The Canadian Galactic Plane Survey (CGPS) is a project to combine radio, millimetre and infrared surveys of the Galactic Plane to provide arc-minute 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 April 1995 and June 2000. The observations provide simultaneous radio continuum images at two frequencies, 408 MHz and 1420 MHz, and spectralline images of the λ21-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 74.2 • < < 147.3 • , with latitude extent of −3.6 • < b < +5.6 • at 1420 MHz and −6.7 • < b < +8.7 • 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 cosec(δ) at 1420 MHz, and 3.4 × 3.4 cosec(δ) at 408 MHz. The continuum images have dynamic range of several thousand, yielding essentially noise-limited images with rms of ∼0.3 mJy/beam at 1420 MHz and ∼3 mJy/beam at 408 MHz. The spectral-line data are noise limited with rms brightness temperature ∆T 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 12 CO (1-0) and in infrared emission from dust, all imaged to an identical Galactic co-ordinate grid and map projection, are being made publicly available through the Canadian Astronomy Data Centre.

To investigate the fundamental principles of H 2 formation in a giant molecular cloud, we derive the Hi and H 2 surface density (Σ Hi and Σ H2 ) images of the Perseus molecular cloud on sub-pc scales (∼0.4 pc). We use the far-infrared data from the Improved Reprocessing of the IRAS Survey and the V -band extinction image provided by the COMPLETE Survey to estimate the dust column density image of Perseus. In combination with the Hi data from the Galactic Arecibo L-band Feed Array Hi Survey and an estimate of the local dust-to-gas ratio, we then derive the Σ H2 distribution across Perseus. We find a relatively uniform Σ Hi ∼ 6-8 M pc −2 for both dark and star-forming regions, suggesting a minimum Hi surface density required to shield H 2 against photodissociation. As a result, a remarkably tight and consistent relation is found between Σ H2 /Σ Hi and Σ Hi + Σ H2 . The transition between the Hi-and H 2 -dominated regions occurs at N (Hi) + 2N (H 2 ) ∼ (8-14) × 10 20 cm −2 . Our findings are consistent with predictions for H 2 formation in equilibrium, suggesting that turbulence may not be of primary importance for H 2 formation. However, the importance of warm neutral medium for H 2 shielding, internal radiation field, and the timescale of H 2 formation still remain as open questions. We also compare H 2 and CO distributions and estimate the fraction of "CO-dark" gas, f DG ∼ 0.3. While significant spatial variations of f DG are found, we do not find a clear correlation with the mean V -band extinction.

We present large ( ) and sensitive continuum maps at 850 and 450 mm of the NGC 1333 star formation 13 # 18 region. We identify 33 submillimeter sources, some of which are extended and may contain multiple condensations. Very few of the submillimeter sources have optical or near-IR counterparts. In addition to the previously known bright class 0 sources, this survey suggests that many of the fainter sources are also likely to be very young low-mass protostars. We find several dust ridges and shells formed by outflows in the cloud, and in two cases we identify protostellar sources whose formation is likely to have been triggered by powerful outflow bow shocks. Thus, outflows have influenced the structure and evolution of the cloud over the entire area we have mapped. We derive a shallow dust clump mass spectrum, with down to rather low masses, suggesting a Ϫ1.4dN/dM ∝ M large population of dust clumps in the brown dwarf mass range.