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A Global View on Star Formation: the GLOSTAR Galactic Plane Survey I

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A Global View on Star Formation: the GLOSTAR Galactic Plane Survey I Astronomy & Astrophysics manuscript no. pilot_final ©ESO 2021 June 2, 2021 A global view on star formation: The GLOSTAR Galactic plane survey I. Overview and first results for the Galactic longitude range 28◦ < l < 36◦ A. Brunthaler1, K. M. Menten1, S. A. Dzib1, W. D. Cotton2; 3, F. Wyrowski1, R. Dokara1?, Y. Gong1, S-N. X. Medina1, P. Müller1, H. Nguyen1;?, G. N. Ortiz-León1, W. Reich1, M. R. Rugel1, J. S. Urquhart4, B. Winkel1, A. Y. Yang1, H. Beuther5, S. Billington4, C. Carrasco-Gonzalez6, T. Csengeri7, C. Murugeshan8, J. D. Pandian9, N. Roy10 1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: [email protected] 2 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA 3 South African Radio Astronomy Observatory, 2 Fir St, Black River Park, Observatory 7925, South Africa 4 Centre for Astrophysics and Planetary Science, University of Kent, Ingram Building, Canterbury, Kent CT2 7NH, UK 5 Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg, Germany 6 Instituto de Radioastronomía y Astrofísica (IRyA), Universidad Nacional Autónoma de México Morelia, 58089, Mexico 7 Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France 8 Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia 9 Department of Earth & Space Sciences, Indian Institute of Space Science and Technology, Trivandrum 695547, India 10 Department of Physics, Indian Institute of Science, Bengaluru 560012, India 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 100- m 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 jbj < 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. Key words. surveys, ISM: general, (ISM:) HII regions, ISM: supernova remnants, radio lines: ISM, radio continuum: general 1. Introduction limetre Astronomy Legacy Team 90 GHz (MALT90; Jackson et al. 2013)); and radio wavelength ranges (e.g., the Multi-Array Stars with more than about ten solar masses dominate galactic Galactic Plane Imaging Survey (MAGPIS; Becker 1990; Becker ecosystems. Understanding the circumstances of their formation et al. 1994), the Sino-German 6 cm survey (Han et al. 2015)1, the is one of the great challenges of modern astronomy. In recent Coordinated Radio and Infrared Survey for High-Mass Star For- years, our view of massive star-forming regions has been dra- arXiv:2106.00377v1 [astro-ph.GA] 1 Jun 2021 mation (CORNISH; Hoare et al. 2012; Purcell et al. 2013), The matically changed by Galactic plane surveys covering the in- H i, OH and Radio Recombination line survey of the Milky Way frared (e.g., Galactic Legacy Infrared Mid-Plane Survey Extraor- (THOR; Beuther et al. 2016; Wang et al. 2020), the Southern dinaire (GLIMPSE; Churchwell et al. 2009), MIPSGAL (Carey Galactic Plane Survey (McClure-Griffiths et al. 2005), the VLA et al. 2009), Hi-GAL (Molinari et al. 2010)); (sub-)millimeter Galactic Plane Survey (VGPS; Stil et al. 2006), the Canadian (e.g., APEX Telescope Large Area Survey of the Galaxy (AT- Galactic Plane Survey (Taylor et al. 2003), the H2O Southern LASGAL; Schuller et al. 2009; Csengeri et al. 2014), Bolocam Galactic Plane Survey (HOPS; Walsh et al. 2011), the Methanol Galactic Plane Survey (BGPS; Aguirre et al. 2011), JCMT Plane Multibeam Survey (MMB; Green et al. 2009a), the Galactic Survey (JPS; Moore et al. 2015; Eden et al. 2017), the Mil- ? Member of the International Max Planck Research School (IM- 1 Data from this and various other large-scale centimeter-wavelength PRS) for Astronomy and Astrophysics at the Universities of Bonn and surveys can be accessed via the MPIfR Survey Sampler at https:// Cologne www.mpifr-bonn.mpg.de/survey.html Article number, page 1 of 18 A&A proofs: manuscript no. pilot_final Ring Survey (GRS; Jackson et al. 2006)). These surveys allow the VLA for an unbiased survey to find and characterize star- us for the first time to study all the evolutionary stages of mas- forming regions in the Galaxy. All fields are observed in the sive star formation (MSF) in an unbiased way (e.g., König et al. most compact D configuration of the