A global view on star formation: The GLOSTAR Galactic plane survey

Abstract

Aims. Surveys of the Milky Way at various wavelengths have changed our view of star formation in our Galaxy considerably in recent years. In this paper we give an overview of the GLOSTAR survey, a new survey covering large parts (145 square degrees) of the northern Galactic plane using the Karl G. Jansky Very Large Array (JVLA) in the frequency range 4 − 8 GHz and the Effelsberg 100m telescope. This provides for the first time a radio survey covering all angular scales down to 1.5 arcsecond, similar to complementary near-IR and mid-IR galactic plane surveys. We outline the main goals of the survey and give a detailed description of the observations and the data reduction strategy. Methods. In our observations we covered the radio continuum in full polarization, as well as the 6.7 GHz methanol maser line, the 4.8 GHz formaldehyde line, and seven radio recombination lines. The observations were conducted in the most compact D configuration of the VLA and in the more extended B configuration. This yielded spatial resolutions of 18" and 1.5" for the two configurations, respectively. We also combined the D configuration images with the Effelsberg 100-m data to provide zero spacing information, and we jointly imaged the D-and B-configuration data for optimal sensitivity of the intermediate spatial ranges. Results. Here we show selected results for the first part of the survey, covering the range of 28 • < l < 36 • and |b| < 1 • , including the full low-resolution continuum image, examples of high-resolution images of selected sources, and the first results from the spectral line data.

A multiwavelength study of the W33 Main ultracompact HII region

“…We obtained the GLOSTAR VLA-D configuration continuum image and the recombination line data cube. The continuum emission image is at a reference frequency of 5.8 GHz and has been constructed from mosaic of images of several frequency bins between 4 and 8 GHz ( Medina et al 2019;Brunthaler et al 2021;Dzib et al, in prep.). The D-configuration continuum images are restored with a circular beam of 18 ′′ .…”

“…The data were gridded and imaged at a spectral resolution of 5 km s −1 and all the line cubes were smoothed to a spatial resolution of 25 ′′ before stacking. The full description of the data reduction and calibration of the RRLs is given in Brunthaler et al (2021) and Rugel et al (in prep).…”

The population of compact radio sources in M 17

“…The extended family of possible radio emitting objects described above implies a wide range of radio flux density expected for them. As a consequence, weak sources found at the lower end of this range become potentially undetectable and surveys might be biased to strong sources (Medina et al 2019;Brunthaler et al 2021). This has been alleviated in recent years thanks to the upgraded instrumentation installed on radio interferometers.…”

The Population of Compact Radio Sources in M17

“…The extended family of possible radio-emitting objects described above implies a wide range of radio flux density expected for them. As a consequence, weak sources found at the lower end of this range become potentially undetectable, and surveys might be biased toward strong sources (Medina et al 2019;Brunthaler et al 2021). This has been alleviated in recent years thanks to the upgraded instrumentation installed on radio interferometers.…”