and/or the public. The supporting images show some of the students involved in this project, the telescope and instrument, and some of the data products comprising the GPIPS repository of high-level results.