VLA with a resolution of 2017; Elia et al. 2017; Urquhart et al. 2018). ∼ 1800 to have good surface brightness sensitivity for extended With the exciting results of the submillimeter and far- structures and in the more extended B configuration that pro- infrared (FIR) surveys from the ground (ATLASGAL) and space vides a ten times higher spatial resolution to investigate compact (Hi-GAL), the massive and cold dust clumps from which mas- sources. The VLA data are then complemented by observations sive clusters form are now being detected galaxy-wide. Comple- with the Effelsberg 100-m telescope to provide zero spacings for mentary to these surveys, the centimeter studies using the VLA the D-configuration data. Finally, the data from the D and B con- allow very powerful and comprehensive radio-wavelength sur- figurations are combined (D+B) to provide the best possible im- veys of the ionized and the molecular tracers of star formation ages of sources with intermediate sizes by combining the surface in the Galactic plane. There have been a number of VLA sur- brightness sensitivity of the D configuration with the high reso- veys of the inner part of the first quadrant of the Galactic plane lution of the B configuration. starting with the pioneering 20 cm (Becker 1990) and 6 cm sur- This survey of the Galactic plane detects tell-tale tracers of veys (Becker et al. 1994) that are now combined in the MAGPIS star formation: compact, ultra-compact, and hyper-compact Hii project.2 More recently the CORNISH team have mapped the regions and molecular masers that trace different stages of early northern GLIMPSE region at 5 GHz with higher resolution and stellar evolution and pinpoints the very centers of the early phase sensitivity than MAGPIS. CORNISH was tailored to specifically of star-forming activity. Combined with the submillimeter and focus on identifying and parameterizing the ultra-compact (UC) infrared surveys, and our ongoing work in the Bar and Spiral H ii region stage of MSF (e.g., Purcell et al. 2013; Kalcheva et al. Structure Legacy (BeSSeL) Survey4 to measure distances by 2018), although it has also been used to investigate the Galac- trigonometric parallaxes to most of the dominant star-forming tic population of planetary nebulae (PNe; Irabor et al. 2018). regions in the Galaxy, it offers a nearly complete census of the These studies have identified many thousands of radio sources number, luminosities, and masses of massive star-forming clus- located towards the Galactic plane, and follow-up work has al- ters in a large range of evolutionary stages and provides a unique lowed many hundreds of Galactic radio sources to be identified data set with true legacy value for a global perspective on star and studied (e.g., Urquhart et al. 2013; Cesaroni et al. 2015; formation in our Galaxy. In addition to information on high-mass Kalcheva et al. 2018; Irabor et al. 2018). However, these inter- star formation, the GLOSTAR survey allows efficient identifica- ferometric snapshot surveys have been limited by the historically tion and imaging of supernova remnants, planetary nebulae, and small bandwidths available (∼50 MHz) and sensitivity to emis- numerous extragalactic background sources. sion on larger angular scales. These surveys have therefore been restricted to continuum studies of relatively compact structures (i.e., <2000 for CORNISH) and are therefore unable to provide 2. The GLOSTAR VLA survey overview us with a global view of star formation in the Galaxy. 2.1. Survey coverage The scope of radio-wavelength Galactic plane surveys and of radio interferometry in general, has been vastly increased The full survey covers the Galactic plane in the range −2◦ < l < with the expansion of the VLA into the Karl G. Jansky Very 60◦ and jbj < 1◦, as well as the Cygnus X star-forming complex Large Array, (JVLA3). The VLA expansion project, beginning at a range of 76◦ < l < 83◦ and −1◦ < b < 2◦, or 145 square in 2001, with Early Science programs starting in early 2010, re- degrees in total. We needed about 341 individual pointings to placed the 1970s electronic and digital hardware with state-of- cover one square degree, or 49463 pointings in total.
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