Abstract
Context. Radio continuum surveys of the Galactic plane are an excellent way to identify different source populations such as planetary nebulae, H IIregions, and radio stars and characterize their statistical properties. The Global View of Star Formation in the Milky Way (GLOSTAR) survey will study the star formation in the Galactic plane between −2° < ℓ < 85° and |b| < 1° with unprecedented sensitivity in both flux density (∼40μJy beam−1) and range ofangular scales (∼1".5 to the largest radio structures in the Galaxy).Aims. In this paper we present the first results obtained from a radio continuum map of a 16-square-degree-sized region of the Galactic plane centered on ℓ = 32° andb = 0° (28° < ℓ < 36° and |b| < 1°). This map has a resolution of 18″ and a sensitivity of ∼60−150μJy beam−1.Methods. We present data acquired in 40 h of observations with the VLA in D-configuration. Two 1 GHz wide sub-bands were observed simultaneously and they were centered at 4.7 and 6.9 GHz. These data were calibrated and imaged using theObitsoftware package. The source extraction was performed using theBLOBCATsoftware package and verified through a combination of visual inspection and cross-matching with other radio and mid-infrared surveys.Results. The final catalog consists of 1575 discrete radio sources and 27 large scale structures (including W43 and W44). By cross-matching with other catalogs and calculating the spectral indices (S(ν) ∝ να), we have classified 231 continuum sources as H IIregions, 37 as ionization fronts, and 46 as planetary nebulae. The longitude and latitude distribution and negative spectral indices are all consistent with the vast majority of the unclassified sources being extragalactic background sources.Conclusions. We present a catalog of 1575 radio continuum sources and discuss their physical properties, emission nature, and relation to previously reported data. These first GLOSTAR results have increased the number of reliable H IIregions in this part of the Galaxy by a factor of four.
Highlights
One of the great challenges in modern astronomy is understanding the circumstances of the formation of high-mass stars (>8 M )
We have investigated a few of the MultiArray Galactic Plane Imaging Survey (MAGPIS) sources not matched in GLOSTAR and find many of these to be associated with sources that are overresolved in MAGPIS
We use the BLOBCAT source extraction algorithm to produce a catalog of radio sources and identify a number of different types of morphologies, from unresolved to compact and extended
Summary
One of the great challenges in modern astronomy is understanding the circumstances of the formation of high-mass stars (>8 M ). 7, 9, and 17 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/ qcat?J/A+A/627/A175 and SEDIGISM; Schuller et al 2017), and radio wavelengths (e.g., CORNISH; Hoare et al 2012, MAGPIS; Helfand et al 2006, THOR; Beuther et al 2016; Bihr et al 2015; Wang et al 2018) These surveys have provided Galaxy-wide and unbiased samples of high-mass star-forming regions (Urquhart et al 2014a, 2018; Elia et al 2017) that include all evolutionary stages and, for the first time, allow star formation to be studied in a global context.
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