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

Abstract

As part of the Global View on Star Formation (GLOSTAR) survey we have used the Karl G. Jansky Very Large Array (VLA) in its B-configuration to observe the part of the Galactic plane between longitudes of 28° and 36° and latitudes from −1° to +1° at the C-band (4–8 GHz). To reduce the contamination of extended sources that are not well recovered by our coverage of the (u, υ)-plane, we discarded short baselines that are sensitive to emission on angular scales >4″. The resulting radio continuum images have an angular resolution of 1.″0 and a sensitivity of ~60 µJy beam−1, making it the most sensitive radio survey covering a large area of the Galactic plane with this angular resolution. An automatic source extraction algorithm was used in combination with visual inspection to identify a total of 3325 radio sources. A total of 1457 radio sources are ≥7σ and comprise our highly reliable catalog; 72 of these are grouped as 22 fragmented sources, for example, multiple components of an extended and resolved source To explore the nature of the cataloged radio sources, we searched for counterparts at millimeter and infrared wavelengths. Our classification attempts resulted in 93 H II region candidates, 104 radio stars, and 64 planetary nebulae, while it is suggested that most of the remaining radio sources are extragalactic sources. We investigated the spectral indices (α, Sv ∝ vα) of radio sources classified as H II region candidates and found that many have negative values. This may imply that these radio sources represent young stellar objects that are members of the star clusters around the high-mass stars that excite the H II regions, but not these H II regions themselves. By comparing the peak flux densities from the GLOSTAR and CORNISH surveys, we have identified 49 variable radio sources, most of them with an unknown nature. Additionally, we provide a list of 1866 radio sources detected within 5 to 7σ levels.