VLA-GBT Wide-band Galactic Plane Survey

In this white paper we discuss strategies for a wide-band continuum and spectral line galactic plane survey in the l-band exploiting the power of the vla’s widar correlator for simultaneous high resolution observations of the h  21cm line, all four oh transitions, 18 radio recombination lines (both h and c), and the 1066mhz transition of formaldehyde. All other existing surveys of the galactic plane in the radio bands are narrow-band surveys. This new survey, using the wide-band capabilities of the evla, besides being able to provide significantly deeper and higher resolution images (up to 10× improvement over cgps in sensitivity and 2−3× improvement in resolution), will for the first time also provide spectral index (si) and rotation measure (rm) maps. The si and rm maps will be the new scientific products (as against improvements over existing products) not available via existing surveys. To allow sensitivity-limited wide-band reconstruction of the omnipresent extended emission and the spatially resolved spectral distribution in the plane, we will also combine these evla observations with similar wide-band observations with the gbt using the vegas back-end. New development in imaging algorithms enable these capabilities by allowing correction for the frequency and time-variable antenna primary beams and reconstruction of the spectral index distribution even for the extended emission at full spatial resolution (as against at the resolution at the low-frequency end of the observing band). Our experience with processing data from two earlier pilot projects (project id vla/10a-148, VLA/11B-157 and GBT/12A-355 & GBT/14A-252) and careful numerical simulations we have done, suggests that the wide-band mosaic imaging performance for total power and spectral index mapping is excellent, all the required algorithmic components exist and the extra computing load looks tractable. Further work is in progress to adopt and deploy these algorithms on High Performance Computing (HPC) platforms to counter the increased computing resources required by these advanced algorithms. Developing an automated (or semi-automated) imaging pipeline and reliable automatic RFI removal remains a challenge, but looks possible with some extra effort. We include brief description of some of the scientific goals possible with such a survey. The focus however is more on the design of the survey and the logistics of producing the scientific products. The scientific goals described here are therefore not intended to be exhaustive and written in relatively general terms. Similarly, collaboration with other groups with similar interests and useful expertise in related areas will also be explored depending on the outcome of the VLA Sky Survey evaluation process.