The BU-FCRAO Galactic Ring Survey: Third Data Release

The Boston University-Five College Radio Astronomy Observatory Milky Way Galactic Ring Survey continues to map J = 1 → 0 CO emission in the First Galactic Quadrant with an excellent combination of sensitivity (0.2 K), angular resolution (45), and spectral resolution (0.2 km s). The GRS constitutes a superb database to investigate molecular cloud structure since it covers large areas of the sky on a completely sampled grid. Here we present images from our Third Release data (www.bu.edu/grs), covering 50 square degrees from 15 > l > 52 & | b |≤ 1. 1. What is the Galactic Ring Survey? The Boston University-Five College Radio Astronomy Observatory (BU-FCRAO) Milky Way Galactic Ring Survey (GRS) images CO from molecular, star– forming clouds in the first Galactic quadrant. We completed FCRAO 14 m observations of nearly 45 square degrees of our target survey range, 15 > l > 52 & | b |≤ 1, at the writing of this text. We employed a number of detection and mapping schemes to obtain the CO J = 1 → 0 emission distribution at ν0 = 110.2 GHz. For the first several seasons (pre-January 2002), we used a correlator system with a bandwidth of 40 MHz and a resolution of 78 kHz or 0.25 km s at 110.2 GHz. In Jan. 2002, we used a new set of correlators to obtain an effective bandwidth of 90 MHz between two IF modules. This allows us to sample all Galactic emission for l ≥ 15. We use the FCRAO multipixel array receiver, SEQUIOA. Prior to January 2002, SEQUOIA consisted of 16–3 mm wavelength receivers. This was doubled in January 2002, improving our sensitivity. On-the-Fly mapping was also included at FCRAO after January 2002. This has lead to a significant improvement in our ability to map large areas of the sky. In less than 1.5 years (since January 2002), we have obtained twice as much area as the previous 4+ years of observing. 2. Why are we doing it? Obtaining distances in the inner Galaxy is difficult because of source confusion along the line–of–sight, but essential for understanding the evolution of the