The Canadian Galactic Plane Survey

The Canadian Galactic Plane Survey (CGPS) is a project to combine radio, millimeter, and infrared surveys of the Galactic plane to provide arcminute-scale images of all major components of the interstellar medium over a large portion of the Galactic disk. We describe in detail the observations for the low-frequency component of the CGPS, the radio surveys carried out at the Dominion Radio Astrophysical Observatory (DRAO), and summarize the properties of the merged database of surveys that comprises the CGPS. The DRAO Synthesis Telescope surveys have imaged a 73° section of the Galactic plane, using ~85% of the telescope time between 1995 April and 2000 June. The observations provide simultaneous radio continuum images at two frequencies, 408 and 1420 MHz, and spectral-line images of the λ=21 cm transition of neutral atomic hydrogen. In the radio continuum at 1420 MHz, dual-polarization receivers provide images in all four Stokes parameters. The surveys cover the region 74.2d<l<147.3d, with latitude extent -3.6d<b<+5.6d at 1420 MHz and -6.7d<b<+8.7d at 408 MHz. By integration of data from single-antenna observations, the survey images provide complete information on all scales of emission structures down to the resolution limit, which is just below 1^'×1^'cscδ at 1420 MHz and 3.4‧×3.4‧cscδ at 408 MHz. The continuum images have a dynamic range of several thousand, yielding essentially noise-limited images with an rms of ~0.3 mJy beam^-1 at 1420 MHz and ~3 mJy beam^-1 at 408 MHz. The spectral-line data are noise limited with rms brightness temperature ΔT_B~3 K in a 0.82 km s^-1 channel. The complete CGPS data set, including the DRAO surveys and data at similar resolution in ¹²CO (1-0) and in infrared emission from dust, all imaged to an identical Galactic coordinate grid and map projection, are being made publicly available through the Canadian Astronomy Data Centre.