A global view on star formation: The GLOSTAR Galactic plane survey XII. Effelsberg's continuum view and data release

TL;DR

To address missing zero-spacing in Galactic-plane radio continuum studies, the paper presents the Effelsberg 100-m continuum survey component of GLOSTAR at $4.89$ GHz and $6.82$ GHz, achieving angular resolution $\lesssim 3'$ and enabling polarization studies. By integrating single-dish data with VLA D-array data, the authors demonstrate recovery of $>90\%$ of the missing flux and reveal a revised power spectrum with a slope near $-2.3$ on scales $>1^{\circ}$. The polarization maps show widespread diffuse structures with RM spanning $-61$ to $44$ rad m$^{-2}$ and median polarization around $8\%$, and the work includes detailed case studies of H II regions (e.g., Sh 2-48) and SNRs (e.g., W28) to illustrate physical diagnostics such as electron temperatures and spectral indices. The Effelsberg data are publicly released to support studies of H II regions, SNRs, and the diffuse ISM, with VLA+Effelsberg combined products to follow.

Abstract

Extended radio continuum emission and its linear polarization play a key role in probing large-scale structures of synchrotron and free-free emission in the Milky Way. Despite the existence of many radio continuum surveys, sensitive and high-angular-resolution single-dish surveys of extended radio continuum emission remain scarce. As part of the GLObal view of STAR formation (GLOSTAR) survey, we will also crucially complement the existing data from the Karl G. Jansky Very Large Array (VLA) by addressing the missing zero-spacing gap. Within the framework of the GLOSTAR Galactic plane survey, we performed large-scale radio continuum imaging observations toward the Galactic plane in the range $-2^{\circ}< \ell <60^{\circ}$ and $|b|<1.1^{\circ}$, as well as the Cygnus X region with the Effelsberg 100-m radio telescope. We present the Effelsberg continuum survey at 4.89GHz and 6.82GHz including linear polarization with angular resolutions of 145$^{\prime\prime}$ and 106$^{\prime\prime}$, respectively. The survey has been corrected for missing large-scale emission using available low-angular-resolution surveys. Comparison with previous single-dish surveys indicates that our continuum survey represents the highest-quality single-dish data collected to date at this frequency. More than 90\% of the flux density missed by the VLA D-array data is effectively recovered by the Effelsberg continuum survey. The improved sensitivity and angular resolution of our survey enable reliable mapping of Galactic magnetic field structures, with polarization data that are less affected by depolarization than in previous surveys. The GLOSTAR single-dish continuum data will be released publicly, offering a valuable resource for studying extended objects including HII regions, supernova remnants, diffuse interstellar medium, and Galactic structure. (Abridged)

Figures (18)

• Figure 1: Effelsberg 4.89 GHz Stokes $I$ continuum map of the whole GLOSTAR survey. Zoom-in plots of each fields are available via https://gongyan2444.github.io/glostar-snr-hii.html, where the green, gray, and red circles represent the known SNRs 2025JApA...46...14G, SNR candidates 2017AA...605A..58A2021AA...651A..86D2025AA...693A.247A, and H II regions from the WISE catalog 2014ApJS..212....1A, respectively.
• Figure 2: Effelsberg 6.82 GHz Stokes $I$ continuum map of the whole GLOSTAR survey.
• Figure 3: Comparison of the Effelsberg 4.89 GHz Stokes $I$ continuum map with those from the Urumqi, GB6, and Parkes surveys at similar frequencies.
• Figure 4: Comparison of the GLOSTAR data with and without incorporating the Effelsberg data at 5.8 GHz. (a): VLA D-array only continuum image. (b): Combination of the VLA D-array and the Effelsberg 100-m single-dish image.
• Figure 5: (a): Angular power spectra of the VLA-D array, Effelsberg-100 m, and VLA-D array+Effelsberg-100 m combined images toward the representative region near the Galactic center (see Fig. \ref{['Fig:mf']}). The 2D Kolmogorov-like spectrum is indicated by the black dashed line for comparison. (b): Percentage of missing flux of the VLA D-array data across the Galactic plane covered by the GLOSTAR survey. The horizontal dashed red line indicates a missing flux fraction of 10%.