Selected in Cycle 8

HyGAL: Characterizing the Galactic Interstellar Medium with Hydrides
PI: David Neufeld (Johns Hopkins University) and Peter Schilke (University of Cologne)
Proposal ID: 08_0038
Instrument: GREAT

Abstract Excerpt: By means of absorption-line spectroscopy towards 22 background Terahertz continuum sources widely distributed within the Galactic plane, we will obtain robust measurements of the column densities of six hydride molecules (OH+, H2O+, ArH+, SH, OH, and CH) and two key atomic constituents (C+ and O) within the diffuse ISM. These observations will allow us to address several related questions: (1) What is the distribution function of H2 fraction in the ISM? (2) How does the density of low-energy cosmic-rays vary within the Galaxy? (3) What is the nature of interstellar turbulence (e.g. typical shear or shock velocities), and what mechanisms lead to its dissipation?

The anticipated results are (1) a determination of the distribution function for the H2 fraction in the Galaxy, and how it varies; (2) a determination of the cosmic-ray ionization rate and how it varies; (3) an improved characterization of turbulence in the diffuse ISM, and its dissipation; (4) the provision of enhanced data products that will serve as a legacy for future ISM studies.

FIELDMAPS: Filaments Extremely Long and Dark: A Magnetic Polarization Survey (Pilot Legacy Program)
PI: Ian Stephens (Harvard & Smithsonian Center for Astrophysics)
Proposal ID: 08_0186
Instrument: HAWC+

Abstract Excerpt: Molecular gas in a galaxy generally follows the spiral arms. In the Milky Way, the densest of this molecular gas can form long, velocity-coherent filaments parallel and in close proximity to the Galactic plane. These dense filaments make up the 'skeleton' of molecular gas of the Milky Way - akin to the dark dust lanes seen in nearby spiral galaxies - and thus have been called 'bones.' For the early stages of star formation, these bones represent the largest star-forming structures in the Galaxy, and previous studies suggest that magnetic fields are critical to their formation. Our pilot survey of 2 bones show that HAWC+ can detect polarization over large angular extents with modest integration time. To understand how gas collects in the magnetized spiral potential, we propose a legacy survey to probe the magnetic fields across the entire extent of 8 additional bones (for a total of 10). We will use these observations in combination with new magnetohydrodynamical simulations of galactic formation of bones to investigate (1) the role of magnetic fields in the formation of bones, (2) how the field varies between arm and inter-arm bones, and (3) whether or not fields bend into filaments to build gas flows to the largest gravitational potential well.

SOFIA Heralds a New Era of Measuring the Magnetic Fields of Galaxies (Pilot Legacy Program)
PI: Enrique Lopez-Rodriguez (SOFIA Science Center)
Proposal ID: 08_0012
Instrument: HAWC+
Team website: http://galmagfields.com/ (including data, tools and publications)

Abstract Excerpt: Our team has made important and unexpected discoveries about the role of the magnetic fields in nearby galaxies. We have found a) that galaxies typically host large-scale and coherent magnetic fields along the spiral arms, b) magnetic field strengths of ~uG with similar contributions from the random and ordered field components, and c) magnetic fields oriented along galactic outflows that are likely responsible for magnetizing the IGM. To date, these results have mostly emerged from single wavelength regimes: radio synchrotron polarization tracing the large-scale field structure in the ionized gas, and optical studies to investigate the effect of scattering and/or extinction by the ISM. These studies access the field on vastly different spatial scales and within different ISM phases. However, the effect of magnetic fields in dense regions of the ISM, outflows, and the ISM of merging galaxies are still poorly described. SOFIA/HAWC+ is key to provide a complete picture using far-infrared (FIR) polarimetric observations. This Joint Legacy Program aims to construct a comprehensive empirical picture of the magnetic field strength and structure in multiphase ISM of galaxies. Using HAWC+, we will conduct a FIR polarimetric survey covering the full disk of nearby galaxies.

Selected in Cycle 7

Constraining Recent Star Formation in the Galactic Center
PI: Matthew Hankins, Caltech
Proposal ID: 07_0189
Instrument: FORCAST
Status: Completed

The Galactic Center presents the most extreme conditions for star formation, containing more than 80 percent of the Milky Way Galaxy’s dense molecular gas, high temperatures, significant turbulence, complex magnetic fields, and a strong gravitational potential well. Despite the large amount of dense gas, observations reveal that the rate of star formation is only 0.1 solar masses per year out of the 1.2 solar masses per year produced by the entire galaxy -- 10 times less than predictions by current theoretical models. 

This program aims at providing high-quality mosaics of bright infrared regions within the Galactic Center using the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST), which excels at producing images and spectroscopic data from infrared-bright areas. The FORCAST 25- and 37-micron bands will be used to create a searchable mid-infrared map of the Galactic Center and a point source catalog with an unprecedented spatial resolution -- six times higher than past observations. 

These infrared maps will greatly aid in the creation of a census of massive young stellar objects, thereby updating constraints for the star formation rate in the Galactic Center and improve star formation models for this region.

This legacy program is now completed!

The inaugural Legacy Program used the FORCAST instrument to observe the Galactic Center using the 25-micron and 37-micron bands. The data have unprecedented spatial resolution – six times higher than past observations — resulting in a vastly improved view of warm dust in the center of the galaxy and revealing signatures of star formation in exquisite detail.

FORCAST created high-quality mosaics of the most active star forming portions of the inner ~200 pc of the galaxy with an angular resolution of 2.3" and 3.4" for the 25 and 37 μm observations, respectively. They cover more than 99% of the hard saturated area in the corresponding Spitzer/MIPS mosaic. An overview paper meant to accompany the first survey data release has recently been published in ApJ. The data are available publicly available in the archive for further research.

Radiative and Mechanical Feedback in Regions of Massive Star Formation 
Co-PIs: Alexander G.G.M. Tielens, University of Maryland; Nicola Schneider, University of Cologne, Germany
Proposal ID: 07_0077
Instrument: GREAT
Team website: https://feedback.astro.umd.edu/index.html

Massive stars are powerful and dynamic energy sources for the interstellar medium, capable of hindering star formation through molecular cloud dissolution or acting as a catalyst through cloud compression. Studying the radiative and mechanical feedback processes of massive stars on their environments therefore yields information about the evolution of the interstellar medium. In a sense, this SOFIA Legacy Program is the expansion of the study of the Orion Nebula published in Nature (see above) to other massive star-forming regions in our galaxy. This program will survey 11 regions including quintessential representatives of their type, including single O- or B-stars, small groups of O stars, rich stellar clusters, and mini starbursts, for a big-picture look at the interaction of massive stars with the interstellar medium throughout the universe.