Metrewave Galactic Plane with the uGMRT (MeGaPluG) Survey: Lessons from the pilot study

Abstract

Context. The advent of wide-band receiver systems on interferometer arrays has enabled the undertaking of high-sensitivity and highresolution radio continuum surveys of the Galactic plane in a reasonable amount of telescope time. Yet, to date, there have been only a few such studies of the first quadrant of the Milky Way carried out at frequencies below 1 GHz. The Giant Metrewave Radio Telescope (GMRT) has recently upgraded its receivers with wide-band capabilities (now called the uGMRT), offering a prime opportunity to conduct high resolution surveys, while also demonstrating sensitivity to the extended structures. Aims. We wish to assess the feasibility of conducting a large-scale snapshot survey, the Metrewave Galactic Plane with the uGMRT Survey (MeGaPluG), to simultaneously map extended sources and compact objects at an angular resolution lower than 10″ and a point source sensitivity of 0.15 mJy beam-1. Methods. We performed an unbiased survey of a small portion of the Galactic plane, covering the W43/W44 regions (l = 29 - 35 and |b| < 1) in two frequency bands: 300- 500 MHz and 550- 750 MHz. The 200 MHz wide-band receivers on the uGMRT were employed to observe the target field in several pointings, spending nearly 14 min on each pointing in two separate scans. We developed an automated pipeline for the calibration and a semi-automated self-calibration procedure was used to image each pointing using multi-scale CLEAN and outlier fields. Results. We produced continuum mosaics of the surveyed region at a final common resolution of 25″ in the two bands that have central frequencies of 400 MHz and 650 MHz, with a point source sensitivity better than 5 mJy beam-1. A spectral index map was also obtained, which is helpful to distinguish between thermal and nonthermal emission. By cross-matching with other surveys, we validated the positions and flux densities obtained from our data. We plan to cover a larger footprint of the Galactic plane in the near future based on the lessons drawn from this study.