THE SPIRAL ARMS OF THE MILKY WAY: THE RELATIVE LOCATION OF EACH DIFFERENT ARM TRACER WITHIN A TYPICAL SPIRAL ARM WIDTH

Abstract

From the Sun's location in the Galactic disk, different arm tracers (CO, H I, hot dust, etc.) have been employed to locate a tangent to each spiral arm. Using all various and different observed spiral arm tracers (as published elsewhere), we embark on a new goal, namely the statistical analysis of these published data (data mining) to statistically compute the mean location of each spiral arm tracer. We show for a typical arm cross-cut, a separation of 400?pc between the mid-arm and the dust lane (at the inner edge of the arm, toward the Galactic center). Are some arms major and others minor??Separating arms into two sets, as suggested by some, we find the same arm widths between the two sets. Our interpretation is that we live in a multiple (four-arm) spiral (logarithmic) pattern (around a pitch angle of 12?) for the stars and gas in the Milky Way, with a sizable interarm separation (around 3?kpc) at the Sun's location and the same arm width for each arm (near 400?pc from mid-arm to dust lane).