| Authors Affiliation: | 1 J. Poojapriyatharsheni
Department of Physics, Lady Doak College, Madurai, Tamil Nadu, 625002, India
1 R. Nimma Elizabeth
Department of Physics, Lady Doak College, Madurai, Tamil Nadu, 625002, India
1 D. Anish Roshi
Florida Space Institute, University of Central Florida, Orlando 32826, USA
Center for Advanced Research in Science and Engineering (CARSE), University of Puerto Rico, Mayaguez, PR-00681, USA
1 Mayumi Sato
Florida Space Institute, University of Central Florida, Orlando 32826, USA
2 Kimberly L.Emig
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
3 Pedro Salas
Green Bank Observatory, 155 Observatory Road, Green Bank, WV 24915, USA
4 Loren D.Anderson
Department of Physics and Astronomy, West Virginia University,
Morgantown, WV 26506, USA ; Adjunct Astronomer at the Green Bank Observatory, P.O.Box 2, Green Bank, WV 24944, USA ; Center for Gravitational Waves and Cosmology, West Virginia
University, Chestnut Ridge Research Building, Morgantown, WV 26505,
USA
|
| Abstract: | We present results from a large-scale Radio Recombination Line (RRL) survey conducted in the Cygnus X region, a prominent star formation area, and the inner Galactic Plane (−5° to 32° in l and |b| < 1°). Observations were made at 340 and 800 MHz with the Robert C. Byrd Green Bank Telescope, in a survey known as GDIGS-low (GBT Diffuse Ionized Gas Survey at low frequency), with angular resolutions of 45′ and 15′, respectively. Data from a previous 5.8 GHz RRL survey (GDIGS; Anderson et al. 2021) was also included. All these surveys provide velocity coverage sufficient to detect hydrogen, helium, and carbon lines.
Cygnus X harbors young star clusters, massive stellar associations, and stellar nurseries, where new stars form. Our observations centered on coordinates l = 80° and b = 1.4°, spanning ±2.75° in both galactic longitude and latitude. The intense radiation from young stars in this region generates Diffuse Ionized Gas (DIG), confirmed by widespread low-frequency RRL detections. One objective was to detect helium RRLs from the DIG. By averaging spectra and masking HII region emissions, we achieved the sensitivity for the first helium line detection from DIG at 800 MHz. The ratio of ionized helium to hydrogen was 0.7, with an interquartile range of 0.05 to 0.11, aligning with values seen in HII regions around O6 or earlier-type stars.
The Galactic plane survey data further examines the relationship between hydrogen RRL emissions and far-infrared NII line emissions observed by the Herschel Space Observatory (Goldsmith et al., 2015; Pineda et al., 2019). Both NII and hydrogen RRL emissions originate from fully ionized gas, but our analysis shows that emission measures (EM) derived from NII lines account for only 5% or less of the EM from RRL data. Further study is needed to explain the low NII emissions from most RRL-emitting ionized gas. |
