THE GREEN BANK TELESCOPE H II REGION DISCOVERY SURVEY. II. THE SOURCE CATALOG

Abstract

The Green Bank Telescope HII Region Discovery Survey has doubled the number\nof known HII regions in the Galactic zone 343deg.\\leql\\leq67deg. with\n|b|\\leq1deg. We detected 603 discrete hydrogen radio recombination line (RRL)\ncomponents at 9GHz (3cm) from 448 targets. Our targets were selected based on\nspatially coincident mid-infrared and 20cm radio continuum emission. Such\nsources are almost invariably HII regions; we detected hydrogen RRL emission\nfrom 95% of our target sample. The sensitivity of the Green Bank Telescope and\nthe power of its spectrometer together made this survey possible. Here we\nprovide a catalog of the measured properties of the RRL and continuum emission\nfrom the survey nebulae. The derived survey completeness limit, 180mJy at 9GHz,\nis sufficient to detect all HII regions ionized by single O-stars to a distance\nof 12kpc. These recently discovered nebulae share the same distribution on the\nsky as does the previously known census of Galactic HII regions. On average,\nhowever, the new nebulae have fainter continuum fluxes, smaller continuum\nangular sizes, fainter RRL intensities and smaller RRL line widths. Though\nsmall in angular size, many of our new nebulae show little spatial correlation\nwith tracers associated with extremely young HII regions, implying that our\nsample spans a range of evolutionary states. We discovered 34 first quadrant\nnegative-velocity HII regions, which lie at extreme distances from the Sun and\nappear to be part of the Outer Arm. We found RRL emission from 207 Spitzer\nGLIMPSE 8.0{\\mu}m "bubble" sources, 65 of which have been cataloged previously.\nIt thus appears that nearly all GLIMPSE bubbles are HII regions and that\n\\sim50% of all Galactic HII regions have a bubble morphology at 8.0{\\mu}m.\n