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

VII. Supernova remnants in the Galactic longitude range 28° < l < 36°^★

¹ Max Planck Institute for Radioastronomy (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: [email protected]
² Center for Astrophysics, Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
³ National Radio Astronomy Observatory, 1003 Lopezville Rd, Socorro, NM 87801, USA
⁴ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA, 22903, USA
⁵ South African Radio Astronomy Observatory, 2 Fir St, Black River Park, Observatory, 7925, South Africa
⁶ IRAM, 300 rue de la piscine, 38406 Saint-Martin-d’Hères, France
⁷ German Aerospace Center, Scientific Information, 51147 Cologne, Germany
⁸ Instituto de Astronomía, Universidad Nacional Autónoma de México (UNAM), Apdo Postal 70-264, Ciudad de México, Mexico
⁹ Centre for Astrophysics and Planetary Science, University of Kent, Ingram Building, Canterbury, Kent CT2 7NH, UK
¹⁰ Department of Physics and Astronomy, West Virginia University, Morgantown, WV, 26506, USA
¹¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹² Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
¹³ Department of Earth & Space Sciences, Indian Institute of Space Science and Technology, Trivandrum 695547, India
¹⁴ Department of Physics, Indian Institute of Science, Bengaluru 560012, India

Received: 31 October 2022
Accepted: 24 November 2022

Abstract

Context. While over 1000 supernova remnants (SNRs) are estimated to exist in the Milky Way, only less than 400 have been found to date. In the context of this apparent deficiency, more than 150 SNR candidates were recently identified in the D-configuration Very Large Array (VLA-D) continuum images of the 4–8 GHz global view on star formation (GLOSTAR) survey, in the Galactic longitude range −2° < l < 60°.

Aims. We attempt to find evidence of nonthermal synchrotron emission from 35 SNR candidates in the region of Galactic longitude range 28° < l < 36°, and also to study the radio continuum emission from the previously confirmed SNRs in this region.

Methods. Using the short-spacing corrected GLOSTAR VLA-D+Effelsberg images, we measure the ~6 GHz total and linearly polarized flux densities of the SNR candidates and the SNRs that were previously confirmed. We also attempt to determine the spectral indices by measuring flux densities from complementary Galactic plane surveys and from the temperature-temperature plots of the GLOSTAR-Effelsberg images.

Results. We provide evidence of nonthermal emission from four candidates that have spectral indices and polarization consistent with a SNR origin, and, considering their morphology, we are confident that three of these (g28.36+0.21, G28.78-0.44, and G29.38+0.10) are indeed SNRs. However, about 25% of the candidates (8 out of 35) have spectral index measurements that indicate thermal emission, and the rest of them are too faint to have a good constraint on the spectral index yet.

Conclusions. Additional observations at longer wavelengths and higher sensitivities will shed more light on the nature of these candidates. A simple Monte Carlo simulation reiterates the view that future studies must persist with the current strategy of searching for SNRs with small angular size to solve the problem of the Milky Way’s missing SNRs.