The Galactic Plane Infrared Polarization Survey (GPIPS): Data Release 4

The Galactic Plane Infrared Polarization Survey (GPIPS) seeks to characterize the magnetic field in the dusty Galactic disk using near-infrared stellar polarimetry. All GPIPS observations were completed using the 1.83 m Perkins telescope and Mimir instrument. GPIPS observations surveyed 76 deg(2)of the northern Galactic plane, from Galactic longitudes 18 degrees-56 degrees and latitudes -1 degrees to +1 degrees, in theHband (1.6 mu m). Surveyed stars span 7th-16th mag, resulting in nearly 10 million stars with measured linear polarizations. Of these stars, ones withm(H) < 12.5 mag and polarization percentage uncertainties under 2% were judged to be high quality and number over one million. GPIPS data reveal plane-of-sky magnetic field orientations for numerous interstellar clouds forA(V)values to similar to 30 mag. The average sky separation of stars withm(H) < 12.5 mag is about 30 ", or about 60 per Planck polarization resolution element. Matching to Gaia DR2 showed the brightest GPIPS stars are red giants with distances in the 0.6-7.5 kpc range. Polarization orientations are mostly parallel to the Galactic disk, with some zones showing significant orientation departures. Changes in orientations are stronger as a function of Galactic longitude than of latitude. Considered at 10 ' angular scales, directions that show the greatest polarization fractions and narrowest polarization position angle distributions are confined to about 10 large, coherent structures that are not correlated with star-forming clouds. The GPIPS polarimetric and photometric data products (Data Release 4 catalogs and images) are publicly available for over 13 million stars.